Low Complexity Decoder Side Motion Vector Refinement for VVC

Inter picture prediction is an essential component of today's hybrid video codecs. In order to reduce the motion vector signaling overhead, a merge mode with subsequent decoder side motion vector refinement (DMVR) is current under investigation for the first working draft of the standardization activity on Versatile Video Coding (VVC). While the DMVR method searches the refined MVs at the decoder side, it heavily increases the decoding complexity and the memory bandwidth requirements. To address these issues, a novel low complexity DMVR scheme is proposed in this paper. The low complexity DMVR approach refines the initial MV from the merge mode by searching the block with the smallest matching cost in the previous decoded reference pictures. The proposed low complexity improvements are added to a previously proposed bilateral matching-based DMVR approach. Experimental results obtained with the VTM 2.0 reference software, after integrating our approaches, show that the previously proposed DMVR provides an average luma BD-rate reduction of 4.59% with 32% additional decoding time and the proposed low complexity DMVR provides an average luma BD-rate reduction of 1.67% with only 6% additional decoding time when using the random access configuration.