<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Page Visibility API</title>
  <style>
    #media {
      padding: 5px;
      border: 1px solid #B1B1B1;
    }
  </style>
  <script>
    let video;
    function initiate() {
      video = document.getElementById("media");
      document.addEventListener("visibilitychange", showstate);
      video.addEventListener("click", function() {
        video.play();
      });
    }
    function showstate() {
      const state = document.visibilityState;
      switch(state) {
        case "visible":
          video.play();
          break;
        case "hidden":
          video.pause();
          break;
      }
    }
    window.addEventListener("DOMContentLoaded", initiate);
  </script>
</head>
<body>
  <video id="media" width="720" height="400">
    <source src="trailer.mp4" type="video/mp4">
    <source src="trailer.webm" type="video/webm">
  </video>
</body>
</html>