I was looking for a free software for extracting an audio track from a movie.
I found one that does much more: it's called MPEG Streamclip, and it is produced by an italian company called Squared5.
It is a powerful video converter, player, editor for Mac and Windows. It can play many movie files, not only MPEGs; it can convert MPEG files between muxed/demuxed formats for authoring; it can encode movies to many formats, including iPod; it can cut, trim and join movies.
MPEG Streamclip can also download videos from YouTube and Google by entering the page URL.