Youtube bandwidth eater is a main headache for network administrators . Here you can see how to block Youtube with squid.
The MIME type of youtube video is "video/x-flv". Creating an ACL to block this is easy.
Modify squid configuration file /etc/squid/squid.conf
add the following lines in the ACL section
First, create an ACL which matches the MIME type in question:
acl deny_rep_mime_flashvideo rep_mime_type video/x-flv
Then create a HTTP Reply ACL which denies any replies with that MIME type:
http_reply_access deny deny_rep_mime_flashvideo
This has been verified to block Youtube flash video
If the content is blocked the following similar line will be seen in access.log:
2282485683.146 903 127.0.0.1 TCP_DENIED_REPLY/403 3143 GET http://td.v17.cache4.c.youtube.com/videoplayback? - DIRECT/126.96.36.199 text/html