I was looking at cave-mplayer last night. Wondering if I could face patching the mplayer sources, and installing onto multiple machines, when I came across this link - which suggested that someone was trying to check-in a similar feature - synced multiple instances of mplayer over UDP.
I followed the thread to the end, to make sure it had actually been checked in.
Checked out the mplayer source from SVN - a bit of 'apt-get build-dep mplayer' brought in everything I need to compile apart from 'yasm'. And what do you know it