HK1173291B - Decoder and method at the decoder for synchronizing the rendering of contents received through different networks - Google Patents

Description

Decoder and method for synchronizing the presentation of content received via different networks

Technical Field

The present invention generally relates to a method for decoding audio video programs received over a broadband network, and in particular to a method of synchronizing the presentation of content received over a broadband network with the presentation of content received over a broadcast network.

Background Art

This section is intended to introduce the reader to various aspects of the technology that may be related to various aspects of the present invention described and/or claimed below. It is believed that this discussion will help provide the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements should be read in this light and not as admissions of prior art.

Over the past few years, the massive rollout of TV and video services over broadband Internet Protocol (IP) networks has expanded the traditional TV broadcast landscape of terrestrial, satellite, and cable networks. These networks complement each other, with broadcast delivery adapted for live events and mass distribution and broadband delivery adapted for on-demand, catch-up, and personalized services. This complementarity offers the prospect of a hybrid model, leveraging the strengths of each network to efficiently deliver enhanced TV and video services. Broadcast events can be enriched with personalized content delivered via broadband, which is previously streamed and pushed. Such hybrid services may require tight synchronization of the components delivered via separate networks. A typical example illustrating the need for this precise synchronization is a user watching a broadcast program selecting a foreign audio sequence that is not broadcast but is available via broadband. Another example is enriching broadcast content by delivering an additional video component via the broadcast, such as a Multiview Video Coding (MVC) component of a Scalable Video Coding (SVC) enhancement layer, to present the event in 3D or in an alternate view of the same scene.

There are several ways to deliver this additional component via broadband. A first solution based on on-demand delivery is to use Hypertext Transfer Protocol (HTTP) streaming, as described in the document "HTTP Live Streaming, draft-pantos-http-live-streaming-01-R. Pantos, Apple Inc. June 8, 2009," or to rely on the Real-time Transport Protocol (RTP) over UDP/IP as defined in the recommendation RFC 3550, "A Transport Protocol for Real-Time Applications." In this latter case, a communication protocol such as the Real-Time Streaming Protocol (RTSP) (described in the recommendation RFC 2326) is associated with RTP. Another solution based on multicast delivery is to use the RTP protocol (RTP/UDP/IP) as defined in the document "A Transport Protocol for Real-Time Applications."

In the case of on-demand delivery, the request for content can embed timing information indicating the presentation timestamp (PTS) of the first audiovisual sample to be delivered. This is not the case when a terminal subscribes to a multicast stream. The terminal cannot request timing information for a given timestamp, and the behavior is similar to that of a broadcast network where the client is subject to content delivery restrictions.

Some networks are characterized by their latency and their jitter. This means that content does not take the same duration to be delivered over one network as it does over another.

The specificity of broadcast networks is that content arrives at the receiver without the receiver having to request anything, that is, the receiver receives the content continuously, and the delivery has limited jitter, which can be treated in the receiver with a buffer of limited size. The content delivery duration includes the duration of content delivery from the server to the terminal over the broadcast network and the duration required by the terminal to demultiplex, buffer and decode the content.

Broadband networks can be considered personalized delivery networks, as they deliver content only when requested by the receiver.

Figure 1 illustrates the delivery of program content over a broadband network. A video server delivers program content to a set-top box (STB). The STB receives and decodes the content in order to display it on a display device. The delivery can be broken down into four main steps and their corresponding durations:

●The duration required for the request to reach the server is T1.

●The duration for the server to process the request and transmit the program content is T2.

●The duration of program content delivery from the server to the set-top box is T3.

The duration that the set-top box needs to use to buffer, decode and display the program content is T4.

Delivery in a hybrid broadcast-broadband environment does not necessarily imply that the time format is the same for all components. In the MPEG-2 transport stream format (commonly used in broadcast networks), the timing information is based on the Program Clock Reference (PCR) format, while the Network Time Protocol (NTP) is a format used for the timing of streams encoded in the Real-Time Transport Protocol (commonly used in broadband networks). In addition, two components can have the same time format, but the time reference can be different (offset value). In order to compensate for the mentioned timing issues between components, a mechanism must be implemented to transform the timing format and/or reference of some of the other components. The timing format and/or reference of the component(s) delivered via broadband is aligned with the timing format and/or reference of the component(s) delivered via broadcast, the latter being the "master" component. In the description herein, it is estimated that when the timing format and/or reference are different, this timing alignment operation is performed implicitly to synchronize the components, and when we evoke timing values, they refer to timing values in the same transformed reference (same format and same initial value). This unique time reference is called the system clock.

The component delivered via broadcast is called the "main component" and the component delivered via broadband is called the "personalized component".

A method for delivering a personalized component is described herein. A terminal requests the personalized component and sends the personalized component via a bidirectional broadband network. The delivery can be linear or nonlinear.

Linear delivery ensures that the terminal receives the components at a fairly constant rate. Due to network jitter, this is not exactly constant. Two scenarios can be considered for the delivery of personalized components to be synchronized with the broadcast main component. The personalized component stream can be received, decoded, and displayed before the corresponding frames of the main component are displayed, or the personalized component stream arrives after, in which case all frames of the personalized component will be useless.

A typical case of a linear delivery mechanism is when a terminal subscribes to a multicast stream by sending a request to join a multicast group (as defined in the Internet Group Management Protocol (IGMP) protocol). With multicast streaming, the terminal cannot receive the stream at a defined timestamp. In this case, if the personalized component arrives later than the corresponding frame of the main component, their presentation cannot be synchronized.

The Real-time Transport Protocol (RTP) is also well-known for linear delivery. The RTP protocol allows requests for content from a given timestamp, which is equal to the current reception time reference plus an offset. The terminal estimates the offset in order to request content in advance so that it is received before decoding and presenting the content. If the offset is estimated incorrectly, the personalized component is received too late to be synchronized with the main component. Therefore, the client must stop receiving the current streaming transmission, must more accurately estimate the offset, and then send a new request based on the newly estimated offset value.

Non-linear delivery is a mechanism in which a terminal receives content non-periodically. Portions of the content are delivered at a higher rate than they are presented. In one example, the frame rate of reception is higher than the frame rate of presentation. The idea behind non-linear delivery is to provide a terminal that initially receives a personalized component later than the presentation with the possibility of catching up with the main component so that it can be presented at a given moment.

Real-Time Streaming Protocol (RTSP) servers can also deliver content in a nonlinear fashion. Depending on the request parameters, they can, for example, deliver the first frame or group of pictures of a program in a burst and then deliver the content at a cruising rate. When using RTSP, the terminal requests a given presentation timestamp.

Hypertext Transfer Protocol (HTTP) streaming is another nonlinear transmission. The personalized component is divided into many continuous parts called chunks. A chunk is a file or a part of a file that includes a piece of information describing it. The piece of information may include, for example, a time slot, a file name, a byte range, a bit rate, or any other information that may be useful for the terminal to decode and present the content of the chunk. The encoding of the chunk containing the video begins with a key frame that can be decoded without reference to the previous frame. The key frame may be, for example, an I picture (or I frame) as defined in the MPEG compression standard (ISO/IEC13818). A chunk contains a whole group or several whole groups of pictures (GOPs) as defined in MPEG compression. When receiving content using HTTP streaming, the terminal requests chunks from the server. The server then sends chunks on a best-effort basis. The content is sent in continuous bursts.

Non-linear transmission offers the terminal the possibility to synchronize the presentation of the personalized component with that of the main component by sending successive requests for segments of the personalized content starting at a key frame synchronized with the main component in terms of the system clock, decoding the time reference and presenting the time reference.

One disadvantage of such synchronization is that when a terminal requests a personalized component to be synchronized with the main component and receives content starting at a key frame (for which the decoding and presentation time reference indications were received too late to be synchronized with the main component), the discarded content may correspond to a time range that is important for presentation (up to many seconds). The terminal must then send one or more new requests and receive new personalized stream content until the decoding and presentation time reference indications can be synchronized in the terminal.

Summary of the Invention

The object of the present invention is to overcome the drawbacks of the prior art. More specifically, the present invention provides for an optimization of the delay required to synchronize the presentation of a personalized component with the presentation of a main component.

In an environment where hybrid broadcast and broadband delivery of components requires tight synchronization, the present invention proposes a method for significantly reducing the latency for accessing on-demand components (personalized components) in order to enhance the user experience. The use of the method of the present invention thus minimizes the impact of bad estimates of the time reference parameters according to which the on-demand (personalized) components must be sent to the terminal in order to be synchronized with the main component. In this method, even if the frames of the component delivered via broadband arrive after the moment when the broadcast content frames to be presented simultaneously are presented, they are processed. The method is based on the fact that the delivery frame rate of the broadband component is higher than the presentation frame rate, so that, at a given moment, a part of the broadband component whose system clock reference coincides with the system clock reference of the broadcast component can be presented simultaneously with the corresponding part of the broadcast component.

The method of the present invention disregards the typical behavior of video decoders, in which frames are decoded at a cadence given by decoding timestamps and decoded frames are systematically presented. The method decodes the first frame of a group of pictures of the late-arriving wideband component as quickly as possible, but does not present it. Therefore, these frames are simply not presented. However, because decoding of non-key frames requires reference to one or more preceding or following frames, the decoded but not presented frames are used to decode the remaining frames of the group of pictures that are presented on time.

A method of the present invention is for decoding second program content received via a broadband network, wherein presentation of the program content is synchronized with presentation of first program content. The method comprises the following steps: decoding the first program content with respect to a program clock reference; decoding second program content with respect to the program clock reference, wherein the second program content includes a second consecutive frame associated with decoding time information and presentation time information. The method further comprises the following steps: decoding a second frame of the second program content when the decoding time information is later than the program clock reference; and presenting the decoded second frame when the presentation time information enables presentation of the second frame to be synchronized with presentation of the first program content.

According to an embodiment of the invention, the step of decoding the second frames comprises the steps of reading a decoding timestamp associated with one of the second frames, and decoding the second frame based on a comparison between the decoding timestamp and a program clock reference.

According to an embodiment of the invention, the step of presenting the decoded second frame comprises the steps of reading a presentation timestamp associated with a second frame and presenting the second frame based on a comparison between the presentation timestamp and a program clock reference.

According to an embodiment of the present invention, the first program content includes: consecutive first frames associated with decoding time information and presentation time information.

According to an embodiment of the present invention, the decoding time information includes a decoding timestamp.

According to an embodiment of the present invention, the presentation time information includes a presentation stamp.

According to an embodiment of the present invention, first program content is received from a broadcast network by a first decoder device, and second program content is received from a broadband network by a second decoder device.

The present invention also concerns a decoder apparatus comprising: decoding means for decoding program content received from a broadband network with respect to a program clock reference, the program content comprising consecutive frames associated with decoding time information and presentation time information. The decoding means of the decoder apparatus is adapted to decode the frames when the decoding time information is inferior to the program clock reference, and the decoding means further comprises means for presenting the decoded frames when the presentation time information is superior to or equal to the program clock reference.

According to an embodiment of the present invention, the decoder device further comprises: a filtering module adapted to parse the decoding time information and the presentation time information, for filtering the frame according to a comparison result between the decoding time information and the presentation information and the program clock reference respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and illustrated by means of the following embodiments and execution examples, with reference to the accompanying drawings, in which:

Figure 1 illustrates delivery over a broadband network;

FIG2 is a block diagram of a system according to a first embodiment of the present invention;

FIG3 is a block diagram of a receiver/decoder according to a first embodiment of the present invention;

FIG4 illustrates a first situation of accelerated decoding according to the first embodiment of the present invention;

FIG5 illustrates a second situation of accelerated decoding according to the first embodiment of the present invention;

FIG6 is a diagram describing a decoding method according to a first embodiment of the present invention;

FIG7 is a block diagram of a receiver/decoder according to a second embodiment of the present invention.

In Figures 2, 3 and 7, the blocks represented are purely functional entities, which do not necessarily correspond to physically separate entities, i.e. they can be developed in the form of hardware or software, or implemented in one or several integrated circuits.

DETAILED DESCRIPTION

It is understood that the drawings and description of the present invention have been simplified to illustrate relevant elements for a clear understanding of the present invention and, for the sake of brevity, to eliminate many other elements found in typical digital multimedia content delivery methods and systems. However, because such elements are known in the art, a detailed discussion of such elements is not provided herein. The disclosure herein is intended to encompass all such variations and modifications known to those skilled in the art.

Figure 2 illustrates a network architecture according to a first embodiment of the present invention. The broadcast timing is taken into account as a reference and the broadband network is adapted for synchronization. A video source 1 delivers a non-encoded main component program to an encoder 2. Encoder 2 encodes the main component and sends it to a transmitter 3. Broadcasting the main component by transmitter 3 can be done synchronously with the encoding by encoder 2 but can also be done later than the encoding by encoder 2. The main component is broadcast over the air to a receiver/decoder 6. Encoder 2 also provides an encoded personalized component program to an on-demand server 4. The personalized component is synchronized with the main component. Encoder 2 can provide the personalized component during encoding, but the personalized component can also be already available on the on-demand server 4. It can be available in a database of personalized components related to the main component to be broadcast. Time reference information of the two components (such as decoding timestamps, presentation timestamps and program clock reference) is synchronized by encoder 2. The way in which the timing formats and/or references are aligned by encoder 2 is not within the scope.

Upon initial request from a user, receiver/decoder 6 requests the personalized component from on-demand server 4 via broadband network 5. On-demand server 4 then delivers the personalized component to receiver/decoder 6 via the broadband network. Receiver/decoder 6 processes the accelerated decoding phase of the personalized component to synchronize its presentation with the presentation of the main component broadcast by transmitter 3. Both components are presented in a synchronized manner and output by receiver/decoder 6 for display on display device 7.

According to an embodiment of the present invention, the synchronization of the personalized component and the main component is defined as common to those skilled in the art. In other words, if both the main component and the personalized component are video contents, the synchronization corresponds, for example, to the fact that the presentation of the personalized component processes a GOP comprising a presentation time reference (for defining the presentation time) which is close to the presentation time reference comprised in the GOP processed for presenting the main component. The two video components can, for example, be considered to be synchronized with respect to presentation if both GOPs, respectively belonging to the first and second video contents, are presented at least partially within a time range of a few seconds or less. With regard to the synchronization of the audio and video components, the synchronization is based on the already well-known "lip sync" synchronization, in which the audio stream comprising the sound work should be synchronized with the movements of the lips of the person who is speaking (or singing). The goal of "lip sync" is to have a match between the lip movements and the sung or spoken sound work.

FIG3 illustrates a receiver/decoder 6 according to a first embodiment of the present invention. The decoder has two input interfaces. A first input interface 601 is connected to receive a broadcast main component. A second input interface 602 is connected to receive a personalized component delivered via a broadband network. Both components are transmitted as consecutive packets identified by program identifiers and containing a number of consecutive groups of pictures (GOPs). The broadcast input interface 601 and the broadband input interface 602 demultiplex the content they receive and store the data corresponding to each component in dedicated buffer areas in a receive buffer 603. Each GOP begins with the first frame of a so-called key frame, which is associated with a decoding timestamp (DTS) and a presentation timestamp (PTS). A first frame decoder 607 performs normal decoding by reading packets of the main component from the receive buffer 603. When a key frame received as a packet from the broadcast input interface 601 has a decoding timestamp equal to the current program clock reference (PCR), the first frame decoder 607 decodes the frame and stores the corresponding decoded frame in a frame buffer 604. When the presentation timestamp of the key frame equals the PCR value, the first frame decoder 607 also reads the frame in the frame buffer 604 and transmits the key frame in the display buffer 605. The display output interface 606 reads the contents of the display buffer and outputs the frame to a connected display device (not shown). The decoding and transmission process in the display buffer is the same for consecutive frames of the current GOP from the broadcast input interface until the next key frame is read in the receive buffer 603 by the first frame decoder 607. The first frame decoder 607 implements the decoding and display of the broadcasted main component by starting to decode a group of pictures when the DTS of the key frame of the GOP equals the PCR value, and by starting to display the decoded frame in the display buffer 605 when the PTS of the key frame equals the PCR value.

The second frame decoder 608 decodes the personalized component received via the broadband input interface 602 by decoding all corresponding frames read from the receive buffer 603 until the DTS of a key frame is greater than or equal to the current PCR value. This is the case for late-arriving GOPs from the broadband input interface 602, which are to be presented synchronously with the corresponding broadcast content received from the broadcast input interface 601. The second frame decoder 608 decodes frames from the receive buffer 603 even if the associated DTS is less than the current PCR value. The decoded frames are stored in the frame buffer 604. When the corresponding PTS equals the current PCR value, the second frame decoder 608 also reads the decoded frame corresponding to the personalized component from the frame buffer 604 and transfers the decoded frame to the display buffer 605. If the associated PTS of a frame of the personalized component is less than the current PTS, the frame is not copied to the display buffer. The second frame decoder 608 operates in an accelerated decoding phase when the DTS information is less than the PCR value, and operates in normal decoding once the DTS value equals or exceeds the PCR value.

FIG4 illustrates an accelerated decoding process according to a first embodiment of the present invention. The figure illustrates a scenario in which the first frame of a personalized component received over a broadband network is too late to be decoded and synchronized with the main component at the normal decoding rate. Synchronous presentation of the two components can therefore be achieved by using an accelerated decoding phase that disregards the DTS value. This scenario depends on network latency. The figure shows that the buffer for the broadband content (personalized component) in the first step fills faster before being transmitted at the cruise rate in the second step, because the broadband network can transmit at a higher rate than the decoding and presentation rate (burst mode). The broadband buffer filling begins at the BTS1 time when the first data of the personalized content is received. When the buffer contains sufficient data (e.g., considering the transmission bit rate as defined by the MPEG compression standard), the accelerated decoding phase begins at the DTS1 time. During accelerated decoding, a frame can be decoded even if its corresponding DTS information is less than the PCR value. The decoding rate is then higher than in the normal mode, when the decoder waits for a PCR value equal to the DTS value to begin decoding the frame. In the illustrated case, because the broadband content is not too late to be presented in a synchronized manner with the broadcast content (primary component), accelerated decoding allows for some decoded pictures from the broadband content with PTS values greater than or equal to the PCR value. No decoded frames are discarded for presentation. When the accelerated decoding phase allows for some pictures with DTS information equal to or greater than the PCR value to be stored in the receive buffer, the accelerated decoding phase ends and decoding continues at the normal rate.

Figure 5 illustrates the scenario of accelerated decoding according to the first embodiment of the present invention with broadband network latency greater than that shown in Figure 4 . The broadband network latency is so long that incoming frames are too late to be decoded and too late to be presented at the start of decoding. The first frame to be decoded from the broadband network is stored in the receive buffer at time BTS1. The buffer fills faster than the content received from the broadcast network due to the broadband network's burst capacity. When sufficient data is available in the receive buffer (e.g., depending on the bit rate according to the compression standard), the accelerated decoding phase begins at time DTS1, but the decoded frame is too late to be presented synchronously with the broadcast content. The decoded frame is discarded and not presented, and only the decoded frame from the broadcast content is presented. During the accelerated decoding period, at time DTSn, the decoded frame of the broadcast content has an associated PTS value that matches the PCR value. This allows the presentation of the broadband and broadcast content to be synchronized. Finally, at time DTSi, the incoming frame from the broadband network has an associated DTS value that is decoded in time according to the normal decoding process. The accelerated decoding phase is completed, and decoding continues at the normal rate.

FIG6 illustrates a method for decoding by a second frame decoder including an accelerated decoding phase. The second frame decoder is responsible for decoding and presenting the personalized component received from the broadband network. Assuming that at step S1, which is the beginning of the decoding process of the second frame decoder, the first frame received in the receive buffer is a key frame associated with a decoding timestamp and a presentation timestamp.

In step S2, the second frame decoder reads a frame and determines in step S3 whether it is a key frame. If it is not a key frame, the decoding process continues with the next frame without considering any decoding timestamp value associated with the previous key frame. Therefore, the process proceeds to step S6. This situation corresponds to a picture in a GOP that is not a key frame. In step S4, the second frame decoder reads the PTS and DTS information associated with the key frame. In step S5, the second frame decoder compares the DTS value with the PCR value. If the DTS value is less than the current PCR value, the frame is read too late to be decoded in time. Therefore, in step S6, the frame is immediately decoded so that it is available in the decoded frame buffer for decoding the next frame. In step S5, if the frame is not too late, when the DTS value is greater than the PCR value, the process loops through step S5 until the PCR value is greater than or equal to the DTS. This is the case in normal decoding mode (without acceleration). In step S7, the second frame decoder compares the PTS value with the PCR value to determine whether the frame must be displayed or discarded. If the PTS value is less than the PCR value, the decoded frame is too late to be presented in a manner synchronized with the main component. The process loops back to step S2. If the PTS is greater than or equal to the PCR value, then the frame is not too late and must be presented in time with the PCR. The process loops at step S8 until the PCR is greater than or equal to the PTS. When this condition is met, at step S9, the second frame decoder copies the frame from the decoded frame buffer to the display buffer for presentation. The process then loops at step S2.

The decoding method used by the second frame decoder is then a method for decoding second program content received via a broadband network, the presentation of the second program content being synchronized with the presentation of first program content, the first program content being received via a broadcast network. The method comprises the following steps: decoding the first program content with respect to a program clock reference, decoding the second program content with respect to the program clock reference, the second program content comprising a second consecutive frame associated with decoding time information and presentation time information. The method is characterized in that it further comprises the following steps: decoding the second frame (S4, S5, S6) when the decoding time information is later than the program clock reference, and presenting the decoded second frame (S8, S9) when the presentation time information allows the presentation of the second frame to be synchronized with the presentation of the first program content.

According to a variant of the embodiment, decoding and presentation of the main component and the personalized component are achieved by two separate devices. Each of the two devices includes means for receiving, decoding and presenting the associated component. The device for decoding the personalized component uses non-traditional decoding that allows decoding of program content received from a broadband network with respect to a program clock reference and the program content includes consecutive frames associated with decoding time information and presentation time information. The decoding means of the device for decoding the personalized component are adapted to decode frames when the decoding time information is inferior to the program clock reference and include means for presenting decoded frames when the corresponding presentation time information is superior to or equal to the program clock reference.

In this case, both devices include means for exchanging information about the decoding and presentation of the current program being received and presented. Specifically, the device decoding the personalized component must know which portion of the main component is currently being decoded and presented in order to select/request the corresponding segment of the personalized component from the remote server. The information sent by the device receiving and decoding the main component to the device receiving and decoding the personalized component is, for example, a time index within the program, a program clock reference value for presentation, or any other value that allows identification of the current portion of the main component currently being decoded and presented.

Such an apparatus may comprise a filtering module adapted to parse the decoding time information and the presentation time information in order to filter the frames based on a comparison between the decoding time information and the presentation information compared to a program clock reference.

The device for decoding the personalized component according to this variant of the embodiment is for example an internet tablet connected to a home gateway, allowing the user to watch views of a multi-view program, the main view being broadcast and presented on another device such as for example a terrestrial digital television set.

FIG7 illustrates a receiver/decoder 6 according to a second embodiment of the invention. The personalized component (coming from the broadband network) consists of a series of blocks containing a number of groups of pictures. The filtering module 609 filters the block content received on the broadband input interface 602 by reading certain time reference information within the blocks and/or groups of pictures. The filtering module 609 compares the time information in the received content with the program time reference used by the receiver/decoder 6 for decoding and presentation. If the filtering module detects that a block or GOP is too late to synchronize the presentation of its content with the presentation of the received broadcast content, the GOP or block is not sent to the receive buffer. This prevents the second frame decoder 608 from decoding content present in the receive buffer 603 that cannot be synchronized with the broadcast content. This filtering makes it possible to present both components earlier.

According to a third embodiment of the present invention, the personalized component received via a bidirectional broadband network is audio content comprising consecutive blocks of audio samples. Each block of audio samples includes time reference information for its decoding and presentation. A filtering module of a receiver/decoder filter parses the time information and transmits the block to a receive buffer only if the time reference information indicates that the sample can be decoded in time for presentation in synchronization with the main component.

Obviously, the present invention is not limited to main components and personalized components including video or audio carried as successive groups of pictures or blocks. The present invention concerns all synchronized program content including time reference information that can be compared with a program clock reference (system clock) required for decoding and presentation of the program content in a receiver.

References disclosed in the specification, claims and drawings may be provided independently or in any appropriate manner.Where appropriate, features may be implemented in hardware, software or a combination of both.

Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments.

Claims (10)

1. A method for decoding program content received from a broadband network, the presentation of said program content being synchronized with the presentation of another program content received from a broadcast network for the synchronized presentation of the two programs, said other program content being decoded with respect to a program clock reference, said program content comprising consecutive frames associated with display time information, said consecutive frames being included in a group of frames of said program content, the method comprising: - When the decoding timing information associated with a keyframe in the consecutive frames of the received program content is lower than the program clock reference, the keyframe is decoded, and Frames in a group containing the decoded keyframes are decoded by using the decoded keyframes. 2. The method as described in claim 1, wherein the method comprises: When the associated display time information is greater than or equal to the program clock reference, the frames of the decoded group are presented. 3. The method of claim 1, wherein the other program content comprises consecutive frames associated with display time information. 4. The method as described in claim 1, wherein the decoding time information includes a decoding timestamp. 5. The method as described in claim 1, wherein the display time information includes a display timestamp. 6. A decoder apparatus for decoding program content received from a broadband network, the presentation of said program content being synchronized with the presentation of another program content received from a broadcast network for the synchronized presentation of the two programs, said other program content being decoded with respect to a program clock reference, said program content comprising consecutive frames associated with display time information, said consecutive frames being included in a group of frames of said program content. The decoder device is characterized in that it includes a frame decoder adapted for: - Decoding the consecutive frames, the decoding operation being performed on a key frame of the consecutive frames, the key frame of the consecutive frames being associated with decoding time information following the program clock reference, the key frame being the beginning of a group of frames of the program content, the key frame being adapted to be decoded without reference to previous frames. Frames in a group containing the decoded keyframes are decoded by using the decoded keyframes. 7. The decoder device as claimed in claim 6, characterized in that, The frame decoder is adapted to decode frames in a group of frames when the decoding time information of the key frame of the group that begins the frame is later than the program clock reference. The decoder device includes a presentation component for presenting frames of the decoded group when the display time information of the frames of the decoded group is greater than or equal to the program clock reference. 8. The decoder device as claimed in claim 7, characterized in that it comprises: A filtering module (609) is adapted to parse the decoding time information and the display time information, and to filter the consecutive frames based on a comparison result between the decoding time information and the display time information and a program clock reference. 9. The decoder device as claimed in claim 6, characterized in that it comprises: A broadcast input interface, adapted for receiving the other program content from the broadcast network; and Another frame decoder, adapted for decoding the other program content with respect to the program clock reference. 10. The decoder apparatus of claim 9, wherein the other program content comprises consecutive frames associated with display time information.