Palasthotel

greatestview

ATTENTION for WP Version 5+: This plugin does not work with Gutenberg (no problems with Classic Editor plugin though)! Gutenberg brings its own HTML structure for oEmbed elements, which is quite difficult to target.
This plugin checks, if the first line of the content is a valid oEmbed URL. If that is the case, it replaces the thumbnail image with the oEmbed element (e. g. with a YouTube video). Now you don’t have to care too much about a thumbnail image, since instead you would see the video or any other oEmbed content. You can even e. g. watch videos on your blogs front page without opening the post.
Works for all WordPress contents, which have a thumbnail set and are not password protected.
The active WordPress Theme must use the_post_thumbnail() or get_the_post_thumbnail() functions for this to work!

Replace Thumbnail with oEmbed

Replaces the thumbnail image with the oEmbed element from the first line of the content.

Ulrich

Standalone JavaScript for fluid YouTube/Vimeo iframe embeds. Add more video players and selectors easily in the media settings.
Description of the Fluidvids script 
“Fluidvids is a 1KB standalone module that provides a fluid solution for video embeds. Fluidvids has the ability for custom players to be added as well as support for dynamically injected (XHR/Ajax/createElement) videos.
Check out a <a href="http://toddmotto.com/labs/fluidvids" rel="nofollow ugc">demo of fluidvids</a>“
<h3>Credits</h3>
The plugin can also be found on <a href="https://github.com/grappler/fluidvids" rel="nofollow ugc">GitHub</a>.
<ul>
<li>Thank you <a href="http://toddmot.to/" rel="nofollow ugc">Todd Motto</a> for <a href="https://github.com/toddmotto/fluidvids" rel="nofollow ugc">fluidvids.js</a></li>
<li>Thank you <a href="http://tommcfarlin.com/" rel="nofollow ugc">Tom McFarlin</a> for the <a href="https://github.com/tommcfarlin/WordPress-Plugin-Boilerplate" rel="nofollow ugc">WordPress Plugin Boilerplate</a></li>
</ul>

Fluidvids for WordPress

Standalone JavaScript for fluid YouTube/Vimeo iframe embeds. Easily add additional video players and selectors in the settings.

Replace Thumbnail with oEmbed vs Fluidvids for WordPress