HTML5 video: How many video formats should I support?

I'm developing a site where users can upload their videos. I'm trying to go the "best practices" route and support playing back these videos using the <video> element, however it seems that there is an immense storage overhead associated with this.

I've read the video portion of "Diving in to HTML5" (along with other web resources), and it seems that in order to ensure cross-platform playback, one has to store the video in several formats:

1. Ogg (Firefox 3.5+, Opera 10.5+ & all Chrome versions before 6.0)
2. WebM (Firefox 4+, Opera 10.6+, Chrome 6.0+, not essential because all browsers that support it also support Ogg, but better than Ogg because of hardware acceleration support)
3. MP4 (Safari 3.0+, Internet Explorer 9, (and mobile devices which I plan on creating apps for if the site is moderately successful, so we'll leave those out))
4. Flash (all versions of browsers with lower numbers than above)

I'm curious about the number of sites that actually do this. That's a lot of storage overhead (imo), especially when the topic of storing the video in different qualities comes in to play. I'm thinking of just supporting WebM and Flash, but that would leave a sizeable portion of users under the impression that my site doesn't support "HTML5 video", when it reality it does.

Does anyone have suggestions on how many formats I should support? 开发者_如何学GoAll? Some (which)? Just flash?

Until the HTML5 video enviroment on the web improves, you should use all of them. Turns out, there are quite a few sites doing this, so for now, you should too.