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Mozilla is going to implement gstreamer backend for html5 video element. See Bug 422540.
Also, Opera developers are going the same way. See this blog post.
Using gstreamer as a backend will eliminate ALL the problems with codecs. Forever. It will be able to play just the same as a usual desktop players, and that means, it will be able to play Ogg Theora, H.264, DivX, whatever you like - it's only a matter of plugins installed.