Sub-picture motion vectors in video coding
A video coding mechanism includes receiving a bitstream comprising a current picture including a sub-picture coded according to inter-prediction. Coded blocks contain candidate motion vectors for a current block of the sub-picture. The coded blocks include a collocated block from a different picture. A candidate list of candidate motion vectors for the current block are derived by excluding collocated motion vectors from the candidate list when the collocated motion vectors are included in the collocated block, when the collocated motion vectors point outside of the sub-picture, and when a flag is set to indicate the sub-picture is treated as a picture. A current motion vector for the current block is determined from the candidate list of candidate motion vectors. The current block is decoded based on the current motion vector. The current block is forwarded for display as part of a decoded video sequence.
1. A method implemented by an encoder, the method comprising:
determining to encode a current block of a sub-picture of a current picture;
deriving a candidate list of candidate motion vectors for the current block based on candidate motion vectors for the current block without adding a collocated motion vector associated with a collocated block from a different picture than the current picture, when the collocated block, from a different picture than the current picture, is located outside the sub-picture, and when a flag indicates the sub-picture is treated as a picture;
determining a current motion vector for the current block from the candidate list of candidate motion vectors; and
encoding the current block into a bitstream based on the current motion vector.
2. The method of claim 1 , further comprising encoding the flag into a sequence parameter set (SPS), wherein the flag is denoted as a subpic_treated_as_pic_flag[i], and wherein i is an index of the sub-picture.
3. The method of claim 2 , wherein the subpic_treated_as_pic_flag[i] is set equal to one to specify that an i-th sub-picture of each coded picture in a coded video sequence (CVS) is treated as a picture in a decoding process excluding in-loop filtering operations.
4. The method of claim 1 , wherein deriving the candidate list of candidate motion vectors for the current block is performed according to temporal luma motion vector prediction.
5. The method of claim 4 , wherein the temporal luma motion vector prediction is performed according to:
xColBr=xCb+cbWidth;
yColBr=yCb+cbHeight;
rightBoundaryPos=subpic_treated_as_pic_flag[SubPicIdx]? SubPicRightBoundaryPos: pic_width_in_luma_samples−1; and
botBoundaryPos=subpic_treated_as_pic_flag[SubPicIdx]? SubPicBotBoundaryPos: pic_height_in_luma_samples−1,
where xColBr and yColBR specify a location of the collocated block, xCb and yCb specify a top left sample of the current block relative to a top left sample of the current picture, cbWidth is a width of the current block, cbHeight is a height of the current block, SubPicRightBoundaryPos is a position of a right boundary of the sub-picture, SubPicBotBoundaryPos is a position of a bottom boundary of the sub-picture, pic_width_in_luma_samples is a width of the current picture measured in luma samples, pic_height_in_luma_samples is a height of the current picture measured in luma samples, botBoundaryPos is a computed position of the bottom boundary of the sub-picture, rightBoundaryPos is a computed position of the right boundary of the sub-picture, SubPicIdx is an index of the sub-picture, and wherein collocated motion vectors are excluded when yColBR is greater than botBoundaryPos or xColBr is greater than rightBoundaryPos.
6. The method of claim 1 , wherein the current block is a luma block of luma samples.
7. The method of claim 1 , wherein the current motion vector is a temporal luma motion vector pointing to reference luma samples in a reference block, and wherein the current block is decoded based on the reference luma samples.
8. An encoder comprising:
a processor configured to:
determine to encode a current block of a sub-picture of a current picture;
derive a candidate list of candidate motion vectors for the current block based on candidate motion vectors for the current block without adding a collocated motion vector associated with a collocated block from a different picture than the current picture, when the collocated block, from a different picture than the current picture, is located outside the sub-picture, and when a flag indicates the sub-picture is treated as a picture; and
determine a current motion vector for the current block from the candidate list of candidate motion vectors; and
a memory coupled to the processor and configured to store a bitstream containing an encoding of the current block based on the current motion vector.
9. The encoder of claim 8 , wherein the processor is further configured to encode the flag into a sequence parameter set (SPS), wherein the flag is denoted as a subpic_treated_as_pic_flag[i], and wherein i is an index of the sub-picture.
10. The encoder of claim 9 , wherein the subpic_treated_as pic_flag[i] is set equal to one to specify that an i-th sub-picture of each coded picture in a coded video sequence (CVS) is treated as a picture in a decoding process excluding in-loop filtering operations.
11. The encoder of claim 8 , wherein deriving the candidate list of candidate motion vectors for the current block is performed according to temporal luma motion vector prediction.
12. The encoder of claim 11 , wherein the temporal luma motion vector prediction is performed according to:
xColBr=xCb+cbWidth;
yColBr=yCb+cbHeight;
rightBoundaryPos=subpic_treated_as_pic_flag[SubPicIdx]? SubPicRightBoundaryPos: pic_width_in_luma_samples−1; and
botBoundaryPos=subpic_treated_as_pic_flag[SubPicIdx]? SubPicBotBoundaryPos: pic_height_in_luma_samples−1,
where xColBr and yColBR specify a location of the collocated block, xCb and yCb specify a top left sample of the current block relative to a top left sample of the current picture, cbWidth is a width of the current block, cbHeight is a height of the current block, SubPicRightBoundaryPos is a position of a right boundary of the sub-picture, SubPicBotBoundaryPos is a position of a bottom boundary of the sub-picture, pic_width_in_luma_samples is a width of the current picture measured in luma samples, pic_height_in_luma samples is a height of the current picture measured in luma samples, botBoundaryPos is a computed position of the bottom boundary of the sub-picture, rightBoundaryPos is a computed position of the right boundary of the sub-picture, SubPicIdx is an index of the sub-picture, and wherein collocated motion vectors are excluded when yColBR is greater than botBoundaryPos or xColBr is greater than rightBoundaryPos.
13. The encoder of claim 8 , wherein the current block is a luma block of luma samples.
14. The encoder of claim 13 , wherein the current motion vector is a temporal luma motion vector pointing to reference luma samples in a reference block, and wherein the current block is decoded based on the reference luma samples.
15. A non-transitory storage medium storing an encoded bitstream for video signals,
wherein the bitstream comprises a current block of a sub-picture of a current picture,
wherein the encoded bitstream further comprises a syntax element indicating a motion vector based on a candidate list of candidate motion vectors,
wherein the candidate list of candidate motion vectors for the current block is derived based on candidate motion vectors for the current block without adding a collocated motion vector associated with a collocated block from a different picture than the current picture, when the collocated block, from a different picture than the current picture, is located outside the sub-picture, and when a flag indicates the sub-picture is treated as a picture.
16. The non-transitory storage medium of claim 15 , wherein the bitstream further comprises the flag in a sequence parameter set (SPS), wherein the flag is denoted as a subpic_treated_as_pic_flag[i], and wherein i is an index of the sub-picture.
17. The non-transitory storage medium of claim 16 , wherein the subpic_treated_as_pic_flag[i] is set equal to one to specify that an i-th sub-picture of each coded picture in a coded video sequence (CVS) is treated as a picture in a decoding process excluding in-loop filtering operations.
18. The non-transitory storage medium of claim 15 , wherein deriving the candidate list of candidate motion vectors for the current block is performed according to temporal luma motion vector prediction.
19. The non-transitory storage medium of claim 18 , wherein the temporal luma motion vector prediction is performed according to:
xColBr=xCb+cbWidth;
yColBr=yCb+cbHeight;
rightBoundaryPos=subpic_treated_as_pic_flag[SubPicIdx]? SubPicRightBoundaryPos: pic_width_in_luma_samples−1; and
botBoundaryPos=subpic_treated_as_pic_flag[SubPicIdx]? SubPicBotBoundaryPos: pic_height_in_luma_samples−1,
where xColBr and yColBR specify a location of the collocated block, xCb and yCb specify a top left sample of the current block relative to a top left sample of the current picture, cbWidth is a width of the current block, cbHeight is a height of the current block, SubPicRightBoundaryPos is a position of a right boundary of the sub-picture, SubPicBotBoundaryPos is a position of a bottom boundary of the sub-picture, pic_width_in_luma_samples is a width of the current picture measured in luma samples, pic_height_in_luma samples is a height of the current picture measured in luma samples, botBoundaryPos is a computed position of the bottom boundary of the sub-picture, rightBoundaryPos is a computed position of the right boundary of the sub-picture, SubPicIdx is an index of the sub-picture, and wherein collocated motion vectors are excluded when yColBR is greater than botBoundaryPos or xColBr is greater than rightBoundaryPos.
20. The non-transitory storage medium of claim 15 , wherein the current block is a luma block of luma samples.