Architectures and Analysis about Video Transcoder
视频码流转换编码器结构及其分析

Along with digital AV and multimedia technology developing, large numbers of video datum need to be compressed. At present ,the International Coding Standards, such as MPEG-1, MPEG-2, MPEG-4, H.261, H.263, H.264 have been established and applied to different application areas. In order to adapt to heterogeneous client terminals and transmission characteristic of networks, pre-encoded video should be transcoded into another coding format. So, the resources of networks can be shared. The content of this paper is about how to convert a previously compressed video bitstreams into a lower bit-rate video bitstreams according to the requirements of heterogeneous client terminals, such as bitrate transform by changing quantizer parameter, spatial resolution transform by down-sampled, temporal resolution transform by skipping frames. In this paper the architectures and mechanism of transcoder are analyzed and the best tradeoff between quality and complexity are offered. Also the core technique: how to obtain the motion vector is anatomied.