Mozilla’s Chris Double has announced on his blog that he’s implemented the (proposed) HTML5 <video> element in a build of Firefox (demo screencast). The element will natively support OGG Theora files.
While I think this is great news and has a lot of potential, I foresee one major obstacle to this becoming standard: proprietary codecs. If they decide to implement it, Apple will want Quicktime in Safari, and Microsoft will want Windows Media Video in Internet Explorer.
As one commenter notes, the idea will be to have fallback options for anyone who doesn’t have an OGG player, probably in Java; there are some examples of how this will work on the Wikipedia Video page (caution: this caused Firefox on OS X to crash, although Firefox on Ubuntu played it perfectly).
Theora is obviously the most common‐sense cross‐browser, cross‐platform, non‐proprietary solution; but since when has the internet been governed by common sense?
Update: Since writing this post, I’ve found out that Opera also has an experimental implementation.