Mpeg-2 To H.264 Transcoding Key Technology Research

The development of multimedia systems brings a major influence in the area of image and video encoding.The interactivity and integration of video data with computer, cellular and television systems becomes a new problem of research worldwide.As the content representation formats increase progressively,interoperability between different systems is becoming more and more important. Video content transcoding is one of the key technology to solve the problem. H.264 as the new video compressing standard, has a better compressing ability than former standards both in video quality and compression rate. Since the most video programs are currently compressed by the standard of MPEG-2, the transcoding between MPEG-2 and H.264 is a vital issue. This thesis is focus on the research of video transcoding.This thesis is goal to reduce bitrate without decreasing the video quality obviously compared with the orignal video compressed by MPEG-2.The structure of this thesis is as following:Firstly the thesis introduces the development of transcoding and the basic theory of video compressing. Then analyses the structure and the flow of the H.264 encoder and MPEG-2 decoder. After that, this thesis uses an algorithm of MV and QP reuse. With the used algorithm, we can get 0.1~0.4dB gain in the PSNR at the same bitrate, compared with the CPDT algorithm, which just connects the MPEG-2 decoder and H.264 encoder directly. This proposal method can save bitrate by 20%~30% with only 0.2~0.5dB decreasing in PSNR,compared with the MPEG-2 encoded stream(The PSNRs of MPEG-2 encoded stream and transcoded stream are both calculated based on the same original yuv sequence). Finaly, the thesis introduces a method to optimize the mode decision of the transcoder. It can save transcoding time by 40% or so, with only 0.1dB decrease in PSNR and 2%~4% increase in bitrate. This method can also be uesd in H.264 encoder.