Search pattern for sub-block motion vector refinement

A method of video encoding performed at a computing system having memory and one or more processors, the method comprising:

• receiving video data comprising a plurality of blocks that includes a current block;
• deriving a set of subblock motion vectors for subblocks of the current block;
• deriving a set of refined subblock motion vectors by applying a subblock motion refinement on the set of subblock motion vectors, the subblock motion refinement comprising performing a single-pass search within a search pattern for a motion vector difference with a lowest associated cost, wherein the search pattern is non-rectangular;
• and
• encoding the current block using the set of refined subblock motion vectors.

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

• obtaining a source video sequence that comprises a plurality of frames;
• and
• performing a conversion between the source video sequence and a video bitstream of visual media data according to a format rule,
• wherein the video bitstream comprises a plurality of encoded blocks including a current block;
• and
• wherein the format rule specifies that:
• a set of subblock motion vectors is to be derived for subblocks of the current block;
• a set of refined subblock motion vectors is to be derived by applying a subblock motion refinement on the set of subblock motion vectors, the subblock motion refinement comprising performing a single-pass search within a search pattern for a motion vector difference with a lowest associated cost, wherein the search pattern is non-rectangular;
• and
• the current block is to be reconstructed using the set of refined subblock motion vectors.