Need to edit AVI movie clip SOUND ONLY and re-save to original movie clip
 

I know that Audacity can extract the audio from a movie clip, then edit it, BUT, how do i save the modified audio back to the original movie? I want the old audio out, and the modified audio put back in in its place. Also, how can I extract ONLY the video from a movie? I only see ways to extract the audio.

Thanks

Take a look at Avidemux2. It is very good at conversions and demuximg, as well as splitting out audio from video.