Momentan verwende ich für den Countdown diesen Code:
<script type="text/ja
vascript">
<!--
 
var countdown = 49;
var countdownDisplay;
var countdownTimer;
// "submit0" ist der Weiter-Knopf,
// mit "buttonsAuto" kann man auch den Zurück-Knopf ausblenden
var buttonID = "submit0";  
 
function countdownStart() {
  // Next button
  var button = document.getElementById(buttonID);
  // Create countdown element
  countdownDisplay = document.createElement("div");
  var cd = countdownDisplay;
  cd.style.display = "inline-block";
  cd.style.textAlign = "center";
  cd.style.fontWeight = "bold";
  cd.style.width = button.offsetWidth + "px";
  cd.style.height = button.offsetHeight + "px";
  // Init countdown
  button.parentNode.appendChild(countdownDisplay);
  countdownRefresh();
  // Hide next button
  button.style.display = "none";
  // Start countdown
  countdownTimer = window.setInterval(countDown, 1000);
}
 
function countDown() {
  if (countdown > 1) {
    countdown--;
    countdownRefresh();
  } else {
    window.clearTimeout(countdownTimer);
    // Display nextbutton
    var button = document.getElementById(buttonID);
    button.style.display = "";
    // Remove countdown
    button.parentNode.removeChild(countdownDisplay);
  }
}
 
function countdownRefresh() {
  // Clear
  while (countdownDisplay.lastChild) {
    countdownDisplay.removeChild(countdownDisplay.lastChild);
  }
  // Display
  var content = document.createTextNode(countdown + " Sek.");
  countdownDisplay.appendChild(content );
}
 
SoSciTools.attachEvent(window, "load", countdownStart);
 
// -->
</script>
Und hier der HTML Code des Videos:
<div style="text-align: center"><iframe width="560" height="315" src="https://www.youtube.com/embed/mfn9CGfksjY" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe></div>