EFFICIENT AFFINE MERGE MOTION VECTOR DERIVATION

1 . A method of coding video data, comprising:

determining, for a conversion between a current video block of a video and a bitstream representation of the video, motion vectors at control points (CPMV) of the current video block based on a rule, wherein the rule specifies to exclude using of non-adjacent neighboring block from one or more neighboring blocks of the current video block; and

performing the conversion between the current video block and the bitstream representation based on the motion vectors.

2 . The method of claim 1 , wherein the rule further specifies to exclude using of invalid neighboring block from the one or more neighboring blocks based on positions of the one or more neighboring blocks.

3 . The method of claim 2 , wherein the current video block belongs to a current slice, and a neighboring block of the one or more neighboring blocks is invalid in a case that the neighboring block belongs to a slice different from the current slice.

4 . The method of claim 2 , wherein the current video block belongs to a current tile, and a neighboring block of the one or more neighboring blocks is invalid in a case that the neighboring block belongs to a tile different from the current tile.

5 . The method of claim 1 , wherein the current video block includes multiple sub-blocks, and performing the conversion comprising:

determining a motion vector for each sub-block of the multiple sub-blocks based on the CPMV and a specific position of the corresponding sub-block.

6 . The method of claim 5 , wherein the specific position is a center of the corresponding sub-block.

7 . The method of claim 6 , wherein the corresponding sub-block has a size M×N and the center is defined as [(M>>1)+a, (N>>1)+b], wherein M and N are natural numbers and a, b is 0 or −1.

8 . The method of claim 1 , further comprising:

determining a CPMV candidate of the current video block to be derived from motion vectors from top adjacent blocks coded with the affine mode based on a position of the current video block.

9 . The method of claim 1 , wherein the conversion includes encoding the current video block into the bitstream representation.

10 . The method of claim 1 , wherein the conversion includes decoding the current video block from the bitstream representation.

11 . An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

determining, for a conversion between a current video block of a video and a bitstream representation of the video, motion vectors at control points (CPMV) of the current video block based on a rule, wherein the rule specifies to exclude using of non-adjacent neighboring block from one or more neighboring blocks of the current video block; and

performing the conversion between the current video block and the bitstream representation based on the motion vectors.

12 . The apparatus of claim 11 , wherein the rule further specifies to exclude using of invalid neighboring block from the one or more neighboring blocks based on positions of the one or more neighboring blocks.

13 . The apparatus of claim 12 , wherein the current video block belongs to a current slice, and a neighboring block of the one or more neighboring blocks is invalid in a case that the neighboring block belongs to a slice different from the current slice.

14 . The apparatus of claim 12 , wherein the current video block belongs to a current tile, and a neighboring block of the one or more neighboring blocks is invalid in a case that the neighboring block belongs to a tile different from the current tile.

15 . The apparatus of claim 11 , wherein the current video block includes multiple sub-blocks, and performing the conversion comprising:

determining a motion vector for each sub-block of the multiple sub-blocks based on the CPMV and a specific position of the corresponding sub-block.

16 . The apparatus of claim 15 , wherein the specific position is a center of the corresponding sub-block.

17 . The apparatus of claim 16 , wherein the corresponding sub-block has a size M×N and the center is defined as [(M>>1)+a, (N>>1)+b], wherein M and N are natural numbers and a, b is 0 or −1.

18 . The apparatus of claim 11 , further comprising:

determining a CPMV candidate of the current video block to be derived from motion vectors from top adjacent blocks coded with the affine mode based on a position of the current video block.

19 . A non-transitory computer-readable storage medium storing instructions that cause a processor to:

determining, for a conversion between a current video block of a video and a bitstream representation of the video, motion vectors at control points (CPMV) of the current video block based on a rule, wherein the rule specifies to exclude using of non-adjacent neighboring block from one or more neighboring blocks of the current video block; and

performing the conversion between the current video block and the bitstream representation based on the motion vectors.

20 . A non-transitory computer-readable recording medium storing a bitstream representation which is generated by a method performed by a video processing apparatus, wherein the method comprises:

determining, for a conversion between a current video block of a video and a bitstream representation of the video, motion vectors at control points (CPMV) of the current video block based on a rule, wherein the rule specifies to exclude using of non-adjacent neighboring block from one or more neighboring blocks of the current video block; and

generating the bitstream representation from the current video block based on the determining.