Wikimedia only accepts video in Ogg Theora format, because it’s not patent encumbered (and Dirac is not yet ready for prime time). Nothing produces this by default. Fortunately, Firefogg will do the job for you on Firefox 3.1 (which is that cool, by the way). Brianna Laugher’s posted (1, 2) a couple of useful guides to the fancy media stuff we’re doing.
The Mozilla Foundation has also given the WMF $100,000 to improve Ogg Theora. The goal is to get it as good as H.264. This is actually considered feasible.
(And MPEG LA plans to charge for H.264 encoding after December 31st, 2010. Some people are going to get a horrible lesson in why encumbered formats are a problem.)
Take that, Apple, Nokia! Lying arseholes.