 probeSupport() {
  var tests = [];
  var testKeySystems = [
    'org.w3.clearkey',
    'com.widevine.alpha',
  ];

  var basicVideoCapabilities = [
    { contentType: 'video/mp4; codecs="avc1.42E01E"' },
    { contentType: 'video/webm; codecs="vp9"' }
  ];

  var basicConfig = {
    videoCapabilities: basicVideoCapabilities
  };
  var offlineConfig = {
    videoCapabilities: basicVideoCapabilities,
    persistentState: 'required',
    sessionTypes: ['persistent-license']
  };

  // Try the offline config f