The Research And Implementation Of H.264Video Decoder Based On Android

With the rapid development of mobile communication technology and multimedia technology, Mobile video service such as mobile video game, mobile video surveillance, mobile TV has developed rapidly, which makes the media streaming service become possible. Therefore, the Smartphone has become the mainstream in today’s mobile phone industry and it has a bright future and potential commercial value. Due to the characteristics of the mobile phones with limited resources, how to achieve H.264video decoder is of great significance.As the most advanced H.264video compression standard, with good quality performance in compression efficiency, data flow and fault tolerance. However, the improvement of H.264’s decoding efficiency is at the cost of the increase of computation complexity. Thus, how to optimize the H.264decoder in the Android system to guarantee smooth playback of the H_.64video is becoming an exact topic. The contents and results of the research are presented as following:1. After studying the decoding principles of H.264video compression standard, the paper analyzes some key technologies in H.264decoding such as inter-frame prediction, intra-frame predicdion, integer changes and quantitative and the effect of deblocking filter. The paper also optimizes the judgment method of the interpolation process in inter-frame prediction and pixels of crossing the line to provide the theoretical foundation for realizing H.264decoding.2. Pose the improved Of CAVLC decoding algorithm,as the length of the code word of CAVLC(Based on the context of the adaptive variable length coding)is not fixed,which has a great impact on decoding speed,it becomes a main reason for the limitation of their widespread.In order to solve this problem,this paper studies the CAVLC decoding algorithm of the H.264standards,after analysis of the characteristics of CAVLC code,proposes an improved CAVLC table lookup algorithm. The algorithm will be appropriate to sub blocks to narrow the scope of its look-up table, the code table can be avoided to look up in process of lookup table,thereby increasing the decoding speed of the decoder in the decoding process.The simulation result shows that this algorithm for each frame image decoding speed is increased by about1.55%, ultimately,this paper achieved certain effect of decoding optimization.3.Due to the characteristics of the mobile phones with limited resources, the paper needs to do cutting optimization for FFmpeg Source Code in order to realize the smooth decoding in Android system, the paper mostly optimizes from two aspects:one is from basic operation which improves the computational efficiency by using shift instruction instead of division; the other is from code level which processes loop structure accordingly to achieve high-activity processing. Finally, using NDK provided by Android to port FFmpeg code to the target platform. According to emulation realization, decoding display is achieved on Android2.3simulator. The result shows that decoder basically meets the demand of real-time.