| H.264/AVC is the newest international video coding standard jointly developed by the ITU-T VCEG and the ISO/IEC MPEG standards committees. It represents the state-of-the-art video compressing technology, and addresses the full range of video applications including low bit-rate wireless video applications, standard-definition and high-definition broadcast television, and streaming over the Intemet. Compared with MPEG-4, H.263, and MPEG-2, H.264/AVC can achieve 39%, 49%, and 64% of bit-rate reduction with equivalent video quality respectively. To achieve such a high coding efficiency, H.264/AVC adopts many new and advanced features such as spatial intra prediction, quarter-pixel accuracy motion compensation, integer 4×4 discrete cosine transform and quantization, variable block sizes, multiple reference frames, adaptive de-blocking filter and context-based entropy coding.As might be expected, the increase in coding efficiency and coding flexibility comes at the expense of several times in complexity with respect to earlier standards. The high coding complexity has significant impact on the applications of real time video coding such as video conference and telephony. In order to reduce the computational complexity in H.264/AVC effectively, many fast algorithms have been developed. In this paper, intra prediction, inter partition mode selection and motion estimation with multiple reference frames are addressed.First, a fast H.264/AVC intra prediction mode selection algorithm is proposed in this work. The objective is to reduce the encoder complexity without significant rate-distortion performance degradation. The proposed method uses the frequency domain features of the target block to filter out the majority of candidate modes. By adopting DCT operation on each block, the algorithm uses the energy ratio and variance to predict the probable modes for current block. Extensive simulations verify that the proposed method speed up the intra prediction process by 67.5% on average without sacrificing the picture quality and compression ratio.When the fast frequency domain features based algorithm has been proved to be effective, its two extended algorithms are proposed. One considers the neighboring pixels to get a more accurate prediction, and the other one uses the integer DCT defined in H.264/AVC to enhance the reusability in hardware implementation. It is demonstrated by the simulation results that the two extended methods are robust and effective.Second, a residual texture based fast block size selection algorithm for inter-frame coding is proposed in this paper. Firstly, motion estimation (ME) is executed for current macroblock and the residual is computed; then the block size is predicted by analyzing the residual texture. Experiment results verify that the proposed method speeds up the block-size selection procedure by 59.85% without sacrificing picture quality and compression ratio. A comparison of the proposed algorithm with other algorithms is also provided.Third, a novel scheme to reduce the complexity of multiple reference frame motion estimation in H.264/AVC is proposed. As we know, the computational complexity of multi-reference frames motion estimation is increased in proportion to the number of searched reference frames. In order to reduce the complexity of multiple reference frames motion estimation in H.264/AVC effectively, the following factors such as frame rate, motion activity and search range are considered by the proposed algorithm. Using the motion continuity, a multiple reference frame motion vector prediction scheme is described in the proposed method. Furthermore, an all zero block detection method is used to speed up the motion estimation process. Experiment results show that the proposed algorithm can reduce the number of reference frame from 5 to 1.7 and save the multiple reference frame motion estimation time by 63.1% on average respectively with little degradation of coding efficiency.
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