Source Distortion Temporal Propagation Analysis for Random-Access Hierarchical Video Coding Optimization

IEEE Due to the widely used inter prediction in the current video coding standards, encoding of units among different frames are temporally dependent on each other, which implies that rate-distortion optimization (RDO) of one unit may affect the optimization of the following units in the temporal domain. To achieve optimal coding solution for a given video sequence, temporal dependency among units needs to be considered in the RDO process, which is known as the temporally dependent RDO problem (TD-RDO). The hierarchical coding structure (HCS) employed in the High Efficiency Video Coding (HEVC) standard further complicates this problem by grouping frames into different layers with different coding strategies, leading to a complex temporal relationship. In our earlier work, we addressed TD-RDO for the low delay HCS (LD-HCS), where only uni-prediction is considered. This work aims to deal with more complicated TD-RDO under random access HCS (RA-HCS), where both uni-prediction and bi-prediction are considered, making the temporal relationship even more intricate. In this paper, the temporal dependency introduced in the RA-HCS is thoroughly examined and an RA-based TD-RDO scheme is formulated for each layer by modeling distortion temporal propagation under different prediction types. The representation of the global Lagrange multiplier, which is hard to be determined under LD-HCS, can be obtained based on the formulation of the highest layer under RA-HCS. Furthermore, the effect of random access point pictures is considered in the RA-based TD-RDO scheme. The proposed method can be realized by adapting the Lagrange multiplier only or combined with adjusting quantization parameter (QP) for better results in terms of BD-rate saving. Experimental results show that under RA-HCS, the proposed method, by adapting the Lagrange multiplier, can achieve about 2.2 & #x0025; bitrate savings in average. With multi-QP optimization, an average BD-rate gain of 5.2 & #x0025; can be obtained