How do Linux distributions distribute H.264 and AAC decoders? Debian does, Ubuntu does, Fedora does, basically everything in the world except GNUsense does--yet they do just fine with themselves.

The best solution would be to simply use system decoders, like Safari does. On Windows, this would be Directshow, on Linux this would be Gstreamer, and on OS X this would be Quicktime. The browser should have ABSOLUTELY NOTHING to do with video and audio decoding.