Systems and methods for generalized multi-hypothesis prediction for video coding
Systems and methods are described for video coding using generalized bi-prediction. In an exemplary embodiment, to code a current block of a video in a bitstream, a first reference block is selected from a first reference picture and a second reference block is selected from a second reference picture. Each reference block is associated with a weight, where the weight may be an arbitrary weight ranging, e.g., between 0 and 1. The current block is predicted using a weighted sum of the reference blocks. The weights may be selected from among a plurality of candidate weights. Candidate weights may be signaled in the bitstream or may be derived implicitly based on a template. Candidate weights may be pruned to avoid out-of-range or substantially duplicate candidate weights. Generalized bi-prediction may additionally be used in frame rate up conversion.
1. A method of encoding a video comprising:
for at least a current block in a current picture of a video, obtaining at least a first weight from among a predetermined set of no more than five bi-prediction weights;
predicting the current block as a weighted sum of a first reference block in a first reference picture and a second reference block in a second reference picture, wherein the first reference block is weighted by the first weight and the second block is weighted by a second weight; and
encoding in a bitstream block-level information identifying at least the first weight in the set of bi-prediction weights using a truncated unary code, wherein the truncated unary code assigns a codeword to each of the weights in the predetermined set of bi-prediction weights, and wherein the predetermined set of bi-prediction weights, arranged in order of increasing codeword length, comprises a first set of weights in ascending order interleaved with a second set of weights in descending order.
2. An apparatus for decoding a video comprising a processor configured to perform at least:
for at least a current block in a current picture of a video, decoding from a bitstream block-level information identifying at least a first weight from among a predetermined set of no more than five bi-prediction weights using a truncated unary code, wherein the truncated unary code assigns a codeword to each of the weights in the predetermined set of bi-prediction weights, and wherein the predetermined set of bi-prediction weights, arranged in order of increasing codeword length, comprises a first set of weights in ascending order interleaved with a second set of weights in descending order; and
predicting the current block as a weighted sum of a first reference block in a first reference picture and a second reference block in a second reference picture, wherein the first reference block is weighted by the first weight and the second block is weighted by a second weight.
3. A method for decoding a video comprising:
for at least a current block in a current picture of a video, decoding from a bitstream block-level information identifying at least a first weight from among a predetermined set of no more than five bi-prediction weights using a truncated unary code, wherein the truncated unary code assigns a codeword to each of the weights in the predetermined set of bi-prediction weights, and wherein the predetermined set of bi-prediction weights, arranged in order of increasing codeword length, comprises a first set of weights in ascending order interleaved with a second set of weights in descending order; and
predicting the current block as a weighted sum of a first reference block in a first reference picture and a second reference block in a second reference picture, wherein the first reference block is weighted by the first weight and the second block is weighted by a second weight.
4. The method of claim 3 , wherein the second weight is derived from the first weight.
5. The method of claim 3 , wherein predicting the current block is performed using affine prediction.
6. The method of claim 3 , wherein the decoding comprises entropy decoding of a truncated unary code binarization of the first weight.
7. The method of claim 3 , further comprising:
for at least a subsequently-coded block in the current picture, decoding from the bitstream information identifying the current block as a selected merge candidate; and
predicting the subsequently-coded block with weighted bi-prediction using at least the first weight.
8. The apparatus of claim 2 , wherein the second weight is derived from the first weight.
9. The apparatus of claim 2 , wherein predicting the current block is performed using affine prediction.
10. The apparatus of claim 2 , wherein the decoding comprises entropy decoding of a truncated unary code binarization of the first weight.
11. The apparatus of claim 2 , wherein the processor is further configured to perform:
for at least a subsequently-coded block in the current picture, decoding from the bitstream information identifying the current block as a selected merge candidate; and
predicting the subsequently-coded block with weighted bi-prediction using at least the first weight.
12. The method of claim 1 , wherein predicting the current block is performed using affine prediction.
13. The method of claim 1 , wherein the encoding comprises entropy encoding of a truncated unary code binarization of the first weight.
14. An apparatus for encoding a video comprising a processor configured to perform at least:
for at least a current block in a current picture of a video, obtaining at least a first weight from among a predetermined set of no more than five bi-prediction weights;
predicting the current block as a weighted sum of a first reference block in a first reference picture and a second reference block in a second reference picture, wherein the first reference block is weighted by the first weight and the second block is weighted by a second weight; and
encoding in a bitstream block-level information identifying at least the first weight in the set of bi-prediction weights using a truncated unary code, wherein the truncated unary code assigns a codeword to each of the weights in the predetermined set of bi-prediction weights, and wherein the predetermined set of bi-prediction weights, arranged in order of increasing codeword length, comprises a first set of weights in ascending order interleaved with a second set of weights in descending order.
15. The apparatus of claim 14 , wherein predicting the current block is performed using affine prediction.
16. The apparatus of claim 14 , wherein the encoding comprises entropy encoding of a truncated unary code binarization of the first weight.
17. The method of claim 1 , wherein the predetermined set of bi-prediction weights is a set of five bi-prediction weights.
18. The apparatus of claim 2 , wherein the predetermined set of bi-prediction weights is a set of five bi-prediction weights.
19. The method of claim 3 , wherein the predetermined set of bi-prediction weights is a set of five bi-prediction weights.
20. The apparatus of claim 14 , wherein the predetermined set of bi-prediction weights is a set of five bi-prediction weights.