Too often, we see Mozilla people promoting some new cool open web idea with a very uncool closed Flash-based video. Which is rather shooting ourselves in the foot. (Kudos to those who at least offer a “click here for Ogg/WebM version” link.)
There isn’t yet, as far as I know, a major hosting site which will serve HTML5 video to supporting browsers by default. (Anyone know different?) But LibrePlanet has now written a HowTo to explain how to get a video on YouTube while guaranteeing it will have a WebM version, which will be served to anyone who has opted into the YouTube HTML5 beta, regardless of the resolution of the video (previously, only high-res videos got transcoded).
DailyMotion, who have been strong supporters or HTML5, also seem to have an opt-in beta. But I don’t know how to guarantee that an uploaded video will be served as WebM.
I also don’t know if anyone is yet serving HTML5 video markup for embedding. Further information would be great.