Distortion Propagation Factor Estimation for VVC Low-Delay Hierarchical Coding

Previous studies have shown that temporally dependent rate-distortion optimization (RDO) methods can enhance the compression performance of video encoders. However, accurately quantifying temporal rate-distortion dependencies in the latest video coding standard, Versatile Video Coding (VVC), remains a significant challenge. To address this issue, this paper proposes a distortion propagation factor (DPF) estimation method tailored for VVC low-delay hierarchical coding, aiming to achieve temporally dependent RDO. Specifically, we first derive a formula for calculating the DPF based on coding distortion and motion-compensated prediction (MCP) errors. Building on this, we present several pre-encoding-based DPF estimation schemes designed for the VVC low-delay hierarchical coding structure. These schemes have very low computational complexity and do not require buffering subsequent unencoded frames for pre-analysis, thereby avoiding additional encoding delays. Finally, the estimated DPFs are used to adaptively adjust the Lagrange multipliers and quantization parameters of each coding tree unit, optimizing the allocation of coding bit resources. After integrating the proposed method into the VVC test model VTM-23.0, experimental results show that one of the proposed DPF estimation schemes achieves average bit rate savings of 4.25% for low-delay B slices and 4.12% for low-delay P slices, with only a 1% increase in computational complexity. The proposed method offers an effective solution for enhancing the compression performance of VVC encoders. Consequently, the proposed DPF estimation approaches have already been adopted by the Joint Video Experts Team (JVET) and officially integrated into the VVC reference software.