Efficient Intra Coding through Hierarchical CU Partition Prediction for VVC

Versatile Video Coding (VVC) has adopted a quad-tree with a nested multi-type tree (QTMT) partition structure to improve the rate-distortion (RD) performance, but this greatly increases complexity due to the brute-force RDO process to search for the best partition type. Some methods cannot fully utilize partition information of deeper CUs when training, while others process large CUs as a whole and may neglect specific information inside smaller CUs. Therefore, in this paper, we propose a learning-based approach to predict the best partition modes for every CU while utilizing the partition modes of deeper CUs. Firstly, we model the searching for the optimal partition split in a hierarchical prediction way. Secondly, we predict a confidence score along with each prediction to select the accurate number of partition types. Lastly, we incorporate the prediction above into a framework with separate predictions for NS/QT/MTT split and MTT split, and modify it according to the mechanism of VTM. Experiments demonstrate that our method can reduce 47.21%∼53.97% complexity of VVC intra coding with negligible 0.81%∼1.26% BD-BR increase, superior to other state-of-the-art methods.

I. Introduction

With the development of the video market, content such as 4K/8K Ultra High Definition (UHD) video, Virtual Reality (VR), and 360-degree video constantly enriches people’s daily lives. Considering that High Efficiency Video Coding (HEVC) cannot meet the growing demand in the video market, the newest standard, Versatile Video Coding (VVC), has been designed to address all existing applications of HEVC essentially. VVC has adopted a series of new coding techniques to achieve a significant improvement in coding efficiency, including a nested multi-type tree using binary and ternary splits (QTMT) for coding unit (CU) partition. However, the new coding techniques also make the coding complexity increase sharply [1]. Therefore, it is essential to optimize the encoding process of VVC for practical applications.