I wasn't even thinking of looking at where the traffic is going. You end up with a very characteristic pattern of bandwidth usage that can be detected, on that

I wasn't even thinking of looking at where the traffic is going. You end up with a very characteristic pattern of bandwidth usage that can be detected, on that basis alone. It'll false positive and false negative sometimes but on average it'll be good enough. We're not talking cutting connections off, just throttling. If something other than video streaming briefly slows down, who's going to know to blame a false positive on the streaming throttling?