Coding concept allowing parallel processing, transport demultiplexer and video bitstream
A raw byte sequence payload describing a picture in slices, WPP substreams or tiles and coded using context-adaptive binary arithmetic coding is subdivided into tranches with continuing the context-adaptive binary arithmetic coding probability adaptation across tranche boundaries. Thereby, tranche boundaries additionally introduced within slices, WPP substreams or tiles do not lead to a reduction in the entropy coding efficiency of these entities. However, the tranches are smaller than the original slices, WPP substreams or tiles and accordingly they may be transmitted earlier, i.e. with lower delay, than the un-chopped original entities. According to another aspect combinable with the first aspect, substream marker NAL units are used within a sequence of NAL units of a video bitstream to enable a transport demultiplexer to assign data of slices within NAL units to the corresponding substreams or tiles so as to be able to, in parallel, serve a multi-threaded decoder with the corresponding substreams or tiles.
1. A decoder configured to decode data representing an encoded picture of a video, the decoder comprising:
an entropy decoder configured to decode data representing the encoded picture using context adaptive binary arithmetic coding (CABAC) entropy decoding to obtain a quantized representation of a residual signal associated with the picture, wherein the picture is encoded as wavefront parallel processing (WPP) substreams with each WPP substream associated with one row of the picture and is segmented into a plurality of tranches, each tranche having a header indicating a boundary of the tranche within the respective WPP substream and including a flag that affects CABAC probability adaptation in CABAC entropy decoding of the tranche within the WPP substream,
the entropy decoder being configured to entropy decode a current tranche of the plurality of tranches of a current WPP substream using CABAC entropy decoding, including (a) responsive to the current tranche starting at a beginning of the current WPP substream and the flag within the header of the current tranche having a first binary value, resetting the CABAC probability adaptation for the current tranche, and (b) responsive to the current tranche not starting at a beginning of the current WPP substream and the flag within the header of the current tranche having a second binary value, adopting CABAC probability of a previous tranche of the plurality of tranches obtained during entropy decoding of the previous tranche across a boundary associated with the previous tranche to the current tranche of the plurality of tranches;
a dequantization module to dequantize the quantized representation of the residual signal; and
a combiner to combine the dequantized residual signal and a prediction signal to reconstruct the picture.
2. The decoder according to claim 1 , wherein the plurality of tranches are packetized using slice headers, and the entropy decoder is configured to, in receiving the plurality of tranches, be responsive, upon receiving a new slice, to a flag in the slice header indicative of the new slice, a slice type of the new slice or a NAL unit type of a NAL unit comprising the new slice, such that the entropy decoder is configured to, based on the flag, either interrupt the CABAC probability adaptation by resetting CABAC probabilities or to continue the CABAC probability adaptation.
3. The decoder according to claim 1 , wherein the plurality of tranches are packetized into packets in manner so that each packet comprises one tranche of each WPP substream of the picture arranged in an order defined among the WPP substreams, each packet comprising a header comprising information revealing positions and/or lengths of the plurality of tranches packed into the respective packet, or markers separating the tranches within the respective packet from each other, wherein the decoder is configured to use the information comprised by the headers or the markers so as to access the tranches within the packets.
4. The decoder according to claim 3 , wherein packets comprising first, in accordance with the order defined among the WPP substreams, tranches of the WPP substreams of the picture, comprise a low delay feature indicator, and packets comprising second or subsequent, in accordance with the order defined among the WPP substreams, tranches of the WPP substreams of the picture, comprise a continuation indicator.
5. The decoder according to claim 3 , wherein the packets are NAL units.
6. The decoder according to claim 1 , wherein the CABAC probability adaptation includes adopting, in starting entropy decoding the second tranche, CABAC probabilities obtained at the end of entropy decoding the first tranche.
7. An encoder to encode a picture of a video, the encoder comprising:
a residual determiner configured to determine a residual signal associated with the picture based on a prediction signal;
a quantization module to quantize the residual signal to obtain a quantized representation of the residual signal; and
an entropy encoder configured to encode data the quantized residual signal using context adaptive binary arithmetic coding (CABAC) entropy encoding, wherein the picture is encoded as wavefront parallel processing (WPP) substreams with each WPP substream associated with one row of the picture and is segmented into a plurality of tranches, each tranche having a header indicating a boundary of the tranche within the respective WPP substream and including a flag that affects CABAC probability adaptation in CABAC entropy decoding of the tranche within the WPP substream,
the entropy encoder being configured to entropy encode a current tranche of the plurality of tranches of a current WPP substream using CABAC entropy encoding, including (a) responsive to the current tranche starting at a beginning of the current WPP substream and the flag within the header of the current tranche having a first binary value, resetting the CABAC probability adaptation for the current tranche, and (b) responsive to the current tranche not starting at a beginning of the current WPP substream and the flag within the header of the current tranche having a second binary value, adopting CABAC probability of a previous tranche of the plurality of tranches obtained during entropy encoding of the previous tranche across a boundary associated with the previous tranche to the current tranche of the plurality of tranches.
8. The encoder according to claim 7 , wherein the plurality of tranches are packetized using slice headers, and the entropy encoder is configured to, in encoding the plurality of tranches, be responsive, upon receiving a new slice, to a flag in the slice header indicative of the new slice, a slice type of the new slice or a NAL unit type of a NAL unit comprising the new slice, such that the entropy encoder is configured to, based on the flag, either interrupt the CABAC probability adaptation by resetting CABAC probabilities or to continue the CABAC probability adaptation.
9. The encoder according to claim 7 , wherein the plurality of tranches are packetized into packets in manner so that each packet comprises one tranche of each WPP substream of the picture arranged in an order defined among the WPP substreams, each packet comprising a header comprising information revealing positions and/or lengths of the plurality of tranches packed into the respective packet, or markers separating the tranches within the respective packet from each other, wherein the encoder is configured to use the information comprised by the headers or the markers so as to access the tranches within the packets.
10. The encoder according to claim 9 , wherein packets comprising first, in accordance with the order defined among the WPP substreams, tranches of the WPP substreams of the picture, comprise a low delay feature indicator, and packets comprising second or subsequent, in accordance with the order defined among the WPP substreams, tranches of the WPP substreams of the picture, comprise a continuation indicator.
11. The encoder according to claim 9 , wherein the packets are NAL units.
12. The encoder according to claim 7 , wherein the CABAC probability adaptation includes adopting, in starting entropy encoding the second tranche, CABAC probabilities obtained at the end of entropy encoding the first tranche.
13. A non-transitory computer-readable medium for storing information related to an encoded picture of a video, comprising instructions, which when executed by a processor, causes generation of:
a data stream stored in the non-transitory computer-readable medium, the data stream comprising encoded information related to a quantized representation of a residual signal associated with a picture of a video, wherein the residual signal is determined based on a prediction signal, and is entropy-decoded using context adaptive binary arithmetic coding (CABAC) entropy decoding, wherein the picture is encoded as wavefront parallel processing (WPP) substreams with each WPP substream associated with one row of the picture and is segmented into a plurality of tranches, each tranche having a header indicating a boundary of the tranche within the respective WPP substream and including a flag that affects CABAC probability adaptation in CABAC entropy decoding of the tranche within the WPP substream,
the plurality of tranches are entropy decoded using CABAC entropy decoding, entropy decoding a current tranche of the plurality of tranches of a current WPP substream includes (a) responsive to the current tranche starting at a beginning of the current WPP substream and the flag within the header of the current tranche having a first binary value, resetting the CABAC probability adaptation for the current tranche, and (b) responsive to the current tranche not starting at a beginning of the current WPP substream and the flag within the header of the current tranche having a second binary value, adopting CABAC probability of a previous tranche of the plurality of tranches obtained during entropy decoding of the previous tranche across a boundary associated with the previous tranche to the current tranche of the plurality of tranches, and the quantized representation of the residual signal is dequantized.
14. The non-transitory computer-readable medium according to claim 13 , wherein the CABAC probability adaptation includes adopting, in starting entropy encoding the second tranche, CABAC probabilities obtained at the end of entropy encoding the first tranche.