The Study And Optimization Research Of Mode Choice And Rate Control In H.264 Encoder

H.264AVC is the newest video coding standard of the ITU-T Video Coding Experts Group and the ISO/IEC Moving Picture Experts Group. The main goals of the H.264/AVC standardization effort have been enhanced compression performance and provision of a "network -friendly" video representation. As a new video codec standard ,H.264 applies many mostly used technologies. It provides fairly good coding quality while achieving a better coding efficiency and more simple syntax expression, and it is the most efficient video coding standard at present. Comparing to prior video codec standards ,H.264 seems will be used in more application areas in the future.Firstly ,the paper discuss these new technical used to H.264 codec: Intra prediction ,multi-picture motion-compensated prediction, Variable Block-sized motion compensation with small block size ,Quanter-sample -accurate motion compensation ,Integer DCT transform, Loop-filter, etc.Secondly, a new intra₄x4 mode selection algorithm based on rate distortion optimization(RDO) was proposed after analyzing the process of mode choice for intra mode .As we all know ,H.264/AVC employed intra-prediction technique in space domain to enhance coding efficiency, There are one size of 8x8 for the chrom a block and two sizes including 4x4 and 16x16 for the luma block. Each kind of block provides many prediction modes ,so that this multi-mode selection increases the coding complexity greatly while improving coding efficiency. In order to decrease the coding complexity of mode choice in H.264/AVC, it employed SATD (Sum of Absolute Transformed Difference)of each block as a judgment and used correlation between prediction modes of adjacent blocks to filter out more than 65% less probable modes beforehand so as to avoid unnecessary computations. The new algorithm reduces the intra-prediction complexity greatly while maintaining coding perform very well.Thirdly ,rate control is focused .Rate control plays an important role in video coding ,without which the applications of any video coding standard would be limited. Rate control player a key role in H.264.Rate control algorithm has been given in encoding reference software(JM).Finally, after describing the structure and performance of IMS320DM624, the paper focuses on the optimizing C codes according to the specialty of IMS320DM624.DM 642 is a kind of DSP chip produced by TI which is especially used in image process. DM642 is based on C64X chips but appends many peripheral equipments and interface ports. These equipments and interface ports make DM 642 more fitful to process video codec streams. The paper puts emphasis on DM 642ps structure and performance which has relation with video encoding and decoding, especially the CPU core, Cache structure, and Video Port structure. With analysis of several components in H.264 standard, the optimizations of the DSP code are carried out according to the features of the DM642 DSP platform, which can decrease the encoding time and delay efficiently.