Posting a video: format ?

I am trying to post a video. I see the video formats supported as AVI, .MOV, .WMV, .MPG, and .3GP.

With that, I am trying to upload a .MP4 video file. I realize that's not listed above, but it's just a newer version of the Mpeg format. Has anyone had success with .MP4 or will I need to downconvert to MPG? When I uploaded, I didn't get any errors, but I can't find the video, so I am assuming it failed. I waited as it said it was processing, but have no results.

If no MP4 now, will it be supported in the future?