B-picture coding in AVS video compression standard

This paper first gives a brief overview of the Chinese audio-video coding standard (AVS¹1The China audio-video coding standard (AVS) referred in this paper all indicates AVS-Part 2. It targets at a better trade-off between coding efficiency and complexity for high-definition video coding.) especially on prediction modes of motion compensation for B-picture. Furthermore, two techniques adopted by AVS about how to improve motion compensation for B-picture coding are discussed in detail. The first one is the proposed symmetrical mode that replaces the conventional bi-directional mode, in which only one motion vector is coded and another is derived from the coded one with the assumption of approximate constant-speed motion. It can achieve a better trade-off between prediction accuracy and the bits for coding motion information. The second one is the improved temporal direct mode. It not only solves the problem in AVS on how to correctly derive reference index under the constraint of two reference buffers for both P- and B-pictures but also improves the accuracy of derived motion vectors in temporal direct mode with division-free operations. In experimental results, the proposed symmetrical mode and the improved temporal direct mode were integrated into the H.264/MPEG-4 AVC reference software to exhibit their performances. Furthermore, the B-picture coding performance in AVS is also evaluated using different GOP coding structures.