Responsive embeds из bootstrap вам в помощь:
getbootstrap.com/components/#responsive-embed
html:
<!-- 16:9 aspect ratio -->
<div class="embed-responsive embed-responsive-16by9">
<iframe class="embed-responsive-item" src="..."></iframe>
</div>
<!-- 4:3 aspect ratio -->
<div class="embed-responsive embed-responsive-4by3">
<iframe class="embed-responsive-item" src="..."></iframe>
</div>
css:
.embed-responsive {
position: relative;
display: block;
height: 0;
padding: 0;
overflow: hidden;
}
.embed-responsive .embed-responsive-item,
.embed-responsive iframe,
.embed-responsive embed,
.embed-responsive object,
.embed-responsive video {
position: absolute;
top: 0;
left: 0;
bottom: 0;
height: 100%;
width: 100%;
border: 0;
}
/* Modifier class for 16:9 aspect ratio */
.embed-responsive-16by9 {
padding-bottom: 56.25%;
}
/* Modifier class for 4:3 aspect ratio */
.embed-responsive-4by3 {
padding-bottom: 75%;
}