Sample array coding for low-delay
The entropy coding of a current part of a predetermined entropy slice is based on, not only, the respective probability estimations of the predetermined entropy slice as adapted using the previously coded part of the predetermined entropy slice, but also probability estimations as used in the entropy coding of a spatially neighboring, in entropy slice order preceding entropy slice at a neighboring part thereof. Thereby, the probability estimations used in entropy coding are adapted to the actual symbol statistics more closely, thereby lowering the coding efficiency decrease normally caused by lower-delay concepts. Temporal interrelationships are exploited additionally or alternatively.
1. A decoder for reconstructing a sample array of a video from an entropy-encoded data stream, the decoder comprising:
an entropy decoder configured to entropy decode a plurality of entropy slices in the entropy-encoded data stream to reconstruct the sample array, the plurality of entropy slices corresponding to a plurality of rows of the sample array,
wherein, for a current entropy slice of the plurality of entropy slices, the entropy decoder is configured to:
initialize, during a starting phase of entropy decoding, a first probability estimate for the current entropy slice before decoding a first block of a current row corresponding to the current entropy slice based on a second probability estimate obtained after completing entropy decoding of a previously-decoded block of a previous row corresponding to a previous entropy slice of the plurality of entropy slices,
wherein the first block is the left-most block of the current row and the previously-decoded block is neighboring the first block, and the current and previous rows are consecutive rows of the sample array, and
perform, during a continuation phase of the entropy decoding, entropy decoding using the first probability estimate along an entropy coding path leading from left to right across the current row, the entropy decoding is performed by adapting the first probability estimate along the entropy coding path using only a previously-decoded part of the current entropy slice.
2. The decoder according to claim 1 , wherein the entropy decoder is configured to entropy-decode the plurality of entropy slices in an order, the order is chosen such that, along the order, the plurality of rows follow each other in a direction angled relative to the entropy coding paths of the entropy slices.
3. The decoder according to claim 1 , wherein the entropy decoder is configured to store the second probability estimate after the previously-decoded block is entropy-decoded, and use the stored second probability estimate for initializing the first probability estimate.
4. The decoder according to claim 1 , wherein the entropy decoder is configured to, in entropy decoding a current part of the current entropy slice, adapt, during the continuation phase of the entropy decoding, the first probability estimate based on a third probability estimate obtained after decoding a portion of the previous entropy slice.
5. The decoder according to claim 1 , wherein the previous row is spatially above the current row, and the entropy decoding of the previous entropy slice begins before the entropy decoding of the current entropy slice.
6. The decoder according to claim 1 , wherein the sample array is a current sample array of a sequence of sample arrays and the entropy decoder is configured to entropy-decode a current entropy slice based on the first probability estimate as adapted using the second probability estimate, the previously-decoded part of the current entropy slice, and a fourth probability estimate used in entropy decoding a previously-decoded frame corresponding to one of the sample arrays other than the current sample array.
7. The decoder according to claim 1 , wherein the decoder is at least a portion of a programmable logic device, programmable gate array, microprocessor, computer or hardware apparatus.
8. A method for reconstructing a sample array from an entropy-encoded data stream coded with the video, the method comprising:
entropy decoding a plurality of entropy slices in the entropy-encoded data stream to reconstruct the sample array, the plurality of entropy slices corresponding to a plurality of rows of the sample array;
for a current entropy slice of the plurality of entropy slices, initializing, during a starting phase of the entropy decoding, a first probability estimate for the current entropy slice before decoding a first block of a current row corresponding to the current entropy slice based on a second probability estimate obtained after completing entropy decoding of a previously-decoded block of a previous row corresponding to a previous entropy slice of the plurality of entropy slices,
wherein the first block is the left-most block of the current row and the previously-decoded block is neighboring the first block, and the current and previous rows are consecutive rows of the sample array; and
the entropy decoding is performed, during a continuation phase of the entropy decoding, using the first probability estimate along an entropy coding path leading from left to right across the current row, the entropy decoding including: adapting the first probability estimate along the entropy coding path using only a previously-decoded part of the current entropy slice.
9. The method according to claim 8 , wherein the entropy decoding of the plurality of entropy slices is performed in an order, wherein the order is chosen such that, along the order, the plurality of rows follow each other in a direction angled relative to the entropy coding paths of the entropy slices.
10. The method according to claim 8 , further comprising storing the second probability estimate after the previously-decoded block is entropy-decoded; and using the stored second probability estimate for initializing the first probability estimate.
11. The method according to claim 8 , further comprising, in entropy decoding a current part of the current entropy slice, adapting the first probability estimate based on a third probability estimate obtained after decoding a portion of the previous entropy slice.
12. The method according to claim 8 , wherein the previous row is spatially above the current row, and the entropy decoding of the previous entropy slice begins before the entropy decoding of the current entropy slice.
13. The method according to claim 8 , wherein the sample array is a current sample array of a sequence of sample arrays and the method comprises entropy decoding a current entropy slice based on the first probability estimate as adapted using the second probability estimate, the previously-decoded part of the current entropy slice, and a fourth probability estimate used in entropy decoding a previously-decoded frame corresponding to one of the sample arrays other than the current sample array.
14. A method for encoding a sample array into an entropy-encoded data stream coded with a video, the method comprising:
entropy encoding a plurality of entropy slices into the entropy-encoded data stream, the plurality of entropy slices corresponding to a plurality of rows of the sample array;
for a current entropy slice of the plurality of entropy slices, initializing, during a starting phase of the entropy encoding, a first probability estimate for the current entropy slice before decoding a first block of a current row corresponding to the current entropy slice based on a second probability estimate obtained after completing entropy encoding of a previously-encoded block of a previous row corresponding to a previous entropy slice of the plurality of entropy slices,
wherein the first block is the left-most block of the current row and the previously-encoded block is neighboring the first block, and the current and previous rows are consecutive rows of the sample array; and
the entropy encoding is performed, during a continuation phase of the entropy encoding, using the first probability estimate along an entropy coding path leading from left to right across the current row, the entropy encoding including adapting the first probability estimate along the entropy coding path using only a previously-encoded part of the current entropy slice.
15. The method according to claim 14 , wherein the entropy encoding of the plurality of entropy slices is performed in an order, the entropy slice order is chosen such that, along the entropy slice order, the different portions follow each other in a direction angled relative to the entropy coding paths of the entropy slices.
16. The method according to claim 14 , further comprising storing the second probability estimate after the previously-encoded block is entropy-encoded, wherein the stored second probability estimate is used for initializing the first probability estimate.
17. The method according to claim 14 , further comprising, in entropy encoding a current part of the current entropy slice, adapting the first probability estimate based on a third probability estimate obtained after encoding a portion of the previous entropy slice.
18. The method according to claim 14 , wherein the previous row is spatially above the current row, and the entropy encoding of the previous entropy slice begins before the entropy encoding of the current entropy slice.
19. The method according to claim 14 , wherein the sample array is a current sample array of a sequence of sample arrays and the method comprises entropy encoding a current entropy slice based on the first probability estimate as adapted using the second probability estimate, the previously-encoded part of the current entropy slice, and a fourth probability estimate used in entropy encoding a previously-encoded frame corresponding to one of the sample arrays other than the current sample array.