Separating Audio and Video

I have several video files that I downloaded from YouTube that I want to extract out the audio to play on a CD.  I use NERO, but after I unlink the audio from the video in Nero Video I can't see how to export or save it as an audio file.  Maybe I need a different program?  I use Windows 7, and would like to end up with an MP3 or WAV file.

Please advise.

Thanks,

Phil