BenJD

This WordPress plugin allows you to use responsive frames in your posts, pages or templates. Implemented via shortcode our responsive iFrames are simple and easy to use. Make sure your iFrames display correctly and adapt to different screen sizes and orientations.
Adding an iFrame to WordPress
Adding a responsive iFrame is simple. A small amount of shortcode is all that is required. The shortcode can be added to a post, a page or a wordpress template. Here is a simple example: [bjd-responsive-iframe src=”https://www.youtube.com/embed/UZr75lLiE6k”] This will create a responsive iframe for a youtube video. the ‘src’ attribute is required. Other optional attributes are also available.
 Attribute 
 Description 
 Example
 src 
 The source url for the iframe. 
 <iframe loading="lazy" class="youtube-player" width="640" height="360" src="https://www.youtube.com/embed/UZr75lLiE6k?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation allow-popups-to-escape-sandbox"></iframe>
 id 
 Sets an id attribute for the iframe 
 youtubeVideo
 name 
 Sets a name attribute for the iframe 
 Example
 width 
 Sets the width attribute for the iframe 
 420
 height 
 Sets the height attribute for the iframe 
 300
 frameborder 
 Sets the frameborder attribute for the iframe 
 0
 scrolling 
 Sets the scrolling attribute for the iframe 
 yes OR no
 marginheight 
 Sets the marginheight attribute for the iframe 
 0
 marginwidth 
 Sets the marginwidth attribute for the iframe 
 0
Here is a more complicated example: [bjd-responsive-iframe src=”https://www.youtube.com/embed/UZr75lLiE6k” id=”youtubeVid” name=”youtubeVid” width=”560″ height=”315″ frameborder=”0″ scrolling=”no” marginheight=”0″ marginwidth=”0″ ]
Demo
A demonstration for the plugin working on wordpress 3 can be found here ( http://www.bj-dehaan-solutions.com.au/demos/wordpress3/responsive-iframe-demo/ ). 
A demonstration for the plugin working on wordpress 4 can be found here ( http://www.bj-dehaan-solutions.com.au/demos/wordpress4/responsive-iframe-demo/ ).

BJD Responsive iFrame

Automattic

Donncha O Caoimh (a11n)

Michael Adams (mdawaffe)

Unfiltered MU gives Administrators and Editors the <code>unfiltered_html</code> capability. This prevents WordPress MU/WordPress 3.0 multisite from stripping <code><iframe></code>, <code><embed></code>, etc. from these users’ posts. Authors and Contributors do not get this capability for security reasons.
The plugin can either be used globally for your entire MU site, or it can be applied on a blog-by-blog basis.
For WordPress MU or WordPress 3.0 multisite only. Regular WordPress already offers this feature and does not need this plugin.
Warning! This is a very dangerous plugin to activate if you have untrusted users on your site. Any user could add Javascript code to steal the login cookies of any visitor who runs a blog on the same site. The rogue user can then inpersonate any of those users and wreak havoc. If all you want is to display videos on your WordPress MU blogs, use the native <a href="https://codex.wordpress.org/Embeds" rel="nofollow ugc">Embed Support</a>, <a href="https://wordpress.org/extend/plugins/vipers-video-quicktags/" rel="ugc">Viper’s Video Quicktags</a> or any of the other <a href="https://wordpress.org/extend/plugins/tags/video" rel="ugc">video plugins</a> on WordPress.org. 
If you use this plugin your site will be hacked in one way or another if you allow anonymous users on the Internet to create blogs on your site. It’s very dangerous.
Are you still 100% sure you want to use this plugin?

Unfiltered MU

I love when plugins are so cleanly written and do their trick without hassle. Especially after 8 years of no updates. Though they should submit an update just to remove the "2 years old" warning...

Still works! March 2017

This WordPress MU/WordPress 3.0 multisite plugin gives blog Administrators and Editors the ability to post whatever HTML they want.

BJD Responsive iFrame vs Unfiltered MU