webvitaly

<ul>
<li><a href="https://r.freemius.com/13759/8047958/" title="Advanced iFrame" rel="nofollow ugc">Advanced iFrame</a></li>
<li><a href="http://web-profile.net/wordpress/plugins/iframe/" title="Plugin page" rel="nofollow ugc">iframe</a></li>
<li><a href="http://web-profile.net/donate/" title="Support the development" rel="nofollow ugc">Donate</a></li>
<li><a href="https://github.com/webvitalii/iframe" title="Fork" rel="nofollow ugc">GitHub</a></li>
</ul>
[iframe src=”http://www.youtube.com/embed/7_nAZQt9qu0″ width=”100%” height=”500″] shortcode 
should show something like this:
<iframe loading="lazy" class="youtube-player" width="750" height="422" src="https://www.youtube.com/embed/7_nAZQt9qu0?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>
WordPress removes iframe html tags because of security reasons. 
Iframe shortcode is the replacement of the iframe html tag and accepts the same params as iframe html tag does. 
You may use iframe shortcode to embed content from YouTube, Vimeo, Google Maps or from any external page.
If you need to embed content from YouTube, Vimeo, SlideShare, SoundCloud, Twitter via direct link, you may use <code>[embed]http://www.youtube.com/watch?v=7_nAZQt9qu0[/embed]</code> shortcode. 
[embed] shortcode is a core WordPress feature and can <a href="https://codex.wordpress.org/Embeds" rel="nofollow ugc">embed content from many resources via direct link</a>.
Important: You can not embed HTTP pages into HTTPS pages and vice versa. 
So the protocol (http or httpS) for parent and embedded page should match.
<h4>iframe params:</h4>
<ul>
<li>src – source of the iframe: <code>[iframe src="http://www.youtube.com/embed/7_nAZQt9qu0"]</code>; by default src=”http://www.youtube.com/embed/7_nAZQt9qu0″;</li>
<li>width – width in pixels or in percents: <code>[iframe width="100%"]</code> or <code>[iframe width="600"]</code>; by default width=”100%”;</li>
<li>height – height in pixels: <code>[iframe height="500"]</code>; by default height=”500″;</li>
<li>scrolling – with or without the scrollbar: <code>[iframe scrolling="no"]</code>; by default scrolling=”yes”;</li>
<li>frameborder – with or without the frame border: <code>[iframe frameborder="0"]</code>; by default frameborder=”0″;</li>
<li>marginheight – height of the margin: <code>[iframe marginheight="0"]</code>; removed by default;</li>
<li>marginwidth – width of the margin: <code>[iframe marginwidth="0"]</code>; removed by default;</li>
<li>allowtransparency – allows to set transparency of the iframe: <code>[iframe allowtransparency="true"]</code>; removed by default;</li>
<li>id – allows to add the id of the iframe: <code>[iframe id="custom_id"]</code>; removed by default;</li>
<li>class – allows to add the class of the iframe: <code>[iframe class="custom_class"]</code>; by default class=”iframe-class”;</li>
<li>style – allows to add the css styles of the iframe: <code>[iframe style="margin-left:-30px;"]</code>; removed by default;</li>
<li>same_height_as – allows to set the height of iframe same as target element: <code>[iframe same_height_as="div.sidebar"]</code>, <code>[iframe same_height_as="div#content"]</code>, <code>[iframe same_height_as="body"]</code>, <code>[iframe same_height_as="html"]</code>; removed by default;</li>
<li>any_other_param – allows to add new parameter of the iframe <code>[iframe any_other_param="any_value"]</code>;</li>
<li>any_other_empty_param – allows to add new empty parameter of the iframe (like “allowfullscreen” on youtube) <code>[iframe any_other_empty_param=""]</code>;</li>
</ul>

iframe

[iframe src="http://www.youtube.com/embed/7_nAZQt9qu0" width="100%" height="500"] shortcode

yehudah

Video Thumbnails makes it easy to automatically display video thumbnails in your template. When you publish a post, this plugin will find the first video embedded and retrieve a thumbnail for you. Thumbnails can be saved to your media library and set as a featured image automatically. There’s even support for custom post types and custom fields!
Video Thumbnails Reloaded is based on Video Thumbnails developed by Sutherland Boswell 
(https://wordpress.org/plugins/video-thumbnails/)
<h4>Supported Sites</h4>
<ul>
<li>YouTube</li>
<li>Vimeo</li>
<li>Facebook</li>
<li>Vine</li>
<li>Twitch</li>
<li>Dailymotion</li>
<li>Metacafe</li>
<li>TED</li>
<li>VK</li>
<li>Blip</li>
<li>Google Drive</li>
<li>Funny or Die</li>
<li>CollegeHumor</li>
<li>MPORA</li>
<li>Livestream</li>
<li>Yahoo Screen</li>
<li>Wistia</li>
<li>Youku</li>
<li>Tudou</li>
<li>SAPO</li>
<li>Rutube</li>
</ul>
<h3>Known Issues</h3>
<ul>
<li>In some cases you may have to manually search for thumbnails on the post editor</li>
</ul>

Video Thumbnails Reloaded

Video Thumbnails simplifies the process of automatically displaying video thumbnails in your WordPress template.

iframe vs Video Thumbnails Reloaded