Bootstrap 4 Responsive Embed
Responsively scale videos and other media to their containing block.
Bootstrap's responsive embed component provides an easy way to scale videos and slide shows to their containing block.
The responsive embed component can be used on <iframe>, <video>, <object>, and <embed> elements.
To apply the responsive embed component to one of these elements, wrap the element within a <div> element with the .embed-responsive class, along with an intrinsic ratio class (eg, .responsive-embed-16by9 or .responsive-embed-4by3).
No need to use frameborder="0" on the <iframe> tag, as Bootstrap overrides that.