Automatic height when embedding a YouTube video?

i've embed a YouTube video on my website but the trouble is that i need the height to automatically adjust based on the width and the aspect ratio of the video. So if my width is 1280, my height should be 720 if the video is 16:9. I've tried using 'VW' and 'VH' units but these don't seem to work with an iframe. My width is already set proportionally.

My code is below:

<iframe style="margin-right: 1%; margin-left: 1%;" width="98%" height="" src="https://www.youtube.com/embed/HwzQbfde-kE" frameborder="0"></iframe>

This article contains a good answer, copied below.

CSS:

.video-container {
	position: relative;
	padding-bottom: 56.25%; /* 16:9 */
	height: 0;
}
.video-container iframe {
	position: absolute;
	top: 0;
	left: 0;
	width: 100%;
	height: 100%;
}

Example Html

<div class="video-container">
    <iframe width="560" height="315" src="https://www.youtube.com/embed/_TyJeKKQh-s?controls=0" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
</div>

How this works: The container element is given a zero height and a percentage bottom padding. The percentage bottom padding is a percentage of the container width, so that gives it a fixed aspect ratio. But in order to get the iframe to show up inside the zero-height container, you need to make the container relative and the iframe absolute, positioned inside the div.

See a live example.

I was able to make a responsive iframe size using vw on both width and height of the style element because I know the amount of horizontal width I want the elements to use and then I calculate the height based on the width and the knowledge that the video is 16:9. If you want the video to consume 45% of the horizontal space above screen sizes of 893px and 90% otherwise, then:

.embedded-video-16-9 {
  width:  90vw;
  height: 50.625vw; /* 90*9/16 */
  margin-left: 5vw;
  margin-right: 5vw;
}

@media (min-width: 893px) {
  .embedded-video-16-9 {
    width: 45vw;
    height: 25.3125vw; /* 45*9/16 */
    margin-left: 2vw;
    margin-right: 2vw
  }
}

Used like:

<iframe 
  class="embedded-video-16-9" 
  src="https://www.youtube.com/embed/_TyJeKKQh-s?controls=0" 
  frameborder="0" 
  allowfullscreen=""
></iframe>

If you go for the entire viewport you can use following code:

iframe{
  width: 100vw;
  height: calc(100vw/1.77);
}

The html width attribute only accepts numbers ("valid non-negative integers"), not strings suffixed with units of measurement (%, px, vw, etc) as in the original question.

If you know the width of the iframe's container (in an absolute unit like px or vw, not %) then you can use css calc() for a one-line height solution in css:

.youtube-embed {
  --container-width: 720px;
  --ratio: calc(16 / 9); /* 1.77 */
  width: 100%;
  height: calc(var(--container-width) / var(--ratio));
}

Here's a responsive solution that accounts for horizontal padding on the container:

:root {
  --video-ratio: calc(16 / 9);
  --video-container-max-width: 640px;
  --video-container-x-padding-sum: 2rem; /* eg, padding: 0 1rem */
}

.youtube-embed {
  --video-container-width: calc(100vw - var(--video-container-x-padding-sum));
  width: 100%;
  height: calc(var(--video-container-width) / var(--video-ratio));
}

@media only screen and (min-width: 672px) {
  .youtube-embed {
    --video-container-width: var(--video-container-max-width);
  }
}