[Ffmpeg-user] How can I get the m4v video stream from a mp4 avi file.

HI ,experts: I want to get the m4v video stream from the avi file , in which the video is mpeg4 and audio is mp3 How can I get the video part out and keep the same subjective quality? I think we need not to do the transcode and just split the video ES stream out is enough. I try to achieve it but failed. I can get the audio part out. The command I use is: $ffmpeg -i test_0000.avi -s cif -f m4v -vcodec mpeg4 MVI_0000video.m4v In this command, the video part is coded again by mpeg4 encoder and the quality degrades too much. Thanks.