getAudioId = (stream) => {
      let id = stream.language + (stream.channelsCount || 0) +
        (stream.audioSamplingRate || 0) + stream.roles.join(',') +
        stream.label + stream.groupId + stream.fastSwitching;
      if (stream.dependencyStream) {
        id += stream.dependencyStream.baseOriginalId || '';
      }
      return id;
    }
@type {!shaka.util.MultiMap<shaka.extern.Variant>}