User blog comment:DaNASCAT/Technical Update: June 11, 2013/@comment-4981281-20130612014407/@comment-3335785-20130613002308

In the interests of complete information, RuneScape Wiki uses a parameter specified in a template to inject an iframe (this is largely how Wikia does it on their file pages), rather than using straight  tags.

If anyone's interested the script can be found here and the relevant template here. We also have a script that automatically converts any youtube tags added to that template which successfully prevent any videos being uploaded to the wiki.