Advanced Motion Vector Difference Coding Beyond AV1

In AV1, for inter coded blocks with compound reference mode, motion vector differences (MVDs) are signaled for reference frame list 0 or list 1 separately with the same MVD precision regardless of the motion vector magnitude. In this paper, two advanced MVD coding methods are proposed. Firstly, to reduce the overhead for signaling MVD, the precision of the MVD is implicitly determined based on the associated MV class and MVD magnitude. Secondly, a new inter prediction mode is added to explore the correlation of MVDs between two reference frames, wherein one joint MVD is signaled for two reference frames. Experimental results demonstrate that, in the random-access common test condition luma coding gains of around 1.1% in terms of BD-rate can be achieved on top of a recent release of AOMedia Video Model (AVM).