APPARATUS AND METHOD FOR CONDITIONAL DECODER-SIDE MOTION VECTOR REFINEMENT IN VIDEO CODING

A method for inter-prediction of a current image block in a current picture of a video is provided. The method includes: when a flag is signaled at a sequence parameter set level and/or a picture level indicating whether a bi-directional optical flow (BIO or BDOF) procedure is enabled at the sequence parameter set level and/or the picture level, determining a value of the flag which is signaled at the sequence parameter set level and/or the picture level; determining whether a first temporal distance is equal to a second temporal distance; and performing the bi-directional optical flow (BIO or BDOF) procedure for the current image block, when a plurality of conditions are satisfied, wherein one of the plurality of conditions comprises: the value of the flag which is signaled at the sequence parameter set level and/or the picture level, indicating the BIO or BDOF procedure is enabled at the sequence parameter set level and/or the picture level; and the first temporal distance is equal to the second temporal distance; and performing no bi-directional optical flow (BIO or BDOF) procedure for the current image block, when the first temporal distance is not equal to the second temporal distance. Thus, the BIO or BDOF procedure is restricted to only the image block with equal-distance references.