An adjust Modernizr test to check for autoplay support on video elements.

modernizr.videoautoplay.js

(function() {
  var addTest = Modernizr.addTest;
  var timeout;
  var waitTime = 300;
  var elem = document.createElement('video');
  var elemStyle = elem.style;

  function testAutoplay(arg) {
    clearTimeout(timeout);
    elem.removeEventListener('playing', testAutoplay, false);
    addTest('videoautoplay', arg && arg.type === 'playing' || elem.currentTime !== 0);
    elem.parentNode.removeChild(elem);
  }

  if (!Modernizr.video || !('autoplay' in elem)) {
    addTest('videoautoplay', false);
  }

  // Fix IE false negative
  var ua = navigator.userAgent;
  if ((ua.indexOf('MSIE') !== -1 ||
       ua.indexOf('Trident') !== -1) &&
       ua.indexOf('Windows Phone') === -1) {
    addTest('videoautoplay', true);
  }

  elemStyle.position = 'absolute';
  elemStyle.height = 0;
  elemStyle.width = 0;

  try {
    if (Modernizr.video.webm) {
      elem.src = 'data:video/webm;base64,GkXfo0AgQoaBAUL3gQFC8oEEQvOBCEKCQAR3ZWJtQoeBAkKFgQIYU4BnQI0VSalmQCgq17FAAw9CQE2AQAZ3aGFtbXlXQUAGd2hhbW15RIlACECPQAAAAAAAFlSua0AxrkAu14EBY8WBAZyBACK1nEADdW5khkAFVl9WUDglhohAA1ZQOIOBAeBABrCBCLqBCB9DtnVAIueBAKNAHIEAAIAwAQCdASoIAAgAAUAmJaQAA3AA/vz0AAA=';
    }
    else if (Modernizr.video.h264) {
      elem.src = 'data:video/mp4;base64,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';
    }
    else {
      addTest('videoautoplay', false);
    }
  }
  catch (e) {
    addTest('videoautoplay', false);
  }

  elem.setAttribute('autoplay', '');
  elem.style.cssText = 'display:none';
  document.documentElement.appendChild(elem);
  setTimeout(function() {
    elem.addEventListener('playing', testAutoplay, false);
    timeout = setTimeout(testAutoplay, waitTime);
  }, 0);
}());