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!

Brandon_Orndorff

Simple light weight plugin that automatically and recursively makes all YouTube and Vimeo video’s site wide responsive.
<h3>Demo</h3>
Go to: http://www.brandonorndorff.com/wordpress/plugins/aas-digg-digg-alternative-wordpress-plugin/ and scroll to the bottom and shrink your browser window and watch the video resize to fit the screen.

WP Responsive Video

Simple light weight plugin that automatically makes all currently and future embedded video's responsive.  There is no setup required, it just wo …

Responsive Video for WordPress vs WP Responsive Video