After we arranged the limit rapidshare, YM, and other now we arrange the limit to youtube
1. Make http-video layer7-protocol

/ip firewall layer7-protocol
add name=http-video regexp="http/(0\.9|1\.0|1\.1)[\x09-\x0d ][1-5][0-9][0-9][\x09-\x0d -~]*(content-type: video)"

2. Make Mangle Mark Packet http-video

/ip frewall mangle
add action=mark-packet chain=prerouting comment="http-video mark-packet" \
disabled=no layer7-protocol=http-video new-packet-mark=http-video \

3. Make Queue Simple http-video

/queue simple
add max-limit=0/64000 name=http-video packet-marks=http-video

Source :