Responsive video iframes (keeping aspect ratio) with only CSS?

Question

I usually use a similar solution to this one. Something like:

.wrapper {
   position: relative;
   width: 100%;
   height: 0;
   padding-bottom: 56.25%;
}
.wr         


        

Answer 1

Use the new CSS viewport units vw and vh (viewport width / viewport height)

FIDDLE

iframe {
    width: 100vw; 
    height: 56.25vw; /* 100/56.25 = 560/315 = 1.778 */
    background:red;  
}

Browser support is also good: IE9+ (caniuse)