On The Backward Refinement In Video Coding

Nowadays, most of the video coding standards are based on the hybrid coding framework, whose information theoretic model was studied by Viswanathan and Berger more than one decade ago. The theoretic model of hybrid coding framework, now known as the Sequential Coding(SC) model, abstracts consecutive frames as correlated random variables. Even the most efficient High Efficiency Video Coding(HEVC) standard can be roughly described by this sequential coding model. Searching for methods and algorithms which can improve the coding efficiency of HEVC is an attractive yet formidable task. In this paper, we propose a Sequential Coding with Backward Refinement(SCBR) model. In this modified theoretic model, after each frame is reconstructed, it can be backward refined by the frames encoded afterwards. Note that the proposed SCBR model does not depend on the coding tools and thus can be implemented on any current video coding standard under hybrid coding framework. So, using this SCBR model, we can further improve the coding efficiency of any video coding standard, with only slight modification of the coding structure. Theoretical analysis is given on the performance of the SCBR model. We also propose two SCBR algorithms for the practical purpose. The first algorithm is implemented and tested on the HEVC standard. Experimental results show a maximum of 2.2% BD-rate saving compared with original HEVC codec. The second algorithm is implemented and tested on the HEVC standard with mixed resolution approach. Experimental results show a maximum of 4.4% BD-rate saving compared with mixed resolution approach without BR module.