I have a bunch of 1080p WMV files where I want to transcode the audio tracks. The files are WMV3 for video and WMAP for audio but there are just so many media players that don't support WMAP audio, VLC on the Mac being my player of choice. I'm looking for a cheap way to transcode just the audio track to WMA2 leaving the video track untouched (cheap meaning as close to free as free can get). Losing a bit of audio quality isn't a big deal to me as long as the track stays in sync.

My primary computer is a Mac but I have a couple Windows laptops running XP Pro that I can use too. Any suggestions would be most welcome.