createVariant_(audioStream, videoStream) {
    const ContentType = shaka.util.ManifestParserUtils.ContentType;

    goog.asserts.assert(!audioStream ||
        audioStream.type == ContentType.AUDIO, 'Audio parameter mismatch!');
    goog.asserts.assert(!videoStream ||
        videoStream.type == ContentType.VIDEO, 'Video parameter mismatch!');

    let bandwidth = 0;
    if (audioStream && audioStream.bandwidth && audioStream.bandwidth > 0) {
      bandwidth += audioStream.bandwidth;
    }
    if (videoStream && videoStream.bandwidth && videoStream.bandwidth > 0) {
      bandwidth += videoStream.bandwidth;
    }

    return {
      id: this.globalId_++,
      language: audioStream ? audioStream.language : 'und',
      disabledUntilTime: 0,
      primary: (!!audioStream && audioStream.primary) ||
          (!!videoStream && videoStream.primary),
      audio: audioStream,
      video: videoStream,
      bandwidth: bandwidth,
      allowedByApplication: true,
      allowedByKeySystem: true,
      decodingInfos: [],
    };
  }
@param {?shaka.extern.Stream} audioStream
@param {?shaka.extern.Stream} videoStream
@return {!shaka.extern.Variant}
@private