ikanaweb

Activate this plugin and reduce you page weight by nearly 1mo !
Because embed videos can dramatically increase your page weight and loading time, Embed Video Thumbnail 
automatically replace them by their corresponding thumbnail. Videos will then only be loaded after click on thumbnails.
This plugin fixes part of the following “defer parsing of javascript” error in GTmetrix :
<blockquote>
xxxx MiB of JavaScript is parsed during initial page load. Defer parsing JavaScript to reduce blocking of page rendering.
</blockquote>
Currently supported video hosting services :
<ul>
<li>Youtube</li>
<li>Vimeo</li>
<li>Dailymotion</li>
<li>Facebook</li>
</ul>
Optional settings :
<ul>
<li>Toggle activation on each hosting services</li>
<li>Toggle activation by device (desktop, tablet, mobile)</li>
<li>Copy thumbnail on local server for performance improvements</li>
<li>Display video title over the thumbnail</li>
<li>Toggle video loop on Vimeo and Youtube</li>
<li>Import/export settings</li>
</ul>
Widget :
You can use our Embed Video Thumbnail widget to transform your videos in sidebars.
Custom hosting services can be added with the <code>ikevt_extension_providers</code> hook. 
Each hosting service extension must implement <code>Ikana\EmbedVideoThumbnail\Provider\ProviderInterface</code>
Requirements :
<ul>
<li>php 5.6+</li>
</ul>

Embed Video Thumbnail

Automatically replace embed videos everywhere with their thumbnail to reduce page load time and improve your GTmetrix score.

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.

Embed Video Thumbnail vs Video Thumbnails Reloaded