Media shifting

Jon Udell is talking about media shifting to listen to just the audio portion of video programs while doing other things. I’ve been looking to do this for a few weeks now. Specifically, I want to be able to pull the video of off my ReplayTV (DVArchive does that for me) and then rip the audio stream out and convert it to MP3 or AAC to listen on the iPod. So far, I have been able to find a nice Mac tool to do this. One tool would be ideal, but even two tools (one for demuxing the video and another for the conversion) would be fine.