Sub-block based constraint on bi-prediction for out-of-boundary conditions

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 coded information of a plurality of subblocks of a current block in a current picture;
• and
• the format rule specifies that:
• a syntax element indicates a prediction mode associated with the current block in the current picture, the prediction mode being one of a uni-prediction mode and a bi-prediction mode;
• when the bi-prediction mode is applied to a first subblock of the plurality of subblocks, (i) a boundary of a first reference subblock is positioned beyond a boundary of the first reference picture and (ii) a boundary of a second reference subblock is positioned within a boundary of the second reference picture are determined;
• and
• when one of (i) the boundary of the first reference subblock being beyond the boundary of the first reference picture or (ii) the boundary of the second reference subblock being beyond the boundary of the second reference picture, the first subblock of the current block is reconstructed based on the uni-prediction mode such that the first subblock is reconstructed based on one of the first reference picture and the second reference picture.

A method of video encoding performed in a video encoder, the method comprising:

• determining whether a uni-prediction or a bi-prediction mode is applied to a first subblock of a plurality of subblocks of current block in a current picture, wherein the first subblock is predicted based on a first reference subblock in a first reference picture and a second reference subblock in a second reference picture;
• when the bi-prediction mode is applied to the first subblock of the plurality of subblocks, determining whether (i) a boundary of the first reference subblock is positioned beyond a boundary of the first reference picture and (ii) a boundary of the second reference subblock is positioned within a boundary of the second reference picture;
• and
• when one of (i) the boundary of the first reference subblock is beyond the boundary of the first reference picture or (ii) the boundary of the second reference subblock is beyond the boundary of the second reference picture, encoding the first subblock of the current block in a bitstream according to the uni-prediction mode such that the first subblock is based on the first reference picture and the second reference picture.