title: Determine DRM system supported by browser
body: <p>I've trying to find out how to determine which DRM system browser is using. And in fact, only chrome say it is use 'com.widevine.alpha' where IE &amp; Safari (Win) throw error on 'requestMediaKeySystemAccess', and firefox do not even try to say it use 'com.adobe.acccess' =]</p>
  
  <pre><code> function isKeySystemSupported(keySystem) {
  
      var dfd = Q.defer();
      console.log('check: ', keySystem);
      navigator.requestMediaKeySystemAccess(keySystem, [{contentType: 'video/webm; codecs="vp9"'}]).then(function() {
          dfd.resolve(true);
      }, function() { dfd.resolve(false); } );
  
      return dfd.promise;
  }
  </code></pre>
  
  <p>is there any solution, like Modernizr or similar to get which keySystem I should use? </p>