Methods and apparatuses of video processing with motion refinement and sub-partition base padding

An apparatus of processing video data in a video coding system, the apparatus comprising one or more electronic circuits configured for:

• receiving input data associated with a current block in a current picture;
• partitioning the current block into sub-partitions;
• for each sub-partition in the current block:
• obtaining a reference block from one or more reference pictures according to an initial Motion Vector (MV);
• deriving a refined MV according to decoder motion vector refinement (DMVR) by performing motion refinement on each sub-partition by searching around the initial MV with N-pixel refinement;
• and
• padding one or more boundary pixels of the reference block, wherein the padding is performed on boundary pixels of a sub-partition of the reference block, the padding performed on a sub-partition basis and surrounding the sub-partition;
• performing motion compensation for the sub-partitions in the current block according to the refined MVs to generate a final predictor for the current block;
• and
• encoding or decoding the current block according to the final predictor.

A non-transitory computer readable medium storing program instruction causing a processing circuit of an apparatus to perform a video processing method for video data, and the method comprising:

• receiving input data associated with a current block in a current picture;
• partitioning the current block into sub-partitions;
• for each sub-partition in the current block:
• obtaining a reference block from one or more reference pictures according to an initial Motion Vector (MV);
• deriving a refined MV according to decoder motion vector refinement (DMVR) by performing motion refinement on each sub-partition by searching around the initial MV with N-pixel refinement;
• padding one or more boundary pixels of the reference block, wherein the padding is performed on boundary pixels of a sub-partition of the reference block, the padding performed on a sub-partition basis and surrounding the sub-partition;
• performing motion compensation for the sub-partitions of the current block according to the refined MVs to generate a final predictor for the current block;
• and
• encoding or decoding the current block according to the final predictor.