title: YouTube miniature and next gen format picture
body: <p>I'm searching for improving my website but I'm using some pictures from YouTube as image covers but those are not next-gen format.</p>
  <p>So I was wondering is there any issue to solve this trouble.</p>
  <p>I'm displaying two videos on my homepage. Though a custom script I'm not displaying the frame first but the image cover.</p>
  <pre><code> var youtube = document.querySelectorAll('.youtube')
          for (var i = 0; i &lt; youtube.length; i++) {
              var source = 'https://img.youtube.com/vi/' + youtube[i].dataset.embed + '/sddefault.jpg'
              var image = new Image()
              image.setAttribute(&quot;src&quot;,source)
              image.setAttribute(&quot;alt&quot;, &quot;Rénovation d'une maison ancienne à Chartres&quot;),
                      image.addEventListener('load', function () {
                          youtube[ i ].appendChild(image)
                      }(i))
              youtube[i].addEventListener('click', function () {
                  var iframe = document.createElement('iframe')
                  iframe.setAttribute('frameborder', '0')
                  iframe.setAttribute('allowfullscreen', '')
                  iframe.setAttribute('src', 'https://www.youtube.com/embed/' + this.dataset.embed + '?rel=0&amp;showinfo=0&amp;autoplay=1')
                  iframe.className = 'embed-responsive-item'
                  this.innerHTML = ''
                  this.appendChild(iframe)
              })
          }
  </code></pre>
  <p>What can I try to resolve this?</p>