http://forums.microsoft.com/msdn !!!
Beaten to my own stories again. You can
be sure that I'll have more to say on this later. At the moment I'm actually
still working to fix an issue with a demo video I did for our internal mail.
Apparently not all codecs are created equal. 
Fonte: http://blogs.msdn.com/jledgard/archive/2005/04/07/406384.aspx