blocking real player ports

I have a frame relay setup to one of my office sites that has suddenly started moving at snails pace.
On a trip there I realised that one of the users has real player using a online radio station.
I’ve asked him to turn it off for a few hours so Ican trouble shoot the slow connection problem.
And I’d like to ensure that its not an issue by blocking the port it comes in on.
Does anyone know what that is ?