This depends on the video format. I tried it with an MP4 and it did not work. What a complete mess. I use Linux and ffmpeg to extract the audio but I would not suggest that to everyone unless you know Linux.
So my impression of what he's asking is can he upload something like an .avi and get an .mp3 back. That is to say uploading a video to the music library would extract the audio only.
I dunna thin this wuhd work cap'n. I don't think this site is that sophisticated in its programming.