ladislav.soukup

This is simple shortcode to embed responsive iframe to your post. Iframe will hold the specified ratio when page is rescaled.
[rframe ratio=”16×9″ src=”http://flixel.com/player/snqi608mlq1h98w5p9jy” width=”60%” /]
<h4>How it Works</h4>
DIV block with specified width is creted. Inside is transparent PNG file with specifed ratio scaled to 100% width and height set to auto. This image will scale the main DIV to size with correct ratio. 
Embeded IFRAME is then set to fill the wrapper DIV, so it is scaled with the image. 
Image is created on the fly via PHP and inserted as inline image directly to src attribute of img tag.
<h4>Credit</h4>
Thanks to Masau ( http://jsfiddle.net/Masau/7WRHM/ ) for the “trick”.

SB-ResponseFrame

This is simple shortcode to embed responsive (fixed-ratio) iframes

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/ ).

SB-ResponseFrame vs BJD Responsive iFrame