How to add videos or slideshows scale properly on any device?

How to  add videos or slideshows scale properly on any device.

Responsive Embeds

Classes can be applied directly to <iframe>, <embed>, <video>, and <object> elements.

The following example creates a responsive video by adding an .embed-responsive-item class to an <iframe> tag (the video will then scale nicely to the parent element). The containing <div> defines the aspect ratio of the video:

Example

<div class="embed-responsive embed-responsive-16by9">  <iframe class="embed-responsive-item" src="..."></iframe></div>