While playing the vid, you can simply capture the audio being produced by your audio card with something like CD Wave. Just make sure you dont have anything else playing at the same time otherwise you'll obviously capture that too.
Its easy to do and there are a few programs around that will do it.I've been using a program called Tubehunter it works well and will automatically convert from .flv (flashvideo) to .avi
Can be found on torrent sites if you aren't willing to fork out the US$29.95
vixy.net will do it, much easier than using a capture program, but the quality kinda sucks. I'm assuming this is youtube in general, but i guess it could be their converters....
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Just make sure you dont have anything else playing at the same time otherwise you'll obviously capture that too.
Can be found on torrent sites if you aren't willing to fork out the US$29.95
Issue is discussed Here in detail