Bandwidth split?

["J Webster" <webster_jack@xxxxxxxxxxx>]

It is becoming apparent that some users are hogging the bandwidth on the 
server by downloading videos instead of streaming them.
Any idea on how I can restrict this?
I would like to keep the server as unlimited downloads but split the 
bandwidth at any one time between the users - I figured that this was shared 
automatically but it seems anyone downloading a lot gets more use of the 
bandwidth?