From LedHed's Wiki
Blocking Youtube and other streaming media
add the following to squid.conf
# streaming download acl fails rep_mime_type ^.*mms.* acl fails rep_mime_type ^.*ms-hdr.* acl fails rep_mime_type ^.*x-fcs.* acl fails rep_mime_type ^.*x-ms-asf.* acl fails2 urlpath_regex dvrplayer mediastream mms:// acl fails2 urlpath_regex \.asf$ \.afx$ \.flv$ \.swf$ acl deny_rep_mime_flashvideo rep_mime_type -i video/flv acl deny_rep_mime_shockwave rep_mime_type -i ^application/x-shockwave-flash$ acl x-type req_mime_type -i ^application/octet-stream$ acl x-type req_mime_type -i application/octet-stream acl x-type req_mime_type -i ^application/x-mplayer2$ acl x-type req_mime_type -i application/x-mplayer2 acl x-type req_mime_type -i ^application/x-oleobject$ acl x-type req_mime_type -i application/x-oleobject acl x-type req_mime_type -i application/x-pncmd acl x-type req_mime_type -i ^video/x-ms-asf$ acl x-type2 rep_mime_type -i ^application/octet-stream$ acl x-type2 rep_mime_type -i application/octet-stream acl x-type2 rep_mime_type -i ^application/x-mplayer2$ acl x-type2 rep_mime_type -i application/x-mplayer2 acl x-type2 rep_mime_type -i ^application/x-oleobject$ acl x-type2 rep_mime_type -i application/x-oleobject acl x-type2 rep_mime_type -i application/x-pncmd acl x-type2 rep_mime_type -i ^video/x-ms-asf$ http_reply_access deny deny_rep_mime_flashvideo http_reply_access deny deny_rep_mime_shockwave #streaming files http_access deny fails http_reply_access deny fails http_access deny fails2 http_reply_access deny fails2 http_access deny x-type http_reply_access deny x-type http_access deny x-type2 http_reply_access deny x-type2