How i stop playing audio or video online,

HOW do i stop then from playing audio or video online,Ii don’t have much bandwith those systems are used for just surfing the net
thanks in advances

there is no difference between surfing and watching video. all that is http traffic through the port 80, mostly you can’t filter it. if you give a reasonable speed limit to each system, the video will be too slow and nobody will want to watch them

Thanks it a school and i use DHCP, the number of users are up to 1200 and it will be very dificult for me to specify per system so is there is way i can do it for the whole subnet?

you can use PCQ that will limit each computer …
http://wiki.mikrotik.com/wiki/PCQ_Examples