mpeg4-es hasn't file header same as avi header , but it have simple mpeg4-es header, about 20 bytes. mpeg4-es file is made up of many mpeg4 frames. So no filters for example divx' filter cann't play the file.
I had the same problem with the MPEG4 files, Windows Media player, and DivX, or Creative cannot open it even though I have a MPEG4 codec, not to mention DivX 5.05 Pro and all the others. Haven't tried it in Linux yet though, maybe see if Knoppix 3.2 will play it back. But then again it was downloaded and I didn't encode it myslef to who's to say it's just not a corrupted file...