HK1220062B - Methods and devices of multi-layer video file format designs - Google Patents

Description

Method and device for designing multi-layer video file format

This application claims the benefit of U.S. Provisional Patent Application No. 61/894,886, filed October 23, 2013, which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to video decoding.

Background Art

Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital live broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video game devices, video game consoles, cellular or satellite radio telephones (so-called "smartphones"), video teleconferencing devices, video streaming devices, and the like. Digital video devices implement video compression techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4 Part 10 Advanced Video Coding (AVC), the High Efficiency Video Coding (HEVC) standard currently under development, and extensions to such standards. By implementing such video compression techniques, video devices can more efficiently transmit, receive, encode, decode, and/or store digital video information.

Video compression techniques perform spatial (intra-picture) prediction and/or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice (i.e., a video frame or portion of a video frame) may be partitioned into video blocks (which may also be referred to as treeblocks), coding units (CUs), and/or coding nodes. Video blocks in an intra-coded (I) slice of a picture may be encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames.

Spatial or temporal prediction results in a predictive block for the block to be encoded. Residual data represents the pixel differences between the coded original block and the predictive block. Inter-coded blocks are encoded according to a motion vector pointing to a block of reference samples forming the predictive block and residual data indicating the difference between the coded block and the predictive block. Intra-coded blocks are encoded according to an intra-coding mode and the residual data. For further compression, the residual data can be transformed from the pixel domain to the transform domain, resulting in residual transform coefficients that can then be quantized. The quantized transform coefficients, initially arranged in a two-dimensional array, can be scanned to produce a one-dimensional vector of transform coefficients, and entropy coding can be applied to achieve even greater compression.

Summary of the Invention

In general, the present invention relates to storing video content in files based on the International Organization for Standardization (ISO) Base Media File Format (ISOBMFF). Some examples of the present invention relate to methods for storing a video stream containing multiple coded layers, where each layer can be a scalable layer, a texture view, a depth view, etc., and the methods can be applied to storing Multi-view High Efficiency Video Coding (MV-HEVC), Scalable HEVC (SHVC), Three-dimensional HEVC (3D-HEVC), and other types of video data.

In one aspect, the present disclosure describes a method for processing multi-layer video data, the method comprising: generating a file including a media data box enclosing media content, the media content including a series of samples, each of the samples being an access unit of the multi-layer video data, wherein generating the file comprises: in response to a determination that at least one access unit of a bitstream of the multi-layer video data includes a decoded picture having a picture output flag equal to a first value and a decoded picture having a picture output flag equal to a second value, storing the bitstream in the file using at least one first playback track and a second playback track, wherein: for each respective playback track from the first playback track and the second playback track, all decoded pictures in each sample of the respective playback track have the same value of the picture output flag; and pictures having the picture output flag equal to the first value are allowed to be output, and pictures having the picture output flag equal to the second value are allowed to be used as reference pictures but are not allowed to be output.

In another aspect, the present invention describes a method for processing multi-layer video data, the method comprising: obtaining a first play track box and a second play track box from a file, the first play track box containing metadata for a first play track in the file, and the second play track box containing metadata for a second play track in the file, wherein: each of the first play track and the second play track includes a series of samples, each of the samples is a video access unit of the multi-layer video data, for each corresponding play track from the first play track and the second play track, all decoded pictures in each sample of the corresponding play track have the same value of a picture output flag, and pictures with a picture output flag equal to a first value are allowed to be output, and pictures with a picture output flag equal to a second value are allowed to be used as reference pictures but are not allowed to be output.

In another aspect, the disclosure describes a video device comprising: a data storage medium configured to store multi-layer video data; and one or more processors configured to: generate a file comprising a media data box enclosing media content, the media content comprising a sequence of samples, each of the samples being an access unit of the multi-layer video data, wherein to generate the file, the one or more processors are configured to: in response to a determination that at least one access unit of a bitstream of the multi-layer video data includes a coded picture having a picture output flag equal to a first value and a coded picture having a picture output flag equal to a second value, store the bitstream in the file using at least one first playback track and a second playback track, wherein: for each respective playback track from the first playback track and the second playback track, all coded pictures in each sample of the respective playback track have the same value of the picture output flag; and allow output of pictures having the picture output flag equal to the first value, and allow use of pictures having the picture output flag equal to the second value as reference pictures but do not allow output of them.

In another aspect, the present invention describes a video device comprising: a data storage medium configured to store multi-layer video data; and one or more processors configured to: obtain a first play track box and a second play track box from a file, the first play track box containing metadata for a first play track in the file, and the second play track box containing metadata for a second play track in the file, wherein: each of the first play track and the second play track includes a series of samples, each of the samples being a video access unit of the multi-layer video data, for each respective play track from the first play track and the second play track, all decoded pictures in each sample of the respective play track have the same value of a picture output flag, and pictures having a picture output flag equal to a first value are allowed to be output, and pictures having a picture output flag equal to a second value are allowed to be used as reference pictures but are not allowed to be output.

In another aspect, the present disclosure describes a video device comprising: a device for generating a file including a media data box enclosing media content, the media content including a series of samples, each of the samples being an access unit of multi-layer video data, wherein generating the file comprises: in response to a determination that at least one access unit of a bitstream of the multi-layer video data includes a decoded picture having a picture output flag equal to a first value and a decoded picture having a picture output flag equal to a second value, storing the bitstream in the file using at least one first playback track and a second playback track, wherein: for each respective playback track from the first playback track and the second playback track, all decoded pictures in each sample of the respective playback track have the same value of the picture output flag; and pictures having the picture output flag equal to the first value are allowed to be output, and pictures having the picture output flag equal to the second value are allowed to be used as reference pictures but are not allowed to be output.

In another aspect, the present disclosure describes a video device comprising: a device for obtaining a first play track box and a second play track box from a file, the first play track box containing metadata for the first play track in the file, and the second play track box containing metadata for the second play track in the file, wherein: each of the first play track and the second play track includes a series of samples, each of the samples is a video access unit of multi-layer video data, for each corresponding play track from the first play track and the second play track, all decoded pictures in each sample of the corresponding play track have the same value of a picture output flag, and pictures with a picture output flag equal to a first value are allowed to be output, and pictures with a picture output flag equal to a second value are allowed to be used as reference pictures but are not allowed to be output.

In another aspect, the present disclosure describes a computer-readable data storage medium having instructions stored thereon that, when executed, cause one or more processors to: generate a file including a media data box enclosing media content, the media content including a sequence of samples, each of the samples being an access unit of multi-layer video data, wherein to generate the file, the instructions cause the one or more processors to: in response to a determination that at least one access unit of a bitstream of the multi-layer video data includes a coded picture having a picture output flag equal to a first value and a coded picture having a picture output flag equal to a second value, store the bitstream in the file using at least one first playback track and a second playback track, wherein: for each respective playback track from the first playback track and the second playback track, all coded pictures in each sample of the respective playback track have the same value of the picture output flag; and allow output of pictures having the picture output flag equal to the first value, and allow use of pictures having the picture output flag equal to the second value as reference pictures but do not allow output of them.

In another aspect, the present disclosure describes a computer-readable data storage medium having instructions stored thereon that, when executed, cause one or more processors to: obtain a first track box and a second track box from a file, the first track box containing metadata for a first track in the file, the second track box containing metadata for a second track in the file, wherein: each of the first track and the second track comprises a sequence of samples, each of the samples being a video access unit of multi-layer video data, for each respective track from the first track and the second track, all coded pictures in each sample of the respective track have the same value of a picture output flag, and pictures having the picture output flag equal to the first value are allowed to be output, and pictures having the picture output flag equal to the second value are allowed to be used as reference pictures but are not allowed to be output.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a block diagram illustrating an example video encoding and decoding system that may use the techniques described in this disclosure.

2 is a block diagram illustrating an example video encoder that may implement the techniques described in this disclosure.

3 is a block diagram illustrating an example video decoder that may implement the techniques described in this disclosure.

4 is a block diagram illustrating an example set of devices forming part of a network.

5 is a conceptual diagram illustrating an example structure of a file, in accordance with one or more techniques of this disclosure.

6 is a conceptual diagram illustrating an example structure of a file, in accordance with one or more techniques of this disclosure.

7 is a flowchart illustrating example operation of a file generation device, in accordance with one or more techniques of this disclosure.

8 is a flowchart illustrating example operation of a computing device performing random access and/or rank switching in accordance with one or more techniques of this disclosure.

9 is a flowchart illustrating example operation of a file generation device, in accordance with one or more techniques of this disclosure.

10 is a flowchart illustrating example operation of a computing device in accordance with one or more techniques of this disclosure.

11 is a flowchart illustrating example operation of a file generation device, in accordance with one or more techniques of this disclosure.

12 is a flowchart illustrating example operation of a destination device in accordance with one or more techniques of this disclosure.

DETAILED DESCRIPTION

The ISO Base Media File Format (ISOBMFF) is a file format for storing media data. ISOBMFF is extensible to support the storage of video data conforming to specific video coding standards. For example, ISOBMFF has previously been extended to support the storage of video data conforming to the H.264/AVC and High Efficiency Video Coding (HEVC) video coding standards. Furthermore, ISOBMFF has previously been extended to support the storage of video data conforming to the Multi-View Coding (MVC) and Scalable Video Coding (SVC) extensions of H.264/AVC. MV-HEVC, 3D-HEVC, and SHVC are extensions of the HEVC video coding standard that support multi-layer video data. The features added to ISOBMFF for the storage of video data conforming to the MVC and SVC extensions of H.264/AVC are insufficient for the efficient storage of video data conforming to MV-HEVC, 3D-HEVC, and SHVC. In other words, if one attempts to use extensions of ISOBMFF for storage of video data conforming to the MVC and SVC extensions of H.264/AVC for efficient storage of video data conforming to MV-HEVC, 3D-HEVC, and SHVC, various problems may arise.

For example, unlike bitstreams conforming to the MVC or SVC extensions of H.264/AVC, bitstreams conforming to MV-HEVC, 3D-HEVC, or SHVC may include access units containing intra random access point (IRAP) pictures and non-IRAP pictures. Access units containing IRAP pictures and non-IRAP pictures can be used for random access in MV-HEVC, 3D-HEVC, and SHVC. However, ISOBMFF and its existing extensions do not provide a way to identify such access units. This can hinder the ability of computing devices to perform random access and layer switching.

Therefore, according to one example of the present invention, a computing device may generate a file that includes a track box containing metadata for a track in the file. The media data for the track includes a series of samples. Each of the samples may be a video access unit of multi-layer video data (e.g., MV-HEVC, 3D-HEVC, or SHVC video data). As part of generating the file, the computing device may generate an additional box in the file that documents all of the samples containing at least one IRAP picture. Being able to determine the samples containing IRAP pictures based on the information in the additional box enables the computing device receiving the file to perform random access and layer switching without parsing and interpreting NAL units. This can reduce complexity and processing time.

Furthermore, multi-layer video data, such as MV-HEVC, 3D-HEVC, and SHVC video data, may include multiple coded pictures for each access unit. However, when multiple coded pictures are present in an access unit, ISOBMFF and its existing extensions do not provide information about the individual coded pictures within the access unit. Therefore, in an example where a computing device (e.g., a streaming server) is determining whether to forward a NAL unit in a file, the computing device may need to parse and interpret the information stored in the NAL unit in order to determine whether to forward the NAL unit. Parsing and interpreting the information stored in the NAL unit may increase the complexity of the computing device and may increase streaming latency.

Thus, according to one example of the present disclosure, a computing device may generate a file comprising a track box containing metadata for a track in the file. The media data for the track comprises a sequence of samples. Each of the samples is a video access unit of multi-layer video data. As part of generating the file, the computing device generates a subsample information box in the file, the subsample information box containing a flag that specifies the type of subsample information provided in the subsample information box. When the flag has a particular value, the subsample corresponding to the subsample information box contains exactly one coded picture and zero or more non-video coding layer (VCL) NAL units associated with the coded picture. In this way, a computing device receiving the file may be able to use the subsample information provided in the subsample information box to make determinations about individual coded pictures within a sample of the file. The non-VCL NAL units associated with the coded pictures may include NAL units for parameter sets (e.g., PPS, SPS, VPS) and SEI applicable to the coded picture.

In multi-layer video data, access units may include coded pictures marked for output and coded pictures marked not for output. A video decoder can use coded pictures marked not for output as reference pictures for decoding coded pictures marked for output. The NAL unit header of a NAL unit for a slice of a picture may include a picture output flag (e.g., pic_output_flag in HEVC) that indicates whether the picture is marked for output. In ISOBMFF files, each sample is required to be associated with an output time (e.g., composition time) indicating when the sample will be output. However, pictures marked not for output do not have an output time. Therefore, the presence of pictures marked not for output may violate this requirement of ISOBMFF or may require non-standard workaround techniques.

Therefore, according to one or more techniques of this disclosure, a computing device may generate a file comprising a media data box enclosing media content. The media content comprises a series of samples. Each of the samples comprises an access unit of multi-layer video data. As part of generating the file, the computing device may store the bitstream in the file using at least two tracks in response to at least one access unit of a bitstream of multi-layer video data including a coded picture having a picture output flag equal to a first value (e.g., 1) and a coded picture having a picture output flag equal to a second value (e.g., 0). For each respective track from the at least two tracks, all coded pictures in each sample of the respective track have the same picture output flag value. Pictures having a picture output flag equal to the first value (e.g., 1) are permitted to be output, and pictures having a picture output flag equal to the second value (e.g., 0) are permitted to be used as reference pictures but are not permitted to be output. The use of at least two tracks can resolve the above-described issues because each sample in each track can be assigned an appropriate output time, and the video decoder can avoid outputting pictures in tracks containing samples that are not permitted to be output.

Although many of the descriptions of the techniques of this disclosure describe MV-HEVC, 3D-HEVC, and SHVC, the reader should appreciate that the techniques of this disclosure may be applicable to other video coding standards and/or extensions thereof.

FIG1 is a block diagram illustrating an example video encoding and decoding system 10 that may use the techniques described in this disclosure. As shown in FIG1 , system 10 includes a source device 12 that generates encoded video data to be later decoded by a destination device 14. Source device 12 and destination device 14 may comprise any of a wide range of devices, including desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets (e.g., so-called "smart" phones), so-called "smart" pads, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, or the like. In some cases, source device 12 and destination device 14 may be equipped for wireless communication. Source device 12 and destination device 14 may be considered video devices.

1 , source device 12 includes a video source 18, a video encoder 20, and an output interface 22. In some cases, output interface 22 may include a modulator/demodulator (modem) and/or a transmitter. In source device 12, video source 18 may include, for example, a video capture device (e.g., a video camera), a video archive containing previously captured video, a video feed interface that receives video from a video content provider, and/or a computer graphics system for generating computer graphics data as source video, or a combination of such sources. However, the techniques described in this disclosure may be applicable to video coding in general and may be applied to wireless and/or wired applications.

Video encoder 20 may encode captured, pre-captured, or computer-generated video. Source device 12 may transmit the encoded video data directly to destination device 14 via output interface 22 of source device 12. The encoded video data may also (or alternatively) be stored on storage device 33 for later access by destination device 14 or other devices for decoding and/or playback.

Destination device 14 includes an input interface 28, a video decoder 30, and a display device 32. In some cases, input interface 28 may include a receiver and/or a modem. Input interface 28 of destination device 14 receives encoded video data via link 16. The encoded video data communicated via link 16 or provided on storage device 33 may include a variety of syntax elements generated by video encoder 20 for use by a video decoder, such as video decoder 30, in decoding the video data. Such syntax elements may be included with the encoded video data transmitted on a communication medium, stored on a storage medium, or stored on a file server.

Display device 32 may be integrated with destination device 14 or external to destination device 14. In some examples, destination device 14 may include an integrated display device and may also be configured to interface with an external display device. In other examples, destination device 14 may be a display device. In general, display device 32 displays decoded video data to a user and may include any of a variety of display devices, such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

Video encoder 20 and video decoder 30 may each be implemented as any of a variety of suitable encoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. When the techniques are implemented in part in software, the device may store instructions for the software in a suitable non-transitory computer-readable medium and execute the instructions in hardware using one or more processors, thereby performing the techniques of this disclosure. Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in the respective device.

Destination device 14 may receive the encoded video data to be decoded via link 16. Link 16 may comprise any type of medium or device capable of moving the encoded video data from source device 12 to destination device 14. In one example, link 16 may comprise a communication medium that enables source device 12 to transmit the encoded video data directly to destination device 14 in real time. The encoded video data may be modulated according to a communication standard (e.g., a wireless communication protocol) and transmitted to destination device 14. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be used to facilitate communication from source device 12 to destination device 14.

Alternatively, output interface 22 may output the encoded data to storage device 33. Similarly, input interface 28 may access encoded data storage device 33. Storage device 33 may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, Blu-ray disc, DVD, CD-ROM, flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data. In yet another example, storage device 33 may correspond to a file server or another intermediate storage device that can hold the encoded video generated by source device 12. Destination device 14 may access the stored video data from storage device 33 via streaming or downloading. A file server may be any type of server capable of storing encoded video data and transmitting it to destination device 14. Example file servers include web servers (e.g., for websites), FTP servers, network attached storage (NAS) devices, and local disk drives. Destination device 14 may access the encoded video data via any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.) suitable for accessing encoded video data stored on a file server, or a combination of both. The transmission of the encoded video data from storage device 33 may be a streaming transmission, a download transmission, or a combination of both.

The techniques of this disclosure are not necessarily limited to wireless applications or settings. The techniques may be applicable to video decoding to support any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, streaming video transmissions over the Internet, encoding of digital video for storage on a data storage medium, decoding of digital video stored on a data storage medium, or other applications. In some examples, system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony.

Furthermore, in the example of FIG. 1 , video coding system 10 includes file generation device 34. File generation device 34 may receive encoded video data generated by source device 12. File generation device 34 may generate a file including the encoded video data. Destination device 14 may receive the file generated by file generation device 34. In various examples, file generation device 34 may include various types of computing devices. For example, file generation device 34 may include a media-aware network element (MANE), a server computing device, a personal computing device, a dedicated computing device, a commercial computing device, or another type of computing device. In some examples, file generation device 34 is part of a content delivery network. File generation device 34 may receive encoded video data from source device 12 via a channel such as link 16. Furthermore, destination device 14 may receive the file from file generation device 34 via a channel such as link 16. File generation device 34 may be considered a video device.

In other examples, source device 12 or another computing device may generate a file including the encoded video data. However, for ease of explanation, this disclosure describes file generation device 34 as generating a file. However, it should be understood that, in general, such descriptions apply to computing devices.

Video encoder 20 and video decoder 30 may operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard or an extension thereof. The HEVC standard may also be referred to as ISO/IEC 23008-2. Recently, the design of HEVC was completed by the Joint Collaboration Team on Video Coding (JCT-VC) of the ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC Motion Picture Experts Group (MPEG). The most recent HEVC draft specification, hereinafter referred to as HEVC WD, is available at http://phenix.int-evry.fr/jct/doc_end_user/documents/14_Vienna/wg11/JCTVC-N1003-v1.zip. A multi-view extension to HEVC, namely MV-HEVC, is also being developed by JCT-3V. A recent working draft (WD) of MV-HEVC, entitled "MV-HEVC Draft Text 5," hereinafter referred to as MV-HEVC WD5, is available at http://phenix.it-sudparis.eu/jct2/doc_end_user/documents/5_Vienna/wg11/JCT3V-E1004-v6.zip. A scalable extension to HEVC, namely SHVC, is also being developed by JCT-VC. A recent working draft (WD) of SHVC, entitled "High Efficiency Video Coding (HEVC) Scalable Extension Draft 3," hereinafter referred to as SHVC WD3, is available at http://phenix.it-sudparis.eu/jct/doc_end_user/documents/14_Vienna/wg11/JCTVC-N1008-v3.zip. A recent working draft (WD) of the range extension of HEVC is available at http://phenix.int-evry.fr/jct/doc_end_user/documents/14_Vienna/wg11/JCTVC-N1005-v3.zip. A recent working draft (WD) of the 3D extension of HEVC (i.e., 3D-HEVC), entitled “3D-HEVC Draft Text 1,” is available at http://phenix.int-evry.fr/jct2/doc_end_user/documents/5_Vienna/wg11/JCT3V-E1001-v3.zip. Video encoder 20 and video decoder 30 may operate according to one or more of these standards.

Alternatively, video encoder 20 and video decoder 30 may operate according to other proprietary or industry standards, such as the ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10, Advanced Video Coding (AVC), or extensions of such standards. However, the techniques of this disclosure are not limited to any particular coding standard. Other examples of video compression standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual, and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its scalable video coding (SVC) and multi-view video coding (MVC) extensions.

Although not shown in FIG1 , in some aspects, video encoder 20 and video decoder 30 may each be integrated with an audio encoder and decoder and may include appropriate MUX-DEMUX units or other hardware and software to handle the encoding of both audio and video in a common data stream or in separate data streams. If applicable, in some examples, the MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol or other protocols, such as the User Datagram Protocol (UDP).

The JCT-VC is working on the development of the HEVC standard. The HEVC standardization effort is based on an evolved model of a video coding device, known as the HEVC Test Model (HM). The HM assumes several additional capabilities of video coding devices relative to existing devices, such as those in ITU-T H.264/AVC. For example, while H.264/AVC provides nine intra-prediction coding modes, the HM can provide up to thirty-three intra-prediction coding modes.

In general, the working model of the HM describes that a video frame or picture can be divided into a sequence of treeblocks or largest coding units (LCUs) that include both luma and chroma samples. A treeblock may also be referred to as a coding tree unit (CTU). A treeblock has a similar purpose to a macroblock of the H.264/AVC standard. A slice includes many consecutive treeblocks in coding order. A video frame or picture can be partitioned into one or more slices. Each treeblock can be split into coding units (CUs) according to a quadtree. For example, a treeblock that is the root node of a quadtree can be split into four child nodes, and each child node can be a parent node and split into another four child nodes. The last unsplit child node that is a leaf node of the quadtree comprises a coding node (i.e., a coded video block). Syntax data associated with the coded bitstream can define the maximum number of times a treeblock can be split, and can also define the minimum size of a coding node.

A CU comprises a coding node and the prediction units (PUs) and transform units (TUs) associated with the coding node. The size of the CU corresponds to the size of the coding node and must be square in shape. The size of a CU can range from 8x8 pixels up to the size of a treeblock with a maximum of 64x64 pixels or larger. Each CU may contain one or more PUs and one or more TUs. Syntax data associated with a CU may describe, for example, the partitioning of the CU into one or more PUs. The partitioning mode may differ between whether the CU is skip or direct mode coded, intra-prediction mode coded, or inter-prediction mode coded. A PU may be partitioned into a non-square shape. Syntax data associated with a CU may also describe, for example, the partitioning of the CU into one or more TUs according to a quadtree. The shape of a TU may be square or non-square.

The HEVC standard allows for transforms to be performed on a per-TU basis, which can be different for different CUs. TUs are typically sized based on the size of the PUs within a given CU defined for a partitioned LCU, but this may not always be the case. TUs are typically the same size as or smaller than the PUs. In some examples, a quadtree structure called a "residual quadtree" (RQT) can be used to subdivide the residual samples corresponding to a CU into smaller units. The leaf nodes of the RQT can be referred to as TUs. Pixel difference values associated with a TU can be transformed to produce transform coefficients that can be quantized.

In general, a PU includes data related to the prediction process. For example, when the PU is intra-mode encoded, the PU may include data describing the intra-prediction mode used for the PU. As another example, when the PU is inter-mode encoded, the PU may include data defining a motion vector for the PU. The data defining the motion vector for the PU may describe, for example, the horizontal component of the motion vector, the vertical component of the motion vector, the resolution of the motion vector (e.g., quarter-pixel precision or eighth-pixel precision), the reference picture to which the motion vector points, and/or the reference picture list for the motion vector (e.g., List 0, List 1, or List C).

In general, TUs are used for transform and quantization processes. A given CU having one or more PUs may also include one or more transform units (TUs). After prediction, video encoder 20 may calculate residual values corresponding to the PUs. The residual values include pixel difference values, which may be transformed into transform coefficients, quantized, and scanned using the TUs to produce serialized transform coefficients for entropy coding. This disclosure generally uses the term "video block" to refer to a coding node (i.e., a coding block) of a CU. In some specific cases, this disclosure may also use the term "video block" to refer to a treeblock (i.e., an LCU) or a CU, which includes a coding node and PUs and TUs.

A video sequence typically includes a series of video frames or pictures. A group of pictures (GOP) generally includes one or more of a series of video pictures. A GOP may include a header for the GOP, a header for one or more of the pictures, or syntax data elsewhere that describes the number of pictures included in the GOP. Each slice of a picture may include slice syntax data that describes the coding mode for the respective slice. Video encoder 20 typically operates on video blocks within individual video slices to encode the video data. A video block may correspond to a coding node within a CU. A video block may have a fixed or varying size and may be sized differently according to a specified coding standard.

As an example, the HM supports prediction at various PU sizes. Assuming a particular CU is 2Nx2N, the HM supports intra prediction at PU sizes of 2Nx2N or NxN, and inter prediction at symmetric PU sizes of 2Nx2N, 2NxN, Nx2N, or NxN. The HM also supports asymmetric partitioning for inter prediction at PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N. In an asymmetric partitioning, the CU is unpartitioned in one direction and partitioned into 25% and 75% in the other direction. The portion of the CU corresponding to the 25% partition is indicated by an "n" followed by an indication of "Up," "Down," "Left," or "Right." Thus, for example, "2NxnU" refers to a 2Nx2N CU partitioned horizontally with a 2Nx0.5N PU at the top and a 2Nx1.5N PU at the bottom.

In this disclosure, "NxN" and "N by N" are used interchangeably to refer to the pixel dimensions of a video block in terms of vertical and horizontal dimensions, e.g., 16x16 pixels or 16 by 16 pixels. Generally, a 16x16 block will have 16 pixels in the vertical direction (y=16) and 16 pixels in the horizontal direction (x=16). Similarly, an NxN block will typically have N pixels in the vertical direction and N pixels in the horizontal direction, where N represents a non-negative integer value. The pixels in a block may be arranged in rows and columns. Furthermore, a block need not necessarily have the same number of pixels in the horizontal and vertical directions. For example, a block may comprise NxM pixels, where M is not necessarily equal to N.

After intra-predictive or inter-predictive coding of the PUs of a CU, video encoder 20 may calculate residual data for the TUs of the CU. The PUs may include pixel data in the spatial domain (also referred to as the pixel domain), and the TUs may include coefficients in the transform domain after applying a transform (e.g., a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform) to the residual video data. The residual data may correspond to pixel differences between pixels of an unencoded picture and prediction values corresponding to the PU. Video encoder 20 may form TUs including the residual data for the CU, and then transform the TUs to produce transform coefficients for the CU.

After performing any transforms to produce transform coefficients, video encoder 20 may perform quantization on the transform coefficients. Quantization generally refers to the process of quantizing the transform coefficients to potentially reduce the amount of data used to represent the coefficients, thereby providing further compression. The quantization process may reduce the bit depth associated with some or all of the coefficients. For example, an n-bit value may be truncated to an m-bit value during quantization, where n is greater than m.

In some examples, video encoder 20 may use a predefined scan order to scan the quantized transform coefficients to produce a serialized vector that can be entropy encoded. In other examples, video encoder 20 may perform adaptive scanning. After scanning the quantized transform coefficients to form a one-dimensional vector, video encoder 20 may entropy encode the one-dimensional vector, for example, according to context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding, or another entropy encoding method. Video encoder 20 may also entropy encode syntax elements associated with the encoded video data for use by video decoder 30 in decoding the video data.

To perform CABAC, video encoder 20 may assign context within a context model to a symbol to be transmitted. The context may relate to, for example, whether neighboring values of the symbol are non-zero. To perform CAVLC, video encoder 20 may select a variable length code for the symbol to be transmitted. Codewords in variable length coding (VLC) may be constructed such that relatively shorter codes correspond to more likely symbols, while longer codes correspond to less likely symbols. In this way, using VLC may achieve bit savings relative to, for example, using equal length codewords for each symbol to be transmitted. Probability determinations may be made based on the context assigned to the symbol.

Video encoder 20 may output a bitstream comprising a sequence of bits forming a representation of a coded picture and associated data. The term "bitstream" may be a collective term used to refer to a network abstraction layer (NAL) unit stream (e.g., a series of NAL units) or a byte stream (e.g., a NAL unit stream containing a start code header and an encapsulation of NAL units as specified by Annex B of the HEVC standard). A NAL unit is a syntax structure containing an indication of the type of data in the NAL unit and bytes of that data in the form of a raw byte sequence payload (RBSP), interspersed with emulation prevention bits as needed. Each NAL unit may include a NAL unit header and may encapsulate an RBSP. The NAL unit header may include a syntax element indicating a NAL unit type code. The NAL unit type code specified by the NAL unit header of the NAL unit indicates the type of the NAL unit. The RBSP may be a syntax structure containing an integer number of bytes encapsulated within the NAL unit. In some cases, the RBSP comprises zero bits.

Different types of NAL units can encapsulate different types of RBSPs. For example, a first type of NAL unit can encapsulate an RBSP for a picture parameter set (PPS), a second type of NAL unit can encapsulate an RBSP for a slice segment, a third type of NAL unit can encapsulate an RBSP for supplemental enhancement information (SEI), and so on. NAL units that encapsulate RBSPs for video coding data (as opposed to RBSPs for parameter sets and SEI messages) can be referred to as video coding layer (VCL) NAL units. NAL units that contain parameter sets (e.g., video parameter sets (VPS), sequence parameter sets (SPS), PPS, etc.) can be referred to as parameter set NAL units.

This disclosure may refer to the NAL unit that encapsulates the RBSP for a segment slice as a coded slice NAL unit. As defined in HEVC WD, a slice segment is an integer number of CTUs that are sequentially ordered in a tile scan and contained in a single NAL unit. In contrast, in HEVC WD, a slice may be an integer number of CTUs contained in an independent slice segment and, if any, all subsequent dependent slice segments preceding the next independent slice segment (if any) within the same access unit. An independent slice segment is a slice segment in which the values of the syntax elements of the slice segment header are not inferred from the values of the previous slice segment. A dependent slice segment is a slice segment in which the values of some syntax elements of the slice segment header are inferred from the values of the previous independent slice segment in decoding order. The RBSP of a coded slice NAL unit may include a slice segment header and slice data. The slice segment header is a portion of the coded slice segment that contains data elements related to the first or all CTUs represented in the slice segment. The slice header is the slice segment header of an independent slice segment, where the independent slice region is the current slice segment or the independent slice segment that is closest to the current dependent slice segment in decoding order.

A VPS is a syntax structure that contains syntax elements applicable to zero or more all coded video sequences (CVSs). An SPS is a syntax structure that contains syntax elements applicable to zero or more all CVSs. An SPS may include syntax elements that identify the VPS that is active when the SPS is active. Thus, syntax elements of a VPS may be more generally applicable than syntax elements of an SPS.

A parameter set (e.g., VPS, SPS, PPS, etc.) may contain an identification referenced directly or indirectly from a slice header of a slice. This reference process is referred to as "activation." Thus, when video decoder 30 is decoding a particular slice, a parameter set referenced directly or indirectly by syntax elements in the slice header of that particular slice is said to be "activated." Depending on the parameter set type, activation may occur on a per-picture or per-sequence basis. For example, a slice header of a slice may include syntax elements identifying a PPS. Thus, when the video coder decodes the slice, the PPS may be activated. Furthermore, the PPS may include syntax elements identifying an SPS. Thus, when the PPS identifying the SPS is activated, the SPS may be activated. The SPS may include syntax elements identifying a VPS. Thus, when the SPS identifying the VPS is activated, the VPS is activated.

Video decoder 30 may receive a bitstream generated by video encoder 20. Furthermore, video decoder 30 may parse the bitstream to obtain syntax elements from the bitstream. Video decoder 30 may reconstruct a picture of the video data based, at least in part, on the syntax elements obtained from the bitstream. The process of reconstructing the video data may be generally reciprocal to the process performed by video encoder 20. For example, video decoder 30 may determine the predictive blocks of the PUs of the current CU using the motion vectors of the PUs. Furthermore, video decoder 30 may inverse quantize the coefficient blocks of the TUs of the current CU. Video decoder 30 may perform an inverse transform on the coefficient blocks to reconstruct the transform blocks of the TUs of the current CU. Video decoder 30 may reconstruct the coding blocks of the current CU by adding samples of the predictive blocks of the PUs of the current CU to corresponding samples of the transform blocks of the TUs of the current CU. By reconstructing the coding blocks of each CU of the picture, video decoder 30 may reconstruct the picture.

In HEVC WD, a CVS can start with an instantaneous decoding refresh (IDR) picture, a broken link access (BLA) picture, or a clean random access (CRA) picture that is the first picture in the bitstream, including all subsequent pictures that are not IDR or BLA pictures. IDR pictures contain only I slices (i.e., slices that use only intra prediction). IDR pictures can be the first picture in the bitstream in decoding order, or they can appear later in the bitstream. Each IDR picture is the first picture of a CVS in decoding order. In HEVC WD, an IDR picture can be an intra random access point (IRAP) picture with nal_unit_type equal to IDR_W_RADL or IDR_N_LP for each VCL NAL unit.

IDR pictures can be used for random access. However, pictures that follow an IDR picture in decoding order cannot use pictures decoded before the IDR picture as references. Therefore, a bitstream that relies on IDR pictures for random access may have significantly lower coding efficiency than a bitstream that uses additional types of random access pictures. In at least some examples, an IDR access unit is an access unit that contains an IDR picture.

HEVC introduces the concept of CRA pictures to allow pictures that follow a CRA picture in decoding order but precede it in output order to reference pictures decoded before the CRA picture. Pictures that follow a CRA picture in decoding order but precede it in output order are called preceding pictures associated with the CRA picture (or preceding pictures of the CRA picture). Specifically, to improve coding efficiency, HEVC introduces the concept of CRA pictures to allow pictures that follow a CRA picture in decoding order but precede it in output order to reference pictures decoded before the CRA picture. A CRA access unit is an access unit whose coded picture is a CRA picture. In HEVC WD, a CRA picture is an intra random access picture with nal_unit_type equal to CRA_NUT for each VCL NAL unit.

The preceding pictures of a CRA picture can be correctly decoded if decoding starts from an IDR picture or a CRA picture that occurs before the CRA picture in decoding order. However, when random access occurs from a CRA picture, the preceding pictures of the CRA picture may be undecodable. Therefore, a video decoder typically decodes the preceding pictures of a CRA picture during random access decoding. To prevent error propagation from reference pictures that may be unavailable depending on where decoding starts, no pictures that follow the CRA picture in both decoding order and output order can use any pictures that precede the CRA picture in decoding order or output order (including the preceding pictures) for reference.

The concept of BLA pictures was introduced in HEVC after the introduction of CRA pictures and is based on the concept of CRA pictures. BLA pictures are usually derived from a bitstream spliced at the position of a CRA picture, and in the spliced bitstream, the splicing point CRA picture is changed to a BLA picture. Therefore, a BLA picture may be a CRA picture at the original bitstream, and the CRA picture is changed by the bitstream splicer to a BLA picture after bitstream splicing at the position of the CRA picture. In some cases, an access unit containing a RAP picture may be referred to herein as a RAP access unit. A BLA access unit is an access unit containing a BLA picture. In HEVC WD, a BLA picture may be an intra-frame random access picture, for which each VCL NAL unit has a nal_unit_type equal to BLA_W_LP, BLA_W_RADL, or BLA_N_LP.

In general, an IRAP picture contains only I slices and can be a BLA picture, a CRA picture, or an IDR picture. For example, HEVC WD indicates that an IRAP picture can be a coded picture for which each VCL NAL unit has a nal_unit_type in the range of BLA_W_LP to RSV_IRAP_VCL23, inclusive. Furthermore, HEVC WD indicates that the first picture in the bitstream in decoding order must be an IRAP picture. Table 7-1 of HEVC WD shows the NAL unit type code and NAL unit type category. Table 7-1 of HEVC WD is reproduced below.

Table 7-1 - NAL unit type code and NAL unit type category

One difference between BLA pictures and CRA pictures is as follows. For a CRA picture, if decoding starts from a RAP picture that precedes the CRA picture in decoding order, the associated leading pictures can be correctly decoded. However, when random access occurs from a CRA picture (i.e., when decoding starts from the CRA picture, or in other words, when the CRA picture is the first picture in the bitstream), the leading pictures associated with the CRA picture cannot be correctly decoded. In contrast, there may not be a situation where the leading pictures associated with a BLA picture are decodable, even when decoding starts from a RAP picture that precedes the BLA picture in decoding order.

Some of the leading pictures associated with a particular CRA picture or a particular BLA picture can be correctly decoded even when the particular CRA picture or the particular BLA picture is the first picture in the bitstream. Such leading pictures may be referred to as decodable leading pictures (DLP) or random access decodable leading (RADL) pictures. In HEVC WD, a RADL picture may be a coded picture with nal_unit_type equal to RADL_R or RADL_N for each VCL NAL unit. Furthermore, HEVC WD indicates that all RADL pictures are leading pictures and that RADL pictures are not used as reference pictures for the decoding process of following pictures of the same associated IRAP picture. When present, all RADL pictures precede all following pictures of the same associated IRAP picture in decoding order. HEVC WD indicates that a RADL access unit may be an access unit whose coded picture is a RADL picture. Following pictures may be pictures that follow the associated IRAP picture in output order (i.e., the previous IRAP picture in decoding order).

Other preceding pictures may be referred to as non-decodable preceding pictures (NLP) or random access skip preceding (RASL) pictures. In HEVC WD, RASL pictures may be coded pictures with nal_unit_type equal to RASL_R or RASL_N for each VCL NAL unit. All RASL pictures are preceding pictures of the associated BLA picture or CRA picture.

Assuming the necessary parameter sets are available when they are needed for activation, an IRAP picture and all subsequent non-RASL pictures in decoding order can be correctly decoded without performing the decoding process for any pictures preceding the IRAP picture in decoding order. There may be pictures in the bitstream that contain only I slices that are not IRAP pictures.

In multi-view coding, there may be multiple views of the same scene from different viewpoints. The term "access unit" may be used to refer to a set of pictures corresponding to the same time instance. Thus, video data may be conceptualized as a series of access units occurring over time. A "view component" may be a coded representation of a view in a single access unit. In this disclosure, a "view" may refer to a sequence or group of view components associated with the same view identifier. A view component may contain a texture view component and a depth view component. In this disclosure, a "view" may refer to a group or sequence of one or more view components associated with the same view identifier.

A texture view component (i.e., a texture picture) may be a coded representation of the texture of a view in a single access unit. A texture view may be a sequence of texture view components associated with the same value of a view order index. The view order index of a view may indicate the camera position of the view relative to other views. A depth view component (i.e., a depth picture) may be a coded representation of the depth of a view in a single access unit. A depth view may be a group or sequence of one or more depth view components associated with the same value of a view order index.

In MV-HEVC, 3D-HEVC, and SHVC, a video encoder may generate a bitstream comprising a series of NAL units. Different NAL units of the bitstream may be associated with different layers of the bitstream. A layer may be defined as a set of VCL NAL units and associated non-VCL NAL units with the same layer identifier. A layer may be equivalent to a view in multi-view video coding. In multi-view video coding, a layer may contain all view components of the same layer at different time instances. Each view component may be a coded picture of a video scene belonging to a particular view at a particular time instance. In some examples of 3D video coding, a layer may contain all coded depth pictures of a particular view or coded texture pictures of a particular view. In other examples of 3D video coding, a layer may contain both texture view components and depth view components of a particular view. Similarly, in the context of scalable video coding, a layer typically corresponds to a coded picture having different video characteristics than coded pictures in other layers. Such video characteristics typically include spatial resolution and quality level (e.g., signal-to-noise ratio). In HEVC and its extensions, temporal scalability can be achieved within a layer by defining groups of pictures with a specific temporal level as sub-layers.

For each corresponding layer of the bitstream, data in the lower layers can be decoded without reference to data in any higher layers. In scalable video coding, for example, data in the base layer can be decoded without reference to data in the enhancement layers. In general, NAL units can encapsulate data for only a single layer. Therefore, NAL units that encapsulate data for the highest remaining layer of the bitstream can be removed from the bitstream without affecting the decodability of data in the remaining layers of the bitstream. In multi-view coding and 3D-HEVC, higher layers may include additional view components. In SHVC, higher layers may include signal-to-noise ratio (SNR) enhancement data, spatial enhancement data, and/or temporal enhancement data. In MV-HEVC, 3D-HEVC, and SHVC, a layer may be referred to as a "base layer" if the video decoder can decode pictures in the layer without reference to data from any other layer. The base layer may conform to the HEVC base specification (e.g., HEVC WD).

In SVC, layers other than the base layer may be referred to as "enhancement layers" and may provide information that enhances the visual quality of video data decoded from the bitstream. SVC may enhance spatial resolution, signal-to-noise ratio (i.e., quality), or temporal rate. In scalable video coding (e.g., SHVC), a "layer representation" may be a coded representation of a spatial layer in a single access unit. For ease of explanation, this disclosure may refer to view components and/or layer representations as "view components/layer representations" or simply as "pictures."

To implement these layers, the NAL unit header may include the nuh_reserved_zero_6bits syntax element. In HEVC WD, the nuh_reserved_zero_6bits syntax element is reserved. However, in MV-HEVC, 3D-HEVC, and SVC, the nuh_reserved_zero_6bits syntax element is referred to as the nuh_layer_id syntax element. The nuh_layer_id syntax element specifies the identifier of a layer. NAL units in a bitstream that specify different values for the nuh_layer_id syntax element belong to different layers of the bitstream.

In some examples, if a NAL unit relates to a base layer in multi-view coding (e.g., MV-HEVC), 3DV coding (e.g., 3D-HEVC), or scalable video coding (e.g., SHVC), the nuh_layer_id syntax element of the NAL unit is equal to 0. Data in the base layer of the bitstream can be decoded without reference to data in any other layer of the bitstream. If a NAL unit does not relate to a base layer in multi-view coding, 3DV, or scalable video coding, the nuh_layer_id syntax element of the NAL unit may have a non-zero value.

Furthermore, some view components/layer representations within a layer can be decodable without reference to other view components/layer representations within the same layer. Thus, NAL units encapsulating data for certain view components/layer representations of a layer can be removed from the bitstream without affecting the decodability of other view components/layer representations in that layer. Removing the NAL units encapsulating data for such view components/layer representations can reduce the frame rate of the bitstream. A subset of view components/layer representations within a layer that can be decodable without reference to other view components/layer representations within the layer may be referred to herein as a "sublayer" or "temporal sublayer."

A NAL unit may include a temporal_id syntax element that specifies the temporal identifier (i.e., TemporalIds) of the NAL unit. The temporal identifier of a NAL unit identifies the sublayer to which the NAL unit belongs. Thus, each sublayer of a bitstream may have a different temporal identifier. In general, if the temporal identifier of the first NAL unit of a layer is less than the temporal identifier of the second NAL unit of the same layer, the data encapsulated by the first NAL unit can be decoded without reference to the data encapsulated by the second NAL unit.

A bitstream can be associated with multiple operation points. Each operation point of the bitstream is associated with a set of layer identifiers (e.g., a set of nuh_layer_id values) and a temporal identifier. The set of layer identifiers can be represented as OpLayerIdSet, and the temporal identifier can be represented as TemporalID. A NAL unit is associated with an operation point if its layer identifier is in the layer identifier set of the operation point and its temporal identifier is less than or equal to the temporal identifier of the operation point. Thus, an operation point can correspond to a subset of NAL units in the bitstream.

As introduced above, this disclosure relates to storing video content in files based on the ISO Base Media File Format (ISOBMFF). Specifically, this disclosure describes various techniques for storing a video stream containing multiple coded layers, where each layer may be a scalable layer, a texture view, a depth view, or other types of layers or views. The techniques of this disclosure may be applied, for example, to the storage of MV-HEVC video data, SHVC video data, 3D-HEVC video data, and/or other types of video data.

File formats and file format standards will now be briefly discussed. File format standards include the ISO Base Media File Format (ISOBMFF, ISO/IEC 14496-12, hereinafter "ISO/IEC 14996-12") and other file format standards derived from ISOBMFF, including the MPEG-4 file format (ISO/IEC 14496-14), the 3GPP file format (3GPP TS 26.244), and the AVC file format (ISO/IEC 14496-15, hereinafter "ISO/IEC 14996-15"). Thus, ISO/IEC 14496-12 specifies the ISO base media file format. Other documents extend the ISO base media file format for specific applications. For example, ISO/IEC 14496-15 describes the carriage of NAL unit structured video in the ISO base media file format. H.264/AVC and HEVC, and their extensions, are examples of NAL unit structured video. ISO/IEC 14496-15 includes a section describing the carriage of H.264/AVC NAL units. In addition, Section 8 of ISO/IEC 14496-15 describes the carriage of HEVC NAL units.

ISOBMFF serves as the foundation for many codec packaging formats (e.g., the AVC file format) and for many multimedia container formats (e.g., the MPEG-4 file format, the 3GPP file format (3GP), and the DVB file format). In addition to continuous media such as audio and video, static media such as images and metadata can be stored in files conforming to ISOBMFF. Files structured according to ISOBMFF can be used for many purposes, including local media file playback, progressive download of remote files, segments for Dynamic Adaptive Streaming over HTTP (DASH), containers for content to be streamed and its packetization instructions, and recording of received real-time media streams. Thus, although originally designed for storage, ISOBMFF has proven its value for streaming (e.g., for progressive download or DASH). For streaming purposes, movie fragments defined in ISOBMFF can be used.

A file conforming to the HEVC file format may include a series of objects called boxes. A box may be an object-oriented building block defined by a unique type identifier and a length. For example, a box may be a basic syntactic structure in ISOBMFF, comprising a four-character coded box type, a byte count for the box, and a payload. In other words, a box may be a syntactic structure that includes a coded box type, a byte count for the box, and a payload. In some cases, all data in a file conforming to the HEVC file format may be included within a box, and data may not be present in the file that is not within a box. Thus, an ISOBMFF file may consist of a series of boxes, and a box may contain other boxes. For example, the payload of a box may include one or more additional boxes. Figures 5 and 6, described in detail elsewhere in this disclosure, show example boxes within a file according to one or more techniques of this disclosure.

An ISOBMFF-compliant file may contain various types of boxes. For example, an ISOBMFF-compliant file may include a file type box, a media data box, a movie box, a movie fragment box, and so on. In this example, the file type box contains file type and compatibility information. The media data box may contain samples (e.g., coded pictures). The movie box ("moov") contains metadata for the continuous media streams present in the file. Each of these continuous media streams may be represented in the file as a track. For example, the movie box may contain metadata about the movie (e.g., the logical and timing relationships between samples, as well as pointers to the locations of the samples). The movie box may contain several types of sub-boxes. A sub-box within a movie box may include one or more track boxes. A track box may contain information about individual tracks of a movie. A track box may include a track header box that specifies the overall information for a single track. Furthermore, a track box may include a media box containing a media information box. A media information box may include a sample table box containing data indexes for media samples within a track. The information in the sample table box can be used to locate the sample in time (and, for each of the samples of a track, by type, size, container, and offset to the container of the sample). Thus, metadata for a track is enclosed in a track box ("trak"), while the media content of the track is enclosed in a media data box ("mdat") or directly in a separate file. The media content for a track includes (e.g., consists of) a sequence of samples, such as an audio or video access unit.

ISOBMFF specifies the following types of tracks: media tracks, which contain elementary media streams; hint tracks, which contain media emission instructions or packet streams indicating reception; and timing metadata tracks, which include metadata for time synchronization. The metadata for each track consists of a list of sample description items, each of which provides the encoding or encapsulation format used in the track and the initialization data required to process that format. Each sample is associated with one of the track's sample description items.

ISOBMFF implements various mechanisms for specifying sample-specific metadata. Certain boxes within the sample table box ("stbl") have been standardized to address common needs. For example, the synchronization sample box ("stss") is a box within the sample table box. The synchronization sample box is used to list random access samples for a track. This disclosure may refer to the samples listed by the synchronization sample box as synchronization samples. In another example, a sample grouping mechanism implements mapping samples into groups of samples sharing the same property, specified as a sample group descriptor in the file, based on a four-character grouping type. Several grouping types have been specified in ISOBMFF.

The Sample Table box may include one or more SampleToGroup boxes and one or more Sample Group Description boxes (i.e., SampleGroupDescription boxes). The SampleToGroup box can be used to identify the sample group to which a sample belongs, along with an associated description of the sample group. In other words, the SampleToGroup box may indicate the group to which the sample belongs. The SampleToGroup box may have a box type of "sbgp." The SampleToGroup box may include a grouping type element (e.g., grouping_type). The grouping type element may be an integer that identifies the type of sample grouping (i.e., the rule used to form sample groups). In addition, the SampleToGroup box may include one or more entries. Each entry in the SampleToGroup box may be associated with a series of different, non-overlapping, consecutive samples in a playback track. Each entry may indicate a sample count element (e.g., sample_count) and a group description index element (e.g., group_description_index). The sample count element of an entry may indicate the number of samples associated with the entry. In other words, the sample count element of an entry may be an integer that specifies the number of consecutive samples with the same sample group descriptor. The group description index element may identify a SampleGroupDescription box containing a description of the samples associated with the item. The group description index elements of multiple items may identify the same SampleGroupDescription box.

The current file format design may have one or more problems. In order to store video content for a specific video codec based on ISOBMFF, a file format specification of that video codec may be needed. For the storage of video streams containing multiple layers such as MV-HEVC and SHVC, some concepts from the SVC and MVC file formats can be reused. However, many parts cannot be directly used for SHVC and MV-HEVC video streams. Direct application of the HEVC file format has at least the following disadvantages: SHVC and MV-HEVC can start with an access unit that contains an IRAP picture in the base layer but may also contain other non-IRAP pictures in other layers, or vice versa. Synchronization samples are currently not allowed for indication of this point in random access.

This disclosure describes potential solutions to the above problems, as well as other potential improvements, for efficient and flexible storage of video streams containing multiple layers. The techniques described in this disclosure are potentially applicable to any file format for storing such video content decoded by any video codec, but the description is directed to storing SHVC and MV-HEVC video streams based on the HEVC file format, which is specified in clause 8 of ISO/IEC 14496-15.

Detailed embodiments of the technology of the present invention will be discussed in detail below. The technology of the present invention can be summarized in the following examples. The following examples can be used separately. Alternatively, various combinations of the following examples can be used together.

In a first example, Compressorname is the value specified in the VisualSampleEntry box. As described in Section 8.5.2.1 of ISO/IEC 14496-12, the VisualSampleEntry box is a type of sample table box for a video track that stores detailed information about the type of decoding used and any initialization information required for that decoding. Compressorname indicates the name of the compressor used to generate the media data. A video decoder can use the value of Compressorname to determine how and/or whether to decode the video data in a file. As defined in Section 8.5.3 of ISO/IEC 14496-12, Compressorname is formatted in a fixed 32-byte field, with the first byte set to the number of bytes to be displayed, followed by the number of bytes of data that can be displayed, and then padded to a total of 32 bytes (including the size byte).

The first example allows two new values for Compressorname. The first new value for Compressorname is "\013SHVC Coding" for files containing SHVC video streams. The second new value for Compressorname is "\016MV-HEVC Coding" for files containing MV-HEVC video streams. This first example can be implemented as shown in Sections 9.5.3.1.3 and 10.5.3.2 below.

As briefly described above, a file may include a movie box containing metadata for the file's tracks. The movie box may include a track box for each track of the file. In addition, the track box may include a media information box containing all objects that declare characteristic information about the media of the track. The media information box may include a sample table box. The sample table box may specify sample-specific metadata. For example, the sample table box may include multiple sample description boxes. Each of the sample description boxes may be an instance of a sample item. In ISO/IEC 14496-12, an instance of the VisualSampleEntry class may be used as a sample item. The class of sample items for a specific video decoding standard may extend the VisualSampleEntry class. For example, the class of sample items for HEVC may extend the VisualSampleEntry class. Therefore, this disclosure may refer to different classes that extend the VisualSampleEntry class as different sample item types.

In a second example, two new sample item (i.e., "sample") types are defined for HEVC tracks—"hev2" and "hvc2". The two new sample item types allow the use of aggregators and extractors. In general, an aggregator aggregates multiple NAL units into a single aggregated unit of data. For example, an aggregator may contain multiple NAL units and/or may actually concatenate multiple NAL units. In general, an extractor indicates the type of data obtained from other tracks. For example, storing media data (e.g., HEVC data) across multiple tracks can result in compact files because data duplication can be avoided by using relatively small data units called extractors (which are embedded in the media data as NAL units) to reference data across media tracks. This second example may be implemented as shown in Sections 9.5.3.1.1, 9.5.3.1.2, 9.5.4, 9.5.6, 10.4.5, 10.5.3.1.1.1, and 10.5.3.2 below.

In a third example, the definition of a sample item associated with specific requirements regarding the storage of parameter sets for a multi-layer bitstream is modified to enable convenient random access to a specific layer or a specific operation point. For example, when an SHVC, MV-HEVC, or 3D-HEVC playback track has a sample item and when a sample contains at least one IRAP picture, all parameters required for decoding the sample should be included in the sample item or the sample itself. In this example, when a sample does not contain any IRAP pictures, all parameter sets (e.g., VPS, SPS, PPS) required for decoding the sample should be included in the sample item or in any sample from the previous sample containing at least one IRAP picture to the sample itself (inclusive). This third example can be implemented as shown below in Section 9.5.3.1.1.

In an alternative version of the third example, when an SHVC, MV-HEVC, or 3D-HEVC track has a sample entry and when a picture in the sample is an IRAP picture, all parameter sets required for decoding the picture should be included in the sample entry or in the sample itself. Furthermore, in this alternative, when the sample does not contain any IRAP pictures, all parameter sets required for decoding the picture should be included in the sample entry or in any sample in the same layer following the previous sample containing at least one IRAP picture, inclusive.

In a fourth example, the following case is defined for existing sample item types. In this example, samples belonging to the sample item types "hev1" and "hvc1" contain HEVC, SHVC, and MV-HEVC configurations for SHVC and MV-HEVC tracks with HEVC VCL NAL units. Furthermore, sample item types "hev1" and "hvc1" containing SHVC and MV-HEVC configurations are defined for SHVC and MV-HEVC tracks without HEVC NAL units but with VCL NAL units with nuh_layer_id greater than 0, where extractors are not allowed. This fourth example can be implemented as shown below in Section 9.5.3.1.1.

In a fifth example, synchronization samples in an SHVC, MV-HEVC, or 3D-HEVC track are defined as samples containing pictures that are all IRAP pictures. This fifth example may be implemented as shown below in Sections 9.5.5 and 10.4.3. As specified below in Section 9.5.5, if every coded picture in an access unit is an IRAP picture, then SHVC samples are considered synchronization samples, as defined in HEVC WD. Furthermore, as specified below in Section 10.4.3, if every coded picture in an access unit is an IRAP picture without a RASL picture, then MV-HEVC samples are considered synchronization samples, as defined in HEVC WD.

Thus, in a fifth example, as part of generating a file, file generation device 34 may generate a synchronization sample box that includes a synchronization sample table that files synchronization samples for a track of multi-layer video data. Each synchronization sample of a track is a random access sample of the track. If each coded picture in an access unit is an IRAP picture, then the scalable video coding sample is a synchronization sample. If each coded picture in an access unit is an IRAP picture without a RASL picture, then the multiview video coding sample is a synchronization sample.

In an alternative version of the fifth example, sync samples in an SHVC, MV-HEVC, or 3D-HEVC track are defined as samples containing pictures that are all IRAP pictures without RASL pictures. A sync sample table documents the sync samples. Optionally, a sync sample sample group documents the sync samples. In other words, the sync sample sample group contains information identifying the sync samples.

In a sixth example, a "rap" sample group is defined as containing samples that contain pictures that are all IRAP pictures (with or without RASL pictures). This sixth example may be implemented as shown below in Section 9.5.5. Alternatively, in the sixth example, a "rap" sample group is defined as containing samples that contain pictures that are all IRAP pictures, but does not include samples indicated as sync samples.

In a seventh example, a new sample group or a new box is defined that documents all samples that contain at least one IRAP picture, the NAL unit type of the VCL NAL units in the IRAP pictures in the sample, whether all coded pictures in the sample are IRAP pictures and, if not, the number of IRAP pictures in the sample, and the layer ID values of such IRAP pictures in the sample.

Thus, in this seventh example, file generation device 34 may generate a file including a track box containing metadata for a track in the file. The media data for the track includes a series of samples. Each of the samples may be an access unit of multiple layers of video data. As part of generating the file, file generation device 34 generates an additional box in the file to document all samples containing at least one IRAP picture.

This seventh example is implemented in part as shown below in Section 9.5.5.1. As shown below in Section 9.5.5.1, the Randomly Accessible Samples Entry class extends the VisualSampleGroupEntry class. An instance of the Randomly Accessible Samples Entry class (i.e., the Randomly Accessible Samples Entry box) corresponds to a sample that contains at least one IRAP picture. Furthermore, the Randomly Accessible Samples Entry box includes an all_pics_are_IRAP value that specifies whether all coded pictures in the corresponding sample are IRAP pictures.

Thus, in a seventh example, file generation device 34 may generate a sample entry including a value, eg, all_pics_are_IRAP. A value equal to 1 specifies that every coded picture in the sample is an IRAP picture. A value equal to 0 specifies that not all coded pictures in the sample are IRAP pictures.

Furthermore, according to the seventh example, when not all coded pictures of a sample are IRAP pictures, file generation device 34 may include, in the sample entry corresponding to the sample, a value indicating the number of IRAP pictures in each sample of the sample group. Additionally, when not all coded pictures in the sample are IRAP pictures, file generation device 34 may include, in the sample entry corresponding to the sample, a value indicating a layer identifier of an IRAP picture in the sample.

Alternatively, in a seventh example, a new sample group or new frame documents such samples, but does not include samples indicated as sync samples or members of a "rap" sample group.

This seventh example can address one or more issues that may arise when using ISOBMFF or its existing extensions to store multi-layer video data. For example, in single-layer video coding, there is typically only a single coded picture per access unit. However, in multi-layer video coding, there is typically more than one coded picture per access unit. ISOBMFF and its existing extensions do not provide a way to indicate which samples contain one or more IRAP pictures. This can hinder a computing device's ability to locate random access points in a file or perform layer switching. For example, without information indicating which of the samples contain one or more IRAP pictures, a computing device may need to parse and interpret NAL units in order to determine whether an access unit can be used as a random access point and/or for layer switching. Parsing and interpreting NAL units can add complexity to the computing device and can consume time and processing resources. Furthermore, some computing devices that perform random access and/or layer switching (e.g., streaming servers) are not configured to parse or interpret NAL units.

In the eighth example, a new type of subsample is introduced, where each subsample contains a coded picture and its associated non-VCL NAL unit. This eighth example can be implemented as shown below in Section 9.5.8. Thus, in this eighth example, the file generator 34 can generate a file including a track box containing metadata for a track in the file. The media data for the track includes a series of samples. Each of the samples is an access unit of multi-layer video data. As part of generating the file, the file generator 34 generates a subsample information box in the file, which contains a flag that specifies the type of subsample information given in the subsample information box. When the flag has a specific value, the subsample corresponding to the subsample information box contains exactly one coded picture and zero or more non-VCL NAL units associated with the coded picture.

This eighth example can address one or more issues that may arise when using ISOBMFF or its existing extensions to store multi-layer video data. For example, in multi-layer video coding, multiple coded pictures may exist per sample. For example, for each layer, a sample may contain one or more pictures. However, in the ISOBMFF extensions for H.264/AVC and HEVC, when a sample contains multiple pictures, the subsample information box does not provide information about individual pictures within the sample. The techniques of this eighth example address this issue by providing a new type of subsample information box that provides information about subsamples containing only one coded picture and non-VCL NAL units associated with the coded picture. Providing information about individual coded pictures in the file structure, as opposed to providing this information only within the NAL units associated with the coded pictures, allows a computing device to determine information about the coded pictures without having to interpret the NAL units. In some cases, to reduce computing device complexity and/or increase computing device throughput, the computing device is not configured to interpret NAL units. In some examples where a computing device is streaming NAL units stored in a file, the computing device may use information in the subsample information box to determine whether to forward the NAL units for the subsample to the client device.

The ninth example relates to the handling of non-output samples in a multi-layer context. Specifically, in the ninth example, when an access unit contains some coded pictures with pic_output_flag equal to 1 and some other coded pictures with pic_output_flag equal to 0, at least two tracks must be used to store the stream so that within each track, all coded pictures in each sample have the same pic_output_flag value. This ninth example can be implemented as shown below in Section 9.5.9.

Thus, in this ninth example, file generation device 34 may generate a file including a media data box enclosing media content. The media content includes a series of samples. Each of the samples is an access unit of multi-layer video data. In response to at least one access unit of the bitstream of multi-layer video data including a coded picture having a picture output flag (e.g., pic_output_flag) equal to 1 and a coded picture having a picture output flag equal to 0, file generation device 34 may store the bitstream in a file using at least two tracks. For each respective track from the at least two tracks, all coded pictures in each sample of the respective track have the same picture output flag value.

This ninth example can address one or more issues that can arise when using ISOBMFF or its existing extensions to store multi-layer video data. For example, if a single track is used to store coded pictures with a picture output flag equal to 0 and a picture output flag equal to 1, various file formatting rules will be violated. For example, file formatting rules typically require that only one sample be present in a track at any time. If a single track stores coded pictures with a picture output flag equal to 0 and a picture output flag equal to 1, then multiple samples will be present in the track at any time. Forcing coded pictures with different picture output flag values to be in different tracks of the file can address this issue.

The following describes example implementations of some of the techniques of this disclosure. The example implementations described below are based on the most recently integrated specification of ISO/IEC 14496-15 in MPEG output document W13478. Included below are changes to Annex A (shown by underlining) and added sections (Section 9 for SHVC and Section 10 for MV-HEVC). In other words, specific examples of this disclosure may modify Annex A of ISO/IEC 14496-15 and may add Sections 9 and/or 10 to ISO/IEC 14496-15. Text shown by underlining and double underlining may have specific relevance to examples of this disclosure. Although the term SHVC is used throughout the examples described herein, the design of this disclosure will actually support not only the SHVC codec, but instead all multi-layer codecs, including MV-HEVC and 3D-HEVC, unless explicitly mentioned otherwise.

9 SHVC basic stream and sample definition

9.1 Introduction

This clause specifies the storage format of SHVC data. It extends the definition of the storage format of HEVC in clause 8.

The file format for storage of SHVC content as defined in this clause and Appendices A to D uses existing capabilities of the ISO base media file format and the normal HEVC file format (i.e., the file format specified in clause 8). In addition, the following structures or extensions are used to support SHVC-specific features.

Aggregator:

The structure of efficient scalable grouping of NAL units is achieved by changing the irregular pattern of NAL units into a regular pattern of aggregated data units.

Extractor:

A structure that enables efficient extraction of NAL units from a different track than the one containing the media data.

Time metadata statement:

A structure for storing time-aligned information for media samples.

HEVC compatibility:

Provides for storing SHVC bitstreams in an HEVC-compatible manner so that the HEVC-compatible base layer can be used by any reader conforming to the normal HEVC file format.

9.2 Basic Stream Structure

SHVC streams are stored according to 8.2, with the following definition of an SHVC video elementary stream:

An SHVC video elementary stream shall contain all video coding related NAL units (i.e., those NAL units that contain video data or signal video structure) and may contain non-video coding related NAL units such as SEI messages and access unit delimiter NAL units. Aggregators (see A.2) or extractors (see A.3) may also be present. Aggregators and extractors shall be processed as defined in this International Standard (e.g., shall not be placed directly in the output buffer when accessing the file). Other NAL units that are not explicitly suppressed may be present and, if not recognized, shall be ignored (e.g., not placed in the output buffer when accessing the file).

SHVC streams shall not be stored with associated parameter set streams.

There may be VCL NAL units with nuh_layer_id equal to 0, VCL NAL units with nuh_layer_id greater than 0, and non-VCL NAL units present in the SHVC video elementary stream. In addition, there may be aggregator NAL units and extractor NAL units present in the SHVC video elementary stream.

9.3 Use of common HEVC file format

The SHVC file format is an extension of the normal HEVC file format defined in clause 8.

9.4 Sample and Configuration Definition

9.4.1 Introduction

SHVC sample: An SHVC sample is also an access unit as defined in Annex H of ISO/IEC 23008-2.

9.4.2 Standard order and restrictions

9.4.2.1 Limitations

In addition to the requirements in 8.3.2, the following restrictions apply to SHVC data.

● VCL NAL unit: In the instance where its composition time is the composition time of a picture represented by an access unit, it shall contain all VCL NAL units in the access unit. An SHVC sample shall contain at least one VCL NAL unit.

Aggregator/Extractor: The order of all NAL units included in an aggregator or referenced by an extractor is exactly in decoding order, as if these NAL units were present in a sample that did not contain the aggregator/extractor. After processing an aggregator or extractor, all NAL units must be in valid decoding order, as specified in ISO/IEC 23008-2.

9.4.2.2 Decoder Configuration Record

When the decoder configuration record defined in 8.3.3.1 is used for a stream that can be interpreted as an SHVC or HEVC stream, the HEVC decoder configuration record should reflect the properties of the HEVC compatible base layer, for example, it should only contain the parameter sets required for decoding the HEVC base layer.

SHVCDecoderConfigurationRecord is structurally identical to HEVCDecoderConfigurationRecord. The syntax is as follows:

aligned(8)class SHVCDecoderConfigurationRecord{

//The same fields as those in the HEVCDecoderConfigurationRecord syntax structure

}

The semantics of the fields in SHVCDecoderConfigurationRecord are the same as defined for HEVCDecoderConfigurationRecord.

9.5 Export from ISO Base Media File Format

9.5.1 SHVC Track Structure

A scalable video stream is represented by one or more video tracks in a file. Each track represents one or more operating points of the scalable stream. Of course, the scalable stream can be further refined if necessary.

Let the lowest operation point be one of all operation points containing NAL units with only nuh_layer_id equal to 0 and only TemporalId equal to 0. The track containing the lowest operation point should be nominated as the "scalable base track". All other tracks that are part of the same scalable coding information should be related to this base track through track references of type 'sbas' (scalable base).

All tracks that share the same scalable base track must share the same timescale as the scalable base track.

9.5.2 Data Sharing and Extraction

Different tracks can logically share data. This sharing can take one of two forms:

a) Copy sample data from one track to another (and possibly compact or re-interleave with other data such as audio). This creates a larger overall file, but for ease of extraction, the low bit rate data can be compacted and/or interleaved with other material.

b) There may be instructions on how to perform this copying when reading the file.

For the second case, an extractor (defined in A.3) is used.

9.5.3 SHVC video stream definition

9.5.3.1 Sample item name and format

9.5.3.1.1 Definition

Type: ‘hvc2’, ‘hev2’, ‘shc1’, ‘shv1’, ‘shcC’

Container: Sample description box (‘stsd’)

Required: 'hvc1', 'hev1', 'hvc2', 'hev2', 'shc1', or 'shv1' sample items are required

Quantity: There can be one or more sample items

When the sample item name is 'shc1', the default and required value of array_completeness is 1 for arrays of all types of parameter sets, and 0 for all other arrays. When the sample item name is 'shv1', the default value of array_completeness is 0 for all arrays.

When the sample item name is 'shv1', the following applies:

• If a sample contains at least one IRAP picture (as defined in ISO/IEC 23008-2), all parameter sets needed for decoding the sample shall be included in the sample entry or in the sample itself.

• Otherwise (the sample does not contain an IRAP picture), all parameter sets needed for decoding the sample shall be included in the sample entry or in any sample from the previous sample containing at least one IRAP picture to the sample itself (inclusive).

●

●

If an SHVC elementary stream contains an HEVC-compatible base layer that can be used, then the HEVC visual samples item ('hvc1' or 'hev1') should be used. Here, the item should initially contain an HEVC configuration box, possibly followed by an SHVC configuration box as defined below. The HEVC configuration box documents the profiles, layers, levels, and possibly parameter sets for the HEVC-compatible base layer, as defined by HEVCDecoderConfigurationRecord. The SHVC configuration box documents the profiles, layers, levels, and possibly parameter sets for the entire stream containing the SHVC-compatible enhancement layers stored in the SHVCConfigurationBox (as defined by HEVCDecoderConfigurationRecord).

If the SHVC elementary stream does not contain an applicable HEVC base layer, then the SHVC visual sample item ('shc1' or 'shv1') shall be used. The SHVC visual sample item shall contain the SHVC configuration box defined below. This contains the SHVCDecoderConfigurationRecord as defined in this International Standard.

The lengthSizeMinusOne field in the SHVC and HEVC configurations in any given sample entry shall have the same value.

The extractor or aggregator may be used for NAL units in an 'hvc1', 'hev1', 'hvc2', 'hev2', 'shc1', or 'shv1' track with a nuh_layer_id greater than 0. The 'extra_boxes' in an 'hvc2' or 'hev2' sample entry may be an SHVCConfigurationBox or other extension box.

Note that when indicating HEVC compatibility, it may be necessary to indicate an unrealistic level for the HEVC base layer to accommodate the bit rate of the entire stream, since all NAL units are considered to be contained in the HEVC base layer and, therefore, can be fed to a decoder with the expectation that the decoder will discard those NAL units it does not recognize. This occurs when using the 'hvc1' or 'hev1' sample entry and both HEVC and SHVC profiles are present.

SHVCConfigurationBox may be present in either 'hvc1' or 'hev1' sample entries. In this case, the following HEVCSHVCSampleEntry definition applies.

The following table shows sample items, configurations, and all possible uses of the SHVC tool for a video track (excluding timing metadata, which is always used in another track):

Table 10 – Use of sample items for HEVC and SHVC tracks

9.5.3.1.2 Syntax

9.5.3.1.3 Semantics

When the stream to which the sample entry applies contains NAL units with nuh_layer_id greater than 0, Compressorname in the base class VisualSampleEntry indicates the name of the compressor used with the value "\013SHVC Coding" being recommended (\013 is 11, the length of the string "SHVC Coding" in bytes).

9.5.4 SHVC visual width and height

If a stream containing a NAL unit with a nuh_layer_id greater than 0 is described by sample entries of type ‘hvc1’, ‘hev1’, ‘hvc2’, or ‘hev2’, the visual width and height documented in the VisualSampleEntry of the stream are the visual width and height of the HEVC base layer; otherwise, they are the visual width and height of the decoded picture of the highest layer by decoding the entire stream.

9.5.5 Synchronous Samples

If each coded picture in the access unit is an IRAP picture, the SHVC samples are considered synchronization samples, as defined in ISO/IEC 23008-2. Synchronization samples are documented by a synchronization sample table and may additionally be documented by synchronization sample sample groups and 'rap' sample groups.

9.5.5.1 Random Access Samples and Sample Groups

9.5.5.1.1 Definition

Group type: ‘ras’

Container: Sample group description box (‘ras’)

Required: No

Quantity: zero or more

A random access sample group identifies samples that contain at least one IRAP picture.

9.5.5.1.2 Syntax

9.5.5.1.3 Semantics

all_pics_are_IRAP equal to 1 specifies that all coded pictures in each sample of the group are IRAP pictures. When the value is equal to 0, the above constraints may or may not apply.

IRAP_nal_unit_type specifies the NAL unit type of the IRAP picture in each sample of the group. The value of IRAP_nal_unit_type should be in the range of 16 to 23, inclusive.

num_IRAP_pics specifies the number of IRAP pictures in each sample of the group.

IRAP_pic_layer_id specifies the value of nuh_layer_id of the i-th IRAP picture in each sample of the group.

9.5.6 Random Access Recovery Points and Random Access Point Sample Groups

For video data described by sample items of type ‘hvc1’, ‘hev1’, ‘hvc2’, or ‘hev2’, random access recovery sample groups and random access point sample groups identify random access recovery points and random access points, respectively, for the HEVC decoder and SHVC decoder (if any) operating on the entire bitstream.

For video data described by type 'shc1' or 'shv1', the random access recovery sample group identifies random access recovery in the entire SHVC bitstream, and the random access point sample group identifies random access points in the entire SHVC bitstream.

If every coded picture in the access unit is an IRAP picture (with or without RASL pictures), SHVC samples are considered random access points, as defined in ISO/IEC 23008-2, and the leading samples in ISO/IEC 14496-2 are samples where all pictures are RASL pictures, as defined in ISO/IEC 23008-2.

9.5.7 Independent Disposable Sample Frames

If used in a track compatible with both HEVC and SHVC, then note that this statement is true regardless of any valid subset of SHVC data used (possibly only HEVC data). If this information varies, then an "unknown" value (a value of 0 for the fields sample-depends-on, sample-is-dependent-on, and sample-has-redundancy) may be required.

9.5.8 Definition of Subsamples for SHVC

This subclause extends the definition of subsamples for HEVC in 8.4.8.

For use of the Subsample Information box (8.7.7 of ISO/IEC 14496-12) in SHVC streams, subsamples are defined based on the values of the flags in the Subsample Information box as specified below. The presence of this box is optional; however, if present in a track containing SHVC data, it shall have the semantics defined here.

The flags specify the type of subsample information given in this box, as follows:

0: Based on NAL unit subsamples. A subsample contains one or more adjacent NAL units.

1: Subsample based on decoding unit. A subsample contains exactly one decoding unit.

2: Tile-based subsample: A subsample contains one tile and the associated non-VCL NAL units (if any) containing the VCL NAL unit of the tile, or contains one or more non-VCL NAL units.

3: CTU-row-based subsample. A subsample contains one CTU row within a slice and the associated non-VCL NAL units (if any) containing the VCL NAL unit of the CTU row, or contains one or more non-VCL NAL units. This type of subsample information shall not be used when entropy_coding_sync_enabled_flag is equal to 0.

4: Slice-based subsample: A subsample contains one slice (where each slice may contain one or more slice segments, each of which is a NAL unit) and associated non-VCL NAL units (if any), or contains one or more non-VCL NAL units.

Other flag values are reserved.

The subsample_priority field shall be set to a value according to the specification of this field in ISO/IEC 14496-12.

This discardable field should be set to 1 only if this sample can still be decoded if this subsample is discarded (e.g., the subsample consists of a SEI NAL unit).

When the first byte of a NAL unit is contained in a subsample, the preceding length field must also be contained in the same subsample.

SubLayerRefNalUnitFlag equal to 0 indicates that all NAL units in the subsample are VCL NAL units of sub-layer non-reference pictures as specified in ISO/IEC 23008-2. A value of 1 indicates that all NAL units in the subsample are VCL NAL units of sub-layer reference pictures as specified in ISO/IEC 23008-2.

RapNalUnitFlag equal to 0 indicates that none of the NAL units in the subsample has a nal_unit_type equal to IDR_W_RADL, IDR_N_LP, CRA_NUT, BLA_W_LP, BLA_W_RADL, BLA_N_LP, RSV_IRAP_VCL22, or RSV_IRAP_VCL23 as specified in ISO/IEC 23008-2. A value of 1 indicates that all NAL units in the subsample have a nal_unit_type equal to IDR_W_RADL, IDR_N_LP, CRA_NUT, BLA_W_LP, BLA_W_RADL, BLA_N_LP, RSV_IRAP_VCL22, or RSV_IRAP_VCL23 as specified in ISO/IEC 23008-2.

VclNalUnitFlag equal to 0 indicates that all NAL units in the subsample are non-VCL NAL units. A value of 1 indicates that all NAL units in the subsample are VCL NAL units.

vcl_idc indicates whether the subsample contains Video Coding Layer (VCL) data, non-VCL data, or both, as follows:

0: The subsample contains VCL data and no non-VCL data

1: The subsample does not contain VCL data and contains non-VCL data

2: A subsample may contain both VCL and non-VCL data that should be associated with each other. For example, a subsample may contain a decoding unit information SEI message, followed by a set of NAL units associated with the SEI message.

3: Keep

log2_min_luma_ctb indicates the units of ctb_x and ctb_y as specified below:

0: 8 brightness samples

1: 16 brightness samples

2: 32 brightness samples

3: 64 brightness samples

ctb_x specifies the zero-based coordinate of the rightmost luma sample of the tile associated with the subsample when the flag is equal to 2 and vcl_idc is equal to 1 or 2, in units derived from log2_min_luma_ctb as specified above.

ctb_y specifies the zero-based coordinate of the bottom-most luma sample of the tile associated with the subsample when flag is equal to 2 and vcl_idc is equal to 1 or 2, in units derived from log2_min_luma_ctb as specified above.

9.5.9 Handling Non-Output Samples

The specifications in 8.4.9 apply, with "HEVC" replaced by "SHVC", and non-output samples are defined as samples whose pictures of the target output layer have pic_output_flag equal to 0. When an access unit contains some coded pictures with pic_output_flag equal to 1 and some other coded pictures with pic_output_flag equal to 0, the stream must be stored using at least two tracks such that within each track, all coded pictures in each sample have the same pic_output_flag value.

10 10 MV-HEVC basic stream and sample definition

10.1 Introduction

This clause specifies the storage format of MV-HEVC data. It extends the definition of the HEVC storage format in clause 8.

The file format for storage of MV-HEVC content as defined in this clause and Appendices A to D uses the existing capabilities of the ISO base media file format and the normal HEVC file format (i.e., the file format specified in clause 8). In addition, the following structures or extensions are used to support MV-HEVC specific features.

Aggregator:

The structure of efficient scalable grouping of NAL units is achieved by changing the irregular pattern of NAL units into a regular pattern of aggregated data units.

Extractor:

A structure that enables efficient extraction of NAL units from a different track than the one containing the media data.

HEVC compatibility:

Provides for storing MV-HEVC bitstreams in an HEVC-compatible manner so that the HEVC-compatible base layer can be used by any reader conforming to the normal HEVC file format.

Support for MV-HEVC includes many tools, and there are various "models" of how it can be used. Specifically, an MV-HEVC stream can be placed in a playback track in many ways, including the following:

1. All views in a playback track, marked with sample groups;

2. Each view in its own playback track, marked in the sample item;

3. Hybrid, one track containing all views, and one or more single-view tracks, each containing independently decodable views;

4. The expected operation points in each track (e.g., HEVC base, stereo pair, multi-view scene).

The MV-HEVC file format allows one or more views to be stored in a track, similar to the support for SHVC in clause 9. The storage of multiple views per track can be used, for example, when a content provider wants to provide a multi-view bitstream that is not intended for subset construction, or when a bitstream has been created for a small set of predefined output views (e.g., 1, 2, 5, or 9 views) (where tracks can be created accordingly). If more than one view is stored in a track and there are several tracks (more than one) representing the MV-HEVC bitstream, the use of a sample grouping mechanism is recommended.

When an MV-HEVC bitstream is represented by multiple playback tracks and a player uses operation points that contain data from multiple playback tracks, the player must reconstruct an MV-HEVC access unit before delivering it to the MV-HEVC decoder. MV-HEVC operation points can be represented explicitly by playback tracks, that is, the access unit is reconstructed simply by parsing all extractor and aggregator NAL units of the samples. If the number of operation points is large, then creating a playback track for each operation point may consume space and be impractical. In this case, the MV-HEVC access unit is reconstructed as specified in 10.5.2. The MV-HEVC decoder configuration record contains a field indicating whether the associated samples are reconstructed using explicit or implicit access units (see the explicit_au_track field).

10.2MV-HEVC Playback Track Structure

MV-HEVC streams are stored according to 8.2, with the following definition of an MV-HEVC video elementary stream:

An MV-HEVC video elementary stream shall contain all video coding-related NAL units (i.e., those NAL units that contain video data or signal video structure) and may contain non-video coding-related NAL units such as SEI messages and access unit delimiter NAL units. Aggregators (see A.2) or extractors (see A.3) may also be present. Aggregators and extractors shall be processed as defined in this International Standard (e.g., shall not be placed directly in the output buffer when accessing the file). Other NAL units that are not explicitly suppressed may be present and, if not recognized, shall be ignored (e.g., not placed in the output buffer when accessing the file).

When required, the MV-HEVC stream shall not be stored with the associated parameter set stream.

There may be VCL NAL units with nuh_layer_id equal to 0, VCL NAL units with nuh_layer_id greater than 0, and non-VCL NAL units present in the MV-HEVC video elementary stream. In addition, there may be aggregator and extractor NAL units present in the MV-HEVC video elementary stream.

10.3 Use of Common HEVC File Format

The MV-HEVC file format is an extension of the normal HEVC file format defined in clause 8.

10.4 Sample and Configuration Definition

10.4.1 Introduction

MV-HEVC sample: An MV-HEVC sample is also an access unit as defined in Annex F of ISO/IEC 23008-2.

10.4.2 Standard order and restrictions

10.4.2.1 Limitations

In addition to the requirements in 8.3.2, the following restrictions apply to MV-HEVC data.

● VCL NAL unit: In the instance where its composition time is the composition time of a picture represented by one access unit, it shall contain all VCL NAL units in the access unit. An MV-HEVC sample shall contain at least one VCL NAL unit.

Aggregator/Extractor: The order of all NAL units included in an aggregator or referenced by an extractor is exactly in decoding order, as if these NAL units were present in a sample that did not contain the aggregator/extractor. After processing an aggregator or extractor, all NAL units must be in valid decoding order, as specified in ISO/IEC 23008-2.

10.4.2.2 Decoder Configuration Record

When the decoder configuration record defined in 8.3.3.1 is used for a stream interpretable as an MV-HEVC or HEVC stream, the HEVC decoder configuration record shall reflect the properties of the HEVC compatible base view, e.g., it shall only contain the parameter sets required for decoding the HEVC base view.

MVHEVCDecoderConfigurationRecord is structurally identical to HEVCDecoderConfigurationRecord. The syntax is as follows:

aligned(8)class MVHEVCDecoderConfigurationRecord{

//The same fields as those in the HEVCDecoderConfigurationRecord syntax structure

}

The semantics of the fields in MVHEVCDecoderConfigurationRecord are the same as defined for HEVCDecoderConfigurationRecord.

10.4.3 Synchronous Samples

If each coded picture in an access unit is an IRAP picture without a RASL picture, the MV-HEVC sample is considered a synchronization sample, as defined in ISO/IEC 23008-2. Synchronization samples are documented by a synchronization sample table and may additionally be documented by synchronization sample sample groups and 'rap' sample groups similarly defined in SHVC.

10.4.4 Independent and disposable sample frame

If used in a track compatible with both HEVC and MV-HEVC, then note that this statement is true regardless of any valid subset of MV-HEVC data used (possibly only HEVC data). If this information varies, then an "unknown" value (a value of 0 for the fields sample-depends-on, sample-is-dependent-on, and sample-has-redundancy) may be required.

10.4.5 Random Access Recovery Points and Random Access Point Sample Groups

For video data described by sample items of type ‘hvc1’, ‘hev1’, ‘hvc2’, or ‘hev2’, random access recovery sample groups and random access point sample groups identify random access recovery points and random access points, respectively, for HEVC decoding and MV-HEVC decoder (if any) operating on the entire bitstream.

For video data described by the MV-HEVC sample item type, a random access recovery sample group identifies random access recovery in the entire MV-HEVC bitstream, and a random access point sample group identifies a random access point in the entire MV-HEVC bitstream.

10.5 Export from ISO Base Media File Format

10.5.1 MV-HEVC Track Structure

A multi-view video stream is represented by one or more video tracks in the file. Each track represents one or more views of the stream.

There is a minimum set of one or more tracks that, when put together, contain a complete set of coded information. All such tracks should have the "complete_representation" flag set in all of their sample entries. This group of tracks that form the complete coded information is called a "complete subset."

Let the lowest operation point be one of all operation points containing NAL units with only nuh_layer_id equal to 0 and only TemporalId equal to 0. The track containing the lowest operation point should be nominated as the "base view track". All other tracks that are part of the same stream should be related to this base track through track references of type 'sbas' (view base).

All tracks that share the same base view track must share the same timescale as the base view track.

If a view represented by a track uses another view represented by another track as an inter-view prediction reference, then a track reference of type 'scal' should be included in the track that references the source track for inter-view prediction.

If edits are applied to view components containing an MV-HEVC bitstream, the edit lists should be consistent across all tracks affected by the edits.

10.5.2 Reconstruction of Access Units

In order to reconstruct an access unit from samples of one or more MV-HEVC tracks, it may be necessary to first determine the target output view.

The views required for decoding the determined target output view can be derived from the reference view identifiers contained in the view identifier box or the 'scal' track reference.

If several tracks contain data for an access unit, alignment of corresponding samples in the tracks is performed at decode time, ie only time-to-sample tables are used without taking edit lists into account.

An access unit is reconstructed from the corresponding samples in the required track by arranging its NAL units in an order conforming to ISO/IEC 23008-02. The following order provides an overview of the procedure for forming a conforming access unit:

• All parameter set NAL units (from the associated parameter set track and from the associated elementary stream track).

• All SEI NAL units (from the associated parameter set track and from the associated elementary stream track).

• View components in descending order of view order index values. NAL units within a view component in the order they appear within the sample.

10.5.3 Sample Items

10.5.3.1 Boxes for Sample Items

10.5.3.1.1 View Identifier Box

10.5.3.1.1.1 Definition

Frame type: ‘vwid’

Container: Sample Item (‘hev1’, ‘hvc1’, ‘hev2’, ‘hvc2’, ‘mhc1’, ‘mhv1’) or MultiviewGroupEntry

Required: Yes (for sample items)

Quantity: Exactly one (for a sample item)

When included in a sample entry, this box indicates the views included in the track. This box also indicates the view order index for each listed view. Additionally, when the View Identifier box is included in a sample entry, it contains the minimum and maximum temporal_id values for the track. Furthermore, this box indicates the reference views required to decode the views included in the track.

10.5.3.1.1.2 Syntax

10.5.3.1.1.3 Semantics

When the view identifier box is included in a sample entry, min_temporal_id and max_temporal_id take the corresponding minimum and maximum values of the temporal_id syntax element present in the NAL unit header extension of the NAL units mapped to the track or layer. For AVC streams, this takes the value that is or will be in the first NAL unit.

num_views indicates the number of views included in the track when the view identifier box exists in the sample item.

layer_id[i] indicates the value of the nuh_layer_id syntax element in the NAL unit header of a layer included in a playback track when a view identifier box is included in a sample entry.

view_id indicates the view identifier of the i-th layer with nuh_layer_id equal to layer_id[i], as specified in Annex F of ISO/IEC 23008-2.

base_view_type indicates whether the view is a base view (virtual or not). It can take the following values:

0 indicates that the view is neither a base view nor a virtual base view.

1 applies to labeling the non-virtual base views of MV-HEVC bitstreams.

The value 2 is reserved and should not be used.

3 indicates that the view with view_id[i] is a virtual base view. The corresponding independently coded non-base view with view_id[i] resides in another playback track. When base_view_type is equal to 3, then num_ref_views shall be equal to 0.

depdent_layer[i][j] indicates that the jth layer with nuh_layer_id equal to j may be a layer directly or indirectly referenced by the layer with nuh_layer_id equal to layer_id[i]. When the view identifier box is included in a sample entry, it is recommended to indicate the referenced view in the same sample entry.

10.5.3.2 Sample Item Definition

Sample item types: ‘hvc2’, ‘hev2’, ‘mhc1’, ‘mhv1’, ‘mhcC’

Container: Sample description box (‘stsd’)

Required: One of the ‘hvc1’, ‘hev1’, ‘hvc2’, ‘hev2’, ‘mhc1’, or ‘mhv1’ boxes is required

Quantity: There can be one or more sample items

If the MV-HEVC elementary stream contains an applicable HEVC-compatible base layer, then the HEVC visual sample items ('hvc1', 'hev1', 'hvc2', 'hev2') shall be used. Here, the items shall initially contain the HEVC Configuration Box, which may be followed by the MV-HEVC Configuration Box as defined below. The HEVC Configuration Box documents the profile, tier, and possibly parameter set information for the HEVC-compatible base layer, as defined by HEVCDecoderConfigurationRecord. The MV-HEVC Configuration Box documents the profile, tier, and possibly parameter set information for the entire stream, including non-base views, stored in the MVHEVCConfigurationBox (as defined by MVHEVCDecoderConfigurationRecord).

For all sample entries 'hvc1', 'hev1', 'hvc2', and 'hev2', the width and height fields in the sample entry document the HEVC base layer. For MV-HEVC sample entries ('mhc1', 'mhv1'), the width and height fields document the resolution achieved by decoding any single view of the entire stream.

If the MV-HEVC elementary stream does not contain an applicable HEVC base layer, then the MV-HEVC visual sample item ('mhc1', 'mhv1') shall be used. The MV-HEVC visual sample item shall contain the MV-HEVC configuration box defined below. This contains the MVHEVCDecoderConfigurationRecord as defined in this International Standard.

The lengthSizeMinusOne field in the MV-HEVC and HEVC profiles in any given sample entry shall have the same value.

The requirements for the same item types 'hvc1' and 'hev1' as documented in 6.5.3.1.1 also apply here.

MVHEVCConfigurationBox may be present in 'hvc1', 'hev1', 'hvc2', or 'hev2' sample entries. In these cases, the following HEVCMVHEVCSampleEntry or HEVC2MVHEVCSampleEntry definitions apply, respectively.

Compressorname in the base class VisualSampleEntry indicates the name of the compressor used, where the recommended value is "\014MV-HEVC Coding" (\016 is 14, the length of the string "MV-HEVC coding" in bytes).

The parameter sets required to decode NAL units present in the sample data of a video stream, either directly or by reference from an extractor, shall be present in the decoder configuration of that video stream or in the associated parameter set stream (if used).

The following table shows sample entries for video tracks (when MV-HEVC elementary streams are stored in one or more tracks), configurations, and all possible uses of MV-HEVC tools.

Table 14: Use of sample items for HEVC and MV-HEVC playback tracks

The sample item mvhevc-type in the following is one of {mhv1,mhc1}.

10.5.3.3 Syntax

10.5.4 Definition of subsamples for MV-HEVC

The definition of subsamples for MV-HEVC is defined similarly to that defined for SHVC.

10.5.5 Handling Non-Output Samples

Non-output samples for MV-HEVC are handled similarly to the handling defined for SHVC.

The following shows the changes to Appendix A.

Appendix A (Standard)

In-stream structure

A.1 Introduction

Aggregators and extractors implement the internal structure of the file format to achieve efficient grouping of NAL units or extract NAL units from other playback tracks.

Aggregators and extractors use NAL unit syntax. These structures are treated as NAL units in the context of a sample structure. When accessing a sample, the aggregator must be removed (leaving the NAL units it contains or references) and the extractor must be replaced by the data it references. Aggregators and extractors must not be present in streams outside the file format.

Such structures use NAL unit types reserved by ISO/IEC 14496-10 or ISO/IEC 23008-2 for the application/transport layer.

Note the following from ISO/IEC 14496-10:

"NOTE—NAL unit types 0 and 24..31 may be used, as determined by the application. The decoding process for these nal_unit_type values is not specified in this Recommended International Standard."

Note the following from ISO/IEC 23008-2:

"NOTE 1—NAL unit types in the range of UNSPEC48..UNSPEC63 may be used, as determined by the application. The decoding process for such nal_unit_type values is not specified in this specification. Because different applications may use these NAL unit types for different purposes, care must be taken in the design of encoders that generate NAL units with such nal_unit_type values and in the design of decoders that interpret the content of NAL units with such nal_unit_type values."

A.2 Aggregator

A.2.1 Definition

This subclause describes the aggregator that enables consistent and repeatable NALU mapping group entries (see Appendix B).

Aggregators are used to group NAL units belonging to the same sample.

For the storage of ISO/IEC 14496-10 video, the following rules apply:

- The aggregator uses the same NAL unit header as the SVC VCL NAL unit or MVC VCL NAL unit but with a different NAL unit type value.

- When the svc_extension_flag of the NAL unit syntax of the aggregator (specified in 7.3.1 of ISO/IEC 14496-10) is equal to 1, the NAL unit header of the SVC VCL NAL unit is used for the aggregator. Otherwise, the NAL unit header of the MVC VCL NAL unit is used for the aggregator.

For storage of ISO/IEC 23008-2 video, the aggregator uses the NAL unit header as defined in ISO/IEC 23008-2, which has the same syntax for normal HEVC, SHVC and MV-HEVC.

An aggregator can aggregate NAL units within it by inclusion (within the size indicated by its length), and also aggregate subsequent NAL units by reference (within the area indicated by the additional_bytes field within it). When the stream is scanned by an AVC or HEVC file reader, only the included NAL units are considered "within the aggregator". This permits an AVC or HEVC file reader to skip an entire set of unneeded NAL units (when they are aggregated by inclusion). This also permits an AVC or HEVC reader to not skip needed NAL units, but keep them in the stream (when they are aggregated by reference).

Aggregators can be used to group base layer or base view NAL units. If such aggregators are used in 'avc1', 'hvc1', or 'hev1' tracks, the aggregator should not use the inclusion of base layer or base view NAL units, but rather references to them (the length of the aggregator includes only its header, and the NAL units referenced by the aggregator are specified by additional_bytes).

When an aggregator is referenced by an extractor with data_length equal to zero or by a mapped sample group, the aggregator is treated as aggregating the bytes included and referenced.

Aggregators may contain or reference extractors. Extractors may extract from an aggregator. An aggregator must not directly contain or reference another aggregator; however, an aggregator may contain or reference an extractor that references an aggregator.

When scanning a stream:

a) If an aggregator is not recognized (e.g., by an AVC or HEVC reader or decoder), it is susceptible to being discarded along with the content it contains;

b) If the aggregator is not needed (i.e. it belongs to the wrong layer), then it and its contents, both by inclusion and reference, can be discarded (using its length and additional_bytes fields);

c) If an aggregator is needed, it is easy to discard its header and keep its content.

Aggregators are stored within samples like any other NAL unit.

All NAL units are kept within the aggregator in decoding order.

A.2.2 Syntax

A.2.3 Semantics

The value of the variable AggregatorSize is equal to the size of the aggregator NAL unit, and the function sizeof(X) returns the size of the field X in bytes.

NALUnitHeader(): The first four bytes of the SVC and MVC VCL NAL unit, or the first two bytes of the ISO/IEC 23008-2 NAL unit.

nal_unit_type shall be set to the aggregator NAL unit type (type 30 for ISO/IEC 14496-10 video and type 48 for ISO/IEC 23008-2 video).

For aggregators that contain or reference SVC NAL units, the following shall apply.

The forbidden_zero_bit and reserved_three_2bits shall be set as specified in ISO/IEC 14496-10.

The other fields (nal_ref_idc, idr_flag, priority_id, no_inter_layer_pred_flag, dependency_id, quality_id, temporal_id, use_ref_base_pic_flag, discardable_flag, and output_flag) shall be set as specified in A.4.

For aggregators that include or reference MVC NAL units, the following shall apply.

The forbidden_zero_bit and reserved_one_ bit.

The other fields (nal_ref_idc, non_idr_flag, priority_id, view_id, temporal_id, anchor_pic_flag, and inter_view_flag) shall be set as specified in A.5.For aggregators containing or referencing ISO/IEC 23008-2 NAL units, the following shall apply.

The forbidden_zero_bit shall be set as specified in ISO/IEC 23008-2.

The other fields (nuh_layer_id and nuh_temporal_id_plus1) shall be set as specified in A.6.

additional_bytes: The number of bytes following this aggregator NAL unit that should be considered as aggregated when this aggregator is referenced by an extractor with data_length equal to zero or a mapped sample group.

NALUnitLength: Specifies the size (in bytes) of the NAL unit to follow. The size of this field is specified by the lengthSizeMinusOne field.

NALUnit: A NAL unit as specified in ISO/IEC 14496-10 or ISO/IEC 23008-2 , including a NAL unit header. The size of the NAL unit is specified by NALUnitLength.

A.3 Extractor

A.3.1 Definition

This subclause describes a compact extractor that implements a track that extracts NAL unit data from other tracks by reference.

Aggregators may contain or reference extractors. Extractors may reference aggregators. When an extractor is processed by a file reader that requires it, the extractor is logically replaced by the bytes it references. Those bytes do not necessarily contain the extractor; an extractor does not necessarily reference another extractor, directly or indirectly.

Note that a referenced track may contain extractors, even though the data referenced by the extractor does not have to.

An extractor contains instructions to extract data from another track via a track reference of type 'scal', the other track being related to the track in which the extractor resides.

The bytes copied should be one of the following:

a) An entire NAL unit; note that when referencing an aggregator, the contained and referenced bytes are copied

b) More than one entire NAL unit

In both cases, the extracted bytes begin with the valid length field and the NAL unit header.

Only bytes are copied from a single identified sample in the track referenced via the indicated 'scal' track reference. Alignment is at decode time, i.e., only the time to the sample table is used, followed by an offset counting the number of samples. Extractors are a media-level concept and are therefore applied to the destination track before any edit lists are considered. (However, it would generally be expected that the edit lists in both tracks would be identical).

A.3.2 Syntax

A.3.3 Semantics

NALUnitHeader(): The first four bytes of the SVC and MVC VCL NAL unit, or the first two bytes of the ISO/IEC 23008-2 NAL unit.

nal_unit_type should be set to the extractor NAL unit type ( type 31 for ISO/IEC 14496-10 video and type 49 for ISO/IEC 23008-2 video).

For extractors that reference SVC NAL units, the following shall apply.

The forbidden_zero_bit and reserved_three_2bits shall be set as specified in ISO/IEC 14496-10.

The other fields (nal_ref_idc, idr_flag, priority_id, no_inter_layer_pred_flag, dependency_id, quality_id, temporal_id, use_ref_base_pic_flag, discardable_flag, and output_flag) shall be set as specified in A.4.

For extractors that reference MVC NAL units, the following shall apply.

The forbidden_zero_bit and reserved_one_bit shall be set as specified in ISO/IEC 14496-10.

The other fields (nal_ref_idc, non_idr_flag, priority_id, view_id, temporal_id, anchor_pic_flag, and inter_view_flag) should be set as specified in A.5.

For extractors referencing ISO/IEC 23008-2 NAL units, the following shall apply.

The forbidden_zero_bit shall be set as specified in ISO/IEC 23008-2.

The other fields (nuh_layer_id and nuh_temporal_id_plus1) shall be set as specified in A.6.

track_ref_index specifies the index of a track reference of type 'scal' used to find the track from which data is to be extracted. The samples in the track from which data is extracted are aligned in time or to the immediately preceding one in the media decoding timeline (i.e., using only the time-to-sample table), adjusted by the offset specified by sample_offset with the sample containing the extractor. The first track reference has index value 1; value 0 is reserved.

sample_offset gives the relative index of the sample in the associated track that should be used as the source of the information. Sample 0 (zero) is the sample with the same or immediately preceding decode time compared to the decode time of the sample containing the extractor; sample 1 (one) is the next sample, sample -1 (minus 1) is the previous sample, and so on.

data_offset: The offset of the first byte of the copy within the reference sample. If the extraction starts at the first byte of data in the sample, then the offset takes the value 0. The offset shall be referenced to the start of the NAL unit length field.

data_length: Number of bytes copied. If this field takes the value 0, then the entire single referenced NAL unit is copied (i.e., the length of the copy is taken from the length field referenced by the data offset, augmented by the additional_bytes field in the case of an aggregator).

Note that if two tracks use different lengthSizeMinusOne values, the extracted data will need to be reformatted to match the length field size of the destination track.

A.4 SVC NAL unit header values

Both extractors and aggregators use the NAL unit header SVC extension. The NAL units extracted by an extractor or aggregated by an aggregator are all those NAL units referenced or included by recursively checking the contents of the aggregator or extractor NAL units.

The fields nal_ref_idc, idr_flag, priority_id, temporal_id, dependency_id, quality_id, discardable_flag, output_flag, use_ref_base_pic_flag, and no_inter_layer_pred_flag shall take the following values:

nal_ref_idc shall be set to the highest value of the field in all extracted or aggregated NAL units.

The idr_flag shall be set to the highest value of the field in all extracted or aggregated NAL units.

priority_id, temporal_id, dependency_id, and quality_id shall each be set to the lowest value of the field in all extracted or aggregated NAL units.

The discardable_flag shall be set to 1 if and only if all extracted or aggregated NAL units have the discardable_flag set to 1, and shall be set to 0 otherwise.

This flag should be set to 1 if at least one of the aggregated or extracted NAL units has output_flag set to 1, and to 0 otherwise.

The use_ref_base_pic_flag shall be set to 1 if and only if at least one of the extracted or aggregated VCL NAL units has the use_ref_base_pic_flag set to 1, and shall be set to 0 otherwise.

The no_inter_layer_pred_flag shall be set to 1 if and only if all extracted or aggregated VCL NAL units have the no_inter_layer_pred_flag set to 1, and shall be set to 0 otherwise.

If the combination of extracted or aggregated NALs is empty, then each of these fields takes a value consistent with the mapped layer description.

Note that the aggregator may group NAL units with different scalability information.

Note that aggregators can be used to group NAL units belonging to scalability levels that may not be signaled by the NAL unit header (e.g., NAL units belonging to related regions). Such aggregators can be described using layer descriptions and NAL unit map groups. In this case, more than one aggregator with the same scalability information can appear in one example.

Note that if multiple scalable playback tracks reference the same media data, the aggregator should only group NAL units with the same scalability information. This ensures that the resulting mode can be accessed by each of the playback tracks.

Note that if there are no NAL units in a particular layer in an access unit, then there may be an empty aggregator (where the length of the aggregator includes only the header, and additional_bytes is zero).

A.5 NAL unit header values for MVC

Both aggregators and extractors use the NAL unit header MVC extension. The NAL units extracted by an extractor or aggregated by an aggregator are all those NAL units referenced or included by recursively examining the contents of aggregator or extractor NAL units.

The fields nal_ref_idc, non_idr_flag, priority_id, view_id, temporal_id, anchor_pic_flag, and inter_view_flag shall take the following values:

nal_ref_idc shall be set to the highest value of the field in all aggregated or extracted NAL units.

The non_idr_flag shall be set to the lowest value of the fields in all aggregated or extracted NAL units.

priority_id and temporal_id shall be set to the lowest value of the fields in all aggregated or extracted NAL units, respectively.

view_id shall be set to the view_id value of the VCL NAL unit with the lowest view order index among all aggregated or extracted VCL NAL units.

The anchor_pic_flag and inter_view_flag shall be set to the highest value of the fields in all aggregated or extracted VCL NAL units, respectively.

If the combination of extracted or aggregated NALs is empty, then each of these fields selects the layer to which the mapping is applied. Describes consistent values.

A.6 NAL unit header values for ISO/IEC 23008-2

Both the Aggregator and the Extractor use the NAL unit header as specified in ISO/IEC 23008-2. NAL units that are fetched or aggregated by an aggregator are referenced or retrieved by recursively examining the contents of aggregator or extractor NAL units. All those NAL units contained.

The fields nuh_layer_id and nuh_temporal_id_plus1 should be set as follows:

nuh_layer_id shall be set to the lowest value of the fields in all aggregated or extracted NAL units.

nuh_temporal_id_plus1 shall be set to the lowest of the fields in all aggregated or extracted NAL units. value.

In one alternative example, a new structure, table, or sample group is defined to document all IRAP access units, as defined in Annex A of MV-HEVC WD5 or SHVC WD3. Alternatively, the new structure, table, or sample group is defined to document all IRAP access units (as defined in Annex F of MV-HEVC WD5 or SHVC WD3), but excluding those access units where all coded pictures are IRAP pictures. In another alternative example, the synchronization sample sample group entry SyncSampleEntry is redefined to include an aligned_sync_flag in a reserved bit specifying that all pictures in samples belonging to this group are one of IDR pictures, CRA pictures, or BLA pictures. In another alternative example, a common file format for SHVC and MV-HEVC is defined to include all common aspects from the SHVC and MV-HEVC file formats, and the SHVC and MV-HEVC file formats are redefined to include only aspects relevant only to the extension. In another alternative example, SHVC metadata sample items SHVCMetadataSampleEntry and SHVCMetadataSampleConfigBox are defined, and a metadata sample statement type scalabilityInfoSHVCStatement is also defined.

FIG2 is a block diagram illustrating an example video encoder 20 that may implement the techniques described in this disclosure. Video encoder 20 may be configured to output single-view, multi-view, scalable, 3D, and other types of video data. Video encoder 20 may be configured to output video to a post-processing entity 27. Post-processing entity 27 is intended to represent an example of a video entity (e.g., a MANE or splicing/editing device) that may process the encoded video data from video encoder 20. In some cases, the post-processing entity may be an example of a network entity. In some video coding systems, post-processing entity 27 and video encoder 20 may be parts of separate devices, while in other cases, the functionality described with respect to post-processing entity 27 may be performed by the same device that includes video encoder 20. Post-processing entity 27 may be a video device. In some examples, post-processing entity 27 may be the same as file generation device 34 of FIG1 .

Video encoder 20 may perform intra- and inter-coding of video blocks within a video slice. Intra-coding relies on spatial prediction to reduce or remove spatial redundancy in video within a given video frame or picture. Inter-coding relies on temporal prediction to reduce or remove temporal redundancy in video within adjacent frames or pictures of a video sequence. Intra-mode (I-mode) may refer to any of several spatial-based compression modes. Inter-mode (e.g., unidirectional prediction (P-mode) or bidirectional prediction (B-mode)) may refer to any of several temporal-based compression modes.

2 , video encoder 20 includes partitioning unit 35, prediction processing unit 41, filter unit 63, reference picture memory 64, summer 50, transform processing unit 52, quantization unit 54, and entropy encoding unit 56. Prediction processing unit 41 includes motion estimation unit 42, motion compensation unit 44, and intra-prediction processing unit 46. For video block reconstruction, video encoder 20 also includes inverse quantization unit 58, inverse transform processing unit 60, and summer 62. Filter unit 63 is intended to represent one or more loop filters, such as a deblocking filter, an adaptive loop filter (ALF), and a sample adaptive offset (SAO) filter. Although filter unit 63 is shown in FIG2 as a loop filter, in other configurations, filter unit 63 may be implemented as a post-loop filter.

The video data memory of video encoder 20 may store video data to be encoded by the components of video encoder 20. The video data stored in the video data memory may be obtained, for example, from video source 18. Reference picture memory 64 may be a reference picture memory that stores reference video data for use by video encoder 20 in encoding video data (e.g., in intra- or inter-coding modes). Video data memory and reference picture memory 64 may be formed from any of a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. Video data memory and reference picture memory 64 may be provided by the same memory device or separate memory devices. In various examples, the video data memory may be on-chip with other components of video encoder 20 or off-chip relative to those components.

As shown in FIG2 , video encoder 20 receives video data, and partitioning unit 35 partitions the data into video blocks. This partitioning may also include partitioning into slices, tiles, or other larger units, as well as video block partitioning, e.g., according to a quadtree structure of LCUs and CUs. Video encoder 20 generally illustrates components that encode video blocks within a video slice to be encoded. A slice may be divided into multiple video blocks (and possibly into sets of video blocks referred to as tiles). Prediction processing unit 41 may select one of multiple possible coding modes for the current video block, e.g., one of multiple intra-coding modes or one of multiple inter-coding modes, based on error generation (e.g., coding rate and level of distortion). Prediction processing unit 41 may provide the resulting intra- or inter-coded block to summer 50 to generate residual block data and to summer 62 to reconstruct the encoded block for use as a reference picture.

Intra-prediction processing unit 46 within prediction processing unit 41 may perform intra-predictive coding of the current video block relative to one or more neighboring blocks in the same frame or slice as the current block to be coded to provide spatial compression. Motion estimation unit 42 and motion compensation unit 44 within prediction processing unit 41 may perform inter-predictive coding of the current video block relative to one or more predictive blocks in one or more reference pictures to provide temporal compression.

Motion estimation unit 42 may be configured to determine an inter-prediction mode for a video slice based on a predetermined pattern for a video sequence. The predetermined pattern may designate a video slice in the sequence as a P slice, a B slice, or a GPB slice. Motion estimation unit 42 and motion compensation unit 44 may be highly integrated but are illustrated separately for conceptual purposes. Motion estimation performed by motion estimation unit 42 is the process of generating motion vectors, which estimate the motion of video blocks. For example, a motion vector may indicate the displacement of a PU of a video block within a current video frame or picture relative to a predictive block within a reference picture.

A predictive block is a block that is found to closely match a PU of the video block to be coded, in terms of pixel difference, which may be determined by sum of absolute difference (SAD), sum of squared difference (SSD), or other difference metrics. In some examples, video encoder 20 may calculate values for sub-integer pixel positions of a reference picture stored in reference picture memory 64. For example, video encoder 20 may interpolate values for quarter-pixel positions, eighth-pixel positions, or other fractional pixel positions of the reference picture. Thus, motion estimation unit 42 may perform motion searches relative to full-pixel positions and fractional pixel positions and output motion vectors with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a video block in an inter-coded slice by comparing the position of the PU to the position of a predictive block of a reference picture. The reference picture may be selected from a first reference picture list (List 0) or a second reference picture list (List 1), each of which identifies one or more reference pictures stored in reference picture memory 64. Motion estimation unit 42 sends the calculated motion vector to entropy encoding unit 56 and motion compensation unit 44.

Motion compensation performed by motion compensation unit 44 may involve extracting or generating a predictive block based on the motion vector determined by motion estimation, possibly performing interpolation with sub-pixel precision. After receiving the motion vector for the PU of the current video block, motion compensation unit 44 may locate the predictive block pointed to by the motion vector in one of the reference picture lists. Video encoder 20 may form a residual video block by subtracting the pixel values of the predictive block from the pixel values of the current video block being coded, forming pixel difference values. The pixel difference values form residual data for the block and may include both luma and chroma difference components. Summer 50 represents the component that performs this subtraction operation. Motion compensation unit 44 may also generate syntax elements associated with the video block and video slice for use by video decoder 30 when decoding the video block of the video slice.

As described above, as an alternative to the inter-prediction performed by motion estimation unit 42 and motion compensation unit 44, intra-prediction processing unit 46 may intra-predict the current block. Specifically, intra-prediction processing unit 46 may determine an intra-prediction mode to use to encode the current block. In some examples, intra-prediction processing unit 46 may encode the current block using various intra-prediction modes, for example, during separate encoding passes, and intra-prediction unit 46 (or, in some examples, mode selection unit 40) may select an appropriate intra-prediction mode to use from the tested modes. For example, intra-prediction processing unit 46 may calculate rate-distortion values using a rate-distortion analysis for the various tested intra-prediction modes and select the intra-prediction mode with the best rate-distortion characteristics among the tested modes. Rate-distortion analysis generally determines the amount of distortion (or error) between an encoded block and the original, unencoded block (which was encoded to generate the encoded block), as well as the bit rate (i.e., the number of bits) used to generate the encoded block. Intra-prediction processing unit 46 may calculate ratios from the distortions and rates for the various encoded blocks to determine which intra-prediction mode exhibits the best rate-distortion value for the block.

In any case, after selecting an intra-prediction mode for a block, intra-prediction processing unit 46 may provide information indicating the selected intra-prediction mode for the block to entropy encoding unit 56. Entropy encoding unit 56 may encode the information indicating the selected intra-prediction mode according to the techniques of this disclosure. Video encoder 20 may include configuration data in the transmitted bitstream, which may include: multiple intra-prediction mode index tables and multiple modified intra-prediction mode index tables (also referred to as codeword mapping tables); definitions of encoding contexts for various blocks; and indications of the most probable intra-prediction mode, intra-prediction mode index tables, and modified intra-prediction mode index tables to be used for each of the contexts.

After prediction processing unit 41 generates a predictive block for the current video block via inter-prediction or intra-prediction, video encoder 20 may form a residual video block by subtracting the predictive block from the current video block. The residual video data in the residual block may be included in one or more TUs and applied to transform processing unit 52. Transform processing unit 52 transforms the residual video data into residual transform coefficients using a transform, such as a discrete cosine transform (DCT) or a conceptually similar transform. Transform processing unit 52 may convert the residual video data from the pixel domain to a transform domain (e.g., the frequency domain).

Transform processing unit 52 may send the resulting transform coefficients to quantization unit 54. Quantization unit 54 quantizes the transform coefficients to further reduce the bit rate. The quantization process may reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter. In some examples, quantization unit 54 may then perform a scan of the matrix containing the quantized transform coefficients. Alternatively, entropy encoding unit 56 may perform the scan.

After quantization, entropy encoding unit 56 may entropy encode syntax elements representing the quantized transform coefficients. For example, entropy encoding unit 56 may perform context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), syntax-based context adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding, or another entropy encoding method or technique. After entropy encoding by entropy encoding unit 56, the encoded bitstream may be transmitted to video decoder 30 or archived for later transmission or retrieval by video decoder 30. Entropy encoding unit 56 may also entropy encode motion vectors and other syntax elements for the video slice currently being coded.

Inverse quantization unit 58 and inverse transform processing unit 60 apply inverse quantization and inverse transform, respectively, to reconstruct the residual block in the pixel domain for later use as a reference block for a reference picture. Motion compensation unit 44 may calculate a reference block by adding the residual block to a predictive block of one of the reference pictures within one of the reference picture lists. Motion compensation unit 44 may also apply one or more interpolation filters to the reconstructed residual block to calculate sub-integer pixel values for use in motion estimation. Summer 62 adds the reconstructed residual block to the motion compensated prediction block produced by motion compensation unit 44 to produce a reference block for storage in reference picture memory 64. The reference block may be used by motion estimation unit 42 and motion compensation unit 44 as a reference block to inter-predict a block in a subsequent video frame or picture.

Video encoder 20 represents an example of a video coder configured to generate video data that may be stored using the file format techniques described in this disclosure.

FIG3 is a block diagram illustrating an example video decoder 30 that may implement the techniques described in this disclosure. Video decoder 30 may be configured to decode single-view, multi-view, scalable, 3D, and other types of video data. In the example of FIG3 , video decoder 30 includes an entropy decoding unit 80, a prediction processing unit 81, an inverse quantization unit 86, an inverse transform processing unit 88, a summer 90, a filter unit 91, and a reference picture memory 92. Prediction processing unit 81 includes a motion compensation unit 82 and an intra-prediction processing unit 84. Video decoder 30 may, in some examples, perform a decoding pass that is generally reciprocal to the encoding pass described with respect to video encoder 20 from FIG2 .

Coded picture buffer (CPB) 79 can receive and store the encoded video data (e.g., NAL units) of the bitstream. The video data stored in CPB 79 can be obtained from link 16, for example, via a wired or wireless network for video data communication or by accessing physical data storage media, e.g., from a local video source such as a camera. CPB 79 can form a video data memory that stores the encoded video data from the encoded video bitstream. CPB 79 can be a reference picture memory that stores reference video data for use by video decoder 30 in decoding the video data (e.g., in intra- or inter-coding modes). CPB 79 and reference picture memory 92 can be formed from any of a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. CPB 79 and reference picture memory 92 can be provided by the same memory device or separate memory devices. In various examples, CPB 79 may be on-chip with other components of video decoder 30 , or off-chip relative to those components.

During the decoding process, video decoder 30 receives an encoded video bitstream representing video blocks of an encoded video slice and associated syntax elements from video encoder 20. Video decoder 30 may receive the encoded video bitstream from network entity 29. Network entity 29 may, for example, be a server, a MANE, a video editor/splicer, or other such device configured to implement one or more of the techniques described above. Network entity 29 may or may not include a video encoder, such as video encoder 20. Some of the techniques described in this disclosure may be implemented by network entity 29 before network entity 29 transmits the encoded video bitstream to video decoder 30. In some video decoding systems, network entity 29 and video decoder 30 may be parts of separate devices, while in other cases, the functionality described with respect to network entity 29 may be performed by the same device that includes video decoder 30. Network entity 29 may be considered a video device. Furthermore, in some examples, network entity 29 is file generation device 34 of FIG.

Entropy decoding unit 80 of video decoder 30 entropy decodes specific syntax elements of the bitstream to generate quantized coefficients, motion vectors, and other syntax elements. Entropy decoding unit 80 forwards the motion vectors and other syntax elements to prediction processing unit 81. Video decoder 30 may receive syntax elements at the video slice level and/or the video block level.

When the video slice is coded as an intra-coded (I) slice, intra-prediction processing unit 84 of prediction processing unit 81 may generate prediction data for the video block of the current video slice based on the signaled intra-prediction mode and data from previously decoded blocks of the current frame or picture. When the video frame is coded as an inter-coded (i.e., B, P, or GPB) slice, motion compensation unit 82 of prediction processing unit 81 generates predictive blocks for the video block of the current video slice based on motion vectors and other syntax elements received from entropy decoding unit 80. The predictive blocks may be generated according to one of the reference pictures within one of the reference picture lists. Video decoder 30 may construct reference frame lists: List 0 and List 1 using a default construction technique based on the reference pictures stored in reference picture memory 92.

Motion compensation unit 82 determines prediction information for a video block of the current video slice by parsing motion vectors and other syntax elements, and uses the prediction information to generate a predictive block for the current video block being decoded. For example, motion compensation unit 82 uses some of the received syntax elements to determine the prediction mode (e.g., intra-prediction or inter-prediction) used to code the video block of the video slice, the inter-prediction slice type (e.g., B-slice, P-slice, or GPB-slice), construction information for one or more of the slice's reference picture lists, motion vectors for each inter-coded video block of the slice, inter-prediction status for each inter-coded video block of the slice, and other information for decoding video blocks in the current video slice.

Motion compensation unit 82 may also perform interpolation based on interpolation filters. Motion compensation unit 82 may use interpolation filters as used by video encoder 20 during encoding of the video blocks to calculate interpolated values for sub-integer pixels of reference blocks. In this case, motion compensation unit 82 may determine the interpolation filters used by video encoder 20 from received syntax elements and may use the interpolation filters to produce the predictive blocks.

Inverse quantization unit 86 inverse quantizes (i.e., dequantizes) the quantized transform coefficients provided in the bitstream and decoded by entropy decoding unit 80. The inverse quantization process may include using the quantization parameters for each video block in the video slice calculated by video encoder 20 to determine the degree of quantization and, likewise, the degree of inverse quantization that should be applied. Inverse transform processing unit 88 applies an inverse transform (e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process) to the transform coefficients in order to produce residual blocks in the pixel domain.

After motion compensation unit 82 generates a predictive block for the current video block based on the motion vectors and other syntax elements, video decoder 30 forms a decoded video block by summing the residual block from inverse transform processing unit 88 with the corresponding predictive block generated by motion compensation unit 82. Summer 90 represents the component that performs this summing operation. If desired, other loop filters (either in the coding loop or after the coding loop) may also be used to smooth pixel transitions or otherwise improve video quality. Filter unit 91 is intended to represent one or more loop filters, such as a deblocking filter, an adaptive loop filter (ALF), and a sample adaptive offset (SAO) filter. Although filter unit 91 is shown in FIG3 as a loop filter, in other configurations, filter unit 91 may be implemented as a post-loop filter. The decoded video block in a given frame or picture is then stored in reference picture memory 92, which stores reference pictures used for subsequent motion compensation. Reference picture memory 92 also stores decoded video for later presentation on a display device (eg, display device 32 of FIG. 1 ).

Video decoder 30 of FIG. 3 represents an example of a video decoder configured to decode video data that may be stored using the file format techniques described in this disclosure.

FIG4 is a block diagram illustrating an example set of devices that form part of network 100. In this example, network 100 includes routing devices 104A, 104B (routing devices 104) and transcoding device 106. Routing devices 104 and transcoding device 106 are intended to represent a small number of devices that may form part of network 100. Other network devices, such as switches, hubs, gateways, firewalls, bridges, and other such devices, may also be included within network 100. Furthermore, additional network devices may be provided along the network path between server device 102 and client device 108. In some examples, server device 102 may correspond to source device 12 ( FIG1 ), while client device 108 may correspond to destination device 14 ( FIG1 ).

Generally speaking, routing device 104 implements one or more routing protocols to exchange network data through network 100. In some examples, routing device 104 may be configured to perform proxy or cache operations. Therefore, in some examples, routing device 104 may be referred to as a proxy device. Generally speaking, routing device 104 executes routing protocols to discover routes through network 100. By executing such routing protocols, routing device 104B can discover a network route from itself via routing device 104A to server device 102.

The techniques of this disclosure may be implemented by network devices such as routing device 104 and transcoding device 106, but may also be implemented by client device 108. In this manner, routing device 104, transcoding device 106, and client device 108 represent examples of devices configured to perform the techniques of this disclosure. Furthermore, the devices of FIG. 1 , encoder 20 illustrated in FIG. 2 , and decoder 30 illustrated in FIG. 3 are also examples of devices that may be configured to perform one or more of the techniques of this disclosure.

FIG5 is a conceptual diagram illustrating an example structure of a file 300 in accordance with one or more techniques of this disclosure. In the example of FIG5 , file 300 includes a movie box 302 and a plurality of media data boxes 304. Although illustrated in the example of FIG5 as being in the same file, in other examples, movie box 302 and media data box 304 may be in separate files. As indicated above, a box may be an object-oriented building block defined by a unique type identifier and length. For example, a box may be a basic syntactic structure in ISOBMFF, including a four-character coded box type, a byte count of the box, and a payload.

Movie box 302 may contain metadata for a track of file 300. Each track of file 300 may comprise a continuous stream of media data. Each of media data boxes 304 may include one or more samples 305. Each of samples 305 may comprise an audio or video access unit. As described elsewhere in this disclosure, in multi-view coding (e.g., MV-HEVC and 3D-HEVC) and scalable video coding (e.g., SHVC), each access unit may comprise multiple coded pictures. For example, an access unit may include one or more coded pictures for each layer.

5 , the movie box 302 includes a track box 306. The track box 306 may enclose metadata for a track of the file 300. In other examples, the movie box 302 may include multiple track boxes for different tracks of the file 300. The track box 306 includes a media box 307. The media box 307 may contain all objects that declare information about the media data within the track. The media box 307 includes a media information box 308. The media information box 308 may contain all objects that declare information about the characteristics of the media of the track. The media information box 308 includes a sample table box 309. The sample table box 309 may specify sample-specific metadata.

In the example of FIG5 , sample table box 309 includes a SampleToGroup box 310 and a SampleGroupDescription box 312. In other examples, sample table box 309 may include other boxes in addition to SampleToGroup box 310 and SampleGroupDescription box 312, and/or may include multiple SampleToGroup boxes and SampleGroupDescription boxes. SampleToGroup box 310 may map a sample (e.g., a particular one of sample 305) to a group of samples. SampleGroupDescription box 312 may specify properties shared by the samples in the group of samples (i.e., a sample group). Furthermore, sample table box 309 may include multiple SampleItem boxes 311. Each of the SampleItem boxes 311 may correspond to a sample in the group of samples. In some examples, SampleItem boxes 311 are instances of a randomly accessible SampleItem class that extends the base SampleGroupDescription class (as defined in Section 9.5.5.1.2 above).

According to one or more techniques of this disclosure, the SampleGroupDescription box 312 may specify that each sample in a sample group contains at least one IRAP picture. In this manner, the file generation device 34 may generate a file including a Track box 306 containing metadata for a track in the file 300. The media data for the track includes a series of samples 305. Each of the samples may be a video access unit of multi-layer video data (e.g., SHVC, MV-HEVC, or 3D-HEVC video data). Furthermore, as part of generating the file 300, the file generation device 34 may generate an additional box (i.e., a Sample Table box 309) in the file 300 that documents all samples 305 that contain at least one IRAP picture. In other words, the additional box identifies all samples 305 that contain at least one IRAP picture. In the example of FIG. 5 , the additional box defines a sample group that documents (e.g., identifies) all samples 305 that contain at least one IRAP picture. In other words, the additional box specifies that the samples 305 that contain at least one IRAP picture belong to the sample group.

Furthermore, in accordance with one or more techniques of this disclosure, each of the sample entry boxes 311 may include a value (e.g., all_pics_are_IRAP) indicating whether all coded pictures in the corresponding sample are IRAP pictures. In some examples, a value equal to 1 specifies that not all coded pictures in the sample are IRAP pictures. A value equal to 0 specifies that not every coded picture in every sample in the sample group is an IRAP picture.

In some examples, when not all coded pictures in a particular sample are IRAP pictures, file generation device 34 may include a value indicating the number of IRAP pictures in the particular sample (e.g., num_IRAP_pics) in one of the sample entry boxes 311 for the particular sample. Additionally, file generation device 34 may include a value indicating the layer identifier of the IRAP picture in the particular sample in the sample entry for the particular sample. File generation device 34 may also include a value indicating the NAL unit type of the VCL NAL unit in the IRAP picture of the particular sample in the sample entry for the particular sample.

Furthermore, in the example of FIG5 , the sample table box 309 includes a subsample information box 314. Although the example of FIG5 shows only one subsample information box, the sample table box 309 may include multiple subsample information boxes. Generally speaking, the subsample information box is designed to contain subsample information. A subsample is a series of contiguous bytes of a sample. ISO/IEC 14496-12 specifies that a specific definition of subsamples should be provided for a given coding system (e.g., H.264/AVC or HEVC).

Section 8.4.8 of ISO/IEC 14496-15 specifies the definition of subsamples for HEVC. Specifically, section 8.4.8 of ISO/IEC 14496-15 specifies that for the use of the subsample information box (8.7.7 of ISO/IEC 14496-12) in an HEVC stream, subsamples are defined based on the value of the flags field of the subsample information box. According to one or more techniques of this disclosure, if the flags field in the subsample information box 314 is equal to 5, then the subsample corresponding to the subsample information box 314 contains one coded picture and associated non-VCL NAL units. Associated non-VCL NAL units may include NAL units containing SEI messages applicable to the coded picture and NAL units containing parameter sets (e.g., VPS, SPS, PPS, etc.) applicable to the coded picture.

Thus, in one example, file generation device 34 may generate a file (e.g., file 300) that includes a track box (e.g., track box 306) containing metadata for a track in the file. In this example, the media data for the track includes a series of samples, each of which is a video access unit of multi-layer video data (e.g., SHVC, MV-HEVC, or 3D-HEVC video data). Furthermore, in this example, as part of generating the file, file generation device 34 may generate a subsample information box (e.g., subsample information box 314) in the file that contains a flag that specifies the type of subsample information given in the subsample information box. When the flag has a particular value, the subsample corresponding to the subsample information box contains exactly one coded picture and zero or more non-VCL NAL units associated with the coded picture.

Furthermore, according to one or more techniques of this disclosure, if the Flags field of the subsample information box 314 is equal to 0, the subsample information box 314 further includes a DiscardableFlag value, a NoInterLayerPredFlag value, a LayerId value, and a TempId value. If the Flags field of the subsample information box 314 is equal to 5, the subsample information box 314 may include a DiscardableFlag value, a VclNalUnitType value, a LayerId value, a TempId value, a NoInterLayerPredFlag value, a SubLayerRefNalUnitFlag value, and a Reserved value.

SubLayerRefNalUnitFlag equal to 0 indicates that all NAL units in the subsample are VCL NAL units of sub-layer non-reference pictures, as specified in ISO/IEC 23008-2 (i.e., HEVC). SubLayerRefNalUnitFlag equal to 1 indicates that all NAL units in the subsample are VCL NAL units of sub-layer reference pictures, as specified in ISO/IEC 23008-2 (i.e., HEVC). Therefore, when the file generation device 34 generates the subsample information box 314 and the flag has a specific value (e.g., 5), the file generation device 34 includes an additional flag in the subsample information box 314 that indicates whether all NAL units in the subsample are VCL NAL units of sub-layer non-reference pictures.

The DiscardableFlag value indicates the value of the discardable_flag value of the VCL NAL units in the subsample. As specified in Section A.4 of ISO/IEC 14496-15, the discardable_flag value should be set to 1 if and only if all the extracted or aggregated NAL units have the discardable_flag set to 1, and otherwise set to 0. If the bitstream containing the NAL unit can be correctly decoded without the NAL unit, then the NAL unit may have the discardable_flag set to 1. Therefore, if the bitstream containing the NAL unit can be correctly decoded without the NAL unit, then the NAL unit may be "discardable". All VCL NAL units in a subsample should have the same discardable_flag value. Therefore, when the file generation device 34 generates the subsample information box 314 and the flag has a specific value (e.g., 5), the file generation device 34 includes an additional flag (e.g., discardable_flag) in the subsample information box 314 that indicates whether all VCL NAL units of the subsample are discardable.

The NoInterLayerPredFlag value indicates the value of the inter_layer_pred_enabled_flag for the VCL NAL units in the subsample. The inter_layer_pred_enabled_flag should be set to 1 if and only if all extracted or aggregated VCL NAL units have the inter_layer_pred_enabled_flag set to 1, and otherwise set to 0. All VCL NAL units in a subsample should have the same inter_layer_pred_enabled_flag value. Therefore, when the file generation device 34 generates the subsample information box 314 and the flag has a specific value (e.g., 5), the file generation device 34 includes an additional value (e.g., inter_layer_pred_enabled_flag) in the subsample information box 314 indicating whether inter-layer prediction is enabled for all VCL NAL units of the subsample.

LayerId indicates the nuh_layer_id value of the NAL units in the subsample. All NAL units in the subsample should have the same nuh_layer_id value. Therefore, when the file generation device 34 generates the subsample information box 314 and the flag has a specific value (e.g., 5), the file generation device 34 includes an additional value (e.g., LayerId) in the subsample information box 314 that indicates the layer identifier of each NAL unit of the subsample.

TempId indicates the TemporalId value of the NAL units in the subsample. All NAL units in a subsample should have the same TemporalId value. Therefore, when the file generation device 34 generates the subsample information box 314 and the flag has a specific value (e.g., 5), the file generation device 34 includes an additional value (e.g., TempId) in the subsample information box 314 indicating the temporal identifier of each NAL unit in the subsample.

VclNalUnitType indicates the nal_unit_type syntax element of the VCL NAL unit in the subsample. The nal_unit_type syntax element is a syntax element in the NAL unit header of a NAL unit. The nal_unit_type syntax element specifies the type of RBSP contained in the NAL unit. All nal_unit_type VCL NAL units in a subsample should have the same nal_unit_type value. Therefore, when the file generation device 34 generates the subsample information box 314 and the flag has a specific value (e.g., 5), the file generation device 34 includes an additional value (e.g., VclNalUnitType) in the subsample information box 314 indicating the NAL unit type of the VCL NAL unit of the subsample. All VCL NAL units of a subsample have the same NAL unit type.

FIG6 is a conceptual diagram illustrating an example structure of a file 300 in accordance with one or more techniques of this disclosure. As specified in Section 8.4.9 of ISO/IEC 14496-15, HEVC allows file format samples that are used only for reference and not for output. For example, HEVC allows for non-displayed reference pictures in a video.

Furthermore, section 8.4.9 of ISO/IEC 14496-15 specifies that when any such non-output samples are present in a playback track, the file should be constrained as follows.

1. Non-output samples should be given a composition time outside the time range of the output samples.

2. An edit list that does not include component times for non-output samples should be used.

3. When the playback track contains CompositionOffsetBox (‘ctts’),

a. Version 1 of CompositionOffsetBox should be used,

b. For each non-output sample, the value of sample_offset should be set to be equal to ‐2 ³¹ ,

c. The SampleTableBox (‘stbl’) of the playback track should contain CompositionToDecodeBox (‘cslg’), and

d. When a CompositionToDecodeBox exists for the playback track, the value of the leastDecodeToDisplayDelta field in the box shall be equal to the smallest composition offset in the CompositionOffsetBox that does not contain sample_offset values for non-output samples.

Note: Therefore, leastDecodeToDisplayDelta is greater than ‐2 ³¹ .

As specified in ISO/IEC 14496-12, the CompositionOffsetBox provides the offset between the decoding time and the composition time. The CompositionOffsetBox contains a set of sample_offset values. Each sample_offset value is a non-negative integer that gives the offset between the composition time and the decoding time. The composition time refers to the time at which the sample will be output. The decoding time refers to the time at which the sample will be decoded.

As indicated above, a coded slice NAL unit may include a slice segment header. The slice segment header may be part of a coded slice segment and may contain data elements relating to the first or all CTUs in the slice segment. In HEVC, the slice segment header includes a pic_output_flag syntax element. Generally, the pic_output_flag syntax element is included in the first slice segment header of a slice of a picture. Therefore, this disclosure may refer to the pic_output_flag of the first slice segment header of a slice of a picture as the pic_output_flag of the picture.

As specified in Section 7.4.7.1 of the HEVC WD, the pic_output_flag syntax element affects the decoded picture output and removal process, as specified in Annex C of the HEVC WD. In general, if the pic_output_flag syntax element of the slice segment header for a slice segment is 1, then the picture including the slice corresponding to the slice segment header is output. Otherwise, if the pic_output_flag syntax element of the slice segment header for a slice segment is 0, then the picture including the slice corresponding to the slice segment header may be decoded for use as a reference picture, but the picture is not output.

According to one or more techniques of this disclosure, references to HEVC in section 8.4.9 of ISO/IEC 14496-15 may be replaced by corresponding references to SHVC, MV-HEVC, or 3D-HEVC. Furthermore, according to one or more techniques of this disclosure, when an access unit contains some coded pictures with pic_output_flag equal to 1 and some other coded pictures with pic_output_flag equal to 0, at least two tracks must be used to store the stream. For each respective one of the tracks, all coded pictures in each sample of the respective track have the same pic_output_flag value. Thus, all coded pictures in the first track have pic_output_flag equal to 0, and all coded pictures in the second track have pic_output_flag equal to 1.

6 , the file generation device 34 may generate a file 400. Similar to the file 300 in the example of FIG5 , the file 400 includes a movie box 402 and one or more media data boxes 404. Each of the media data boxes 404 may correspond to a different track of the file 400. The movie box 402 may contain metadata for the tracks of the file 400. Each track of the file 400 may include a continuous stream of media data. Each of the media data boxes 404 may include one or more samples 405. Each of the samples 405 may include an audio or video access unit.

As indicated above, in some examples, when an access unit contains some coded pictures with pic_output_flag equal to 1 and some other coded pictures with pic_output_flag equal to 0, at least two tracks must be used to store the stream. Thus, in the example of FIG6 , movie box 402 includes track box 406 and track box 408. Each of track boxes 406 and 408 encloses metadata for a different track of file 400. For example, track box 406 may enclose metadata for tracks with coded pictures with pic_output_flag equal to 0 and no pictures with pic_output_flag equal to 1. Track box 408 may enclose metadata for tracks with coded pictures with pic_output_flag equal to 1 and no pictures with pic_output_flag equal to 0.

Thus, in one example, file generation device 34 may generate a file (e.g., file 400) that includes a media data box (e.g., media data box 404) that encloses (e.g., includes) media content. The media content includes a series of samples (e.g., sample 405). Each of the samples may be an access unit of multi-layer video data. In this example, when file generation device 34 generates a file in response to a determination that at least one access unit of a bitstream includes a coded picture having a picture output flag equal to 1 and a coded picture having a picture output flag equal to 0, file generation device 34 may store the bitstream in the file using at least two tracks. For each respective track from the at least two tracks, all coded pictures in each sample of the respective track have the same picture output flag value. Pictures having a picture output flag equal to 1 are permitted to be output, and pictures having a picture output flag equal to 0 are permitted to be used as reference pictures, but are not permitted to be output.

FIG7 is a flowchart illustrating an example operation of a file generation device 34 according to one or more techniques of this disclosure. The operation of FIG7 , along with the operations illustrated in other flowcharts of this disclosure, is an example. Other example operations according to the techniques of this disclosure may include more, fewer, or different actions.

In the example of FIG7 , the file generation device 34 generates a file ( 500 ). As part of generating the file, the file generation device 34 generates a track box ( 502 ) containing metadata for a track in the file. In this manner, the file generation device 34 generates a file that includes a track box containing metadata for a track in the file. The media data for the track includes a series of samples. Each of the samples is a video access unit of multi-layer video data. In some examples, the file generation device 34 encodes the multi-layer video data.

Furthermore, as part of generating the file, file generation device 34 identifies all samples that contain at least one IRAP picture (504). Furthermore, file generation device 34 may generate an additional box in the file that documents all samples that contain at least one IRAP picture (506). In some examples, the additional box is a new box not defined in ISOBMFF or its existing extensions. In some examples, the additional box defines a sample group that documents all samples that contain at least one IRAP picture. For example, the additional box may be or include a sample table box that includes a SampleToGroup box and a SampleGroupDescription box. The SampleToGroup box identifies samples that contain at least one IRAP picture. The SampleGroupDescription box indicates that the sample group is a group of samples that contain at least one IRAP picture.

7 , file generation device 34 may generate a sample entry for a particular one of the samples that include at least one IRAP picture (508). In some examples, file generation device 34 may generate a sample entry for each respective one of the samples that include at least one IRAP picture. The sample entry may be a RandomAccessibleSampleEntry, as defined in Section 9.5.5.1.2 above.

7 , as part of generating a sample entry for a particular sample, file generation device 34 may include in the sample entry for the particular sample a value indicating whether all coded pictures in the particular sample are IRAP pictures ( 510 ). In this manner, file generation device 34 may generate in a file a sample entry that includes a value indicating whether all coded pictures in a particular sample in the series of samples are IRAP pictures. Furthermore, file generation device 34 may include in the sample entry for the particular sample a value indicating the NAL unit type of the VCL NAL units in the IRAP pictures of the particular sample ( 512 ).

Furthermore, file generation device 34 may determine whether all coded pictures in a particular sample are IRAP pictures (514). When not all coded pictures in a particular sample are IRAP pictures ("No" of 514), file generation device 34 may include, in the sample entry for the particular sample, a value indicating the number of IRAP pictures in the particular sample (516). Additionally, file generation device 34 may include, in the sample entry for the particular sample, a value indicating a layer identifier (e.g., nuh_layer_ids) of the IRAP pictures in the particular sample.

As indicated above, FIG. 7 is provided only as an example. Other examples do not include every action of FIG. 7 . For example, some examples do not include steps 502, 504, and 508. Furthermore, some examples do not include each of steps 510 through 518. Furthermore, some examples include one or more additional actions. For example, some examples include the additional action of generating a synchronization sample box as part of generating the file, wherein the synchronization sample box includes a synchronization sample table that records synchronization samples for a track of multi-layer video data in a file. Each synchronization sample of a track is a random access sample of the track. In this example, if each coded picture in the access unit is an IRAP picture, then the scalable video coding sample is a synchronization sample. Furthermore, in this example, if each coded picture in the access unit is an IRAP picture without a RASL picture, then the multiview video coding sample is a synchronization sample.

FIG8 is a flowchart illustrating example operations of a computing device performing random access and/or level switching according to one or more techniques of this disclosure. In the example of FIG8 , the computing device receives a file (550). In the example of FIG8 , the computing device may be an intermediate network device (e.g., a MANE, a streaming server), a decoding device (e.g., destination device 14), or another type of video device. In some examples, the computing device may be part of a content delivery network.

In the example of FIG8 , the computing device may obtain a track box ( 552 ) containing metadata for a track in the file from a file. The media data for the track includes a series of samples. In the example of FIG8 , each of the samples is a video access unit of multi-layer video data.

8 , the computing device may obtain an additional box from the file (554). The additional box records all samples containing at least one IRAP picture in the file. Therefore, the computing device may determine all samples containing at least one IRAP picture based on the information in the additional box (556).

Furthermore, in some examples, the computing device may obtain from a file a sample entry including a value indicating whether all coded pictures in a particular sample in the series of samples are IRAP pictures. When not all coded pictures in the particular sample are IRAP pictures, the computing device may obtain from the sample entry a value indicating the number of IRAP pictures in the particular sample. Furthermore, the computing device may obtain from the sample entry a value indicating a layer identifier for the IRAP pictures in the particular sample. Furthermore, in some examples, the computing device may obtain from the sample entry a value indicating the NAL unit type of a VCL NAL unit in the IRAP picture of the particular sample. Furthermore, in some examples, the computing device may obtain from the file a synchronization sample box including a synchronization sample table that records synchronization samples for a track of video data in the file. In these examples, each synchronization sample of the track is a random access sample of the track, scalable video coding samples are synchronization samples if each coded picture in the access unit is an IRAP picture, and multiview video coding samples are synchronization samples if each coded picture in the access unit is an IRAP picture without a RASL picture.

8 , the computing device may begin forwarding or decoding NAL units for samples containing at least one IRAP picture without forwarding or decoding NAL units for files that precede the sample in decoding order ( 558 ). In this manner, the computing device may perform random access or layer switching. For example, the computing device may begin decoding multi-layer video data at one of one or more samples containing at least one IRAP picture.

FIG9 is a flowchart illustrating example operations of a file generation device 34 according to one or more techniques of this disclosure. In the example of FIG9 , the file generation device 34 may generate a file (600) including a track box containing metadata for a track in the file. The media data for the track includes a sequence of samples. In the example of FIG9 , each of the samples is a video access unit of multi-layer video data. In some examples, the file generation device 34 encodes the multi-layer video data.

As part of generating the file, file generation device 34 may determine whether the subsample contains exactly one coded picture and zero or more non-VCL NAL units associated with the coded picture (602). In response to determining that the subsample contains exactly one coded picture and zero or more non-VCL NAL units associated with the coded picture ("Yes" of 602), file generation device 34 may generate a subsample information box in the file, the subsample information box containing a flag with a value (e.g., 5) indicating that the subsample contains exactly one coded picture and zero or more non-VCL NAL units associated with the coded picture (604). Otherwise ("No" of 602), file generation device 34 may generate a subsample information box in the file containing a flag with another value (e.g., 0, 1, 2, 3, 4).

In this manner, file generation device 34 can generate a file that includes a track box containing metadata for a track in the file. The media data for the track includes a sequence of samples, each of which is a video access unit of multi-layer video data. As part of generating the file, file generation device 34 generates a subsample information box in the file that contains a flag that specifies the type of subsample information given in the subsample information box. When the flag has a particular value, the subsample corresponding to the subsample information box contains exactly one coded picture and zero or more non-VCL NAL units associated with the coded picture.

FIG10 is a flowchart illustrating an example operation of a computing device according to one or more techniques of this disclosure. In the example of FIG10 , a computing device receives a file (650). In the example of FIG10 , the computing device may be an intermediate network device, such as a MANE or a streaming server. In some examples, the computing device may be part of a content delivery network. Furthermore, in the example of FIG10 , the computing device may obtain a track frame (651) from the file. The track frame contains metadata for a track in the file. The media data for the track includes a series of samples. In the example of FIG10 , each of the samples is a video access unit of multi-layer video data.

Furthermore, in the example of FIG. 10 , the computing device may obtain a subsample information box from the file ( 652 ). The computing device uses the information in the subsample information box to extract a sub-bitstream ( 654 ). The sub-bitstream may include each NAL unit of an operation point of the bitstream stored in the file. In other words, the NAL units of the sub-bitstream may be a subset of the NAL units stored in the file. The computing device may obtain the subsample information box from the file and may extract the sub-bitstream without parsing or interpreting the NAL units included in the sequence of samples. Not parsing or interpreting NAL units when extracting the sub-bitstream may reduce the complexity of the computing device and/or may speed up the process of extracting the sub-bitstream.

Furthermore, in some examples, when the flag has a particular value, the computing device may obtain one or more of the following from the subsample information box:

● an additional flag indicating whether all VCL NAL units of the subsample can be discarded,

an additional value indicating the NAL unit type of the VCL NAL units of a subsample, where all VCL NAL units of the subsample have the same NAL unit type,

● an additional value for the layer identifier of each NAL unit indicating a subsample,

● an additional value for the temporal identifier of each NAL unit indicating a subsample,

● an additional flag indicating whether inter-layer prediction is enabled for all VCL NAL units of the subsample, or

• An additional flag indicating whether all NAL units in the sub-sample are VCL NAL units of sub-layer non-reference pictures.

In the example of FIG10 , as part of extracting the sub-bitstream, the computing device may determine whether the “flag” value of the subsample information box has a specific value (e.g., 5) indicating that the subsample information box corresponds to exactly one coded picture and zero or more non-VCL NAL units associated with the coded picture (656). When the “flag” value of the subsample information box has the specific value (“yes” of 656), the computing device may determine whether the coded picture is required to decode the operation point based on the information specified in the subsample information box (658). For example, the computing device may determine, based on the discardable flag, a VCL NAL unit type indicator, a layer identifier, a temporal identifier, a no inter-layer prediction flag, and/or a sub-layer reference NAL unit flag, whether the coded picture is required to decode the operation point. When the coded picture is required to decode the operation point (“yes” of 658), the computing device may include the NAL unit of the subsample in the sub-bitstream (660). Otherwise, in the example of FIG. 10 , when no coded picture is needed to decode the operation point (“NO” of 658 ), the computing device does not include NAL units for the sub-sample in the sub-bitstream ( 662 ).

10, the computing device may output the sub-bitstream (664). For example, the computing device may store the sub-bitstream to a computer-readable storage medium or transmit the sub-bitstream to another computing device.

As indicated above, Figure 10 is an example. Other examples may include or omit specific actions of Figure 10. For example, some examples omit actions 650, 651, 654, and/or 664. In addition, some examples omit one or more of actions 656-662.

FIG11 is a flowchart illustrating an example operation of file generation device 34 according to one or more techniques of this disclosure. In the example of FIG11 , file generation device 34 may generate a file (700) including a media data box enclosing media content. The media content may include a series of samples, each of which is an access unit of multi-layer video data. In various examples, the multi-layer video data may be SHVC data, MV-HEVC data, or 3D-HEVC data. In some examples, file generation device 34 encodes the multi-layer video data.

11 , as part of generating a file, file generation device 34 may determine whether at least one access unit of a bitstream of multi-layer video data includes a coded picture having a picture output flag equal to a first value (e.g., 1) and a coded picture having a picture output flag equal to a second value (e.g., 0) ( 702 ). Pictures having the picture output flag equal to the first value (e.g., 1) are permitted to be output, and pictures having the picture output flag equal to the second value (e.g., 0) are permitted to be used as reference pictures but are not permitted to be output. In other examples, other devices may perform the determination of whether at least one access unit of a bitstream of multi-layer video data includes a coded picture having a picture output flag equal to the first value and a coded picture having a picture output flag equal to the second value.

In response to at least one access unit of the bitstream of multi-layer video data including a coded picture having a picture output flag equal to a first value and a coded picture having a picture output flag equal to a second value (YES at 702 ), the file generation device 34 stores the bitstream in a file using at least a first track and a second track ( 704 ). For each respective track from the first track and the second track, all coded pictures in each sample of the respective track have the same picture output flag value.

11 , in response to determining that no access unit in the bitstream includes a coded picture having a picture output flag equal to a first value (e.g., 1) and a coded picture having a picture output flag equal to a second value (e.g., 0) ("No" of 702), file generation device 34 may store the bitstream in a file using a single track (706). In other examples, file generation device 34 may generate a file with multiple tracks even when no access unit in the bitstream includes a coded picture having a picture output flag equal to a first value (e.g., 1) and a coded picture having a picture output flag equal to a second value (e.g., 0).

As indicated above, Figure 11 is an example. Other examples may include fewer actions. For example, some examples omit actions 702 and 706.

FIG12 is a flowchart illustrating an example operation of a destination device 14 according to one or more techniques of the present disclosure. In the example of FIG12 , the destination device 14 receives a file ( 750 ). The file may include a media data box enclosing media content, the media content including a series of samples. Each of the samples may be an access unit of multi-layer video data. In various examples, the multi-layer video data may be SHVC data, MV-HEVC data, or 3D-HEVC data. Furthermore, in the example of FIG12 , the destination device 14 may obtain a first track box and a second track box ( 751 ) from the file. The first track box contains metadata for the first track in the file. The second track box contains metadata for the second track in the file. For each respective track from the first track and the second track, all coded pictures in each sample of the respective track have the same picture output flag value. Pictures with a picture output flag equal to a first value (e.g., 1) are allowed to be output, and pictures with a picture output flag equal to a second value (e.g., 0) are allowed to be used as reference pictures, but are not allowed to be output.

Video decoder 30 of destination device 14 may decode pictures in the track for pictures with a picture output flag equal to a first value (e.g., 1), and may decode pictures in the track for pictures with a picture output flag equal to a second value (e.g., 0) (752). In some cases, video decoder 30 may decode pictures with a picture output flag equal to 0 using pictures with a picture output flag equal to 1, and vice versa. Destination device 14 may output pictures with a picture output flag equal to the first value (754). Destination device 14 does not output pictures with a picture output flag equal to the second value (756). In this manner, for each respective track from the first and second tracks, destination device 14 may decode a coded picture in each sample of the respective track and output a decoded picture with a picture output flag equal to the first value.

As indicated above, Figure 12 is provided merely as an example. Other examples may omit certain actions of Figure 12, such as actions 752 to 756.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored or transmitted as one or more instructions or codes on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media (which corresponds to tangible media such as data storage media), or communication media including any media that facilitates the transfer of a computer program from one place to another (e.g., according to a communication protocol). In this manner, computer-readable media may generally correspond to (1) non-transitory, tangible computer-readable storage media, or (2) communication media such as signals or carrier waves. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, codes, and/or data structures for implementing the techniques described herein. A computer program product may include computer-readable media.

By way of example, and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Moreover, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwaves, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwaves are included in the definition of medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transient media, but instead refer to non-transitory, tangible storage media. As used herein, disk and disc include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc. Disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuits. Thus, the term "processor," as used herein, may refer to any of the aforementioned structures or any other structure suitable for implementing the techniques described herein. Furthermore, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated into a combined codec. Moreover, the techniques may be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a variety of devices or apparatuses, including wireless handsets, integrated circuits (ICs), or sets of ICs (e.g., chipsets). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require implementation by different hardware units. Rather, as described above, the various units may be combined with appropriate software and/or firmware in a codec hardware unit or provided by a collection of interoperable hardware units, including one or more processors as described above.

Various examples have been described. These and other examples are within the scope of the following claims.

Claims (38)

1. A method for processing multi-layer video data, the method comprising: Generate a file including movie frames, the movie frames containing metadata for a continuous media stream existing in the file, wherein generating the file includes: In response to the determination of at least one access unit of the bitstream of the multi-layer video data, which includes a decoded image having an image output flag equal to a first value and a decoded image having an image output flag equal to a second value different from the first value, the bitstream is stored in the file using at least one first playback track and a second playback track, wherein: For each corresponding playback track from the first playback track and the second playback track, all decoded images in each sample of the corresponding playback track have the same value for the image output flag; and Images with an image output flag equal to the first value are allowed to be output, and images with an image output flag equal to the second value are allowed to be used as reference images, but are not allowed to be output; and For each corresponding playback track of the file, the corresponding playback track frame is enclosed in the movie frame, the corresponding playback track frame enclosing the metadata for the corresponding playback track, wherein each of the media streams present in the file is represented in the file as the corresponding playback track of the file, the media stream for the corresponding playback track includes a corresponding sample sequence, the corresponding sample sequence includes the access unit of the multi-layer video data, wherein the media stream for the corresponding playback track is enclosed in the media data frame of the file. 2. The method of claim 1, wherein generating the file comprises: In response to determining that no access unit in the bitstream contains a decoded image with an image output flag equal to the first value and a decoded image with an image output flag equal to the second value, the bitstream is stored in the file using a single playback track. 3. The method according to claim 1, wherein the multi-layer video data is Scalable High Efficiency Video Decoding (SHVC) data. 4. The method according to claim 1, wherein the multi-layer video data is multi-view high-efficiency video decoding (MV-HEVC) data. 5. The method according to claim 1, wherein the multi-layer video data is 3D high-efficiency video decoding 3D-HEVC data. 6. The method of claim 1, wherein the first value is equal to 1 and the second value is equal to 0. 7. The method of claim 1, further comprising: Encode the multi-layer video data. 8. A method for processing multi-layer video data, the method comprising: A first playback track frame and a second playback track frame are obtained from the file. The first playback track frame and the second playback track frame are located within a movie frame. The movie frame contains metadata for a continuous media stream existing in the file, wherein: For each corresponding playback track of the file, each of the media streams existing in the file is represented in the file as the corresponding playback track of the file. The media stream for the corresponding playback track contains a corresponding sample sequence, the corresponding sample sequence contains access units for the multi-layer video data, and the media stream for the corresponding playback track is enclosed in the media data frame of the file. The first playback track frame contains metadata from the file for the first playback track, and the second playback track frame contains metadata from the file for the second playback track. For each corresponding playback track from the first playback track and the second playback track, all decoded images in each sample of the corresponding playback track have the same value for the image output flag, and Images with an image output flag equal to the first value are allowed to be output, and images with an image output flag equal to a second value different from the first value are allowed to be used as reference images, but they are not allowed to be output. 9. The method according to claim 8, wherein the multi-layer video data is Scalable High Efficiency Video Decoding (SHVC) data. 10. The method according to claim 8, wherein the multi-layer video data is multi-view high-efficiency video decoding (MV-HEVC) data. 11. The method according to claim 8, wherein the multi-layer video data is 3D-HEVC data with high efficiency video decoding. 12. The method of claim 8, wherein the first value is equal to 1 and the second value is equal to 0. 13. The method of claim 8, further comprising: For each corresponding playback track from the first playback track and the second playback track: Decode the decoded image in each sample of the corresponding playback track; and The decoded image is output with an image output flag equal to the first value. 14. A video apparatus for processing multi-layer video data, the video apparatus comprising: Data storage media configured to store the multi-layer video data; and One or more processors, configured to: Generate a file including movie frames, the movie frames containing metadata for a continuous media stream existing in the file, wherein, in order to generate the file, the one or more processors are configured to: In response to the determination of at least one access unit of the bitstream of the multi-layer video data, which includes a decoded image having an image output flag equal to a first value and a decoded image having an image output flag equal to a second value different from the first value, the bitstream is stored in the file using at least one first playback track and a second playback track, wherein: For each corresponding playback track from the first playback track and the second playback track, all decoded images in each sample of the corresponding playback track have the same value for the image output flag; Images with an image output flag equal to the first value are allowed to be output, and images with an image output flag equal to the second value are allowed to be used as reference images, but are not allowed to be output; and for each corresponding playback track of the file, the corresponding playback track frame is contained within the movie frame, the corresponding playback track frame encloses the metadata for the corresponding playback track, wherein each of the media streams present in the file is represented in the file as the corresponding playback track of the file, the media stream for the corresponding playback track contains a corresponding sample sequence, the corresponding sample sequence contains the access unit of the multi-layer video data, wherein the media stream for the corresponding playback track is enclosed in the media data frame of the file. 15. The video apparatus of claim 14, wherein, in order to generate the file, the one or more processors are configured to: In response to determining that no access unit in the bitstream contains a decoded image with an image output flag equal to the first value and a decoded image with an image output flag equal to the second value, the bitstream is stored in the file using a single playback track. 16. The video apparatus of claim 14, wherein the multilayer video data is one of the following: Scalable High Efficiency Video Coding (SHVC) data, Multi-View High Efficiency Video Coding (MV-HEVC) data, or 3D High Efficiency Video Coding (3D-HEVC) data. 17. The video apparatus of claim 14, wherein the first value is equal to 1 and the second value is equal to 0. 18. The video apparatus of claim 14, wherein the one or more processors are configured to encode the multilayer video data. 19. The video apparatus of claim 14, wherein the video apparatus comprises at least one of the following: integrated circuit; microprocessor; or Wireless communication device. 20. A video apparatus for processing multi-layer video data, the video apparatus comprising: Data storage media configured to store the multi-layer video data; and One or more processors, configured to: A first playback track frame and a second playback track frame are obtained from the file. The first playback track frame and the second playback track frame are located within a movie frame. The movie frame contains metadata for a continuous media stream existing in the file, wherein: For each corresponding playback track of the file, each of the media streams existing in the file is represented in the file as the corresponding playback track of the file. The media stream for the corresponding playback track contains a corresponding sample sequence, the corresponding sample sequence contains access units for the multi-layer video data, and the media stream for the corresponding playback track is enclosed in the media data frame of the file. The first playback track frame contains metadata from the file for the first playback track, and the second playback track frame contains metadata from the file for the second playback track. For each corresponding playback track from the first playback track and the second playback track, all decoded images in each sample of the corresponding playback track have the same value for the image output flag, and Images with an image output flag equal to the first value are allowed to be output, and images with an image output flag equal to a second value different from the first value are allowed to be used as reference images, but they are not allowed to be output. 21. The video apparatus of claim 20, wherein the multi-layer video data is one of the following: Scalable High Efficiency Video Coding (SHVC) data, Multi-View High Efficiency Video Coding (MV-HEVC) data, or 3D High Efficiency Video Coding (3D-HEVC) data. 22. The video apparatus of claim 20, wherein the first value is equal to 1 and the second value is equal to 0. 23. The video apparatus of claim 20, wherein the one or more processors are configured to: For each corresponding playback track from the first playback track and the second playback track: Decode the decoded image in each sample of the corresponding playback track; and The decoded image is output with an image output flag equal to the first value. 24. The video apparatus of claim 20, wherein the video apparatus comprises at least one of the following: integrated circuit; microprocessor; or Wireless communication device. 25. A video apparatus for processing multi-layer video data, the video apparatus comprising: A device for storing the multi-layer video data; and A means for generating a file including a movie frame, the movie frame containing metadata for a continuous media stream existing in the file, wherein the means for generating the file includes: At least one access unit for responding to the bitstream of the multi-layer video data includes determining a decoded image having an image output flag equal to a first value and a decoded image having an image output flag equal to a second value different from the first value, and means for storing the bitstream in the file using at least one first playback track and a second playback track, wherein: For each corresponding playback track from the first playback track and the second playback track, all decoded images in each sample of the corresponding playback track have the same value for the image output flag; Images with an image output flag equal to the first value are allowed to be output, and images with an image output flag equal to the second value are allowed to be used as reference images, but are not allowed to be output. For each corresponding playback track of the file, means for enclosing the corresponding playback track frame within the movie frame, the corresponding playback track frame enclosing metadata for the corresponding playback track, wherein each of the media streams present in the file is represented in the file as the corresponding playback track of the file, the media stream for the corresponding playback track includes a corresponding sample sequence, the corresponding sample sequence includes access units for the multi-layer video data, wherein the media stream for the corresponding playback track is enclosed within the media data frame of the file. 26. The video apparatus of claim 25, comprising: A means for storing the bitstream in the file using a single playback track in response to determining that no access unit in the bitstream contains a decoded image with an image output flag equal to the first value and a decoded image with an image output flag equal to the second value. 27. The video apparatus of claim 25, wherein the multilayer video data is one of the following: Scalable High Efficiency Video Coding (SHVC) data, Multi-View High Efficiency Video Coding (MV-HEVC) data, or 3D High Efficiency Video Coding (3D-HEVC) data. 28. The video apparatus of claim 25, wherein the first value is equal to 1 and the second value is equal to 0. 29. A video apparatus for processing multi-layer video data, the video apparatus comprising: A device for receiving documents; and A means for obtaining a first playback track frame and a second playback track frame from the file, the first playback track frame and the second playback track frame being in a movie frame, the movie frame containing metadata for a continuous media stream existing in the file, wherein: For each corresponding playback track of the file, each of the media streams existing in the file is represented in the file as the corresponding playback track of the file. The media stream for the corresponding playback track contains a corresponding sample sequence, the corresponding sample sequence contains access units for the multi-layer video data, and the media stream for the corresponding playback track is enclosed in the media data frame of the file. The first playback track frame contains metadata from the file for the first playback track, and the second playback track frame contains metadata from the file for the second playback track. For each corresponding playback track from the first playback track and the second playback track, all decoded images in each sample of the corresponding playback track have the same value for the image output flag, and Images with an image output flag equal to the first value are allowed to be output, and images with an image output flag equal to a second value different from the first value are allowed to be used as reference images, but they are not allowed to be output. 30. The video apparatus of claim 29, wherein the multi-layer video data is one of the following: Scalable High Efficiency Video Coding (SHVC) data, Multi-View High Efficiency Video Coding (MV-HEVC) data, or 3D High Efficiency Video Coding (3D-HEVC) data. 31. The video apparatus of claim 29, wherein the first value is equal to 1 and the second value is equal to 0. 32. A non-transitory computer-readable data storage medium having instructions stored thereon, which, when executed, cause one or more processors to: Generate a file including movie frames, the movie frames containing metadata for a continuous media stream existing in the file, wherein, in order to generate the file, the instructions cause the one or more processors to: In response to the determination of at least one access unit of the bitstream of multi-layer video data, which includes a decoded image having an image output flag equal to a first value and a decoded image having an image output flag equal to a second value different from the first value, the bitstream is stored in the file using at least one first playback track and a second playback track, wherein: For each corresponding playback track from the first playback track and the second playback track, all decoded images in each sample of the corresponding playback track have the same value for the image output flag; and Images with an image output flag equal to the first value are allowed to be output, and images with an image output flag equal to the second value are allowed to be used as reference images, but are not allowed to be output; and For each corresponding playback track of the file, the corresponding playback track frame is enclosed in the movie frame, the corresponding playback track frame enclosing the metadata for the corresponding playback track, wherein each of the media streams present in the file is represented in the file as the corresponding playback track of the file, the media stream for the corresponding playback track includes a corresponding sample sequence, the corresponding sample sequence includes the access unit of the multi-layer video data, wherein the media stream for the corresponding playback track is enclosed in the media data frame of the file. 33. The non-transitory computer-readable data storage medium of claim 32, wherein the instructions cause one or more processors to: In response to determining that no access unit in the bitstream contains a decoded image with an image output flag equal to the first value and a decoded image with an image output flag equal to the second value, the bitstream is stored in the file using a single playback track. 34. The non-transitory computer-readable data storage medium of claim 32, wherein the multi-layer video data is one of the following: Scalable High Efficiency Video Coding (SHVC) data, Multi-View High Efficiency Video Coding (MV-HEVC) data, or 3D High Efficiency Video Coding (3D-HEVC) data. 35. The non-transitory computer-readable data storage medium of claim 32, wherein the first value is equal to 1 and the second value is equal to 0. 36. A non-transitory computer-readable data storage medium having instructions stored thereon, which, when executed, cause one or more processors to: A first playback track frame and a second playback track frame are obtained from the file. The first playback track frame and the second playback track frame are located within a movie frame. The movie frame contains metadata for a continuous media stream existing in the file, wherein: For each corresponding playback track of the file, each of the media streams existing in the file is represented in the file as the corresponding playback track of the file. The media stream for the corresponding playback track contains a corresponding sample sequence, the corresponding sample sequence contains access units for multiple layers of video data, and the media stream for the corresponding playback track is enclosed in the media data frame of the file. The first playback track frame contains metadata from the file for the first playback track, and the second playback track frame contains metadata from the file for the second playback track. For each corresponding playback track from the first playback track and the second playback track, all decoded images in each sample of the corresponding playback track have the same value for the image output flag, and Images with an image output flag equal to the first value are allowed to be output, and images with an image output flag equal to a second value different from the first value are allowed to be used as reference images, but they are not allowed to be output. 37. The non-transitory computer-readable data storage medium of claim 36, wherein the multi-layer video data is one of: Scalable High Efficiency Video Coding (SHVC) data, Multi-View High Efficiency Video Coding (MV-HEVC) data, or 3D High Efficiency Video Coding (3D-HEVC) data. 38. The non-transitory computer-readable data storage medium of claim 36, wherein the first value is equal to 1 and the second value is equal to 0.