.h.264/avc The Rate Control Algorithm

H.264/AVC which is the newest video coding standard is published by the ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC Moving Picture Experts Group (MPEG) in March, 2003. Because of the advantages in terms of both coding efficiency enhancement and flexibility for effective use over a broad variety of network types and application domains and so on, it catch more and more attention.As the most important part of video coding system, the purpose of the rate control is to make the encoding output bit-rate fit the pre-defined target bit-rate while obtaining the best encoding quality.Based on studying rate control algorithm of H.264/AVC - G012, this article has mainly done three optimize works:1. The idea of equal distribution is presented in the frame layer bit allocation adopted by the G012, which makes a good effect for source of low motions and no scene change (on the other word: the complexity of every frame is nearly the same). But when the difference of per frame complexity is large for high motions and scene change, the number of bit is largely different in order to reach the unifying reconstruction quality. Then the G012 will be little effective. Using a scene change factor as the measure of the level of scene changes and motions, and then adaptively adjust bit budget for per P frame to compensate the lack of equal bit allocation in G012.2. When G012 processes the GOP with B frames, the distribution of the bit at the middle and tail of the GOP isn't proper, which not only makes the encoding quality decrease seriously due to lack of bit, but also makes the actual bit-rate higher than the target bit-rate. This paper will analyses the reason and proposes an improving method.3. Hierarchical B frame is a newly proposed coding tool after G012 published, which can greatly improve the code efficiency. In this thesis, through studying the statistical changes after using this new tool and finely dividing modeling the B frame, we can get more precisely bit allocation. At the same time we improve the calculation of the quantization parameter of B frames, which makes the most of temporal relativity enhanced by hierarchical B frame coding structure.