I'm really not that big of a fan of the mplayer plugin. Why not apt-get kaffeine and the kaffeine plug in? I think they work much better. The kaffeine plugin will not embed the video into your browser. It will open up kaffeine and play your video there. The upside is that it seems to pretty much just work whereas I find that the mplayer plugin just chokes on a lot of streams. Also kaffeine will let you save any stream that it opens. This comes in handy some times.