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!

Sibin Grasic

Responsive Videos plugin will allow you to automatically resize and scale your embedded videos on mobile devices. 
CSS selector option is provided so you can target only your post / page content container.
Features
<ul>
<li>Automatic configuration option</li>
<li>Automatically resizes / scales all your embedded videos</li>
<li>Works on all browsers</li>
<li>Highly compatible – you can change the css selector for the text highlight</li>
<li>Customizable – you can select the page type on which to activate the fitVids script</li>
</ul>

Responsive videos – Fitvids

Nice one

Good

Make your Embedded videos responsive on mobile devices with jQuery FitVids plugin

Responsive Video for WordPress vs Responsive videos – Fitvids