Research And Implementation For Video Bitstream Transcoder Between H.263 And MPEG-4

Digital video is much better than analog video, The development of digital video accelerates the development of multimedia, video communication and digital TV. Many international video compression standards have been established for various applications and periods. These standards have many differences on syntax, resolution, bitrate and compression efficiency. The corresponding transmission media and the ability of terminal processing are different too. The technology of video transcoding solves these problems and makes the communication between different system and terminals seamlessly. The transcoding of compressed bitstreams is to transcode a compressed video stream from one format or standard to another.Based on heterogeneous transcoding, the transcoding between H.263 and MPEG-4 is researched in this paper, including the transform of bitrate and space resolution. And the transcoding system is implemented on PC.First, the transcoding technology is introduced, after discuss the two video coding standards, a detail compare of them is made and some problems of tramscoding are discussed. In this paper, a transcoding architecture based on pixel domain is proposed. In order to improve the transcoding efficiency, some algorithm including MV mapping and mode mapping are used. Due to these algorithms, the computation quantity is reduced greatly, and the transcoder works faster. Motion re-estimation is used to improve image quality. Spatial resolution transition is realized in pixel domain, three downscaling algorithm are compared in this paper. And the rate transition is controlled by rate control algorithm. Finally, the paper realizes a near real-time transcoder operating between H.263 and MPEG-4 on PC, with the structure and algorithms mentioned above.