Taking the audio out of a video is very easy when using GarageBand. You can even add the audio clip to iTunes and listen to it on your iPhone.
The first step is selecting your .m4v file and dragging it into GarageBand. Then GarageBand will create a Movie Track Thumbnail and an Audio Track. You will need to select the Movie Track and delete it by pressing Command + Delete.
After, crop the section of audio you want by dividing the track using Command + T (make sure the track is selected) and then select the part you would like to get rid of and select Delete.
Finally, when you are done go up to the menu bar and select Share and scroll to Send Song to iTunes. Fill out the Song Name, Artist Name, and other information. Press the Share button on the bottom and it will load into iTunes.