Earlier we discussed about WP Fluid Images plugin that automatically makes all your website images fluid that takes up the screen size. This tutorial is on similar plugin that works in keeping YouTube and Vimeo videos proportional and smooth according to the screen width.
Install and activate Fluid Video Embed. After activation your YouTube and Vimeo embeds should start to ignore the setting in Dashboard -> Settings -> Media -> Maximum embed size and it makes all “auto embedded” YouTube and Vimeo videos appear in full width (100%) while maintaining their original aspect ratio. You may view its live demo here: Fluid Video Embeds Demo.
Other than this the plugin also allows you to use the [fve] shortcode inside your posts, page and CPTs content:
[fve]http://youtu.be/oHg5SJYRHA0[/fve]
Or you can use the Fluid Video Embeds method in a php template file by digging in your theme, you can use the do_shortcode method:
<?php echo do_shortcode('[fve]http://youtu.be/oHg5SJYRHA0[/fve]'); ?>