Research And Implementation For Video Bitstream Transcoder From H.264 To MPEG-4

The technology of digital video is receiving increasing applications, and as the rapid development of the Internet and wireless communication, the transmission and processing of digital video has been a research hotspot. Several international organizations have created some excellent video compression standard, for example, MPEG series standards, H.26x series standards and AVS audio and video coding standard of our country. These standards have some differences in aspects of grammar format, compression ability, output code rate and resolution, which seriously limits the interaction between different systems of video standards. Therefore, people are focusing on the video transcoder technology, which aims to obtain more efficient and qualified transcoding of video data between different types of systems.The purpose of this thesis is to implement an efficient transcode algorithm from H.264 to MPEG-4, at the mean time, keeping the image quality unchanged.At first, current development of video transcoding technique is introduced, and then basic principle and relevant techniques of video encoding and transcoding are presented. Through comparing H.264 and MPEG-4, a new transcoding scheme is proposed in this thesis.The maincontributions in this thesis include:(1) Reuse move vector from H.264 to MPEG-4.(2) Reuse ICT result from H.264 to MPEG-4.(3) Transcoding from H.264 baseline to MPEG-4 simple profile.A hybrid transcoder scheme based on spatial and frequency domain is proposed in this thesis. The proposed scheme adopts frequency domain scheme to increase transcoding speed of intra macroblock, and spatial domain scheme to ensure transcoding quality of inter macroblock. In this way, the scheme combines the advantages of spatial domain scheme and frequency domain scheme, achieving the trade-off between the efficiency and quality of transcoding. Since there is great difference between the H.264 and MPEG-4 standards, to realize the proposed scheme, some key techniques of transcoding are also proposed in this thesis, such as mapping algorithm from multi reference frames to single reference frame, mapping algorithm for intra prediction mode, mapping algorithm from integer DCT result to DCT result, mapping algorithm for inter block. mapping algorithm for move vector and move vector refinement algorithm. At last, based on the proposed transcoding scheme and key techniques, a transcoding system from H.264 to MPEG-4 is realized on PC.,The results tested by standard video sequences show that the proposed transcoding system achieves good performance in both efficiency and quality.