Hierarchical temporal dependent rate-distortion optimization for low-delay coding

Hierarchical coding structure (HCS) is one of the most important components in High Efficiency Video Coding (HEVC) that improves the coding performance greatly, especially for Low-Delay (LD) coding. It groups frames into different layers and enc odes them with different quantization parameters (QP) and different reference mechanisms. Due to the extensively used inter-prediction, the coding of frames in different layers is highly dependent and an appropriate QP and reference selection scheme may significantly improve the performance by taking advantage of such temporal dependency. However in the current HEVC codec, a predefined HCS, such as the Low-Delay HCS (LD-HCS), is performed without considering the different characteristic of different video contents, thus leading to a suboptimal coding solution. In this paper, the hierarchical temporal relationship under LD-HCS is first investigated and a hierarchical temporal propagation chain is constructed to describe the temporal dependency among frames. Then a hierarchical temporal dependent rate-distortion optimization scheme is developed specifically for the LD-HCS in HEVC. Experiments results show that the proposed scheme achieves BD-rate saving of 2.9% and 2.8% in average against HEVC codec under LD-HCS of P and B frames, respectively, with a negligible increase in encoding time.