bogdan

Embeds are needed to embed video from youtube or to embed Google Map or just to embed content from external page. 
WordPress removes embed when you switch from “HTML” to “Visual” tab because of the security reasons. 
So you can embed object code using this shortcode <code>[iframe src="http://player.vimeo.com/video/3261363" width="100%" height="480"]</code>.

iframe to embed

Embeds are needed to embed video from youtube or to embed Google Map or just to embed content from external page.

flynsarmy

Allows the insertion of code to display an external webpage within an iframe. A WYSIWYG button is included to make adding the code easy.
See the ‘Other Notes’ tab for usage information.
<h3>Usage</h3>
The tag to insert the code is: 
 [iframe src=”http://yoururl.com” width=”100%” height=”600″]
You can use any attribute and it will work.

IFrame Shortcode

Allows the insertion of code to display an external webpage within an iframe.

Requires PHP 5.3 or later.

iframe to embed vs IFrame Shortcode