constructor(streamFormat, assetKey) {
    streamFormat = streamFormat.toLowerCase();
    if (streamFormat !== 'hls' && streamFormat !== 'dash') {
      window.console.error('VodStream error: incorrect streamFormat.');
      return;
    } else if (streamFormat === 'dash') {
      window.console.error('streamFormat error: DASH streams are not' +
                           'currently supported by this plugin.');
      return;
    } else if (typeof assetKey !== 'string') {
      window.console.error('assetKey error: value must be string.');
      return;
    }
    this.streamFormat = streamFormat;
    this.assetKey = assetKey;
  }
LiveStream class constructor used for DAI live streams.
@param {string} streamFormat stream format, plugin currently supports only
'hls' streams.
@param {string} assetKey live stream's asset key.