The way I extract just the audio from a video is probably not very professional but its rather easy and still sounds good.
just play the video on youtube and click the record button in audition.
you'll have to go first into your computers recording devices and select Stereo Mix so it records it without outside noise but like you'd hear it if you had earphones in.
then just record it and it should work.
i did that once for a song and it sounded pretty good.
hope it helps and there probably are far better ways to do this than i know. :)