Affine motion model derivation method

A video decoding apparatus comprising one or more processors configured to perform at least:

• obtaining an affine motion model for prediction of a current block;
• selecting a sub-block size for sub-blocks of the current block, wherein the sub-block size is based on a shape of the current block, wherein the sub-block size has a first lateral dimension selected to be a minimum lateral size and a second lateral dimension selected according to an aspect ratio of the current block, and wherein the minimum lateral size is determined based on whether the current block is uni-predicted or bi-predicted;
• determining a respective motion vector for each of the sub-blocks using the affine motion model;
• and
• predicting the sub-blocks of the current block based on the respective motion vectors.

A video encoding method comprising:

• obtaining an affine motion model for prediction of a current block;
• selecting a sub-block size for sub-blocks of the current block, wherein the sub-block size is based on a shape of the current block, wherein the sub-block size has a first lateral dimension selected to be a minimum lateral size and a second lateral dimension selected according to an aspect ratio of the current block, and wherein the minimum lateral size is determined based on whether the current block is uni-predicted or bi-predicted;
• determining a respective motion vector for each of the sub-blocks using the affine motion model;
• and
• predicting the sub-blocks of the current block based on the respective motion vectors.

A video encoding apparatus comprising one or more processors configured to perform at least:

• obtaining an affine motion model for prediction of a current block;
• selecting a sub-block size for sub-blocks of the current block, wherein the sub-block size is based on a shape of the current block, wherein the sub-block size has a first lateral dimension selected to be a minimum lateral size and a second lateral dimension selected according to an aspect ratio of the current block, and wherein the minimum lateral size is determined based on whether the current block is uni-predicted or bi-predicted;
• determining a respective motion vector for each of the sub-blocks using the affine motion model;
• and
• predicting the sub-blocks of the current block based on the respective motion vectors.