i don't think mplayer has ever officially been in the debian distro.
i think it was either depending on non-free code or proprietary
codecs that technically made binary redistribution illegal. i'm not sure
if this is even true anymore (i hear it's now completely GPL too), but
i don't think it's yet made its way into debian in any case. *however*,
mplayer ships with a ./debian directory, letting debian users create
their own debs from the latest cvs source, and i think there are a few
pre-made debs on the net as well.