For Mobile Video Applications, Mpeg-2 To Avs-m And H.264 Video Transcoding Technology Research

With the development of mobile video services, the mobile terminal devices are widely used, such as mobile telephone, PDA etc. So high performance video services are deeply needed and are becoming a new focus. As we know, the terminal devices have some common characteristic, such as small display screen, low computational ability etc. And limited by the channel bandwidth, the transmitted video stream is usually in low bitrate and low spatial resolution. MPEG-2 video compression standard is designed for digital video broadcast, HDTV and DVD. Now, it is widely used in our daily life and various industries, so most of the video data is compressed and kept in MPEG-2 format. But the video data bitrate in MPEG-2 is a little high and it is not suitable for wireless lan application. To meet such a demond, the new generation video compression standard (e.g. AVS-M, H.264/AVC) is invented which can be well used in accessing multimedia resource. Video transcoding is such a key technique to realize such a conversion.In this thesis we first review the development of video compression standard and video transcoding techniques. Then point out the new problems with the new compression standard in transcoding and show what we will focus on.Second, we mainly focus on fast mode decision in reducing spatial resolution transcoding from MPEG-2 to AVS-M or H.264/AVC. As the video standards adopt more modes for motion estimation, the computation complexity increases more. Our resolvent considers such new characteristic abundantly. In reducing spatial resolution transcoding, we analyse the decoded information and do some merge or split operations to directly find the best motion estimation mode. By reducing the complexity of motion estimation which consumes the most time of encoding, the transcoding speed is highly increased.Third, we focus on the research of dynamic frame skip in transcoding. In low bitrate transmission, to increase the subjective video quality, we designed a new dynamic frame skip algorithm which is based our frame similarity concept. Comparing all the existing judge rules in frame skip, we select the most suitable one to implement in our scheme. Furthermore we consider the decoded motion information to improve the utility of our dynamic frme skip algorithm.In the end, a simulative stream system is introduced. Our transcoding algorithm is applied in it which could prove the performance of our algorithm.