Video Processing Methods and Apparatuses for Sub-block Motion Compensation in Video Coding Systems

A video processing method for sub-block motion compensation in a video coding system, comprising:

• receiving input video data associated with a current block in a current picture to be encoded or decoded;
• checking whether a sub-block motion compensation coding tool is applied to the current block based on a size, width, or height of the current block, a size, area, shape, width, or height of sub-blocks partitioned from the current block, an inter prediction direction of a sub-block Motion Vector (MV), primary MV, or one of control point MVs of the current block, a primary MV, the control point MVs, affine parameters, or a combination thereof;
• encoding or decoding the current block using the sub-block motion compensation coding tool or another coding tool according to a result of the checking indicating whether application of the sub-block motion compensation coding tool is valid or invalid;
• a MV clipping process is applied to each sub-block in the current block if the checking result is false, indicating the validity is invalid;
• and
• wherein the MV clipping process includes setting all the sub-block MVs equal to the primary MV.