Based On Dsp H.264 Encoder Implementation And Optimization

In recent years, with the increasing popularization of the Internet, the rapid development of mobile communication and multimedia operation, video applications have been expanding seriously. Thus, an efficient and smart embedded video compression system has not only theoretical significance, but also practical value. As a latest international video coding standard, H.264 has improved the coding efficiency remarkably compared with previous standards. At the same time, the computational complexity of the encoder is increased dramatically. Furthermore, rapid development of the digital signal processor (DSP) makes the portable digital video communication terminals possible. With its strong parallel processing ability and signal processing capacity, TMS320DM642 which developed by TI Corporation is an ideal platform for developing H.264 encoder. The main achievements of this thesis are focused on implementation and optimization of H.264 encoder based on TMS320DM642 platform.According to the analysis of key techniques exploited by H.264, the thesis analyses the prediction algorithm which is the most time-consuming module in detail. For intra prediction case, utilizes the characteristics of high probability of most possible mode and the correlation of optimal mode and sub-optimal mode are utilized to make a fast selection for Intra4×4 mode. Meanwhile, the texture characteristic of the macroblock is adopted to decide whether or not to skip Intra16×16 mode, which reduces the complexity of full search algorithm. An improved motion estimation algorithm based on adaptive hexagon-diamond pattern and half-stop strategy to reduce search points and improve coding efficiency. In the algorithm of inter prediction mode selection,fast selection of prediction mode is achieved according to the correlation of video sequence and elimination of some inter prediction modes by comparing the results of searched modes with adaptive threshold combining with the rules of block merge.On the aspect of DSP solution, firstly, according to the structure of DM642 and the characteristics of H.264 encoder, this paper adjusts data flow and variable definition and allocates memory reasonably so as to make the framework of redesigned encoder adapt to the embedded system. Meanwhile, the QDMA data transfer mechanism is adopted to eliminate the bottleneck of data access inside and outside the chip. Secondly, Several techniques such as compiler option, data packing, inline assembly and application of pipeline, linear assembly language and characteristic of two-level cache structure of DM642 are adopted in the process of H.264 encoder optimization.Through the optimization of algorithms and DSP, the encoding speed of H.264 encoder has been improved largely compared to original code in the case of a little losses of image quality.