The Realization Of Real-Time MPEG-2 Transrating System And Research On Rate Control Algorithm

As the popularization of digital television, the development of mobile television, IP television and video exchange on the Internet,,in order to satisfy the varies transmission bandwidth, Appliances on demand for coded video processing is widely used. So we need to develop a digital video transrating head-end system. The main function of the system is transcoding the MPEG-2 coded video to the target bit rate.In order to get better video quality after transrating, the system uses the close loop transrating algorithm. first store the drift error cause by quantization in reference frames and then compensate the drift error to P and B frames according to motion vectors.Rate control play a key role in the transrating system, it is the only part that dos not prescript in the coding standards, so it can be realized in varies forms. This paper first study the TM5 rate control algorithm for MPEG-2 and propose an improved transrating rate control algorithm based on TM5. Next, based on the analysis of coded stream, two rate control algorithms with stream analyzed are proposed. One is transrating rate control based onρdomain model, the other is flexible complexity fast rate control. Test results show that these two algorithms can control the output bit rate accurately。The average Relative Rate Control Error is up to 4%, less than TM5 1% to 6%.This transrating system is first developed on the TI DM642 platform, can handle one real-time D1 format video stream. Then it was transplanted to a 32-channel transrating board with one DSP C6455 and two FPGA XC4VLX60 chips. This paper gives a detailed description of the 32-channel transrating system.