HK1242091B - Method for encoding/decoding video stream and device for decoding video stream - Google Patents

Description

Method for encoding/decoding video stream and device for decoding video stream

This application is a divisional application of Chinese patent application CN201280050538.2 ("Tracking a reference picture based on a selected picture on an electronic device"), whose application date is October 12, 2012 and whose earliest priority date is October 13, 2011.

Related references

This application is a continuation-in-part of U.S. patent application No. 13/291,961, filed on November 8, 2011, entitled “TRACKING A REFERENCE PICTURE BASED ON A DESIGNATED PICTURE ON AN ELECTRONIC DEVICE,” which is a continuation-in-part of U.S. patent application No. 13/287,015, filed on November 1, 2011, entitled “TRACKING A REFERENCE PICTURE BASED ON A DESIGNATED PICTURE ON AN ELECTRONIC DEVICE,” which is a continuation-in-part of U.S. patent application No. 13/273,191, filed on October 13, 2011, entitled “TRACKING A REFERENCE PICTURE ON AN ELECTRONIC DEVICE,” all of which are incorporated herein by reference in their entireties.

Technical Field

The present disclosure relates generally to electronic devices and more particularly to enabling tracking of reference pictures.

Background Art

Electronic devices have become smaller and more powerful to meet consumer demand and improve portability and convenience. Consumers have become dependent on electronic devices and increasingly expect increased functionality. Some examples of electronic devices include desktop computers, laptop computers, cellular phones, smartphones, media players, integrated circuits, and the like.

Some electronic devices are used to process and display digital media. For example, portable electronic devices now allow consumers to consume digital media almost anywhere they are. In addition, some electronic devices can provide downloading or streaming of digital media content for consumers to use and enjoy.

The increasing popularity of digital media has presented a number of problems. For example, efficiently representing high-quality digital media for storage, transmission, and playback presents a number of challenges. As can be seen from this discussion, systems and methods for more efficiently representing digital media can be beneficial.

Summary of the Invention

A preferred embodiment is a method for decoding a video bitstream, comprising: receiving a reference description of a decoded reference picture from the bitstream; determining a picture order count (POC) of a current picture for decoding; identifying a decoded reference picture of the current picture from a decoded picture cache based on the picture order count and the reference description; decoding the current picture using inter-frame prediction based on the decoded reference picture; and caching the decoded picture in the decoded picture cache for future prediction, wherein the reference description includes modification parameters for a long-term reference picture; and the identifying using the modification parameters to modify a reference to at least a portion of a set of decoded reference pictures.

Another preferred embodiment is an electronic device configured to decode a video bitstream, comprising: a processor; a memory in electronic communication with the processor; instructions stored in the memory, the instructions executable to: receive a reference description of a decoded reference picture from the bitstream; determine a picture order count (POC) of a current picture for decoding; identify the decoded reference picture of the current picture from a decoded picture cache based on the picture order count and the reference description; decode the current picture using inter-frame prediction based on the decoded reference picture; and cache the decoded picture in the decoded picture cache for future prediction, wherein the reference description includes modification parameters for a long-term reference picture; and the modification parameters are used to modify a reference to at least a portion of a set of decoded reference pictures.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a block diagram illustrating an example of one or more electronic devices in which systems and methods for tracking a reference picture based on a selected picture may be implemented;

FIG2 is a block diagram showing one configuration of a decoder;

3 is a flow chart illustrating one configuration of a method for tracking a reference picture using reduced overhead referencing based on a selected picture;

4 is a flow chart illustrating a more specific configuration of a method for tracking a reference picture using reduced overhead referencing based on a selected picture;

FIG5 is a diagram showing an example of a plurality of picture sets referenced by a loop parameter;

FIG6 is a schematic diagram showing another example of a plurality of picture sets;

FIG7 is a schematic diagram showing a more specific example of a plurality of picture sets referenced by a loop parameter;

8 is a flow chart illustrating one configuration of a method for tracking a reference picture using reduced overhead referencing based on a selected picture;

9 is a flow chart illustrating another configuration of a method for tracking a reference picture using reduced overhead referencing based on a selected picture;

10 is a flow chart illustrating another configuration of a method for tracking a reference picture using reduced overhead referencing based on a selected picture;

FIG11 is a diagram illustrating one example of signaling a wrap indicator according to the systems and methods disclosed herein;

FIG12 is a diagram illustrating one example of signaling a wrap indicator according to the systems and methods disclosed herein;

13 is a flow chart illustrating another more specific configuration of a method for tracking a reference picture using reduced overhead referencing based on a selected picture;

FIG14 is a flow chart illustrating one configuration of a method for determining whether a transition occurs between picture sets;

15 is a flow chart illustrating another more specific configuration of a method for tracking a reference picture using reduced overhead referencing based on a selected picture;

FIG16 illustrates various components that may be utilized in an electronic device; and

FIG. 17 is a diagram illustrating an example of a use case according to the systems and methods disclosed herein.

DETAILED DESCRIPTION

A method for tracking reference pictures on an electronic device is described. The method includes receiving a bitstream. The method also includes decoding a portion of the bitstream to generate a decoded reference picture. The method also includes tracking a decoded reference picture in a decoded picture buffer (DPB) using a reduced overhead reference based on a selected picture. The method also includes decoding a picture based on the decoded reference picture. The selected picture may be an Instantaneous Decoding Refresh (IDR) picture. Additionally, a cache description of the decoded reference picture may include a picture order count (POC), a loop parameter, a temporal identifier, and a scaling parameter.

Tracking the decoded reference picture may include determining a loop parameter based on the selected picture.The loop parameter may be reset based on the selected picture.

Tracking the decoded reference picture may include determining a picture order count (POC) based on the selected picture. A picture order count (POC) sequence may be reset based on the selected picture.

A resolution of the decoded reference picture may be different from a resolution of the picture.The method may further include processing transform coefficients of the decoded reference picture based on the scaling parameter to decode the picture.

Tracking the decoded reference picture may include tracking a decoded reference picture set including the decoded reference picture. Tracking the decoded reference picture may also include obtaining a cache description and modifying the cache description. Modifying the cache description may include deleting an entry, adding an entry, and/or replacing an entry.

An electronic device configured to track reference pictures is also described. The electronic device includes a processor and instructions stored in a memory in electronic communication with the processor. The electronic device receives a bitstream. The electronic device also decodes a portion of the bitstream to generate a decoded reference picture. The electronic device also tracks a decoded reference picture in a decoded picture buffer (DPB) using a reduced overhead reference based on a selected picture. The electronic device also decodes a picture based on the decoded reference picture.

The systems and methods disclosed herein describe multiple configurations for tracking reference pictures based on selected pictures on an electronic device. For example, the systems and methods disclosed herein describe tracking decoded reference pictures in a decoded picture buffer (DPB) using reduced overhead referencing. For example, multiple schemes for long-term reference picture signaling are described. It should be noted that a decoded picture buffer (DPB) can be a buffer specified for a hypothetical reference decoder that stores decoded pictures for reference, output reordering, or output delay.

On electronic devices, a decoded picture buffer (DPB) can be used to store reconstructed (e.g., decoded) pictures at the decoder. These stored pictures can then be used, for example, in inter-frame prediction mechanisms. When pictures are decoded out of order, they can be stored in the DPB so that they can be displayed in order later.

In the H.264 or Advanced Video Coding (AVC) standard, DPB management (e.g., picture deletion, picture addition, picture reordering, etc.) is performed using memory management control operations (MMCO). More reliable DPB management schemes are under consideration for the upcoming High Efficiency Video Coding (HEVC) standard. One example of a more reliable scheme is based on absolute signaling of reference pictures, as detailed in the document JCTVC-F493, "Absolute signaling of reference pictures," from the Joint Collaborative Team on Video Coding (JCT-VC).

JCTVC-F493 outlines absolute signaling of reference pictures for identifying which reference pictures should be stored in the decoded picture buffer (DPB). Specifically, JCTVC-F493 outlines two different schemes for identifying which reference pictures to store in the DPB based on a picture order count (POC). The picture order count (POC) can be a variable associated with each coded picture and has a value that increases with increasing picture position in a wrap-around output order.

In one example, assume that all pictures have a temporal identifier (temporalID) of 0. Also assume that the current POC is 5 and the current DPB contains [ ] = {3, 2}. Furthermore, assume that the definition of the picture parameter set (PPS) is: BufferDescription0 = {deltaPOC = -1, temporalID = 0}, {deltaPOC = -2, temporalID = 0}. The deltaPOC specifies the distance between the POC value of the reference picture and the current picture, where the current picture may be the picture being decoded. One proposed solution is to reference the buffer description in the PPS. In this solution, the slice header of a picture with POC = 5 contains a reference to BufferDescription0 in the PPS. The assumed action is to discard decoded pictures with POC = 2 from the DPB and add decoded pictures with POC = 4 to the DPB. Therefore, the DPB then contains [ ] = {4, 3}.

In one configuration, the cache description is defined as two lists (denoted as POCBD and TemporalIDBD) and a variable NumberOfPicturesInBD given for all pictures. This is so that POCBD contains the picture order count value of the reference picture, and TemporalIDBD contains the corresponding temporal identifier of the reference picture, and both lists contain the NumberOfPicturesInBD value.

It should be noted that temporalID may be defined in the Joint Collaborative Team on Video Coding (JCT-VC) document JCTVC-F803 as follows: "temporalID specifies a temporal identifier for a NAL unit. The value of temporalID shall be the same for all NAL units of an access unit. When an access unit contains any NAL unit with nal_unit_type equal to 5, temporalID shall be equal to 0." It should be noted that NAL may be an abbreviation for "Network Abstraction Layer".

Another approach is to explicitly signal the contents of the DPB using deltaPOC relative to the current POC. In this approach, the slice header of a picture with POC=5 contains {deltaPOC=-1, temporalID=0} and {deltaPOC=-2, temporalID=0}. Assume the action is to drop decoded pictures with POC=2 from the DPB and add decoded pictures with POC=4 to the DPB. Therefore, the new DPB contains {4, 3}.

The advantages of the solution proposed in JCTVC-F493 are as follows: The solution in JCTVC-F493 provides a simple mechanism. Furthermore, picture loss is easily detected at the decoder. Furthermore, the loss of entire layers of pictures with higher temporal IDs can be detected and better supported.

However, some disadvantages of the approach presented in JCTVC-F493 are described below. The bit overhead for signaling long-term reference pictures can become large. Furthermore, a fixed number of bits may be allocated to convey the POC. Therefore, when the maximum allowed by the number of bits being used is reached, the POC number should wrap around to 0. Consequently, there may be no guarantee that the POC can be used to uniquely identify a picture.

The systems and methods disclosed herein may help alleviate these shortcomings. Specifically, the systems and methods disclosed herein may be beneficial by reducing the overhead associated with absolute long-term picture references, and may enable unique identification of pictures (e.g., a long-term (reference) picture may not be confused with other short-term or long-term pictures, and vice versa).

The systems and methods disclosed herein can provide one or more additional benefits as described below. One or more configurations of the systems and methods disclosed herein can make full use of the available POC number space [0, ..., MaxPOC-1], where MaxPOC = 2 ^{log2_max_pic_order_cnt_minus4+4} and log2_max_pic_order_cnt_minus4 specifies the value of the variable MaxPOC used for the picture order count in the decoding process. For example, one existing solution for reusing [0, ..., MaxPOC-1] after POC wraparound advocates skipping the currently used POC when assigning an identifier (e.g., POC number) to a picture. This results in a portion of the POC space being unused. However, the systems and methods disclosed herein can solve the problem of skipping POCs and the associated reduction in POC space.

Another benefit may be that some configurations for signaling of the systems and methods disclosed herein may be independent per picture. Thus, error resilience may be better than schemes that rely on propagation of information from previous pictures (which may be lost or discarded). For example, one configuration described by the decoded picture buffer (DPB) does not rely on information embedded in other pictures to maintain the same DPB as the encoder.

Another benefit of some configurations of the systems and methods disclosed herein may be that if a picture is lost, the loss can be detected as soon as a buffered description is available at the decoder (which is at the next received picture). This allows the decoder to take corrective action. Another benefit is that if the POC resolution is sufficient, no additional bits are required.

Various configurations will now be described with reference to the accompanying drawings, in which like reference numerals may indicate functionally similar elements. The systems and methods, as generally described and illustrated in the drawings herein, may be arranged and designed in a variety of different configurations. Therefore, the following more detailed description of the various configurations, as represented in the drawings, is not intended to limit the scope of what is claimed, but is merely representative of the systems and methods.

FIG1 is a block diagram illustrating an example of one or more electronic devices 104 in which systems and methods for tracking a reference picture based on a selected picture may be implemented. In this example, electronic device A 104 a and electronic device B 104 b are shown. However, it should be noted that in some configurations, the features and/or functionality described with respect to electronic device A 104 a and electronic device B 104 b may be combined into a single electronic device.

Electronic device A 104a includes an encoder 108 and an overhead signaling module 112. Each of the elements included in electronic device A 104a (e.g., encoder 108 and overhead signaling module 112) may be implemented in hardware, software, or a combination of hardware and software.

Electronic device A 104a may obtain an input screen 106. In some configurations, the input screen 106 may be captured on electronic device A 104a using an image sensor, retrieved from memory, and/or received from another electronic device.

The encoder 108 may encode the input pictures 106 to generate encoded data 110. For example, the encoder 108 may encode a series of input pictures 106 (e.g., a video). In one configuration, the encoder 108 may be a High Efficiency Video Coding (HEVC) encoder. The encoded data 110 may be digital data (e.g., a bitstream).

The overhead signaling module 112 may generate overhead signaling based on the coded data 110. For example, the overhead signaling module 112 may add overhead data to the coded data 110, such as slice header information, picture parameter set (PPS) information, picture order count (POC), reference picture indication, etc. In some configurations, the overhead signaling module 112 may generate a wrap indicator that indicates a transition between two picture sets.

The following provides further details on various overhead signaling that may be generated by electronic device A 104a. Specifically, the overhead signaling module 112 may generate zero, one, or more of the parameters, indicators, or various information described below with respect to decoding, depending on the configuration. It should be noted that in some configurations, the overhead signaling module 112 may be included in the encoder 108. The overhead signaling module 112 may enable picture tracking using reduced overhead references.

The encoder 108 (and, for example, the overhead signaling module 112) can generate a bitstream 114. The bitstream 114 can include coded picture data based on the input picture 106. In some configurations, the bitstream 114 can also include overhead data, such as slice header information, PPS information, etc. More details on the overhead data are provided below. When encoding additional input pictures 106, the bitstream 114 can include one or more coded pictures. For example, the bitstream 114 can include one or more coded reference pictures and/or other pictures.

The bitstream 114 can be provided to the decoder 102. In one example, a wired link or a wireless link can be used to send the bitstream 114 to the electronic device B 104b. In some cases, this can be accomplished by a network (such as the Internet or a local area network (LAN)). As shown in Figure 1, the decoder 102 can be implemented on the electronic device B 104b separately from the encoder 108 on the electronic device A 104a. However, it should be noted that in some configurations, the encoder 108 and the decoder 102 can be implemented on the same electronic device. In the implementation mode that the encoder 108 and the decoder 102 are implemented on the same electronic device, for example, the bitstream 114 can be provided to the decoder 102 by a bus, or the bitstream 114 can be stored in a memory for the decoder 102 to retrieve.

The decoder can be implemented in hardware, software, or a combination of hardware and software. In one configuration, the decoder 102 can be a High Efficiency Video Coding (HEVC) decoder. The decoder 102 can receive (e.g., obtain) a bitstream 114. The decoder 102 can generate a decoded picture 118 (e.g., one or more decoded pictures 118) based on the bitstream 114. The decoded picture 118 can be displayed, played back, stored in a memory, and/or transmitted to another device, etc.

The decoder 102 may include a reference picture tracking module 116. The reference picture tracking module 116 may enable the decoder 102 to track reference pictures using reduced overhead referencing. For example, the reference picture tracking module 116 may track reference pictures in a decoded picture buffer (DPB) using less overhead than that required by existing schemes, such as the scheme given in JCTVC-F493.

For example, in existing solutions, non-reduced overhead references can be used to specify the relationship between the current picture and long-term reference pictures. For example, in existing solutions, the POC wraparound problem can be avoided by increasing the POC number space to specify the relationship between the current picture and long-term reference pictures. However, increasing the POC number space can only be achieved at the expense of increased bit requirements for the POC. This example is one of several possible mechanisms that can be used to avoid the POC wraparound problem in existing solutions. However, this particular example illustrates the significant overhead associated with long-term pictures in existing solutions.

For example, for long-term pictures, JCTVC-F493 used the longterm_poc[i] field in the buffer description to specify the absolute POC and the longterm_temporal_id[i] field in the buffer description to specify the temporal ID. This was later removed in JCTVC-F803, which does not include a mechanism for long-term pictures. In the subsequent discussion, a solution for skipping the POC (for long-term pictures) is presented.

Existing solutions may present problems. First, a large amount of overhead data may be required to specify the relationship between a long-term reference picture and another picture. For example, a large number of overhead bits may need to be allocated to properly represent the POC integer difference between a long-term reference picture and another picture. Second, if a limited number of bits are allocated to represent this difference, the difference may be ambiguously indicated when numbers are reused (e.g., due to periodic rotation of number sets).

The reference picture tracking module 116 may use one or more schemes or methods described in more detail below to reduce reference overhead. Some examples include using a loop parameter and decrementing the loop parameter based on a wrap indicator or a transition between picture sets.

It should be noted that in some configurations, the "reference picture" described herein may be replaced by a reference picture set (e.g., a frame group). Thus, in some configurations, the "decoded reference picture" described herein may be replaced by a "decoded reference picture set." For example, a reference picture set may be applied instead of a single reference picture as described in conjunction with the systems and methods disclosed herein. A reference picture set may include one or more reference pictures. Two or more reference pictures in a reference picture set may correspond to the same instant in time or to different (e.g., similar) instants in time. For example, in a three-dimensional (3D) coding scenario, the bitstream 114 may contain multiple pictures, some of which may relate to a left view and some of which may relate to a right view. Thus, a reference picture set may identify a left picture and a right picture corresponding to a particular display time.

In another example (eg, scalable coding scenario), the bitstream may contain pictures of different resolutions. In this example, the reference picture set may include (eg, identify) different resolution versions of the same picture.

FIG2 is a block diagram illustrating one configuration of a decoder 202. The decoder 202 may be included in an electronic device 204. For example, the decoder 202 may be a High Efficiency Video Coding (HEVC) decoder. The decoder 202 and/or one or more of the elements included in the decoder 202 as shown may be implemented in hardware, software, or a combination of hardware and software. The decoder 202 may receive a bitstream 214 for decoding (e.g., one or more coded pictures included in the bitstream 214). In some configurations, the received bitstream 214 may include received overhead information, such as a received slice header, a received PPS, received buffer description information, etc. The coded pictures included in the bitstream 214 may include one or more coded reference pictures and/or one or more other coded pictures.

Entropy decoding module 254 may entropy decode received symbols (in one or more encoded pictures included in bitstream 214 ) to produce motion information signal 256 and quantized, scaled, and/or transformed coefficients 258 .

The motion information signal 256 may be combined with a portion of the reference frame signal 284 from the frame memory 264 at the motion compensation module 260, which may produce an inter-frame prediction signal 268. The inverse module 262 may inverse quantize, upscale, and inverse transform the quantized, downscaled, and/or transformed coefficients 258 to produce a decoded residual signal 270. The decoded residual signal 270 may be added to the prediction signal 278 to produce a combined signal 272. The prediction signal 278 may be a signal selected from the inter-frame prediction signal 268 or the intra-frame prediction signal 276 generated by the intra-frame prediction module 274. In some configurations, this signal selection may be based on (e.g., controlled by) the bitstream 214.

The intra-frame prediction signal 276 may be predicted based on previously decoded information (e.g., in the current frame) from the combined signal 272. The combined signal 272 may also be filtered by a deblocking filter 280. The resulting filtered signal 282 may be written to the frame memory 264. The resulting filtered signal 282 may include a decoded picture.

Frame memory 264 may include a decoded picture buffer (DPB) as described herein. The DPB may include one or more decoded pictures stored as short-term reference frames or long-term reference frames. Frame memory 264 may also include overhead information corresponding to the decoded pictures. For example, frame memory 264 may include slice headers, picture parameter set (PPS) information, loop parameters, buffer description information, etc. One or more of this information may be signaled by an encoder (e.g., encoder 108, overhead signaling module 112). Frame memory 264 may provide decoded pictures 218.

The decoder 202 may include a reference picture tracking module 216. The reference picture tracking module 216 may track one or more reference pictures in the frame memory 264 with reduced reference overhead. In one example, the reference picture tracking module 216 may track long-term reference pictures using a loop parameter and modifying (e.g., decrementing) the loop parameter based on a received wrap indicator. In another example, an update of all reference picture loop parameters may be performed with respect to the picture being decoded. This update process may be performed once for the current picture (e.g., the picture being decoded). Transitions between loops may be tracked implicitly with the help of a POC. The loop parameter may sometimes be increased (e.g., when transitioning from picture set "n" to picture set "n-1"), as may occur in out-of-order picture decoding. More details regarding one or more schemes for tracking reference pictures based on a selected picture are provided below.

Some configurations of the systems and methods disclosed herein may utilize modified cache descriptions. Examples of modified cache descriptions are provided below. The cache description may be modified to include "POC," "poc_cycle," and "temporalID" for long-term reference pictures. It should be noted that "poc_cycle" may be an example of a cycle parameter as described herein. The (modified) cache descriptions, (modified) syntax, and/or parameters provided by the systems and methods disclosed herein may enable reduced overhead references.

Table (1) below gives an example of comparing the cache description within the PPS in an existing solution with a proposed solution according to the system and method disclosed herein. The existing solution is described in detail in the document "candidate working draft text of ad-hoc group 21" (AHG21), which was created to further describe the work of JCTVC-F493. It should be noted that AHG21 (JCTVC-F803) groups and specifies "negative pictures" (e.g., pictures with negative deltaPOC values) and "positive pictures" (e.g., pictures with positive deltaPOC values) separately.

Table (1)

In the above table (1), (POC ₀ , poc_cycles ₀ , temporalID ₃ ) and (POC ₁ , poc_cycles ₁ , temporalID ₄ ) represent long-term (reference) pictures. It should be noted that the cache description can contain two lists POCBD and TemporalIDBD for short-term reference pictures (corresponding to the POC field and TemporalID field, respectively). In addition, the cache description can contain three lists POCBD, POC_CYCLE_BD and TemporalIDBD for long-term reference pictures (corresponding to the POC field, poc_cycle field and TemporalID field, respectively).

In some configurations, multiple buffer descriptions are defined in a picture parameter set. Each buffer description with index i contains the lists for a reference picture: POCBD_pps[i], POC_CYCLE_pps[i], DeltaPOCBD_pps[i], and TemporalIDBD_pps[i], as well as the variable NumberOfPicturesInBD_pps[i]. The i-th list POCBD_pps[i] contains the picture sequence count value of the reference picture. The i-th list POC_CYCLE_pps[i] contains the poc_cycle value of the reference picture. The i-th list TemporalIDBD_pps[i] contains the corresponding temporal identifier of the reference picture. In addition, the i-th list TemporalIDBD_pps[i] contains NumberOfPicturesInBD_pps[i] entries. The list sets are referred to as POC_pps, POC_CYCLE_pps, DeltaPOCBD_pps, and TemporalIDBD_pps. For deltaPOC references, a single list, DeltaPOCBD_pps[i], contains the deltaPOC values for the reference pictures. Note that in the candidate working draft text for ad-hoc Group 21, DeltaPOCBD_pps may be referred to as DeltaPOCBD. The total number of entries in the POCBD_pps[i] and DeltaPOCBD_pps[i] lists may be given by the value NumberOfPicturesInBD_pps[i]. Furthermore, the number of entries in POCBD_pps[i] and POC_CYCLE_pps[i] is the same.

It should be noted that the syntax given in AHG21 does not fully support fixed long-term references. The following list (1) illustrates an example of the bitstream syntax modifications required for the candidate working draft text of ad-hoc group 21 (AHG21). Changes due to existing solutions are given in bold text in list (1).

List (1)

positive_pictures_in_buffer_descriptions_flag specifies whether there are any buffer description pictures with a positive deltaPOC. bits_for_temporal_id_in_buffer_descriptions specifies the number of bits used for temporal_id_negative_pps[i][j], temporal_id_positive_pps[i][j], temporal_id_poc_pps[i][j], temporal_id_negative[i], and temporal_id_positive[i]. number_of_bds specifies the number of buffer descriptions in the picture parameter set. number_of_negative_pictures_pps[i] specifies the number of entries with negative values in the list DeltaPOCBD_pps[i]. number_of_negative_pictures_pps[i] defines the value of OffsetBD[i] as OffsetBD[i] = number_of_negative_pictures_pps[i]. The value of number_of_negative_pictures_pps[i] should be in the range of 0 to max_num_ref_frames, inclusive. negative_delta_poc_minus_one_pps[i][j] specifies the absolute distance of the POC values. max_num_ref_frames specifies the maximum number of reference frames, supplementary reference field pairs, and unpaired reference fields that can be used by the decoding process for inter-frame prediction of any picture in the sequence. Here, a reference field represents a portion of a reference frame. For example, in an application using interlaced video, a reference frame may consist of two reference fields. The first reference field may contain a first subset of data in the reference frame, and the second reference field may contain a second subset of data in the reference frame, where the first subset and the second subset correspond to different data.

negative_delta_poc_minus_one_pps[i][j] defines the value of the variable DeltaPOCBD_pps[i][j] as DeltaPOCBD_pps[i][j] = -(negative_delta_poc_minus_one_pps[i][j] + 1) if j is equal to 0. Additionally, negative_delta_poc_minus_one_pps[i][j] defines the value of the variable DeltaPOCBD_pps[i][j] as DeltaPOCBD_pps[i][j] = DeltaPOCBD_pps[i][j] = DeltaPOCBD_pps[i][j - 1] - (negative_delta_poc_minus_one_pps[i][j] + 1) if j > 0. DeltaPOCBD_pps[i][j] should be in the range of -1 to -MaxPOC/2.

temporal_id_negative_pps[i][j] specifies a temporal identifier and should be represented by bits_for_temporal_id_in_buffer_descriptions bits. temporal_id_negative_pps[i][j] is added to the list TemporalIDBD_pps[i]. In one configuration, the add operation is an append operation. In another configuration, the append operation is an operation that replaces the items in the list in a predefined order. temporal_id_negative_pps[i][j] should be in the range of 0 to max_temporal_layers_minus1 (inclusive). max_temporal_layers_minus1+1 specifies the maximum number of temporal layers present in the sequence.

number_of_positive_pictures_in_bd_pps[i] specifies the number of entries with positive values in the list DeltaPOCBD_pps[i]. The value of number_of_positive_pictures_in_bd_pps[i] shall be in the range of 0 to max_num_ref_frames-OffsetBD[i] (inclusive). When the number_of_positive_pictures_in_bd_pps[i] syntax element is not present, the value of number_of_positive_pictures_in_bd_pps[i] shall be inferred to be equal to 0.

delta_poc_minus_one_pps[i][j] specifies the absolute distance of the POC value. delta_poc_minus_one_pps[i][j] defines the value of the variable DeltaPOCBD_pps[i][j+OffsetBD[i]] as DeltaPOCBD_pps[i][j+OffsetBD[i]]=delta_poc_minus_one_pps[i][j]+1 if j is 0, and as DeltaPOCBD_pps[i][j+OffsetBD[i]]=DeltaPOCBD_pps[i][j-1+OffsetBD[i]]+delta_poc_minus_one_pps[i][j]+1 if j>0. DeltaPOCBD_pps[i][j+OffsetBD[i]] should be in the range of 1 to MaxPOC/2-1.

temporal_id_positive_pps[i][j] specifies the temporal identifier and shall be represented by bits_for_temporal_id_in_buffer_descriptions bits. temporal_id_positive_pps[i][j] defines the value of the variable TemporalIDBD_pps[i][j] as TemporalIDBD_pps[i][j+OffsetBD[i]]=temporal_id_positive_pps[i][j]. temporal_id_positive_pps[i][j] shall be in the range of 0 to max_temporal_layers_minus1, inclusive.

An example of a description of the parameters in List (1) is given below. number_of_longterm_pictures_pps[i] specifies the number of entries in the lists POCBD_pps[i] and POC_CYCLE_BD_pps[i]. The value of number_of_longterm_pictures_pps[i] should be in the range of 0 to max_num_ref_frames (inclusive). max_num_ref_frames specifies the maximum number of short-term reference frames and long-term reference frames. poc_pps[i][j] specifies the POC value and defines the value to be added to the list POCBD_pps[i] as POCBD[i][j]=poc[j]. In one configuration above, the add operation is an append operation. In another configuration, the append (or add) operation is an operation of replacing items in a list in a predefined order. poc_pps[i][j] should be in the range of 0 to MaxPOC-1.

poc_cycle_pps[i][j] specifies the poc_cycle (e.g., cycle parameter) value and defines the value to be added to the list POC_CYCLE_BD_pps[i]. In one configuration, the add operation is an append operation. In another configuration, the append (or add) operation is an operation that replaces items in a list in a predefined order. In some configurations, poc_cycle_pps[i][j] (e.g., cycle parameter) can be less than or equal to zero. In this case, a signed integer can be used to represent the cycle parameter. In other configurations, an unsigned integer can be used to represent the cycle parameter.

temporal_id_poc_pps[i][j] specifies a temporal identifier and should be present if bits_for_temporal_id_in_buffer_descriptions > 0. temporal_id_poc_pps[i][j] defines the value of an entry in the list TemporalIDBD_pps[i]. temporal_id_poc_pps[i][j] is added to the list TemporalIDBD_pps[i]. In one configuration, the append operation is an append operation. In another configuration, the append (or add) operation is an operation that replaces items in a list in a predefined order. temporal_id_poc_pps[i][j] should be in the range of 0 to max_temporal_layers_minus1 (inclusive). max_temporal_layers_minus1+1 specifies the maximum number of temporal layers present in the sequence. It should be noted that the variable NumberOfPicturesInBD_pps[i] can be calculated as number_of_negative_pictures_pps[i]+number_of_positive_pictures_pps[i]+number_of_longterm_pictures_pps[i].

The negative deltaPOC value and the positive deltaPOC value for the reference picture transmitted in the buffer description of the i-th picture parameter set are added to the list DeltaPOCBD_pps[i]. In one configuration above, the adding operation is an appending operation. In another configuration, the appending (or adding) operation is an operation of replacing items in the list in a predefined order.

The following Listing (2) shows an alternative exemplary configuration, where multiple cache descriptions can be created in the PPS using the following syntax with different cycle parameters (eg, poc_cycle). Changes due to existing solutions are given in bold text in Listing (2).

List (2)

In Listing (2), examples of descriptions of other parameters are given below. When set to 1, the poc_cycle_steps_flag specifies that additional cache descriptions should be generated for a signaled cache description model that is identical to the signaled cache description model except for the poc_cycle count. The poc_cycle_steps_flag should default to 0. In addition, the poc_cycle_steps specifies the number of additional cache descriptions that should be generated for the signaled cache description model. The additional cache descriptions should be identical to the signaled cache description except that the poc_cycle count should be decremented. In one configuration, the generated additional cache descriptions have poc_cycle_pps[i][j] values -1, -2, -3, ..., -(poc_cycle_steps).

In some configurations, resolution switching can be enabled in the bitstream. In these configurations, the resolution of the reference picture can be different from the resolution of the current picture. Therefore, it may be beneficial to know which mechanism can be used to scale the reference picture to the correct resolution. One way to signal this mechanism is to explicitly signal it along with the buffer description. For example, the encoder 108 (e.g., the overhead signaling module 112) can signal the scaling parameter s to the decoder 102. Therefore, the alternative buffer descriptions can be shown in Table (2).

Alternative cache description

Table (2)

In table (2), the first two entries have resolutions that match the resolution of the current picture. However, the remaining three entries have different resolutions and may use scaling parameters s ₀ , s ₁ , s ₂ , respectively. The scaling parameters may be signaled selectively. For example, the scaling parameters may be signaled only when the current picture and the reference picture have different resolutions. In another configuration, the scaling parameters may be signaled at all times. In another configuration, the scaling parameters may be inferred implicitly (by the decoder), for example, by using a lookup table indexed by the current picture characteristics (e.g., resolution) and the reference picture characteristics (e.g., resolution).

In another configuration, scaling parameters may be signaled for any subset of the pictures defined in the buffer description. For example, scaling parameters may be signaled for a subset of reference pictures signaled using positive deltaPOC values, a subset of reference pictures signaled using negative deltaPOC values, a subset of pictures signaled using POC and poc_cycle. In one configuration, the subset may include the entire list. An example is illustrated in the following table (3), where negativeDeltaPOC ₀ and negativeDeltaPOC ₁ are negative deltaPOC values, positiveDeltaPOC ₂ is a positive deltaPOC value, and s ₀ , s ₁ , s ₂ , s ₃ , and s ₄ are scaling parameters for the first, second, third, fourth, and fifth entries, respectively.

Alternative cache description

Table (3)

In another configuration, the scaling parameters may indicate one or more resolutions of reference pictures to be stored in the decoded picture buffer. In another configuration, the scaling parameters may be used to signal the resolution of the reference pictures to be used for the motion compensation process. In another configuration, if the reference pictures are not of the same resolution as the picture being decoded, the scaling parameters indicate the motion compensation process to be used to generate the prediction.

In one configuration, the scaling parameter signals (e.g., indicates) a change in horizontal and/or vertical resolution (in pixels). In one configuration, the scaling parameter signals (e.g., indicates) a ratio between a desired horizontal and/or vertical resolution and an original horizontal and/or vertical resolution. In one configuration, the scaling parameter is a two-tuple where a first value identifies a scaling ratio for the horizontal resolution and a second value identifies a scaling ratio for the vertical resolution.

In some configurations, the transform coefficients of the reference picture may be processed based on the scaling parameters to obtain the desired resolution. This may be beneficial to enable better resolution adaptation by only allowing block sizes larger than a certain threshold when encoding the reference picture.

In another configuration, the reconstructed pixels of the reference picture may be processed based on the scaling parameters to obtain a desired resolution.It should be noted that these configurations may be applied to all reference picture indexing schemes disclosed herein.

Listing (3) illustrates another example of syntax modifications from AHG21 for PPS. Specifically, Listing (3) illustrates an example of the cache description syntax outlined in AHG21 for use in a slice header. However, the modifications to the syntax given in AHG21 according to the systems and methods disclosed herein are indicated in bold text in Listing (3).

List (3)

The following gives an example of the description of the parameters in Listing (3). number_of_negative_pictures specifies the number of negative delta POC entries. number_of_negative_pictures defines the value of Offset as Offset = number_of_negative_pictures. The value of number_of_negative_pictures shall be in the range of 0 to max_num_ref_frames (inclusive).

negative_delta_poc_minus_one[i] specifies the absolute distance of the POC value. negative_delta_poc_minus_one[i] defines the value of the variable POCBD[i] as POCBD[i] = (pic_order_cnt + MaxPOC - (negative_delta_poc_minus_one[i] + 1)) % MaxPOC if i is 0, and as POCBD[i] = (POCBD[i-1] + MaxPOC - (negative_delta_poc_minus_one[i] + 1)) % MaxPOC if i > 0. Here, pic_order_cnt is the POC of the current picture as signaled in the slice header. The value of negative_delta_poc_minus_one[i] should be in the range of 0 to MaxPOC-1, inclusive. The value of POCBD[i] should be such that the value of DiffPOC(currPic, refPic) is in the range of -1 to -MaxPOC/2. Here, refPic is the reference picture whose pic_order_cnt is equal to POCBD[i].

DiffPOC(picA, picB) is defined as follows:

The function POC(picX) is defined as follows: POC(picX) = pic_order_cnt of picX. POC_CYCLE_BD[i] is set to the poc_cycle of the i-th negative deltaPOC reference picture. The poc_cycle of the i-th negative deltaPOC reference picture is calculated based on the selected picture.

temporal_id_negative[i] specifies the temporal identifier and shall be represented by bits_for_temporal_id_in_buffer_descriptions bits, where bits_for_temporal_id_in_buffer_descriptions is a syntax element from the picture parameter set used by the current picture. temporal_id_negative[i] defines the value of the variable TemporalIDBD[i] as TemporalIDBD[i] = temporal_id_negative[i]. temporal_id_negative[i] shall be in the range of 0 to max_temporal_layers_minus1, inclusive. The value of TemporalIDBD[i] is constrained so that TemporalIDBD[i] must be equal to the temporal_id signaled in the NAL-header of the reference picture whose pic_order_cnt is equal to POCBD[i].

number_of_positive_pictures specifies the number of entries with positive values in the list DeltaPOCBD_pps[i]. The value of number_of_positive_pictures shall be in the range of 0 to max_num_ref_frames-Offset (inclusive). When the number_of_positive_pictures syntax element is not present, the value of number_of_positive_pictures shall be inferred to be equal to 0.

delta_poc_minus_one[i] specifies the absolute distance between the POC values. delta_poc_minus_one[i] defines the value of the variable POCBD[i+Offset] as POCBD[i+Offset] = (pic_order_cnt + (delta_poc_minus_one[i]+1))% MaxPOC if i is 0, and as POCBD[i+Offset] = (POCBD[i-1+Offset] + (delta_poc_minus_one[i]+1))% MaxPOC if i > 0. Here, pic_order_cnt is the POC of the current picture as signaled in the slice header. The value of delta_poc_minus_one[i] should be in the range of 0 to MaxPOC-1, inclusive. The value of POCBD[i+Offset] should be such that the value of DiffPOC(currPic, refPic) is in the range of 1 to MaxPOC/2-1, where refPic is the reference picture with pic_order_cnt equal to POCBD[i+Offset]. POC_CYCLE_BD[i+Offset] is set to the poc_cycle of the i-th positive deltaPOC reference picture. The poc_cycle of the i-th positive deltaPOC reference picture is calculated based on the selected picture.

temporal_id_positive[i] specifies the temporal identifier and shall be represented by bits_for_temporal_id_in_buffer_descriptions bits, where bits_for_temporal_id_in_buffer_descriptions is a syntax element from the picture parameter set used by the current picture. temporal_id_positive[i] defines the value of the variable TemporalIDBD[i+Offset] as TemporalIDBD[i+Offset] = temporal_id_positive[i]. temporal_id_positive[i] shall be in the range of 0 to max_temporal_layers_minus1, inclusive. The value of TemporalIDBD[i] is constrained so that TemporalIDBD[i] must be equal to the temporal_id signaled in the NAL-header of the reference picture whose pic_order_cnt is equal to POCBD[i].

bd_poc_cycle_update_flag equal to 1 specifies that POC_CYCLE_BD_pps[bd_idx][j] of the reference buffer description should be overridden for the current picture. In some configurations, future frames may also override the poc_cycle information. If bd_poc_cycle_update_flag is 0, the original POC_CYCLE_BD_pps[bd_idx][j] of the reference buffer description is used. poc_cycle_pps_override[j] specifies the value to be used to override the value in POC_CYCLE_BD_pps[bd_idx][j] for the current picture only. In an alternative configuration, poc_cycle_pps_override[j] specifies an offset. For the current picture only, (POC_CYCLE_BD_pps[bd_idx][j] + poc_cycle_pps_override[j]) may be used instead of POC_CYCLE_BD_pps[bd_idx][j].

poc_pps_override[j] specifies the value to be used to override the value in POCBD_pps[bd_idx][j] for the current picture only. In an alternative configuration, poc_pps_override[j] specifies an offset. For the current picture only, (POCBD_pps[bd_idx][j]+poc_pps_override[j]) can be used instead of POCBD_pps[bd_idx][j]. temporal_id_pps_override[j] specifies the value to be used to override the value in TemporalIDBD_pps[bd_idx][j] for the current picture only. In an alternative configuration, temporal_id_pps_override[j] specifies an offset. For the current picture only, (TemporalIDBD_pps[bd_idx][j]+temporal_id_pps_override[j]) can be used instead of TemporalIDBD_pps[bd_idx][j].

number_of_longterm_pictures specifies the number of long-term picture entries in the lists POCBD and POC_CYCLE_BD. The value of number_of_longterm_pictures should be in the range of 0 to max_num_ref_frames (inclusive). max_num_ref_frames specifies the maximum number of short-term reference frames and long-term reference frames. poc[j] specifies the POC value to be added to the list POCBD as POCBD[bd_idx][j] = poc[j]. In one of the above configurations, the add operation is an append operation. In another configuration, the append (or add) operation is an operation that replaces items in a list in a predefined order. poc[j] should be in the range of 0 to MaxPOC-1.

poc_cycle[j] (e.g., a cycle parameter) specifies the value of poc_cycle and defines the value to be added to the list POC_CYCLE_BD. In one configuration, the add operation is an append operation. In another configuration, the append (or add) operation is an operation that replaces items in the list in a predefined order. poc_cycle[j] can be less than or equal to zero, or can occupy a different range of values.

temporal_id_poc[j] specifies a temporal identifier and should be represented by bits_for_temporal_id_in_buffer_descriptions bits. temporal_id_poc[j] defines the value to be added to the list TemporalIDBD. In one configuration, the add operation is an append operation. In another configuration, the append (or add) operation is an operation that replaces items in a list in a predefined order. temporal_id_poc[i][j] should be in the range of 0 to max_temporal_layers_minus1 (inclusive). max_temporal_layers_minus1+1 specifies the maximum number of temporal layers present in the sequence.

In some configurations, number_of_longterm_pictures_pps[bd_idx] can be sent before the "for" loop described in Listing (3), thereby avoiding the reliance on the slice header and PPS. Alternatively, bd_poc_cycle_update_flag can be replaced with another parameter num_longterm_poccycle_override_count. For example, the relevant code in Listing (3) can be replaced with "If num_longterm_poccycle_override_count＞0then For(j＝0； j＜num_longterm_poccycle_override_count； j++){....}".

bd_reference_flag equal to 1 specifies that the cache description for the current picture should be created using syntax elements not sent in the slice header. In one configuration, the cache description for the current picture is created using syntax elements in the picture parameter set. bd_reference_flag equal to 0 specifies that the cache description for the current picture can be created by a combination of the cache description sent in the slice header and the cache description not sent in the slice header. In one configuration, the cache description not sent in the slice header is sent in the picture parameter set.

bd_idx identifies a cache description in the set of available cache descriptions. In one configuration, bd_idx indicates an index into the lists POCBD_pps, DeltaPOCBD_pps, POC_CYCLE_BD_pps and TemporalIDBD_pps that should be used for the creation of the cache description for the current picture.

The values corresponding to the deltaPOC reference pictures in (DeltaPOCBD_pps[bd_idx], TemporalIDBD_pps[bd_idx]) are converted into a picture sequence count (e.g., POC), a cycle parameter (e.g., poc_cycle), and a temporal identifier, and are added to the picture cache description lists POCBD, POC_CYCLE_BD, and TemporalIDBD. The values corresponding to the reference pictures in the lists (POCBD_pps[bd_idx], POC_CYCLE_BD_pps[bd_idx], TemporalIDBD_pps[bd_idx]) are added to the picture cache description lists POCBD, POC_CYCLE_BD, and TemporalIDBD. In one configuration, the addition operation is an append operation. In another configuration, the append (or add) operation is an operation of replacing items in the lists in a predefined order.

combine_with_reference_flag equal to 1 specifies that the syntax elements from the active PPS are used to combine the values in the explicitly signaled assignment lists POCBD, POC_CYCLE_BD and TemporalIDBD. When the combine_with_reference_flag syntax element is not present, the value of combine_with_reference_flag shall be inferred to be equal to 0.

bd_combination_idx specifies the index into the lists DeltaPOCBD_pps and TemporalIDBD_pps that should be used to create the buffer description for the current picture in conjunction with explicit signaling. bd_combination_idx should be represented by ceil(log2(number_of_bds)) bits. The value of bd_combination_idx should be in the range 0 to number_of_bds-1, where number_of_bds is a syntax element from the picture parameter set used by the current picture. The values from the lists DeltaPOCBD_pps[bd_idx], POCBD_pps[bd_idx], POC_CYCLE_BD_pps[bd_idx], and TemporalIDBD_pps[bd_idx] are then added to the current picture in the lists POCBD, POC_CYCLE_BD, and TemporalIDBD using a predefined mechanism. In the above configuration, the add operation is an append operation. In another configuration, an append (or add) operation is an operation that replaces items in a list in a predefined order.

In the following, some examples of how the systems and methods described herein can be applied are given. Assume that a picture with POC=0 is a long-term (reference) picture used by a picture with POC=MaxPOC-1 and a picture with POC=0 from a subsequent picture set. A long-term (reference) picture can be indicated in different ways.

In the first approach, there are two cache descriptions in the PPS, including cache description A: {POC=0, poc_cycle=0, temporalID} and cache description B: {POC=0, poc_cycle=-1, temporalID}. Pictures with POC=MaxPOC-1 will point to cache description A. Pictures with POC=0 from subsequent picture sets will reference cache description B.

In the second alternative, a picture with POC = MaxPOC - 1 will point to cache description A. Pictures from subsequent picture sets with POC = 0 will reference cache description A. Cache description A corresponds to {POC = 0, poc_cycle = 0, temporalID}. To reference the correct picture, poc_cycle should be set to -1, since the reference picture belongs to the previous [0, ..., MaxPOC - 1] picture set. Therefore, the poc_cycle value of cache description A, currently set to 0, can be overridden (e.g., set to a different value) for only the current slice by sending "-1" in the slice header. In some configurations, the first slice in a picture can be used to override the poc_cycle value in the cache description for only the current picture.

In some configurations, the reference picture list signaled at a higher level may be modified at a finer level. For example, the reference picture list may be signaled (e.g., signaled at a higher level) in a cache description sent in the PPS. However, the cache description sent in the PPS may be modified (e.g., modified at a finer level). For example, the cache description may be modified by deleting existing entries. Additionally or alternatively, the cache description information from the PPS may be modified to add new entries or replace entries. For example, if no empty slots are available, the cache description information from the PPS may also be modified to use a predefined mechanism to add new entries and replace current entries. The benefit of allowing modifications is that a higher level of control may be obtained. This may alternatively use the unmodified cache description from the PPS, or additionally or alternatively replace only the first "n" entries.

In some configurations, additional syntax may be defined to replace an entry in a slot list. In this case, the index to replace in the list and the entry that can replace the current entry at that index are specified.

Additionally or alternatively, if the slot list is not empty, additional syntax can be defined to add entries to the list using replacement. In this case, the index in the list that should be replaced can be explicitly signaled (e.g., from the encoder 108 or overhead signaling module 112) or implicitly inferred (e.g., by the decoder 102) using some information previously sent in the bitstream.

Listing (4) illustrates another example of syntax modifications from AHG21 for PPS. Specifically, Listing (4) illustrates another example of the cache description syntax outlined in AHG21 for use in a slice header. However, the modifications to the syntax given in AHG21 according to the systems and methods disclosed herein are indicated in bold text in Listing (4).

List (4)

Listing (4) contains many elements similar to those of Listing (3). Listing (4) also contains syntax modifications to the slice header to allow for the deletion and/or addition of reference pictures.

An example of the description of the parameters in List (4) is given below. bd_poc_cycle_delete_count specifies the number of entries to be deleted from the lists POCBD_pps[bd_idx], temporalIDBD_pps[bd_idx], and POC_CYCLE_BD_pps[bd_idx] for the current picture (e.g., only for the current picture). In some configurations, bd_poc_cycle_delete_count may be greater than or equal to 0.

bd_pps_delete_idx[j] specifies that for the current picture, the entries POC_CYCLE_BD_pps[bd_idx][bd_pps_delete_idx[j]], temporalIDBD_pps[bd_idx][bd_pps_delete_idx[j]], and POCBD_pps[bd_idx][bd_pps_delete_idx[j]] in the lists are deleted. In some configurations, once a picture is deleted, it may no longer be referenced by subsequently decoded pictures. In other configurations, once all deletions are complete, the remaining entries in the lists POCBD_pps[bd_idx], temporalIDBD_pps[bd_idx], and POC_CYCLE_BD_pps[bd_idx] may be moved to the initial index (e.g., the zeroth index) to occupy the vacated slots. This process can be performed so that no empty slots remain between any two occupied slots. Here, a slot corresponds to an entry in the cache description. For example, if the list is [Slot0=A][Slot1=Empty][Slot2=B][Slot3=C][Slot4=Empty][Slot5=D], then after deletion, entries are moved to Slot0 until no empty slots remain between any two occupied slots. In this example, the resulting list is [Slot0=A][Slot1=B][Slot2=C][Slot3=D][Slot4=Empty][Slot5=Empty].

bd_poc_cycle_append_count specifies the number of entries to be appended to the lists POCBD_pps[bd_idx], temporalIDBD_pps[bd_idx], and POC_CYCLE_BD_pps[bd_idx] for the current picture. In some configurations, bd_poc_cycle_append_count may be greater than or equal to 0.

poc_pps_append[j] specifies the POC value to be appended to the list POCBD_pps[bd_idx] for the current picture (e.g., only the current picture). In some configurations, if there are any empty slots in the list, the addition is performed starting with the empty slot closest to the zero-index and then in increasing order of slot index.

poc_cycle_pps_append[j] specifies the poc_cycle value to be appended to the list POC_CYCLE_BD_pps[bd_idx] for the current picture (e.g., only the current picture). In some configurations, if there are any empty slots in the list, the empty slot closest to the zero index may be filled first. Additionally, the slots may be filled in order of increasing slot index. In some configurations, operations such as reloading entries, deleting entries, and adding entries to POCBD_pps[bd_idx] and POC_CYCLE_BD_pps[bd_idx] are performed in a predefined order.

temporal_id_pps_append[j] specifies the temporal identifier value to be appended to the list TemporalIDBD_pps[bd_idx] for the current picture (e.g., only for the current picture). In some configurations, if there are any empty slots in the list, the addition is performed starting with the empty slot closest to the zero-index and then in increasing order of slot index.

Some examples of configurations of the systems and methods disclosed herein are given below. In one configuration, the triple (POC, poc_cycle, temporalID) can be replaced with a binary (LTSlotIdx, temporalID). LTSlotIndex can be a slot index pointing to a location in the long-term DPB. One possible benefit of this solution is reduced bitrate overhead.

In another configuration, the triplet (POC, poc_cycle, temporalID) may be replaced with (f(POC, poc_cycle), temporalID), where f(POC, poc_cycle) is a function (e.g., a lookup table) that maps the two-tuple (POC, poc_cycle) to an index. In another configuration, an absolute POC value may be used instead of (POC, poc_cycle). In one example, this absolute POC value will be different from the longterm_poc[i] field in the cache description in JCTVC-F493 that specifies the absolute POC. Specifically, the longterm_poc[i] field of JCTVC-F493 is only capable of signaling values in the range 0 to MaxPOC. However, according to the systems and methods disclosed herein, the absolute POC value may be signaled (and possibly derived) using the most significant bit (MSB) and least significant bit (LSB) scheme of AVC, thereby providing greater bit resolution. Alternatively, a larger number space than MaxPOC may be used to signal the absolute POC value.

In another configuration, the absolute POC according to the systems and methods disclosed herein can be used to reference all reference pictures (e.g., short-term pictures and long-term pictures). In another configuration, the absolute POC according to the systems and methods disclosed herein can be used instead of deltaPOC signaling. In some configurations, the POC and poc_cycle can be replaced with absolute POC values, as shown in the following example (and may not be limited to the following example):

In this example, absolute_poc_pps[i][j] is the absolute picture order count for the j-th long-term picture entry in the i-th buffer description in the PPS.

In this example, absolute_poc[j] is the absolute picture order count for the j-th long-term picture entry in the cache description.

In some configurations, some or all of the information typically included in a PPS and/or in a buffer description may additionally or alternatively be carried in an adaptation slice parameter set or adaptation parameter set (APS). This information includes one or more of the following: number_of_longterm_pictures, poc[j], poc_cycle[j], temporal_id_poc[j], number_of_longterm_pictures_pps[i], poc_pps[i][j], poc_cycle_pps[i][j], and temporal_id_poc_pps[i][j]. For example, an adaptive slice parameter set or adaptation parameter set (APS) may include one or more of the following: the number of reference pictures (e.g., number_of_longterm_pictures), a picture order count (e.g., poc[j]), a picture order count cycle parameter (e.g., poc_cycle[j]), a temporal identifier picture order count parameter (e.g., temporal_id_poc[j]), a picture parameter set number of reference pictures (e.g., number_of_longterm_pictures_pps[i]), a picture parameter set picture order count (e.g., poc_pps[i][j]), a picture parameter set picture order count cycle parameter (e.g., poc_cycle_pps[i][j]), and a picture parameter set temporal identifier picture order count parameter (e.g., temporal_id_poc_pps[i][j]).

In some configurations, the information poc_cycle[j] may only be signaled (eg, from the encoder 108 to the decoder 102, 202) if the information poc_cycle[j] is different from 0. In this case, an alternative syntax may be defined.

In another configuration, some or all of the information typically included in the PPS and/or in the cache description may be carried in addition or alternatively in the slice header separately from the cache description information. For example, the slice header may carry (separately from the cache description container) one or more of the following: the number of reference pictures (e.g., number_of_longterm_pictures), the picture sequence count (e.g., poc[j]), the picture sequence count cycle parameter (e.g., poc_cycle[j]), the temporal identifier picture sequence count parameter (e.g., temporal_id_poc[j]), the number of picture parameter sets for reference pictures (e.g., number_of_longterm_pictures_pps[i]), the picture parameter set picture sequence count (e.g., poc_pps[i][j]), the picture parameter set picture sequence count cycle parameter (e.g., poc_cycle_pps[i][j]), and the picture parameter set temporal identifier picture sequence count parameter (e.g., temporal_id_poc_pps[i][j]).

In an alternative configuration, a long-term (reference) picture may be signaled by indexing it as x.y, where x = poc[j] or poc_pps[i][j], and y is a new information sub-index that defines an additional namespace/number space for sub-indexing the long-term (reference) picture. In this case, the x and y entries for each long-term (reference) picture may be sent in the PPS and/or the buffer description (in the slice header).

In some configurations, all (reference) pictures (e.g., long-term and short-term) may be referenced using incremental references (using, for example, deltaPOC and temporalID) or absolute references (using, for example, POC, poc_cycle, and temporalID). For example, the entire decoded picture buffer (DPB) may contain a set of received pictures. A subset of these received pictures may use incremental references, while the remaining received pictures may use absolute references. It should be noted that existing solutions do not provide for absolute references that are identical to those given according to the systems and methods disclosed herein (e.g., using POC and poc_cycle). It should be noted that one or more of the described configurations of cache descriptions and syntax may be implemented in conjunction with one or more of the methods and/or solutions described herein.

3 is a flow chart illustrating one configuration of a method 300 for tracking reference pictures using reduced overhead referencing based on a selected picture. An electronic device 204 (e.g., a decoder 202) may receive 302 a bitstream. For example, the decoder 202 may receive 302 a bitstream 214 that includes a coded reference picture (and, for example, other coded pictures). In some configurations, the bitstream 214 may also include overhead information (e.g., PPS, buffer description information, parameters, wrap indicators, reference picture indications or identifiers, etc.).

The electronic device 204 may decode 304 a portion of the bitstream 214 to generate a decoded reference picture. For example, the decoder 202 may decode 304 a portion of the bitstream 214 to generate a decoded reference picture, which is stored in the frame memory 264. It should be noted that one or more portions of the bitstream 214 may be decoded 304 to generate one or more decoded reference pictures.

The electronic device 204 can utilize reduced overhead referencing to track 306 decoded reference pictures in a decoded picture buffer (DPB). For example, the electronic device 204 can associate a loop parameter with the decoded reference picture and modify (e.g., decrement or increment) the loop parameter if a wrap indicator is received or if a transition between picture sets is determined. Other schemes can be used to track 306 decoded reference pictures. More details are provided below. It should be noted that a DPB can include one or more decoded reference pictures.

The electronic device 204 can decode 308 a picture based on one or more decoded reference pictures. For example, a portion of the bitstream 214 (not the portion used to generate the decoded reference pictures by decoding 304) can be decoded 308 based on the reference pictures. For example, the decoded reference pictures (already tracked in the DPB) can be provided to the motion compensation module 260 to generate an inter-frame prediction signal 268 based on an inter-frame prediction mechanism. The inter-frame prediction signal 268 can then be used to decode 308 the picture. In some configurations or instances, one or more decoded reference pictures can be tracked 306 and used to decode 308 the picture.

FIG4 is a flow chart illustrating a more specific configuration of a method 400 for tracking reference pictures using reduced overhead referencing based on a selected picture. This method 400 can be one approach for tracking which picture is being referenced when a POC is reused. An electronic device 204 (e.g., a decoder 202) can receive 402 a bitstream 214. For example, the decoder 202 can receive 402 a bitstream 214 that includes a coded reference picture (and, for example, other coded pictures). In some configurations, the bitstream 214 can include overhead information (e.g., PPS, buffer description information, parameters, wrap indicators, reference picture indications or identifiers, etc.).

The electronic device 204 may decode 404 a portion of the bitstream 214 to generate a decoded reference picture. For example, the decoder 202 may decode 404 a portion of the bitstream 214 to generate a decoded reference picture, which is stored in the frame memory 264. It should be noted that one or more portions of the bitstream 214 may be decoded 404 to generate one or more decoded reference pictures.

The electronic device 204 may associate 406 a cycle parameter with a decoded picture set including the decoded reference picture. For example, the electronic device 204 may associate 406 a cycle parameter "poc_cycle" with a decoded picture set including the decoded reference picture.

The cycle parameter "poc_cycle" can be defined as follows. When a fixed number of bits is used to represent the POC of a picture in the range [0, ..., MaxPOC-1], there are MaxPOC unique integer values. If the number of pictures being encoded exceeds MaxPOC, the picture numbering mechanism must reuse already assigned POC values. In one example, the POC numbering then proceeds as follows: ..., [0, ..., MaxPOC-1] _n-2 , [0, ..., MaxPOC-1] _n-1 , [0, ..., MaxPOC-1] _n , [0, ..., MaxPOC-1] _n+1 , .... The subscript in this example indicates the number of times the set [0, ..., MaxPOC-1] has been repeated. This subscript or the number of times the set [0, ..., MaxPOC-1] has been repeated can be denoted as MaxPOCSetIndex. For example, a picture with POC=0 and MaxPOCSetIndex=n represents the (n*MaxPOC+1)th picture in the sequence (assuming, for example, that picture set numbering starts at 1). Additional details on the cycle parameter "poc_cycle" are given below in conjunction with FIG.

The electronic device 204 may determine 408 whether a wrap indicator has been received. For example, whenever the encoder 108 or the transmitting electronic device A 104a reaches a predetermined maximum number of pictures in a picture set, the encoder 108 or the transmitting electronic device A 104a may transmit a wrap indicator that is received by the decoder 102 or the receiving electronic device B 104b to indicate that another picture set is being transmitted (e.g., the POC is being reset or another cycle is starting). More details are provided below in conjunction with FIG. 12 .

If the electronic device 204 determines 408 that a wrap indicator has been received, the electronic device 204 may modify 410 (e.g., decrement) the loop parameter. For example, the electronic device 204 decrements the loop parameter for each picture or each picture set in the DPB. In another example, the electronic device 204 may increment the loop parameter.

The electronic device 204 can decode 412 a picture based on a decoded reference picture. For example, a portion of the bitstream 214 (not the portion used by the decoder 404 to generate the decoded reference picture) can be decoded 412 based on the reference picture. For example, the decoded reference picture (already tracked in the DPB) can be provided to the motion compensation module 260 to generate an inter-frame prediction signal 268 based on an inter-frame prediction mechanism. The inter-frame prediction signal 268 can then be used to decode 412 the picture. In some configurations or instances, one or more decoded reference pictures can be used to decode 412 the picture.

FIG5 is a diagram illustrating an example of multiple picture sets referenced by cycle parameters. More specifically, FIG5 illustrates an example of using cycle parameters to track reference pictures based on a selected picture using reduced overhead referencing. Specifically, FIG5 illustrates cycle parameters associated with picture set A 507a (e.g., poc_cycle = -1), cycle parameters associated with picture set B 507b (e.g., poc_cycle = 0), and cycle parameters associated with picture set C 507c (e.g., poc_cycle = +1). However, it should be noted that picture set A 507a may or may not be the first picture set in a frame sequence. For example, one or more picture sets may precede picture set A 507a. Furthermore, it should be noted that picture set C 507c may or may not be the last picture set in a frame sequence. For example, one or more picture sets may follow picture set C 507c.

Each picture set 507a-c may include one or more pictures 501a-n, 503a-n, 505a-n. In this example, each picture set 507a-c includes MaxPOC pictures 501, 503, 505. Specifically, each picture 501, 503, 505 may have a corresponding picture order count (POC), which is represented as [0, 1, 2, ..., MaxPOC-1] in FIG5.

In one example, the poc_cycle of the picture set containing the currently decoded picture can be set to 0 to be used to calculate the poc_cycle of other pictures. In some cases, the pictures can be decoded out of order. For example, the decoder may see 503b, then 505a, and then 503c. In this example, it is assumed that the picture currently being decoded is picture 503b with POC=1 in picture set B 507b. The poc_cycle of another picture (e.g., a reference picture) can then be calculated based on the poc_cycle of the currently decoded picture.

FIG6 is a schematic diagram illustrating another example of multiple picture sets. FIG6 includes picture sets 607a-c similar to the picture sets 507a-c described above in conjunction with FIG5 . Each picture set 607a-c may include one or more pictures 601a-c, 603a-n, 605a-n. Picture sets 607a-c may include MaxPOC pictures. Furthermore, each picture 601a-c, 603a-n, 605a-n may have a corresponding picture order count (POC) belonging to the set [0, 1, 2, ..., MaxPOC-1] as shown in FIG6 .

A picture set 607 may include one or more pictures. For example, pictures 603a-n in picture set B 607b may be grouped into a picture set. Similarly, pictures 605a-n in picture set C 607c may be grouped together into a picture set. A picture set may include pictures that are adjacent to each other when encoded, or may be composed of randomly grouped pictures. In another example, a picture set may be composed of a poc_cycle consisting of pictures [0, 1, 2, ..., MaxPOC-1].

In some configurations, the picture set 607a may include an Instantaneous Decoding Refresh (IDR) picture 603a (e.g., an IDR access unit). The encoder may signal the IDR picture 603a in the bitstream. Additionally or alternatively, an IDR picture may be identified based on the picture type. In some configurations, the IDR picture 603a may indicate to the decoder 202 that no subsequent pictures in the bitstream 214 will need to reference previous pictures in the bitstream 214.

When decoder 202 decodes IDR picture 603a, the POC can be reset to a predetermined value. For example, after decoding picture set A 607a, IDR picture 603a is received or signaled. At this point, the POC can be reset to 0 and a new picture set (picture set B 607b) can be started. In other words, IDR picture 603a can specify a reference picture with respect to a selected picture. One benefit of transmitting IDR picture 603a can be the introduction of a new reference picture. This benefit is described in more detail below in conjunction with FIG. 7 .

FIG7 is a diagram illustrating a more specific example of multiple picture sets referenced by a cycle parameter. FIG7 illustrates picture sets 707a-d and pictures 701, 703, 705, and their associated POCs and poc_cycles. Picture sets 707a-d and pictures 701, 703, 705 are similar to components 507a-c, 501, 503, 505 described above in conjunction with FIG5 . Additionally, FIG7 illustrates an additional picture set 707d and associated pictures 731a-n.

7 also shows a selected picture 703a. In one configuration, a cycle parameter (e.g., poc_cycle) for the selected picture may be set to 0. For example, when the first picture in a picture set (e.g., POC=0) is a selected picture (e.g., an IDR picture), then the poc_cycle for the selected picture may be equal to 0. Cycle parameters (e.g., poc_cycle) for subsequent picture sets may be calculated with reference to the picture set whose cycle parameter is set to 0 (e.g., poc_cycle=0).

An example of a selected picture is an IDR picture 703a (e.g., an IDR access unit) similar to the IDR picture 603a described above in conjunction with FIG6 . For convenience, the selected picture 703a will be described as an IDR picture. However, it should be noted that the selected picture 703a can be any picture indicated by the encoder using signaling in the bitstream or can be implicitly determined by the decoder.

In some configurations, the encoder may send a signal in the bitstream indicating an IDR picture 703a. The value of the POC counter may be determined based on this signal. For example, the signal may indicate (to the decoder) that the POC for the IDR picture is set to 0 (if, for example, the POC for the IDR picture is not 0). For example, the IDR picture 703a may cause the decoder to reset the POC counter to an initial value, such as 0. The poc_cycle may also be based on the IDR picture 703a. Similar to the POC, the signal may indicate that the poc_cycle should be reset to the initial value. In another example, the signal may indicate that the POC or poc_cycle does not need to be modified (if the POC or poc_cycle for the IDR picture 703a is at the initial value).

IDR picture 703a may be used to set or reset the POC and poc_cycle (and/or other cycle parameters, for example) that can be used to track reference pictures with respect to selected picture 703a. For example, decoder 202 may decode pictures 701a-c in set A 707a. Picture set A 707a may have cycle parameters associated with it, poc_cycle=m. IDR picture 703a may then be signaled via bitstream 214. IDR picture 703a may indicate new cycle parameters (e.g., poc_cycle=0) and may indicate POC=0. Picture sets 707b-d may then be decoded, and their associated cycle parameters may be incremented from their initial values (e.g., poc_cycle=0, poc_cycle=+1, poc_cycle=+2, respectively). In this example, subsequent picture sets 707b-d are calculated with reference to the newly set cycle parameters and POC.

As described above, IDR picture 703a can indicate to decoder 202 that no subsequent pictures in the bitstream will need to reference pictures before the picture in bitstream 214. However, IDR picture 703a can only signal a reset of the POC or cycle parameter. For example, picture set A can have a cycle parameter poc_cycle=m, where m=+5. When IDR picture 703a is received, m can be changed to m=-1. Therefore, IDR picture 703a can count the poc_cycle of reference pictures with respect to a selected picture. In other words, IDR picture 703a can signal a poc_cycle count to calculate reference pictures with respect to selected pictures in the sequence, not just the current picture.

FIG8 is a flow chart illustrating one configuration of a method 800 for tracking a reference picture using reduced overhead referencing based on a selected picture. An electronic device 204 (e.g., decoder 202) may receive 802 a bitstream and decode 804 a portion of the bitstream 214 to generate a decoded reference picture. This may be performed in a manner similar to that described above in conjunction with FIG3 .

The electronic device 204 may utilize reduced overhead referencing to track decoded reference pictures in a decoded picture buffer (DPB) based on the selected picture. This may be accomplished as follows. The electronic device 204 (e.g., the decoder 202) may determine 806 the selected picture. In one configuration, the electronic device 204 may make this determination 806 based on explicit signaling received in the bitstream 214. For example, the bitstream 214 may include an indicator designating the selected picture. In one example, the selected picture may be an Instantaneous Decoding Refresh (IDR) picture indicated by signaling received in the bitstream 214 (e.g., a Picture Parameter Set (PPS), a buffer description, etc.).

The electronic device 204 may determine 808 a picture order count (POC) based on the selected picture. For example, the electronic device 204 may set or reset the POC associated with the selected picture. For example, the POC associated with the selected picture may be set to 0. Accordingly, the electronic device 204 may reset the POC order based on the selected picture. For example, the POCs for other pictures may be numbered based on the POC associated with the selected picture 603a as shown in FIG.

The electronic device 204 may determine 810 a cycle parameter (e.g., poc_cycle) based on the selected picture. For example, the cycle parameter associated with the picture set including the selected picture may be set or reset to 0. Cycle parameters for other picture sets may be determined (e.g., calculated) based on the picture set including the selected picture (e.g., an IDR picture). An example of this is shown and described in conjunction with FIG7 .

When the POC and cycle parameters (e.g., poc_cycle) are determined based on a selected picture, the POC and cycle parameters of the decoded reference pictures can be updated when needed. This enables tracking of decoded reference pictures in the decoded picture buffer (DPB). Therefore, decoded reference pictures can be tracked based on a selected picture (e.g., an IDR picture).

The electronic device 204 may obtain 812 a decoded reference picture from the DPB. For example, the electronic device 204 may retrieve the decoded reference picture from the DPB based on the POC and a cycle parameter (e.g., poc_cycle) based on the selected picture.

The electronic device 204 may decode the picture based on the decoded reference picture 814. This may be done in a similar manner as described above in conjunction with FIG3. It should be noted that a set of one or more decoded reference pictures may be tracked according to the method 800.

FIG9 is a flow chart illustrating another configuration of a method 900 for tracking reference pictures using reduced overhead referencing based on a selected picture. As described above, the electronic device 204 may receive 902 a bitstream. The electronic device 204 may also decode 904 one or more portions of the bitstream to generate a reference picture set. The decoded reference picture set may include one or more decoded reference pictures.

The electronic device 204 may track 906 a decoded reference picture set in a decoded picture buffer (DPB) using reduced overhead referencing based on the selected picture. This may be done as described above in conjunction with FIG8. As described above, two or more decoded reference pictures in a decoded reference picture set may relate to the same or different time instants (e.g., similar time instants).

The electronic device 204 may optionally determine 908 whether a resolution of a decoded reference picture (used for decoding the picture) in the decoded reference picture set is different from a resolution of the current picture. If the resolutions between the two pictures are different, the electronic device 204 may process 910 transform coefficients of the decoded reference picture based on the scaling parameter to decode the picture. A more detailed description of scaling parameters and resolution switching is provided above in conjunction with Table (2). It should be noted that the scaling parameter can be determined by explicitly receiving the scaling parameter or by implicitly determining the scaling parameter (e.g., using a lookup table, picture resolution characteristics, etc.).

Regardless of whether the resolutions are the same or different, the electronic device 204 may decode 912 a picture based on a decoded reference picture set (eg, a decoded reference picture in a decoded reference picture set).

FIG10 is a flow chart illustrating another configuration of a method 1000 for tracking a reference picture using reduced overhead referencing based on a selected picture. An electronic device 204 may receive 1002 a bitstream and decode 1004 a portion of the bitstream to generate a decoded reference picture. The electronic device 204 may track 1006 a decoded reference picture in a decoded picture buffer (DPB) using reduced overhead referencing based on the selected picture. This may be accomplished as described above.

The electronic device 204 may also obtain 1008 a cache description. Some examples of cache descriptions are described in detail above. For example, Table (1) and Table (2) above contain examples of various cache descriptions. The decoder may receive the cache description from the encoder as part of a parameter picture set (PPS). The decoder may also receive an index to an appropriate cache description as part of a slice header. Once the cache description is obtained 1008, the electronic device 204 may determine 1010 whether to modify the cache description. If the cache description does not need to be modified, the electronic device 204 may decode the picture based on the decoded reference picture 1014. However, if the cache description needs to be modified, the electronic device 204 may modify 1012 one or more entries. Examples of modification 1012 may include: deleting an entry, adding an entry, or replacing an entry. A more detailed description of deleting, adding, or replacing entries can be found above in conjunction with the description of List (4). Once the modification 1012 is completed, the electronic device 204 may decode the picture based on the decoded reference picture 1014.

FIG11 is a diagram illustrating an example of signaling a wrap indicator according to the systems and methods disclosed herein. In this example, multiple pictures 1101a-n, 1103a are shown. The first picture 1101a with POC=0 is a reference picture for the remaining pictures 1101b-n, 1103a shown in FIG11 . Specifically, FIG11 illustrates an association or correspondence 1109 between the reference picture 1101a and the other pictures 1101b-n, 1103a. For example, the picture 1101a with POC=0 may be a long-term reference picture 1101a to be stored in the DPB for decoding of the other pictures 1101b-n, 1103a.

As shown in FIG11 , POC numbers 0 to MaxPOC-1 and reuse 0 may correspond to pictures 1101a-n and 1103a, respectively. The first picture set 1101a-n may correspond to POC numbers 0 to MaxPOC-1. As described above, each picture set (having POC numbers 0 to MaxPOC-1) may correspond to a cycle parameter (e.g., poc_cycle).

In one configuration, a wrap indicator may be signaled 1133 upon the first transition between one picture set and a subsequent picture set. For example, the wrap indicator may be signaled 1133 upon the first transition of the POC number from one set [0, ..., MaxPOC-1] to the next. In some configurations, the signaled wrap indicator may be a protected message denoted as "poc_wraparound." As used herein, "signaling" may mean transmitting between an encoder and a decoder. In some configurations, "signaling" may also mean transmitting between different electronic devices.

Protected messages can be messages that the electronic device 204 must receive to maintain desired functionality (e.g., detection of lost images). One mechanism for sending messages as protected messages is to assign a higher priority to protected messages when compared to other information messages. An intelligent device (e.g., a network congestion control agent) can then examine this priority assignment and discard lower priority messages to meet constraints such as available network bandwidth.

In some configurations, a wrap indicator (e.g., poc_wraparound) message may be signaled in a picture parameter set (PPS), a slice header, an adaptation parameter set (APS), or any suitable location in the bitstream. Additionally or alternatively, the wrap indicator may be signaled out-of-band (e.g., separately from the picture bitstream). Whenever the decoder 102 receives a wrap indicator (e.g., poc_wraparound message), a cycle parameter (e.g., poc_cycle) for each picture (e.g., each picture set) in the DPB may be decremented (e.g., decremented by 1).

FIG12 is a diagram illustrating an example of signaling a wrap indicator 1133 according to the systems and methods disclosed herein. In this example, a plurality of pictures 1137a-n, 1139a-n, 1141a-n, 1143a-n, 1145a-n and picture sets 1107a-e are illustrated. Specifically, FIG12 illustrates the reference buffer status 1135 over time, along with the corresponding current frame and the timing 1149 of the wrap indicator.

In this example, it is assumed that picture _B0 1139a in picture set B 1107b with poc_cycle = 0 is the current picture or frame at a first moment in time. When transition A 1147a occurs, a wrap indicator is signaled 1133a. At a second moment in time, picture _C0 1141a in picture set C 1107c is the current picture or frame. It is assumed that picture _C0 1141a is a reference picture for all subsequent pictures (e.g., in picture set D 1107d and picture set E 1107e). For example, picture _C0 1141a is a long-term reference picture to be stored in the DPB for use in decoding subsequent pictures 1141b-n, 1143a-n, and 1145a-n. When transition B 1147b occurs, another wrap indicator is signaled 1133b. As described, the poc_cycle parameter is updated when the wrap indicator is signaled 1133. This process may be used to track reference pictures according to the systems and methods disclosed herein. Additionally, it should be noted that the POC and poc_cycle may be reset or restarted based on a decoded reference picture as described herein.

12 , POC numbers 0 to MaxPOC-1 repeatedly correspond to pictures 1137a-n, 1139a-n, 1141a-n, 1143a-n, 1145a-n. As described above, each picture set 1107a-e (having POC numbers 0 to MaxPOC-1) may correspond to a cycle parameter (e.g., poc_cycle).

In one configuration, a wrap indicator may be signaled 1133a upon the first transition 1147a between a current picture set (e.g., picture set B 1107b) and a subsequent picture set (e.g., picture set C 1107c). For example, the wrap indicator may be signaled 1133 the first time a POC number transitions from one set [0, ..., MaxPOC-1] to the next. In some configurations, the wrap indicator may be signaled 1133 when a POC number transitions from one set [0, ..., MaxPOC-1] to another. Alternatively, the wrap indicator may be signaled 1133 the first time a poc_cycle number transitions for the next set [0, ..., MaxPOC-1]. In some configurations, the wrap indicator may be signaled 1133 when a poc_cycle number transitions for the next set [0, ..., MaxPOC-1]. In some configurations, the wrap indicator may be signaled 1133 when a poc_cycle number transitions for the next set [0, ..., MaxPOC-1]. In some configurations, the signaled wrap indicator may be a protected message denoted as "poc_wraparound." As used herein, "signaling" may mean transmitting between an encoder and a decoder. In some configurations, "signaling" may also mean transmitting between different electronic devices.

Protected messages can be messages that the electronic device 204 must receive to maintain desired functionality (e.g., detection of lost images). One mechanism for sending messages as protected messages is to assign a higher priority to protected messages when compared to other information messages. An intelligent device (e.g., a network congestion control agent) can then examine this priority assignment and discard lower priority messages to meet constraints such as available network bandwidth.

In some configurations, a wrap indicator (e.g., poc_wraparound) message may be signaled in a picture parameter set (PPS), a slice header, an adaptation parameter set (APS), or any suitable location in the bitstream. Additionally or alternatively, the wrap indicator may be signaled out-of-band (e.g., separately from the picture bitstream). Whenever the decoder 102 receives a wrap indicator (e.g., poc_wraparound message), a cycle parameter (e.g., poc_cycle) for each picture (e.g., each picture set) in the DPB may be decremented (e.g., decremented by 1).

The following Listing (5) illustrates an example of the bitstream syntax modifications required to signal the wrap indicator in the picture parameter set:

List (5)

wrap_indicator_flag equal to 1 specifies that the POC number has transitioned from one [0, ..., MaxPOC-1] picture set to the next picture set for the first time. wrap_indicator_flag equal to 0 specifies otherwise. In some configurations, wrap_indicator_flag equal to 1 specifies that the POC number has transitioned from one [0, ..., MaxPOC-1] picture set to another picture set. wrap_indicator_flag equal to 0 specifies otherwise.

In some configurations, wrap_indicator_flag equal to 1 specifies that the poc_cycle has been switched for the first time for the next [0, ..., MaxPOC-1] picture set. wrap_indicator_flag equal to 0 specifies otherwise.

In some configurations, wrap_indicator_flag equal to 1 specifies that the poc_cycle has transitioned from one [0, ..., MaxPOC-1] picture set to another picture set. wrap_indicator_flag equal to 0 specifies otherwise.

In some configurations, wrap_indicator_flag may use more than one bit to indicate additional information, such as the direction of the conversion. In another configuration, wrap_indicator_flag may be signaled as an unsigned integer that is variable-length encoded using entropy coding. In another configuration, wrap_indicator_flag is a signed integer that is variable-length encoded using entropy coding.

seq_parameter_set_id identifies the sequence parameter set referenced by the picture parameter set.The value of seq_parameter_set_id should be in the range of 0 to 31 (inclusive).

pic_parameter_set_id identifies the picture parameter set referenced in the slice header.The value of pic_parameter_set_id shall be in the range of 0 to 255 (inclusive). entropy_coding_mode_flag selects the entropy decoding method to be applied to the syntax element.

num_temporal_layer_switching_point_flags specifies how many temporal switching point markers there are. If temporal_id_nesting_flag is equal to 1, then num_temporal_layer_switching_point_flags shall be equal to 0.

temporal_layer_switching_point_flag[i] specifies whether the current access point is a temporal switching point that allows decoding of higher temporal_id layers following this access unit. If temporal_id_nesting_flag is equal to 1, then temporal_layer_switching_point_flag[i] shall be inferred to be equal to 1. If temporal_id_nesting_flag is equal to 0 and num_temporal_layer_switching_point_flags is less than i, then temporal_layer_switching_point_flag[i] shall be inferred to be equal to 0. It should be noted that when starting decoding of a higher temporal layer i, the availability of the required reference picture can be ensured immediately following an IDR or a picture with temporal_id value j less than i and temporal_switching_flag[j] equal to 1.

num_ref_idx_10_default_active_minus1 specifies how num_ref_idx_10_active_minus1 is inferred for P slices and B slices with num_ref_idx_active_override_flag equal to 0. The value of num_ref_idx_10_default_active_minus1 should be in the range of 0 to 31, inclusive.

num_ref_idx_11_default_active_minus1 specifies how num_ref_idx_11_active_minus1 is inferred for B slices with num_ref_idx_active_override_flag equal to 0. The value of num_ref_idx_11_default_active_minus1 should be in the range of 0 to 31 (inclusive).

pic_init_qp_minus26 specifies that for each slice, the initial value of SliceQPY is subtracted by 26. The initial value is modified at the slice layer when a non-zero value of slice_qp_delta is decoded, and further modified when a non-zero value of cu_qp_delta is decoded at the coding unit layer. The value of pic_init_qp_minus26 should be in the range of -(26+QpBdOffsetY) to +25, inclusive.

constrained_intra_pred_flag equal to 0 specifies that intra prediction is allowed to use residual data and decoded samples from neighboring macroblocks coded using inter macroblock prediction mode for prediction of macroblocks coded using intra macroblock prediction mode. constrained_intra_pred_flag equal to 1 specifies constrained intra prediction, in which case prediction of macroblocks coded using intra macroblock prediction mode uses only residual data and decoded samples from I macroblock type.

slice_granularity indicates the slice granularity in the picture. The value of slice_granularity should not be greater than Min(Log2MaxCUSize-4, log2_diff_max_min_coding_block_size). The variable SliceGranularity is set to the value of (slice_granularity<<1).

shared_pps_info_enabled_flag specifies that the shared information in the picture parameter set RBSP should be used for the referenced slice. If shared_pps_info_enabled_flag is equal to 1, the alf_param() in the picture parameter set RBSP should be applied to the referenced slice. Otherwise, the alf_param() in the slice header should be applied.

max_cu_qp_delta_depth specifies the maximum allowed depth for specifying QPY values for a coding unit. The value of max_cu_qp_delta_depth should be in the range of 0 to 15, inclusive.

The variable log2MinCUDQPSize specifies the minimum coding unit size that can further modify the QPY value as follows: log2MinCUDQPSize = Log2MaxCUSize - max_cu_qp_delta_depth. alf_param() is a function that determines the syntax of the adaptive loop filter parameters. rbsp_trailing_bits() is a function that corresponds to a stop bit (equal to 1) followed by zero bits until byte alignment is achieved.

The following listing (6) illustrates an example of the bitstream syntax modifications required to signal the wrap indicator in the slice header:

List (6)

lightweight_slice_flag equal to 1 specifies that the value of an absent slice header syntax element should be inferred to be equal to the value of the slice header syntax element in the previous slice. lightweight_slice_flag equal to 0 specifies that the value of the slice header syntax element is sent in the current slice header. slice_type specifies the coding type of the slice, P, B, or I.

idr_pic_id identifies an Instantaneous Decoding Refresh (IDR) picture. The value of idr_pic_id shall remain constant in all slices of an IDR picture. When two consecutive access units in decoding order are both IDR access units, the value of idr_pic_id in the slices of the first such IDR access unit shall be different from the value of idr_pic_id in the slices of the second such IDR access unit. The value of idr_pic_id shall be in the range of 0 to 65535, inclusive.

pic_order_cnt specifies the picture order count of the coded picture and is used as an identifier in the cache description application process and the reference picture list creation process. The pic_order_cnt syntax element shall be represented by log2_max_pic_order_cnt_minus4+4 bits. The value of pic_order_cnt shall be in the range of 0 to MaxPOC-1 (inclusive).

num_ref_idx_active_override_flag equal to 1 specifies that for P slices and B slices, the syntax element num_ref_idx_10_active_minus1 is present, and for B slices, the syntax element num_ref_idx_11_active_minus1 is present. num_ref_idx_active_override_flag equal to 0 specifies that the syntax elements num_ref_idx_10_active_minus1 and num_ref_idx_11_active_minus1 are not present.

When the current slice is a P slice or a B slice and field_pic_flag is equal to 0 and the value of num_ref_idx_10_default_active_minus1 in the picture parameter set exceeds 15, num_ref_idx_active_override_flag shall be equal to 1. When the current slice is a B slice and field_pic_flag is equal to 0 and the value of num_ref_idx_11_default_active_minus1 in the picture parameter set exceeds 15, num_ref_idx_active_override_flag shall be equal to 1. num_ref_idx_10_active_minus1 specifies the maximum reference index of reference picture list 0 that should be used for decoding the slice.

When the current slice is a P slice or a B slice and num_ref_idx_10_active_minus1 is not present, num_ref_idx_10_active_minus1 shall be inferred to be equal to num_ref_idx_10_default_active_minus1. The range of num_ref_idx_10_active_minus1 is specified as follows. If field_pic_flag is 0, num_ref_idx_10_active_minus1 shall be in the range of 0 to 15 (inclusive). When MbaffFrameFlag is 1, num_ref_idx_10_active_minus1 is the maximum index value for decoding of frame macroblocks, and 2*num_ref_idx_10_active_minus1+1 is the maximum index value for decoding of field macroblocks. Otherwise (when field_pic_flag is 1), num_ref_idx_10_active_minus1 shall be in the range of 0 to 31 (inclusive).

num_ref_idx_11_active_minus1 specifies the maximum reference index of reference picture list 1 that should be used for decoding the slice. When the current slice is a B slice and num_ref_idx_11_active_minus1 is not present, num_ref_idx_11_active_minus1 should be inferred to be equal to num_ref_idx_11_default_active_minus1. The range of num_ref_idx_11_active_minus1 is limited, as specified in the syntax of num_ref_idx_10_active_minus1, which replaces 10 and list 0 with 11 and list 1, respectively.

no_output_of_prior_pics_flag specifies how to handle previously decoded pictures in the decoded picture buffer after decoding of an IDR picture. When the IDR picture is the first IDR picture in the bitstream, the value of no_output_of_prior_pics_flag has no effect on the decoding process. When the IDR picture is not the first IDR picture in the bitstream and the values of PicWidthInMbs, FrameHeightInMbs, or max_dec_frame_buffering derived from the active sequence parameter set are different from the values of PicWidthInMbs, FrameHeightInMbs, or max_dec_frame_buffering derived from the active sequence parameter set for the previous picture, the decoder may (but should not) infer that no_output_of_prior_pics_flag is equal to 1, regardless of the actual value of no_output_of_prior_pics_flag.

cabac_init_idc specifies the index used to determine the initialization table used in the initialization process of context variables. The value of cabac_init_idc should be in the range of 0 to 2 (inclusive).

first_slice_in_pic_flag indicates whether the slice is the first slice of the picture. If first_slice_in_pic_flag is equal to 1, the variables SliceAddress and LCUAddress are both set to 0, and decoding starts at the first largest coding unit (LCU) in the picture.

The slice_address specifies the address of the start of the slice at slice granularity resolution and should be represented by (Ceil(Log2(NumLCUsInPicture))+SliceGranularity) bits in the bitstream, where NumLCUsInPicture is the number of LCUs in the picture. The variable LCUAddress is set to (slice_address>>SliceGranularity) and represents the LCU portion of the slice address with row-by-row scan order. The variable GranularityAddress is set to (slice_address-(LCUAddress<<SliceGranularity)) and represents the sub-LCU portion of the slice address expressed in z-scan order. Then, the variable SliceAddress is set to (LCUAddress<<(log2_diff_max_min_coding_block_size<<1))+(GranularityAddress<<((log2_diff_max_min_coding_block_size<<1)-SliceGranularity), and slice decoding starts at the largest coding unit possible at the slice start coordinates.

slice_qp_delta specifies the initial value of the luma quantization parameter QPY to be used for all macroblocks in the slice before being modified by the cu_qp_delta value in the coding unit layer. The initial QPY quantization parameter for a slice is calculated as follows: SliceQPY = 26 + pic_init_qp_minus26 + slice_qp_delta. The value of slice_qp_delta should be constrained so that SliceQPY is in the range of -QpBdOffsetY to +51, inclusive. "QpBdOffsetY = 6*bit_depth_luma_minus8" specifies the luma quantization parameter range offset value. "bit_depth_luma_minus8+8" specifies the bit depth of samples for the luma array. pic_init_qp_minus26 specifies the initial value of SliceQPY for each slice, minus 26.

collocated_from_10_flag equal to 1 specifies that pictures containing co-located horizontal partitions should be derived from list 0, otherwise the pictures should be derived from list 1. ref_pic_list_modification() is a function that identifies the syntax for reference picture list modification. ref_pic_list_combination() is a function that identifies the syntax for reference picture list combination. alf_cu_control_param() is a function that identifies the syntax for adaptive loop filter coding unit control parameters. sao_param() is a function that identifies the syntax for sample adaptive offset parameters.

disable_deblocking_filter_idc equal to 1 disables the application of the deblocking filter for a particular block edge. disable_deblocking_filter_idc equal to 0 enables the application of the deblocking filter for a particular block edge. The deblocking process is controlled using the values of the syntax elements slice_alpha_c0_offset_div2 and slice_beta_offset_div2.

The following Listing (7) illustrates an example of the bitstream syntax modifications required to signal the wrap indicator in an Adaptation Parameter Set (APS):

List (7)

aps_id identifies the adaptation parameter set referenced in the slice header. aps_sample_adaptive_offset_flag equal to 1 specifies that SAO is on for slices referencing the current APS. When aps_sample_adaptive_offset_flag equal to 0, this specifies that SAO is off for slices referencing the current APS. If no active APS exists, the aps_sample_adaptive_offset_flag value is inferred to be 0.

aps_adaptive_loop_filter_flag equal to 1 specifies that ALF is on for slices referencing the current APS. When aps_sample_adaptive_offset_flag is equal to 0, this specifies that ALF is off for slices referencing the current APS. If no active APS exists, the aps_adaptive_loop_filter_flag value is inferred to be 0.

aps_cabac_use_flag equal to 1 specifies that when sao_param() is present, the CABAC decoding process should be used for sao_param(), and when alf_param() is present, the CABAC decoding process should be used for alf_param(). When aps_cabac_use_flag is equal to 0, this specifies that when sao_param() is present, the CAVLC decoding process should be used for sao_param(), and when alf_param() is present, the CAVLC decoding process should be used for alf_param().

aps_cabac_init_idc specifies the index used to determine the initialization table used during the initialization of context variables for SAO and ALF. The value of cabac_init_idc should be in the range of 0 to 2 (inclusive). aps_cabac_init_qp_minus26 specifies the quantization parameter minus 26, which is used during the initialization of context variables for SAO and ALF. alf_data_byte_count specifies the number of bytes. sao_data_byte_point specifies the number of bytes. byte_align() inserts 0 to 7 bits until alignment is achieved.

In some configurations, a picture parameter set may include multiple buffer descriptions corresponding only to long-term pictures. Listing (8) below sets forth an example of a bitstream syntax modification for signaling multiple buffer descriptions corresponding only to long-term pictures.

List (8)

longterm_pictures_only_flag_pps[i] equal to 1 indicates that the i-th buffer description contains only long-term picture references. longterm_pictures_only_flag_pps[i] equal to 0 indicates that the i-th buffer description contains deltaPOC and long-term picture references.

In some configurations, the cache description may refer to pictures that are unavailable for reference. A picture that is unavailable for reference refers to a picture that has not been decoded before the current picture. Furthermore, a picture that is unavailable for reference refers to a picture that has been decoded before the current picture but has been identified as no longer available for reference. One example of a process for identifying pictures that are no longer available for reference is through the use of IDR frames. An IDR frame indicates that the IDR frame and all subsequently received pictures do not reference pictures received before the IDR frame. Therefore, for the IDR frame and subsequently received frames, all frames received before the IDR frame are no longer available for reference.

In configurations where the cached description refers to a picture that is unavailable for reference, the decoder is prohibited from using the unavailable picture in predicting information used to decode the current frame. In one configuration, this is accomplished by not including the frame in the process of creating a reference frame set. Thus, the output of the process of creating a reference frame set may be the same if the cached description refers to a picture that is unavailable for reference and if the cached description does not refer to a picture that is unavailable for reference, and if the other pictures referred to by the two cached descriptions are the same. In another configuration, the process of creating a reference frame set includes the unavailable picture. Thus, the output of the process of creating a reference frame set is different if the cached description refers to a picture that is unavailable for reference and if the cached description does not refer to a picture that is unavailable for reference. In this configuration, the decoder is prohibited from selecting a picture that is unavailable for reference to predict information used to decode the current frame.

In some configurations, the i-th reference picture list POCBD_pps[i], temporalIDBD_pps[i], POC_CYCLE_BD_pps[i] and the lists POCBD, temporalIDBD, and POC_CYCLE_BD defined in the PPS are divided based on whether the reference picture is in the past or future in display order relative to the current picture (being decoded). It should be noted that i can take values from 0 to number_of_bds-1.

In some configurations, the temporal identifier can be replaced by a flag that signals or indicates whether the current picture (being decoded) uses the corresponding reference picture. Thus, the lists usedByCurPicBD and usedByCurPicBD_pps[i] containing the above flag replace the temporalID list temporalIDBBD and the i-th temporalID list temporalIDBD_pps[i] in the PPS, respectively. In some configurations, the value of the flag can be used to divide the i-th reference picture list POCBD_pps[i], usedByCurPicBD_pps[i], POC_CYCLE_BD_pps[i] and the lists POCBD, usedByCurPicBD, POC_CYCLE_BD defined in the PPS into one or more lists. In one configuration, entries with a zero value for the flag are assigned to one list, and those with a non-zero value (e.g., 1) are assigned to another list. It should be noted that i can take values from 0 to number_of_bds-1.

Listing (9) illustrates another example of syntax modifications from AHG21 for PPS. Specifically, Listing (9) illustrates another example of the cache description syntax used in the slice header as outlined in the AHG21 working draft. However, the modifications to the syntax given in the AHG21 working draft according to the systems and methods disclosed herein are indicated in bold text in Listing (9).

List (9)

Listing (9) contains many elements similar to those of Listing (4). Listing (9) also contains syntax modifications to the slice header to allow for selective replacement of reference pictures.

bd_poc_cycle_replace_count specifies the number of entries to be selectively replaced in the lists POCBD_pps[bd_idx], POC_CYCLE_BD_pps[bd_idx], and temporalIDBD_pps[bd_idx]. In some configurations, bd_poc_cycle_replace_count may be greater than or equal to 0. bd_pps_replace_idx[j] identifies the index of the entry to be replaced in the lists POCBD_pps[bd_idx], POC_CYCLE_BD_pps[bd_idx], and temporalIDBD_pps[bd_idx].

The referenced cache description POC_CYCLE_BD_pps[bd_idx][bd_pps_replace_idx[j]] shall be replaced for the current picture. In some configurations, future frames may also overwrite the poc_cycle information. poc_cycle_pps_replace[j] specifies the value to be used to replace the value in POC_CYCLE_BD_pps[bd_idx][bd_pps_replace_idx[j]] for the current picture only.

poc_pps_replace[j] specifies the value to be used to replace the value in POCBD_pps[bd_idx][bd_pps_replace_idx[j]] for the current picture only. temporal_id_pps_replace[j] specifies the value to be used to replace the value in TemporalIDBD_pps[bd_idx][bd_pps_replace_idx[j]] for the current picture only.

In some configurations, if the i-th reference picture list POCBD_pps[i], usedByCurPicBD_pps[i], POC_CYCLE_BD_pps[i] defined in the PPS is partitioned, then selective replace, reload, delete, and append operations are first performed on the derived list generated using the partitioned list. After all or a subset of the operations are completed, the entries in the derived list can be partitioned back (e.g., restored) to the original list from which the derived list was derived. It should be noted that i can take values from 0 to number_of_bds-1.

In some configurations, selective replace, overload, delete, and append operations are signaled separately for each list set belonging to the cache description in the PPS (e.g., the (negative deltaPOC list, negative deltaPOC usedByCurPicBD list) set, the (positive deltaPOC list, positive deltaPOC usedByCurPicBD list) set, and the (poc list, poc_cycle list, poc and poc_cycleusedByCurPicBD list) set). In another configuration, a scaling parameter list may exist in each list set.

In some configurations, if the bitstream contains a first picture having a first resolution and a second picture having a second resolution, if the first resolution and the second resolution are not equal, and if the second picture is not an IDR picture or a sequence parameter set (SPS) is not received after the first picture and before the second picture, then the decoded picture buffer may contain pictures with different resolutions. The encoder may then signal to the decoder to modify the reference pictures in the decoded picture buffer (DPB) such that the reference pictures include one of the following options:

(a) first resolution,

(b) a second resolution, or

(c) First resolution and second resolution

Some example use cases are given below. Option (a) is useful if the reference picture will only be used for motion prediction at a lower resolution. The first example 1653a shown in FIG17 gives an example of option (a).

Option (b) is useful when the bitstream contains a third picture after the second picture, where the third picture is at the first resolution and the long-term pictures stored in the DPB can be used for motion prediction. The second example 1653b shown in Figure 17 gives an example of option (b).

Option (c) is useful when a lower-resolution version of the reference picture is used in motion prediction for the lower-resolution picture. Furthermore, a higher-resolution version of the reference picture is used for motion prediction when decoding a third picture following the second picture, where the third picture is at the first resolution. Option (c) is exemplified by the third example 1653c shown in FIG17 .

Resolution switching may be signaled using syntax modifications as shown in Listing (10) below. Modifications according to the systems and methods described herein are indicated below in bold text.

List (10)

If adaptive_res_coding_flag is equal to 0, the sequence does not perform resolution switching. If adaptive_res_coding_flag is equal to 1, the sequence performs resolution switching.

refPicS0Height[i] and refPicS0Width[i] represent the original height and width of the i-th reference picture corresponding to the negative deltaPOC. refPicS1Height[i] and refPicS1Width[i] represent the original height and width of the i-th reference picture corresponding to the positive deltaPOC. curPicHeight and curPicWidth represent the height and width of the current picture being decoded.

num_negative_pics specifies the number of the following delta_poc_s0_minus1[i] and used_by_curr_pic_s0_flag[i] syntax elements. num_positive_pics specifies the number of the following delta_poc_s1_minus1[i] and used_by_curr_pic_s1_flag1[i] syntax elements.

delta_poc_s0_minus1[i] plus 1 specifies the absolute difference between two picture order count values. The value of delta_poc_s0_minus1[i] should be in the range of 0 to 215-1, inclusive. delta_poc_s0_minus1[i] corresponds to a negative deltaPOC value.

used_by_curr_pic_s0_flag[i] equal to 0 specifies that the i-th reference picture with a picture order count smaller than the picture order count of the current picture is not used for reference by the current picture. delta_poc_s1_minus1[i] plus 1 specifies the absolute difference between the two picture order count values. The value of delta_poc_s1_minus1[i] should be in the range of 0 to 215-1, inclusive. delta_poc_s1_minus1[i] corresponds to positive deltaPOC values.

used_by_curr_pic_s1_flag[i] equal to 0 specifies that the i-th reference picture having a picture order count greater than the picture order count of the current picture is not used for reference by the current picture.

used_by_curr_pic_longterm_flag[i] equal to 0 specifies that the i-th long-term reference picture is not used for reference by the current picture.

ref_pic_s0_resolution_idx[i] equal to 0 specifies that the reference picture is scaled to match the resolution of the current picture being decoded. ref_pic_s0_resolution_idx[i] equal to 1 specifies that the reference picture is preserved at its original resolution. ref_pic_s0_resolution_idx[i] equal to 2 specifies that the resolution of the reference picture is maintained at both its original resolution and the resolution of the current picture. ref_pic_s0_resolution_idx[i] is inferred to be 0 when ref_pic_s0_resolution_idx[i] is not present.

ref_pic_s1_resolution_idx[i] equal to 0 specifies that the reference picture is scaled to match the resolution of the current picture being decoded. ref_pic_s1_resolution_idx[i] equal to 1 specifies that the reference picture is preserved at its original resolution. ref_pic_s1_resolution_idx[i] equal to 2 specifies that the resolution of the reference picture is maintained both at its original resolution and at the resolution of the current picture. ref_pic_s1_resolution_idx[i] is inferred to be 0 when ref_pic_s1_resolution_idx[i] is not present.

In one configuration, if a bitstream includes a first picture having a first resolution and a second picture and a fourth picture having a second resolution, wherein the first resolution and the second resolution are not equal, and the second picture is not an IDR picture or a sequence parameter set (SPS) is not received after the first picture and before the second picture, then the second picture may refer to only one reference picture having the first resolution. In a second configuration, if a bitstream includes a first picture having a first resolution and a second picture having a second resolution, wherein the first resolution and the second resolution are not equal, and the second picture is not an IDR picture or a sequence parameter set (SPS) is not received after the first picture and before the second picture, then the fourth picture may refer to only one reference picture having the first resolution that is not referenced by other pictures having the second resolution.

For example, if another picture of the same resolution precedes the fourth picture, the fourth picture may reference a reference picture of the first resolution in addition to the reference pictures used by the pictures of the same resolution preceding the fourth picture. In other words, when decoding a picture of the second resolution, only one reference picture of the first resolution may be used for reference when decoding the picture. Once a picture of the first resolution is used for reference when decoding a picture of the second resolution, the picture of the first resolution used for reference is considered to have the resolution of the second resolution used for decoding subsequent pictures.

FIG13 is a flow chart illustrating another more specific configuration of a method 1200 for tracking reference pictures using reduced overhead referencing based on a selected picture. This method 1200 may be another approach for tracking which picture is being referenced when reusing a POC. An electronic device 204 (e.g., a decoder 202) may receive 1202 a bitstream. For example, the decoder 202 may receive 1202 a bitstream 214 including coded reference pictures. In some configurations, the bitstream 214 may also include overhead information (e.g., PPS, buffer description information, parameters, reference picture indications or identifiers, etc.).

The electronic device 204 may decode 1204 a portion of the bitstream to generate a decoded reference picture. For example, the decoder 202 may decode 1204 a portion of the bitstream 214 to generate a decoded reference picture, which is stored in the frame memory 264. It should be noted that one or more portions of the bitstream 214 may be decoded 404 to generate one or more decoded reference pictures.

The electronic device 204 may associate a cycle parameter with a decoded picture set including a decoded reference picture 1206. For example, the electronic device 204 may associate a cycle parameter "poc_cycle" with a decoded picture set including a decoded reference picture or each picture in a decoded picture set 1206. The cycle parameter "poc_cycle" is described in more detail below.

The electronic device 204 may determine 1208 whether a transition has occurred between picture sets. For example, the transition may be determined 1208 by examining the POC of the current picture being decoded (e.g., CurPOC) and comparing it to the POC of the last decoded picture (e.g., LastPOC). For example, if the POC of the current picture being decoded (e.g., CurPOC) is less than the POC of the last decoded picture (e.g., LastPOC), and LastPOC minus CurPOC is greater than a threshold value TH_FWD, then a transition from the previous picture set to the subsequent picture set may be determined 1208. However, if the POC of the current picture being decoded (e.g., CurPOC) is greater than the POC of the last decoded picture (e.g., LastPOC), and CurPOC minus LastPOC is greater than a threshold value TH_BCKWD, then a transition from the subsequent picture set to the previous picture set may be determined 1208. For all other cases, it may be determined 1208 that no transition has occurred. In some configurations, the threshold may take the value TH_FWD=TH_BCKWD=MaxPOC/2.

If the electronic device 204 determines 1208 that a conversion has occurred between two picture sets, the electronic device 204 may modify 1210 the loop parameters. For example, when the conversion is from the previous picture set, the electronic device 204 may decrement the loop parameters for each picture or each picture set in the DPB. In another example, when the conversion is from the subsequent picture set, the electronic device 204 may increment the loop parameters for each picture or each picture set in the DPB. Thus, all reference picture loop parameters may be updated for the picture being decoded. This update process (e.g., determining 1208 whether a conversion has occurred between picture sets and possibly modifying 1210 the loop parameters) may be performed once for each picture being decoded.

An alternative definition of the cycle parameter "poc_cycle" may be that the poc_cycle of the picture being (currently) decoded is 0. Therefore, the picture set including the picture currently being decoded may be zero.

The poc_cycle of any other picture (e.g., a reference picture) can be calculated by subtracting the MaxPOCSetIndex of the picture being decoded from the MaxPOCSetIndex of the reference picture. For example, if the MaxPOCSetIndex of the picture being decoded is n and the MaxPOCSetIndex of the reference picture is n-1, the poc_cycle of the reference picture can be (n-1)-n=-1.

It should be noted that the poc_cycle for a reference picture may depend on the MaxPOCSetIndex distance between the reference picture and the picture being decoded. This may be determined implicitly by tracking the transitions between one picture set [0, ..., MaxPOC-1] and another picture set [0, ..., MaxPOC-1] at both the encoder 108 and the decoder 102 (e.g., determining 1208 whether a transition has occurred).

The electronic device 204 may decode the picture based on the decoded reference picture 1212. For example, a portion of the bitstream 214 (not the portion used by the decoder 1204 to generate the decoded reference picture) may be decoded 1212 based on the decoded reference picture. For example, the decoded reference picture (already tracked in the DPB) may be provided to the motion compensation module 260 to generate an inter-frame prediction signal 268 based on an inter-frame prediction mechanism. The inter-frame prediction signal 268 may then be used to decode the picture 1212. In some configurations or instances, one or more decoded reference pictures may be used to decode the picture 1212.

FIG14 is a flow chart illustrating one configuration of a method 1300 for determining whether a transition has occurred between picture sets. For example, FIG14 provides an example of determining 1208 whether a transition has occurred between picture sets as shown in FIG13. The electronic device 204 may determine 1302 whether the POC of a current picture being decoded (e.g., denoted as "CurPOC") is less than the POC of a last decoded picture (e.g., denoted as "LastPOC"). For example, the electronic device 204 may compare the POC of the current picture being decoded (e.g., CurPOC) with the POC of a last decoded picture (e.g., LastPOC) to make this determination 1302.

If CurPOC < LastPOC, the electronic device 204 may determine 1308 whether LastPOC - CurPOC is greater than a threshold value TH_FWD. If LastPOC - CurPOC is greater than the threshold value TH_FWD, the electronic device 204 may determine 1308 that a transition from the previous picture set to the subsequent picture set has occurred. However, if LastPOC - CurPOC is not greater than TH_FWD, the electronic device 204 may determine 1308 that no transition has occurred.

If CurPOC is not less than LastPOC, the electronic device 204 may determine 1304 whether CurPOC is greater than LastPOC. If the electronic device 204 determines 1304 that CurPOC is greater than LastPOC, the electronic device 204 may determine 1306 whether CurPOC minus LastPOC is greater than a threshold value TH_BCKWD. If the electronic device determines 1306 that CurPOC minus LastPOC is greater than the threshold value TH_BCKWD, the electronic device 204 may determine 1306 that a transition from a subsequent picture set to a previous picture set has occurred. If the electronic device determines 1306 that CurPOC minus LastPOC is not greater than the threshold value TH_BCKWD, the electronic device 204 may determine 1306 that no transition has occurred.

If the electronic device 204 determines 1304 that CurPOC is not greater than the threshold LastPOC, the electronic device may determine that no transition occurred 1304. In some configurations, the threshold may take the value TH_FWD = TH_BCKWD = MaxPOC/2.

FIG15 is a flow chart illustrating another more specific configuration of a method 1400 for tracking reference pictures using reduced overhead referencing based on a selected picture. This method 1400 can be one approach for tracking which picture is being referenced when reusing a POC. An electronic device 204 (e.g., a decoder 202) can receive 1402 a bitstream 214. For example, the decoder 202 can receive 1402 a bitstream 214 that includes coded reference pictures (and, for example, other coded pictures). In some configurations, the bitstream 214 can also include overhead information (e.g., PPS, buffer description information, parameters, reference picture indicators or identifiers, etc.).

The electronic device 204 may decode 1404 a portion of the bitstream 214 to generate a decoded reference picture. For example, the decoder 202 may decode 1404 a portion of the bitstream 214 to generate a decoded reference picture, which is stored in the frame memory 264. It should be noted that one or more portions of the bitstream 214 may be decoded 1404 to generate one or more decoded reference pictures.

The electronic device 204 may associate 1406 a cycle parameter with a decoded picture set including the decoded reference picture. For example, the electronic device 204 may associate 1406 a cycle parameter "poc_cycle" with a decoded picture set including the decoded reference picture.

The electronic device 204 may determine 1408 whether a transition has occurred between picture sets. For example, each time the decoder 102 decodes a predetermined number of pictures in a picture set, the decoder 102 or the electronic device B 104 b may determine 1408 that a transition has occurred between two picture sets. In another example, each time the decoder 102 detects a POC loop (e.g., restarting from a maximum value to a minimum value), the decoder 102 or the electronic device B 104 b may determine 1408 that a transition has occurred between two picture sets.

If the electronic device 204 determines 1408 that a transition has occurred between picture sets, the electronic device 204 may modify 1410 (e.g., decrement) the loop parameter. For example, the electronic device 204 decrements the loop parameter for each picture or each picture set in the DPB. In another example, the electronic device 204 may increment the loop parameter.

The electronic device 204 may decode the picture based on the decoded reference picture 1412. For example, a portion of the bitstream 214 (not the portion used by the decoder 1404 to generate the decoded reference picture) may be decoded 1412 based on the reference picture. For example, the decoded reference picture (already tracked in the DPB) may be provided to the motion compensation module 260 to generate an inter-frame prediction signal 268 based on an inter-frame prediction mechanism. The inter-frame prediction signal 268 may then be used to decode the picture 1412. In some configurations or instances, one or more decoded reference pictures may be used to decode the picture 1412.

16 illustrates various components that may be utilized in an electronic device 1504. The electronic device 1504 may be implemented as one or more of the previously described electronic devices (e.g., electronic devices 104, 204).

Electronic device 1504 includes a processor 1517 that controls the operation of electronic device 1504. Processor 1517 may also be referred to as a CPU. Memory 1511 (which may include read-only memory (ROM), random access memory (RAM), or any other type of device capable of storing information) provides instructions 1513a (e.g., executable instructions) and data 1515a to processor 1517. A portion of memory 1511 may also include non-volatile random access memory (NVRAM). Memory 1511 may be in electronic communication with processor 1517.

Instructions 1513b and data 1515b may also reside in processor 1517. Instructions 1513b and/or data 1515b loaded into processor 1517 may also include instructions 1513a and/or data 1515a loaded from memory 1511 for execution or processing by processor 1517. Instructions 1513b may be executed by processor 1517 to implement the systems and methods disclosed herein.

The electronic device 1504 may include one or more communication interfaces 1519 for communicating with other electronic devices. The communication interface 1519 may be based on wired communication technology, wireless communication technology, or both. Examples of the communication interface 1519 include a serial port, a parallel port, a universal serial bus (USB), an Ethernet adapter, an IEEE 1394 bus interface, a small computer system interface (SCSI) bus interface, an infrared (IR) communication port, a Bluetooth wireless communication adapter, a wireless transceiver compliant with the Third Generation Partnership Project (3GPP) specification, and the like.

The electronic device 1504 may include one or more output devices 1523 and one or more input devices 1521. Examples of output devices 1523 include speakers, printers, and the like. One type of output device that may be included in the electronic device 1504 is a display device 1525. The display device 1525 used with the configurations disclosed herein may utilize any suitable image projection technology, such as a cathode ray tube (CRT), liquid crystal display (LCD), light emitting diode (LED), gas plasma, electroluminescence, and the like. A display controller 1527 may be provided for converting data stored in the memory 1511 into text, graphics, and/or moving images (as appropriate) displayed on the display 1525. Examples of input devices 1521 include a keyboard, a mouse, a microphone, a mobile control device, buttons, a joystick, a trackball, a touchpad, a touch screen, a light pen, and the like.

The various components of electronic device 1504 can be coupled together via bus system 1529. In addition to the data bus, bus system 1529 may also include a power bus, a control signal bus, and a status signal bus. However, for clarity, the various buses are shown as bus system 1529 in FIG16 . The electronic device 1504 shown in FIG16 is a functional block diagram rather than a listing of specific components.

FIG17 is a diagram illustrating an example of a use case according to the systems and methods disclosed herein. Specifically, three examples 1653a-c as described above are shown. These three examples may occur if the bitstream contains a first picture having a first resolution and a second picture having a second resolution, if the first resolution and the second resolution are not equal, and if the second picture is not an IDR picture or a sequence parameter set (SPS) is not received after the first picture and before the second picture.

A first example 1653a shows a picture 1655a at a first resolution and a picture 1657a at a second resolution stored in a decoded picture buffer. In the first example 1653a, the encoder can signal to the decoder that the reference picture in the decoded picture buffer (DPB) is modified so that the reference picture is at the first resolution. This may be useful if the reference picture will only be used for motion prediction at a lower resolution.

A second example 1653b shows a picture 1655b at a first resolution and a picture 1657b at a second resolution stored in a decoded picture buffer. In the second example 1653b, the encoder can signal to the decoder that the reference picture in the decoded picture buffer (DPB) is modified so that the reference picture is at the second resolution. This can be useful when the bitstream contains a third picture after the second picture, where the third picture is at the first resolution and the long-term pictures stored in the DPB can be used for motion prediction.

A third example 1653c shows a picture 1655c having a first resolution and a picture 1657c having a second resolution stored in a decoded picture buffer. In the third example 1653c, the encoder can signal to the decoder that a reference picture in the decoded picture buffer (DPB) is modified so that the reference picture has both the first resolution and the second resolution. This can be useful when a higher resolution version of the reference picture is used for motion prediction when decoding a third picture subsequent to the second picture, where the third picture is at the first resolution.

The term "computer-readable medium" refers to any available medium that can be accessed by a computer or processor. The term "computer-readable medium" as used herein may refer to a non-transient and tangible computer-readable medium and/or a processor-readable medium. By way of example and not limitation, a computer-readable medium or a processor-readable medium may include a RAM, a ROM, an EEPROM, a CD-ROM or other optical disk storage device, a magnetic disk storage device or other magnetic storage device, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer or processor. Disks and optical disks as used herein include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks, and optical discs, with disks typically reproducing data magnetically and optical discs reproducing data optically using lasers.

It should be noted that one or more of the methods described herein may be implemented and/or executed using hardware. For example, one or more of the methods described herein may be implemented and/or realized using a chipset, an application specific integrated circuit (ASIC), a large scale integrated circuit (LSI), or an integrated circuit.

Each of the methods disclosed herein includes one or more steps or actions for implementing the method. Method steps and/or actions may be interchanged with one another and/or combined into a single step without departing from the scope of the claims. In other words, unless proper operation of the described method requires a specific order of steps or actions, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.

It should be understood that the claims are not limited to the precise configuration and components described above, and that various modifications, changes, and variations may be made in the arrangement, operation, and details of the systems, methods, and apparatus described herein without departing from the scope of the claims.

Claims (7)

1. A method for decoding a video bitstream, comprising: Receive a bitstream including entropy-encoded quantization transform coefficients; Receive a reference description of the decoded reference frame from the bitstream; Determine the frame sequence count (POC) for the current frame to be decoded, where each decoding reference frame is associated with a frame sequence count (POC). Sort the frame sequence count (POC) of the decoding reference frames in multiple sets, each set having a POC value range of [0,…MaxPOC-1]. The specific value of MaxPOCSetIndex corresponds to the specific set of [0,…MaxPOC-1]. The reference description mentioned therein includes modification parameters for the long-term reference frame. The modification parameter of the long-term reference frame is the difference between the MaxPOCSetIndex of the decoded reference frame and the MaxPOCSetIndex of the current frame. Based on the frame sequence count and the reference description, the decoded reference frame of the current frame is identified from the decoded frame buffer; Based on the aforementioned decoding reference frame, inter-frame prediction is used to decode the current frame; and The decoded images are cached in the decoded image cache for future prediction. 2. The method according to claim 1, wherein the modified parameter is a POC loop parameter. 3. The method of claim 1, wherein the modified parameter is an indicator for starting another POC cycle. 4. The method according to any one of claims 1 to 3, wherein the reference description includes a frame sequence count of the decoded reference frame. 5. The method according to claim 2, wherein the POC cycle parameter is located in the chip header. 6. A method for encoding a video stream, comprising: Determine the frame sequence count (POC) of the current frame being encoded; Identify a reference frame for the current frame from the decoded frame buffer; The current frame is encoded using inter-frame prediction based on reference frames, wherein each reference frame is associated with a frame sequence count (POC), and the frame sequence count (POC) of the reference frames is sorted in multiple sets, each set having a POC value range of [0,…MaxPOC-1], and the specific value of MaxPOCSetIndex corresponds to the specific set of [0,…MaxPOC-1]. Determine the reference description for the reference image; Send a bitstream including the encoded screen and a reference description of the reference screen; The bitstream mentioned therein includes entropy-encoded quantization transform coefficients. The reference description mentioned therein includes modification parameters for the long-term reference frame. The modification parameter for the long-term reference frame is the difference between the MaxPOCSetIndex of the reference frame used to encode the current frame and the MaxPOCSetIndex of the current frame. Inter-frame prediction is used to decode the current frame based on a reference frame used for encoding the current frame; and The decoded images are cached in the decoded image cache for future prediction. 7. An apparatus for decoding a video bitstream, comprising: Processor; and A data memory that is in electrical communication with the processor, wherein instructions are stored in the data memory; The processor thereon can execute the instructions to perform the method of claim 1.