Fast Coding Unit Splitting Decisions for the Emergent AVS3 Standard

AVS3 adopts quad-tree (QT) with nested binary tree (BT) and extended quad-tree (EQT) partitioning, which shows promising compression performance when compared to the conventional QT partitioning in AVS2 and HEVC. However, the interleaved and recursive splitting manner significantly increases the computational complexity of the encoder, which may impede the real applications of AVS3. This paper proposes fast coding unit splitting decision methods for QT, BT and EQT partitioning. In particular, the Bayesian decision rule is employed with Skip states, and BT and EQT partitioning can be early terminated. Additionally, the average splitting depth that is produced by BT partitioning, is incorporated as the prior information for terminating the EQT and QT splittings. Moreover, we explore the splitting settings for CUs that are predicted with Skip mode, with the aim of eliminating unnecessary partition attempts. Experimental results show that the proposed fast algorithms are effective and provide a good trade-off between computational complexity and coding performance. In particular, 69% encoding time reduction is achieved with only 0.55% increase in terms of BD-Rate on average, which greatly benefits the practical implementations of the AVS3 in real applications. The proposed methods have been adopted into TAVS3 reference software.