You're right on the former, I was under the impression that it was an economy-of-effort thing rather than an ideological thing. However, I'm not sure I agree that it would be as hard as you think. The mime types are registered here[1] and the impls are here[2]. Each media type is implemented as a state machine that could wrap ffmpeg. That's where I would start, I suspect.<p>EDIT:
Looks like someone's already blazing that trail[3]. They're using gstreamer, but the research they do for that will show anyone how to add a new one.<p>--<p>1) <a href="http://hg.mozilla.org/mozilla-central/file/b27f05c8743b/content/html/content/src/nsHTMLMediaElement.cpp" rel="nofollow">http://hg.mozilla.org/mozilla-central/file/b27f05c8743b/cont...</a><p>2) <a href="http://hg.mozilla.org/mozilla-central/file/b27f05c8743b/content/media/" rel="nofollow">http://hg.mozilla.org/mozilla-central/file/b27f05c8743b/cont...</a><p>3) <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=422540" rel="nofollow">https://bugzilla.mozilla.org/show_bug.cgi?id=422540</a>