Optical flow based video inter prediction

A non-transitory computer-readable media storing computer instructions for bi-directional optical flow (BDOF) based inter prediction for a current block of a video signal, that when executed by one or more processors, cause the one or more processors to perform the operations of:

• determining a horizontal motion offset vx and a vertical motion offset vy of the current block, and wherein the vertical motion offset is determined based on the horizontal motion offset and a fifth variable s5, wherein:
• the fifth variable s5 indicates a sum of a first plurality of terms, wherein each of the first plurality of terms is obtained from a sign of an element of a second matrix and an element of a first matrix, and the element of the first matrix corresponds to the element of the second matrix;
• each element of the first matrix is obtained from a sum of a first horizontal predicted sample gradient that corresponds to a first reference frame of the current block and a second horizontal predicted sample gradient that corresponds to a second reference frame of the current block, wherein the first horizontal predicted sample gradient and the second horizontal predicted sample gradient correspond to the element of the first matrix;
• and
• each element of the second matrix is obtained from a sum of a first vertical predicted sample gradient that corresponds to the first reference frame of the current block and a second vertical predicted sample gradient that corresponds to the second reference frame of the current block, wherein the first vertical predicted sample gradient and the second vertical predicted sample gradient correspond to the element of the second matrix;
• and
• determining prediction sample values in the current block using prediction sample values corresponding to the first reference frame, prediction sample values corresponding to the second reference frame, and the horizontal motion offset and the vertical motion offset.

A device for coding video data, comprising:

• a video data memory;
• and
• a video coder, wherein the video coder is configured to:
• determine a horizontal motion offset, vx and a vertical motion offset, vy of a current block, and wherein the vertical motion offset is determined based on the horizontal motion offset and a fifth variable s5, wherein:
• the fifth variable s5 indicates a sum of a first plurality of terms, wherein each of the first plurality of terms is obtained from a sign of an element of a second matrix and an element of a first matrix, and the element of the first matrix corresponds to the element of the second matrix;
• each element of the first matrix is obtained from a sum of a first horizontal predicted sample gradient that corresponds to a first reference frame of the current block and a second horizontal predicted sample gradient that corresponds to a second reference frame of the current block, wherein the first horizontal predicted sample gradient and the second horizontal predicted sample gradient correspond to the element of the first matrix;
• and
• each element of the second matrix is obtained from a sum of a first vertical predicted sample gradient that corresponds to the first reference frame of the current block and a second vertical predicted sample gradient that corresponds to the second reference frame of the current block, wherein the first vertical predicted sample gradient and the second vertical predicted sample gradient correspond to the element of the second matrix;
• and
• determine prediction sample values in the current block using prediction sample values corresponding to the first reference frame, prediction sample values corresponding to the second reference frame, and the horizontal motion offset and the vertical motion offset.