Template Matching-Based Subblock Motion Refinement Towards Next Generation Video Coding

Subblock-based motion compensation (SMC) has shown re-markable effectiveness in handling non-uniform motions for inter video coding. However, existing strategies typically derive subblock motion rely solely on the inherited information from an already coded region, lacking content-adaptive optimization and potentially lead to deviations from the real motion. In this paper, we propose an overhead-free adaptive refinement scheme towards SMC, which leverages template matching (TM) to enhance the fidelity of subblock motion derivation for affine and subblock-based TMVP (SbTMVP) prediction. In particular, TM-based control point motion vector (CPMV) refinement is proposed to facilitate affine MC, where TM cost serves as a fidelity metric during the seeking of optimal translational affine motion offset. Additionally, the motion shift (MS) to locate SbTMVP is also refined by TM before specifying the subblock motion. The proposed method has been adopted into ECM-11.0. Experimental results on ECM-10.0 demonstrate overall 0.09% coding gains under random-access (RA) configuration, with negligible runtime increase.