Complexity Optimization For H.264 Of Wireless Application Environment

With the rapid development of wireless networking and mobile systems,video streaming in wireless environment has attracted more and more focusand research. H.264, the newest video standard, is suitable for wirelessenvironment, because it has very high compressing quality and can be robustin network transmission. However, it has a rather high computationalcomplexity in the encoding and decoding process. It is difficult to performrealtime application with the reference software provided by ITU. So we haveto optimize the process in the encoder and decoder to decrease the complexity. By analyzing the encoding process, we can find that the inter prediction isthe most time consuming module, and the multi inter modes adopted by H.264intensify the complexity greatly in inter prediction. Several fast modedecision methods have been brought forward, most of which are concernedwith the spatially information in the current picture, and some are designatedto simplify the RD process. After researching and analyzing the methods, anew scheme on temporal information is proposed. The results of interprediction in the reference P pictures are taken into consideration, not only thevariable block size modes, but also sub blocks' moving tendencies. With theirmoving status, the small blocks are reconstructed in the frames to be coded,and then the mode decisions can be made. Experiment results have shown thatthe new method will decrease the times of motion estimation at about 40%with negligible impact on coding performance. As for the decoder in wireless video environment, it is difficult todecrease the complexity by changing the decoding methods, because they arealmost fixed. So the work mainly forcus on adapting the decoding process to aspecial system architecture. Decoders with XScale CPU and WinCE OS areselected as the most typical application environment. The memoryarchitechure, cache features, and pipeline abilities are examined, and a seriesof optimization schemes are brought forward. By rearranging the memory,changing the flow of some decoding modules, locking data cache and usingassembly language to perform the function in certain modules, the decodingspeed increases remarkably and realtime decoding has been achieved.