Method and apparatus for decoding an enhanced video stream
A method of decoding an enhanced video stream composed of base layer video access units and enhancement layer video access units, each access unit comprising a plurality of syntax structures, includes passing the syntax structures of the base layer access units to a base layer buffer, passing syntax structures of the enhancement layer access units to an enhancement layer buffer, outputting the syntax structures passed to the base layer buffer in a predetermined sequence, outputting the syntax structures passed to the enhancement layer buffer in a predetermined sequence, and recombining the sequences of syntax structures output by the base layer buffer and the enhancement layer buffer respectively to form a complete enhanced access unit, composed of base layer syntax structures and enhancement layer syntax structures in a predetermined sequence.
1. A method of demultiplexing an enhanced video stream conveying, in a plurality of packetized elementary streams of an MPEG-2 systems layer, base layer video VCL access units and enhancement layer Video Coding Layer (VCL) and non-VCL access units, each access unit comprising a plurality of syntax structures, said method comprising:
receiving a multiplexed transport stream in the MPEG-2 systems layer, the transport stream conveying, with different respective program identifiers, a base layer transport stream comprising both the syntax structures of the base layer VCL access units and the enhancement layer non-VCL units, and an enhancement layer transport stream containing the syntax structures of said enhancement layer VCL units;
demultiplexing the transport stream using the respective program identifiers to separate the base layer transport stream from the enhancement layer transport stream;
passing the syntax structures of the base layer transport stream a base layer buffer, which syntax structures include the non-VCL syntax structures of the enhancement layer;
passing syntax structures of the enhancement layer transport stream to an enhancement layer buffer, where the syntax structures include all of the syntax structures of the VCL enhancement layer access units and none of the syntax structures of the non-VCL enhancement layer access units;
outputting the syntax structures passed to the base layer buffer in a predetermined sequence;
outputting the syntax structures passed to the enhancement layer buffer in a predetermined sequence; and
recombining the sequences of syntax structures output by the base layer buffer and the enhancement layer buffer respectively to form a complete enhanced access unit, comprising base layer syntax structures of the MPEG-2 systems layer and enhancement layer syntax structures of the MPEG-2 systems layer in a predetermined sequence.
2. A method according to claim 1 , wherein the enhanced video stream conveys a succession of enhanced access units each comprising a base layer access unit and at least one enhancement layer access units, and the method comprises separating the syntax structures of the base layer access units from the succession of enhanced access units.
3. A method according to claim 2 , wherein the step of separating the syntax structures of the base layer access units from the succession of enhanced access units includes separating non-video layer syntax structures of the enhancement layer access units from the succession.
4. A method according to claim 2 , wherein the syntax structures of an enhancement layer access unit in the succession of enhanced access units comprise video layer syntax structures, non-video layer syntax structures, and a delimiting syntax structure marking a boundary of the video layer syntax structures of the access unit, and the step of separating the syntax structures of the base layer access units from the unitary succession of access units includes passing syntax structures prior to the delimiting syntax structure to the base layer buffer and passing syntax structures after the delimiting syntax structure to the enhancement layer buffer.
5. A method according to claim 1 , wherein the base layer buffer includes an elementary stream buffer segment and the enhancement layer buffer includes an elementary stream buffer segment, and the method comprises dynamically adjusting the combined sizes of the elementary stream buffer segments to optimize decoding of the enhanced video stream while restricting the maximum size of the elementary stream buffer segment of the base layer buffer.
6. A method according to claim 1 , comprising passing the complete enhanced access unit to a video decoder.
7. A method according to claim 1 , wherein the enhancement layer access units contain syntax structures of at least first and second enhancement layers, and the step of passing syntax structures of the enhancement layer transport stream to an enhancement layer buffer includes passing syntax structures of the first and second enhancement layers to first and second enhancement layer buffers respectively.
8. A method according to claim 7 , wherein the enhanced video stream is composed of a succession of enhanced access units each comprising a base layer access unit and at least first and second enhancement layer access units, and the method comprises separating the syntax structures of the base layer access units from the succession of enhanced access units.
9. A method according to claim 8 , wherein the syntax structures of each enhancement layer access unit comprise video layer syntax structures and non-video layer syntax structures, and the step of separating the syntax structures of the base layer access units from the succession of enhanced access units includes separating non-video layer syntax structures of the first and second enhancement layer access units from the succession, whereby the syntax structures passed to the base layer buffer include enhancement layer non-video syntax structures, and wherein all the video layer syntax structures of the first and second enhancement layer access units pass to the first and second enhancement layer buffers respectively.
10. A method according to claim 8 , wherein the syntax structures of an enhancement layer access unit in the succession of enhanced access units comprise video layer syntax structures, non-video layer syntax structures, and a delimiting syntax structure marking a boundary of the video layer syntax structures of the access unit, and the step of separating the syntax structures of the base layer access units from the unitary succession of access units includes passing syntax structures prior to the delimiting syntax structure to the base layer buffer and passing syntax structures after the delimiting syntax structure to the enhancement layer buffer.
11. A method according to claim 7 , comprising receiving a multiplexed transport stream conveying the syntax structures of the base layer access units with a first program identifier, syntax structures of the first enhancement layer with a second program identifier, and syntax structures of the second enhancement layer with a third program identifier, demultiplexing the transport stream to create at least first, second and third program streams based on the first, second and third program identifiers respectively, and passing the first, second and third program streams to the base layer buffer and the first and second enhancement layer buffer respectively.
12. A method according to claim 7 , wherein the base layer buffer includes an elementary stream buffer segment and the first and second enhancement layer buffers includes a first and second elementary stream buffer segments respectively, and the method comprises dynamically adjusting the combined sizes of the elementary stream buffer segments to optimize decoding of the enhanced video stream while restricting the maximum size of the elementary stream buffer segment of the base layer buffer.
13. A method according to claim 7 , comprising passing the complete enhanced access unit to a video decoder.