Research On Reducing Spatial Resolution Transcoding From MPEG-2 To H.264

With the abroad application of multimedia and the rapid development of the internet, video coding technology become more and more mature, different coding standards(MPEG-1,MPEG-2,MPEG-4,H.263,H.264 and so on) have abroad application during different time and in different environment, in order to make these video resource transparent transmission and effectual share, video transcoding technology has become a study focus internationally.Although MPEG-2 standard have been widely used in digital TV and DVD and have a lot of good quality video resources, but its bit-rate too high, not suit to the application of wireless network. At the same time, the mobile device(such as 3G telephone and PDA) commonly have low spatial resolution and bad computing ability. Therefore, the video data in wireless network must have low bit-rate and low spatial resolution. But H.264 as the new generation video compression standard have the good performance, such as low bite-rate, good video quality and transmission credibility, suitably applied in wireless network. So the research on MPEG-2 to H.264 transcoding with reducing spatial resolution has become a new attractive topic in video transcoding.Firstly, this paper analyzed the key technology of MPEG-2 and H.264 standard, compared the similarities and differences of them. Then discussed the advantage and disadvantage of the four typical video transcoder, researched the two key questions of transcoding:the composition of motion vector and coding mode decision. Finally, an algorithm of MPEG-2 to H.264 with reducing spatial resolution was presented, it used the useful information of MPEG-2 to accelerate the procedure of H.264 recoding, reduced the motion estimation procedure which take up 70% time of coding. The main innovation is mainly reflected in the following:(1)After video 2:1 downsampling, the composition procedure of 8×8 blocks considered the direction of MV, which make the composition procedure more accurate; (2)Presented an algorithm of using the composition of AC coefficient to partition the 8×8 block after 2:1 downsampling, considered all of the seven block mode of H.264 standard during transcoding, it can improve the quality of transcoding and have less computation, easy to implement.The experimental results demonstrate that compared to Full mode algorithm, it can save 87.02% of average coding mode decision time with negligible degradation in video quality, and in favor of the real time application.