The Research And Optimization Of The Open Source XAVS Project

In recent years, video coding technology has been developed rapidly. AVS standard which is the second-generation encoding standard is launched in China and have the completely independent intelligent property. In order to achieve better data compression effect, AVS encoder uses more new algorithms, which increase the complexity of video compression algorithms. The reference software rm52j provided by the AVS Working Group has shortcomings in the program structural, so that it has been limited in real-time applications in the PC-platform. On this basis, the research group undertook development task which is the open source xAVS encoder of workgroup. And the research group submitted the open source encoder xAVS in 2010. Through large testing show that on the basis of pure C code, xAVS encoder performance is much better than rm52j. It not only has high encode efficiency, but also has much better imsubjective quality. Compared with the X264's performance its performance is fair. In February 2010, Shanxi Science and Technology Department organized experts identified and appraised the "high-performance xAVS encoder" which achieved the international advanced level. But xAVS encoding speed still have much room for improvement.The purpose of this project is to further optimize the xAVS encoder based on pure C code and make it a outstanding performance of open-source encoder. This paper mainly completes the following tasks:Firstly, based on depth understanding and analysis of the xAVS encoder, this project optimizes it in the C code level. In the mode selection, using the method of decision-made beforehand in Skip mode improves the coding rate. The code table of Entropy coding that is improved on the storage structure and the look-up table method, whaic makes valid code word relative centralization and reduces the offset of the search code word. The method improves the look-up table efficiency and saves Sixty percent of storage space. The multi-threading technology which is introduced into xAVS encoder completes the frame-level and macroblock-level parallel coding algorithm, while it adds the parallel processing of the read file and determining frame type. At the same time the application of the thread pool model reduces the time of the thread creation and destruction, resulting in that the encoding speed has been greatly improved.Secondly, through analyse each function module of the xAVS encoder, the most time-consuming parts of the code are found. And these modules are optimized by using SIDM (Single Instruction Multiple Data) instructions. The results show that Intel multimedia instruction has a very significant role in improving the speed of xAVS video coding encoder and has no effect on image quality.Finally, in order to facilitate the storage and transmission stream, transmission of data need to be dealt with further processing. Based on analysis of the xAVS video stream and understanding of the organizational structure of TS stream, the encoded original stream is treated twice. First of all, the original stream is packaged into a PES packet. Then PES packets are packed into the fixed-length 188B TS stream format. TS stream can play in the set-top box which supports AVS standard decoder.In summary, this paper develops a high performance open source encoder xAVS. The xAVS video encoder will become more perfect. And the encoding speed has greatly improved compared with the previouser encoding speed.