QuickTime X has a drop-dead simple way to extract the audio from a movie file and save it out as a separate entity. Here’s how easy it is.
First, you’ll just open your video in QuickTime and choose File > Export.
The familiar Mac OS X dialog box will pop up, asking you where you’d like to put your exported file.
If you toggle the Format option near the bottom to Audio Only before you start the export, QuickTime will save just the audio out as an .m4a file, ready to be imported into iTunes.
Or ready to be put anywhere else you like, really. You are the boss of your .m4a files, my friends.