I usually try to look them up on Youtube + download them using Youtube to Mp3 first BEFORE I do anything myself.
If such a thing does not exist- there is a chance that you can download the video directly from the site,
edit it in a video editor (I just use Windows Movie Maker so it doesn't have to be super fancy), save it and then use a separate
site to convert the video to an MP3 file.
The problem with this though is that it does NOT work with background music. Trust me, I've tried to do so with G3 movie background music, and
the voices are embedded within the music files. UGH. I was so mad.
So it depends on what you want but it's probably possible.