The Research On H.264 Spatial Downscaling Video Transcoding

With the development of network and multimedia communication technology, the need for providing video services on mobile devices is stronger and stronger. For these mobile terminals, they share some common characteristics, such as small display screen, low computational ability etc. Moreover, they are restricted by the bandwidth of mobile wireless network. MPEG-2 is one of the most widely used video coding standards. Because of its high bit rate after compression, it is not appropriate for application in wireless network. H.264 is the latest video standard. Because of its excellent performance, it will be widely used in near future. To meet the need of mobile video terminals, this thesis researches on the video transcoding between MPEG-2 and H.264.After a brief introduction of video coding principles, especially the MPEG-2 and H.264 video standards, the techniques for video transcoding are summarized. The main work of this thesis is outlined as follows.First, a spatial downscaling transcoding algorithm between MPEG-2 and H.264 is proposed. It full utilizes the motion vectors and predictive residues gathered in MPEG-2 decoding to greatly decrease the computational complexity of macroblock coding mode decision and motion vector re-estimation in H.264, and generates the H.264 bit streams. Experimental results on several video sequences demonstrate that it can significantly reduce the computational complexity of the transcoder with just slight sacrificing the rate-distortion performance, which does benefit to real time transcoding.Second, a fast multiple reference frames selection algorithm is proposed to decrease the high computational complexity in H.264 encoder. It adjusts the search range of every reference frame according to the analysis of the probability of frequently occurred best reference frame and the best reference frames of neighboring blocks. The proposed approach is faster than the reference software, while keeping almost the same video quality and bit rate. It can do benefit to the real time application of H.264 codec.