Research And Optimization Of MPEG-4 Video Decoding System Based On MX21 Platform

People obtain information mainly through acquiring the video information,now with the development and improvement of chip manufacturing technology and digital image theory,the embedded multimedia productions are more and more popular in markets,and strongly attentioned by public.Most of all,The multimedia ones put embedded processor as the core,such as ARM,PPC,MIPS,and so on; Integrated the Linux or WINCE operation software and GUI,these productions have such features:convenience,stability,and more powerful,can be satisfied with people, so very popular with public.The content of the paper is discussing the encode and decode technology of MPEG-4,propose several important optimizations,enhance the speed of decoding MPEG-4,get the achievement of real-time playing multimedia files smoothly on Embedded Platform.The paper introduces the hard-ware,i.MX21 platform from the corp FreeScale;Introduces Linux OS and Mplayer software;Introduces the encoding and decoding algorithms and features of MPEG-4,emphasis on texture decoding and motion compensation,texture decoding consists of VLD,Inverse Scan,Inverse AC/DC,IQ and IDCT;With the Gprof tool,analyse some equations that work on decoding base the MX21 platform,and summarize two ways of optimization:the decoding and video out by hardware;analyse the structure of Mplayer;propose the arithmetic of simple IDCT, Half-pixel interpolation,simple division,Float-point to Fixed-point and video out with PP hardware module,these optimizations are all done in Mplayer.Lastly, introduce the result of testing on MX21 platform.For the view of testing result,Mplayer plays slowly while decoding a multimedia file before optimized,the phenonmenon with serious off-frame,but after optimized,Mplayer plays well and smoothly with no off-frame,basically the QVGA decoding speed can be 25f/s,fully able to be satisfied with the requirements of video appreciation,and real-time playback.