| Summary: | 碩士 === 義守大學 === 電子工程學系碩士班 === 99 === The embedded system of video encoder/decoder has become a new trend due to the applications of mobile multimedia and the consuming electronic products required in the life. For the considerations of low cost and high efficiency, we adopt the ADSP-BF548 developed by ADI to embed the H.264 main profile (BP) video encoder system. Though H.264 can achieve the transmitting of high quality video, the encoding complexity is relatively high. In the H.264 encoder, we can find that the motion estimation (ME) module of H.264 encoder consume much encoding time. In order to reduce the encoding complexity, we proposed an efficient sub-pixel ME algorithm (ESPMEA).
In the thesis, we first exploit the high correlation of the neighbor blocks to find the prediction motion vector (PMV). We use the PMV to predict the corresponding motion vectors (MV) of 7 modes. If a block it is likely to have a small cost at MV(0,0). Therefore, we define the thresholds (THZs) of zero-motion blocks for seven block sizes to determine if the ME will be early terminated. The THZs for different block sizes is selected according to experiments on many sequences. In mode 1, since one macroblock (MB) contains only one 16×16 block, if the zero- motion cost is smaller than the mode threshold (THS), the 16×16 mode is the best mode of this MB and the ME is stopped. In addition, in order to further speed up the encoding time and improve video quality of H.264, we also combine the methods of fast ME algorithm (UMHSA) [14] and fast hierarchical sub-pixel ME algorithm (FHSPMEA) . Finally, the proposed ESPMEA and full search algorithm (FSA) are implemented to the embedded H.264 BP video encoder.
Experimental results show that the proposed ESPMEA can achieve an average time improving ratio (TIR) about 99% and TIR about 73% when compared the FSA embedded in ADSP-548 for ME module and overall H.264 encoder, respectively, with insignificant loss of image quality.
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