The Study, Based On The H.264/avc Rate Control Algorithm

H.264/AVC video coding standard is developed formally by JVT(Joint Video Team) in March 2003, and it will be the second successful video compression standard after the MPEG-2/H.262. The standard is designed to give a new technical solution to a broad range of applications, such as very low bit rate conversational services and low delay broadcast, interactive video services etc. So this standard obtains much attention from academic and industrial fields.Firstly, the system and key techniques in H.264/AVC, which including transform, inter-prediction, intra-prediction, entropy coding and block filtering, are discussed,. Compared to existing video coding standards, H.264/AVC's improvements are mainly on the system blocks, but not the whole system.Secondly, Rate control algorithm is discussed. Rate control is one of the key techniques for video coding. It will affect the bandwidth of generated bits and the reconstruct image quality directly. Because the complexity and motility of images are not the same, it will lead to the output bits change obviously. So it is necessary that the change is controlled to a limited range by some rate control algorithms. Three classical rate control algorithms, including TM5, VM8, and TMN8, are introduced in this paper. Because the RDO mode is related to the H.264 JM10.1 rate control algorithm, The RDO(Rate Distortion Optimization)mode, which is based on Lagrange optimization algorithm and used to determine the micro block's coding mode, is especially discussed. And then JM10.1 rate control algorithm which including GOP layer rate control, frame-layer rate control and basic unit layer rate control is elaborated.Lastly, by noticing that the JM10.1 rate control algorithm has some disadvantages such as, in the bit allocation process the picture complexity is not considered, the mismatch of actual bits generated by the coded frame and the bits allocated for this frame isn't well adjusted and the buffer bit occupation level isn't controlled well when the scene changing frames exist in the video sequence. Aiming at these disadvantages, three rate control improvement methods are discussed, they are seperately based on the bit allocation, the rdo mode and detection of scene changing frames. All simulations are performed on the JM10.1 platform which including the frame skip scheme. The simulation results show us, the improved algorithms do have some advantages over the JM10.1 rate control algorithm, such as the buffer controlling and the smoothness of the decoded sequence.