Since no one could agree on what video format should HTML 5's video tag support, why not allow it to support all the common ones like (mp4,avi,ogg...) and then to specify the type it is using like ? Or maybe why not force all html5 compliant browsers to support all the common video format using the ffmpeg codec libraries...etc.
This question about supporting video format is all about politics and saving one's own skin and making money rather than about the users. If you can put your own video format to be supported, you would be the standard and everyone follows you. Patent rules , copyrights ...etc... all the ugly side of human selfish nature emerges so seamlessly that it makes anyone feel revolting.
Or maybe why not just drop the support for html 5's video tag forever because there would always be disagreement for these stuff.
What I recommend to support is just to totally drop the idea of a video tag and wait until everyone can agree on or some open source patent and royalty free and good quality video format can be created...then can we think about adding the video tag.
On a second thought, why don't W3C or some ISO choose a standard video format or even create one if there isn't and create video converters ? This is a long way around a problem but nevertheless , it would allow the html 5's video tag to be used and the converters allow users to convert this 'new' video format to any other video format they like?