Method and apparatus of constrained overlapped block motion compensation in video coding

An apparatus of video coding using OBMC (Overlapped Block Motion Compensation), the apparatus of video coding comprising one or more electronic circuits or processors arranged to:

• receive input data associated with a current block, wherein the input data correspond to pixel data to be coded at an encoder side or coded data to be decoded at a decoder side;
• determine whether to apply the OBMC to the current block depending on one or more constraints, wherein said one or more constraints correspond to whether the block width, block height, or block size of a target block is smaller than or equal to a threshold or is greater than or equal to a threshold, wherein the threshold is selected from any one of a block size of 16, 32, 64, 128, or 256, or any one of a width or height of 4, 8, 16, 32, or 64;
• and
• signal an OBMC syntax conditionally at the encoder side or parse the OBMC syntax conditionally at the decoder side for the current block based on the determination, wherein the OBMC syntax indicates whether the OBMC is applied to the current block, wherein when the current block is smaller than the threshold, the OBMC is disabled and the OBMC syntax is not signaled.