Variable block-size overlapped block motion compensation in the next generation open-source video codec
Traditional motion compensation is based on a simplistic assumption of a piecewise constant and pure translational motion field. Premised on the inefficiency of such block-copying-based algorithms in compressing real-life videos, this paper proposes overlapped block motion compensation for AV1, a next generation open-source video codec. Motions assigned to surrounding blocks will contribute to predicting a current block, via a well-defined overlapping scheme appropriately designed for advanced variable block-size partitioning frameworks. To efficiently incorporate the proposed tool, the encoder is optimized with proper early termination to manage complexity in conjunction with weighted motion search accounting for non-uniformly weighted distortion in overlapped prediction. Moreover as an extension, by re-arranging decoding operations, we enable non-causal overlapping which also utilizes motions of bottom and right neighbors. Being verified by integration in the AV1 codec, the tools achieve considerable coding gains on various test sets.