<iframe id="iframe" width="615" height="315" src="" class="hidden" frameborder="0" allowfullscreen></iframe>

    <input type="text" id="url" size="61" placeholder="Paste Youtube URL Here">
    <button type="button" id="play" onclick="playvideo()">Play</button>
    <button type="button" id="close" onclick="closevideo()">Close</button>

    <style>
      .show {
        display: block;
      }
      .hidden {
        display: none;
      }
    </style>

    <script>
      function playvideo() {
        var url = document.getElementById("url").value;

        document.getElementById("iframe").setAttribute("src", url);
        document.getElementById("iframe").setAttribute("class", "show");
      }

      function closevideo() {
        document.getElementById("iframe").setAttribute("class", "hidden");
        document.getElementById("url").value = "";
      }
    </script>