Affine inter prediction refinement with optical flow

A method of video encoding by a video encoder, comprising:

• determining an intermediate motion vector MVblock of a current block having a first precision that is higher than a second precision supported by an interpolation filter;
• rounding the intermediate motion vector MVblock to generate a rounded motion vector MVround of the current block having the second precision supported by the interpolation filter;
• obtaining a prediction block of the current block based on the rounded motion vector MVround and the interpolation filter;
• determining a prediction refinement offset for a prediction sample of the prediction block based on gradients of the prediction sample of the prediction block and motion vector differences between the intermediate motion vector MVblock and the rounded motion vector MVround;
• and
• adding the prediction refinement offset to the prediction sample of the prediction block to generate a refined prediction sample.

A method of processing visual media data, the method comprising:

• processing a bitstream that includes the visual media data according to a format rule, wherein
• the bitstream includes prediction information of a current block;
• and
• the format rule specifies that
• when an intermediate motion vector MVblock of the current block has a first precision that is higher than a second precision supported by an interpolation filter, the intermediate motion vector MVblock is rounded to generate a rounded motion vector MVround of the current block having the second precision supported by the interpolation filter,
• a prediction block of the current block is generated based on the rounded motion vector MVround and the interpolation filter,
• a prediction refinement offset for a prediction sample of the prediction block is determined based on gradients of the prediction sample of the prediction block and motion vector differences between the intermediate motion vector MVblock and the rounded motion vector MVround, and
• the prediction refinement offset is added to the prediction sample of the prediction block to generate a refined prediction sample.