Unified constrains for the merge affine mode and the non-merge affine mode
Devices, systems and methods for sub-block based prediction are described. In a representative aspect, a method for video processing comprises determining a block size constrain, making a determination, based on the block size constrain, about whether or not a merge affine mode and a non-merge affine mode are allowed for a video block in a video frame, and generating a bitstream representation of the video block based on the making the determination.
1. A method of processing video data, comprising:
determining, for a conversion between a current video block of a video and a bitstream of the video, that whether or not a first affine mode and a second affine mode are allowed for the current video block based on a same dimension constrain; and
performing, based on the determining, the conversion between the current video block and the bitstream.
2. The method of claim 1 , wherein in the first affine mode, motion information of control points of the current video block is derived at least based on an affine candidate of the current video block and without applying motion vector differences (MVD).
3. The method of claim 2 , wherein the first affine mode is a merge affine mode, and the second affine mode is a non-merge affine mode.
4. The method of claim 2 , wherein the first affine mode is a direct affine mode, and the second affine mode is a non-direct affine mode.
5. The method of claim 1 , comprising:
determining that the bitstream omits an indication of the first affine mode at least based on a dimension of the current video block.
6. The method of claim 1 , comprising
determining that the bitstream omits an indication of the second affine mode at least based on a dimension of the current video block.
7. The method of claim 1 , wherein the first affine mode and the second affine mode are not allowed in response to either a height of the current video block or a width of the current video block being smaller than or equal to 8.
8. The method of claim 1 , wherein the first affine mode and the second affine mode are not allowed in response to a height and a width of the current video block being both smaller than or equal to a threshold.
9. The method of claim 1 , wherein the conversion includes encoding the current video block into the bitstream.
10. The method of claim 1 , wherein the conversion includes decoding the current video block from the bitstream.
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:
make a determination, for a conversion between a current video block of a video and a bitstream of the video, that whether or not a first affine mode and a second affine mode are allowed for the current video block based on a same dimension constrain; and
perform, based on the determination, the conversion between the current video block and the bitstream.
12. The apparatus of claim 11 , wherein in the first affine mode, motion information of control points of the current video block is derived at least based on an affine candidate of the current video block and without applying motion vector differences (MVD).
13. The apparatus of claim 12 , wherein the first affine mode is a merge affine mode, and the second affine mode is a non-merge affine mode.
14. The apparatus of claim 12 , wherein the first affine mode is a direct affine mode, and the second affine mode is a non-direct affine mode.
15. The apparatus of claim 11 , wherein the instructions cause the processor to:
determine that the bitstream omits an indication of the first affine mode at least based on a dimension of the current video block.
16. The apparatus of claim 11 , wherein the instructions cause the processor to:
determine that the bitstream omits an indication of the second affine mode at least based on a dimension of the current video block.
17. The apparatus of claim 11 , wherein the first affine mode and the second affine mode are not allowed in response to either a height of the current video block or a width of the current video block being smaller than or equal to 8.
18. The apparatus of claim 11 , wherein the first affine mode and the second affine mode are not allowed in response to a height and a width of the current video block being both smaller than or equal to a threshold.
19. A non-transitory computer-readable storage medium storing instructions that cause a processor to:
determine, for a conversion between a current video block of a video and a bitstream of the video, that whether or not a first affine mode and a second affine mode are allowed for the current video block based on a same dimension constrain; and
perform, based on the determining, the conversion between the current video block and the bitstream.
20. A non-transitory computer-readable recording medium storing a bitstream 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 of the video, that whether or not a first affine mode and a second affine mode are allowed for the current video block based on a same dimension constrain; and
generating the bitstream based on the determining.