Methods and devices for candidate derivation for affine merge mode in video coding

An apparatus for video decoding, comprising:

• one or more processors;
• and
• a memory coupled to the one or more processors and configured to store instructions executable by the one or more processors,
• wherein the one or more processors, upon execution of the instructions, are configured to perform operations comprising:
• obtaining a plurality of sub-blocks by dividing an affine-coded block;
• obtaining, based on a plurality of control point motion vectors (CPMVs) of the affine-coded block, a plurality of sub-CPMVs of one sub-block from the plurality of sub-blocks, wherein the one sub-block has a size of a minimum affine block;
• and
• storing the plurality of sub-CPMVs of the one sub-block as motion information of the one sub-block;
• wherein obtaining, based on the plurality of CPMVs of the affine-coded block, the plurality of sub-CPMVs of the one sub-block comprises:
• using the plurality of CPMVs of the affine-coded block as the plurality of sub-CPMVs of the one sub-block;
• or
• projecting the plurality of CPMVs of the affine-coded block to the one sub-block to obtain the plurality of sub-CPMVs of the one sub-block.

A non-transitory computer-readable storage medium storing a bitstream formed by instruction which when executed by a computer device having one or more processors, cause the one or more processors to perform a decoding method, the decoding method comprising:

• obtaining a plurality of sub-blocks by dividing an affine-coded block;
• obtaining, based on a plurality of control point motion vectors (CPMVs) of the affine-coded block, a plurality of sub-CPMVs of one sub-block from the plurality of sub-blocks, wherein the one sub-block has a size of a minimum affine block;
• and
• storing the plurality of sub-CPMVs of the one sub-block as motion information of the one sub-block;
• wherein obtaining, based on the plurality of CPMVs of the affine-coded block, the plurality of sub-CPMVs of the one sub-block comprises:
• using the plurality of CPMVs of the affine-coded block as the plurality of sub-CPMVs of the one sub-block;
• or
• projecting the plurality of CPMVs of the affine-coded block to the one sub-block to obtain the plurality of sub-CPMVs of the one sub-block.