https://codepen.io/angelagiese/pen/ygYReO

.html

//js
$(window)
    .resize(function () {
      $('iframe[src*="youtube.com"]').each(function () {
        if (!$(this).parents(".video-container").length) {
          $(this).wrap("<div class='video-container'></div>");
        }
      });
    })
    .resize();

// css
.video-container {
  position: relative;
  padding-bottom: 56.25%; /* 16:9 */
  padding-top: 25px;
  height: 0;

  iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: none;
  }
}