Dustin Lammiman

This plugin takes advantage of WordPress’ built in <a href="https://codex.wordpress.org/Embeds" rel="nofollow ugc">oEmbed functionality</a> to make it easy to insert responsive videos into your site or blog. Just copy the URL of the video you want to embed and paste it into the WordPress editor. This plugin will maintain the default aspect ratio of the video at any page size.
This plugin has been tested as working with the following video sites:
<ul>
<li>
YouTube
</li>
<li>
Vimeo
</li>
<li>
blip.tv
</li>
<li>
Flickr (videos)
</li>
<li>
DailyMotion
</li>
<li>
Hulu
</li>
<li>
WordPress.tv
</li>
<li>
FunnyOrDie.com (WordPress 3.0+)
</li>
<li>
Revision3
</li>
</ul>
View the source <a href="https://github.com/nosecreek/Responsive-Video-for-WordPress" rel="nofollow ugc">on GitHub</a>.

Responsive Video for WordPress

Using a responsive WordPress theme? Make your videos responsive too! Just activate this plugin, and your videos will be instantly responsive!

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.

Responsive Video for WordPress vs Fluidvids for WordPress