bootstrap embed responsive 4by3

1<!-- 21:9 aspect ratio -->
2<div class="embed-responsive embed-responsive-21by9">
3  <iframe class="embed-responsive-item" src="..."></iframe>
4</div>
5
6<!-- 16:9 aspect ratio -->
7<div class="embed-responsive embed-responsive-16by9">
8  <iframe class="embed-responsive-item" src="..."></iframe>
9</div>
10
11<!-- 4:3 aspect ratio -->
12<div class="embed-responsive embed-responsive-4by3">
13  <iframe class="embed-responsive-item" src="..."></iframe>
14</div>
15
16<!-- 1:1 aspect ratio -->
17<div class="embed-responsive embed-responsive-1by1">
18  <iframe class="embed-responsive-item" src="..."></iframe>
19</div>

1codigo fonte teste