Adaptive Motion Vector Resolution for Affine-Inter Mode Coding

Affine Motion Model (AMM) based inter prediction, which can represent complex motions such as zooming, rotation or shearing, has been adopted into the Versatile Video Coding (VVC) standard. AMM is defined by Control Point Motion Vectors (CPMVs) in VVC. On the other hand, Adaptive Motion Vector Resolution (AMVR) has also been adopted into VVC standard due to a favorable trade-off between the Motion Vector (MV) precision and the bit consumption on MV Differences (MVDs). However, AMVR is only applied to the Translational Motion Model (TMM), and AMM cannot benefit from it. In this paper, it is proposed to extend AMVR to AMM. Specifically, 1-pixel, 1/4-pixel and 1/16-pixel MV precisions are allowed and can be selected adaptively by each affine-inter mode coded Coding Unit (CU). Simulation results reportedly show that the proposed method can achieve 0.32% BD-rate saving on average under the Random Access configuration.