limited youtube streaming videos

hey guys
any one know how i limited speed of youtube streaming in mikrotik
please i want method working correctly 100%

i do this method but not working with usermangers users that i made it
L7Protocol =streaming
regexp=^.+(c.youtube.com).*$
ip firewall mangle
add action=mark connection chain=prerouting L7protocol=streaming passthrough=yes
add action=mark packet chain=prerouting mark connection=streaming new mark packet=streaming-packet passthrough=yes

i do this method with facebook it worked correctly