| H.264 is the newest international video coding standard, and it was developed by the JVT (Joint video team) which is composed of MPEG (moving picture expert group) of ISO/IEC and VCEG (video coding expert group) of ITU-T. It is also called MPEG-4 Part 10 Advanced Video Coding. H.264 owns many new technologies, compared with others coding standards previously. It has made great improvement in coding efficiency, image quality and network adaptability, and demonstrated a good application prospects.However, because of the use of a wide range of advanced coding techniques, H.264 encoding complexity is also much higher than the previous standards, and the codec complexity are 3 times and 2 times of H.263 respectively. Therefore, the research and development of fast algorithm based on H.264, thereby reducing code complexity, and improving encoding speed, will have important theoretical and application value for the wide range applications of H.264, as well as further study and development of video compression and multimedia communication technology.In the H.264 encoder, macro block mode selection is an import reason which causes the encoder's high complexity, especially the inter-frame mode selection. Since inter-frame mode selection also includes motion estimation. The computation of motion estimation takes on about 70% of the whole encoder. So, if the inter-frame mode decision can be optimized effectively, thereby reducing the computation of the motion estimation will greatly reduce the computing complexity and improving encoding speed.In the first chapter of this paper describes the significance of video compression, the development process of video coding standard, basic knowledge of video coding, and the characteristics of some video coding standards. Then in the second chapter, H.264 standard is analyzed comprehensively, and some core technologies of H.264 are described in detail. In the third chapter, analysis and research on the inter-frame mode selection which is optimized in this paper have been done. At the same time describes the concepts of motion estimation, motion compensation and block matching etc. which are relevant with inter-frame mode selection. Finally, makes analysis to the process and complexity of inter-frame mode selection in the standard reference soft model JM8.6.In the chapter four, a fast mode selection scheme based on the image correlation and statistical probability of mode is proposed. It is used in JM8.6 soft reference model and compared with standard JM8.6 reference software. Experimental results are given to demonstrate the proposed scheme can reduce encoding time 35% on average. At the same time, picture quality degradation in PSNR is 0.27dB and bit rate rising is 0.66% on average. The experimental results prove that the new algorithm reduces the number of mode selection effectively. The encoding time is decreased greatly, thereby increases the encoding speed of the whole system in the case of the small changes in image quality and bit rate.In chapter five, mode selection function model of H.264 encoder are designed using FPGA. FPGA has a certain research and development advantages as a semi-custom integrated circuits in compared to DSP and the full-custom ASIC. There are some disadvantages to DSP and ASIC, such as slow calculating speed of DSP, the long development cycle of ASIC, the high cost of silicon, not flexible and so on. But FPGA is reusable and it is flexible to be changed. With the extension of resources in FPGA, especially with the DSP model, FPGA can achieve complex algorithms which were implemented on DSP previously in high speed. Studies on the realization of H.264 models using FPGA are done. The function models are described using VHDL hardware description language, compiled, optimized and simulated by the QuartusII 7.2 software of Altera cooperation. |
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