This doesn't work.
Code:
mplayer tv://
However, specifying fps does.
Code:
mplayer -fps ## tv://
Just replace ## with however many Frames Per Second you want.
If you're not root, then type sudo before mplayer.

I also don't think that mplayer is designed for video chat, but, correct me if I'm wrong.
Don't know why anyone would want to video chat in BT, but w/e, who am I to judge?