OK so everyone’s been raving about how the fall update has added divx playback to the 360 which is all good and well but then there’s the folks out there that use iTunes.
Apparently, when you download/subscribe to vidcasts through iTunes, some of them are in mp4 format (the extension is actually m4v). OK, enough of this boring stuff, how do you get these files to work with your 360? Easy: just change the extension to .avi. I only use iTunes for audio podcasts so I can’t say I’ve tested this but hey, if you’ve got vidcasts lying around that you want to stream to your Xbox, try it.
Source: Random Nothings Blog