Youtube video embed preserves aspect ratio across all screen sizes.

Youtube Video Embed Responsive Styling

.youtube-video-wrap {
    width: 100%;
    max-width: 640px;
    margin: 3rem auto;
  }
  .video-container {
    position: relative;
    padding-bottom: 56.25%; //16:9 aspect ratio, 9/16 = .5625. Padding is percentage of container width
    height: 0;
    overflow: hidden;
    iframe {
      position:absolute;
      top:0;
      left:0;
      width:100%;
      height:100%;
    }
  }