i recently ran across avidemux, “a free video editor designed for simple cutting, filtering and encoding tasks”. i actually only use it for demuxing the audio streams of video downloads, but recommend it over the other demux options that i’ve tried. i’m not interested in video editing, i don’t want to change the audio format at all (except for listening in my car ^^ )… i just want an unchanged, demuxed copy of the audio stream. and avidemux seems to do just that, quickly, and even lets you pick which audio stream if there’s more than one. there have been a few shows that wouldn’t demux – i’m not sure why – but generally it’s worked great.