Some times network admins want to block flash videos from  being played on the network. You can configure  Squid proxy server to do the same if we block the appropriate MIME type.
The MIME Type reply is generally set correctly so browsers are able to pass the reply to the correct module (image, text, html, flash, music, mpeg, etc.)

The MIME type for flash videos  is “video/x-flv“. Creating an ACL to block this is easy.

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

If the content is blocked the following similar line will be seen in access.log:

1282485682.146    903 127.0.0.1 TCP_DENIED_REPLY/403 3143 GET http://tc.v15.cache3.c.youtube.com/videoplayback? – DIRECT/208.117.252.163 text/html