Multi-stage affine motion estimation fast algorithm for versatile video coding using decision tree

Abstract

Affine motion estimation (AME) which is newly introduced in versatile video coding (VVC) plays a significant role in the bit-rate reduction for rotation and zooming scenes. However, it brings the complexity extremely increased. In this paper, a fast AME algorithm is designed to cope with the high-complexity problem. Three crucial stages are involved in the fast algorithm, which is the optimal inter-mode decision based on the coding unit (CU) partition, the fast algorithm in affine motion search (AMS), and the fast inter-mode decision based on a decision tree. Specifically, the optimal inter-mode will be determined straightforwardly when the parent CU is checked whether it is translational motion estimation (TME). Then, three fast algorithms are made in AMS, which are early termination based on control point motion vector (CPMV), early termination of the iteration process, and fast fine granularity CPMV search. Finally, the optimal inter-mode is predicted using a decision tree based on eight essential features. Experimental results show that the proposed algorithm achieves 10.20% and 10.33% encoding time-saving on average under Low Delay B (LDB) and Random Access (RA) configuration, while the BD-Rate loss is only 0.12% and 0.14%, respectively.