FAQ: Why will by embed/iframe code not work?
When I paste embed or iframe HTML code on the “Text” tab and then “Publish” the post, my embed and iframe code is stripped out. I am the site administrator, why is this happening?
WordPress Multisite (which is what Virginia Tech is running) does not permit straight embed codes or iframes (i.e. unfiltered HTML) for anyone but network administrators. It’s a security precaution, as embedding and iframes are two ways malicious code gets injected into WordPress sites.
Good news, though: there’s an “internal whitelist” built into WordPress that allows embedding of YouTube and Vimeo videos. See the Whitelist for a complete list and more information: http://codex.wordpress.org/Embeds. The trick is simply to put the plain URL into the visual editor box (i.e. the “Visual” tab). Once you do that, the video is embedded automatically.