Originally Posted by jhoak
<iframe width="560" height="315" src="http://www.youtube.com/embed/Yn0ey0vePwI" frameborder="0" allowfullscreen></iframe>
HTTP won't work here, you need BBCode, or rather, the module's version of it.
To embed Youtube in TCF you need to encapsulate youtube's video id code (in your case "Yn0ey0vePwI" inside [YT] tags.
[YT="video caption, your choice"]Yn0ey0vePwI[/YT]
Will get you: