static generateAudioKey_(a) {
    return shaka.util.PeriodCombiner.generateKey_([
      a.fastSwitching,
      a.channelsCount,
      a.language,
      a.bandwidth,
      a.label,
      shaka.util.PeriodCombiner.getCodec_(a.codecs),
      a.mimeType,
      a.roles,
      a.audioSamplingRate,
      a.primary,
      a.dependencyStream ? a.dependencyStream.baseOriginalId : null,
      Array.from(a.keyIds),
    ]);
  }
@param {T} a
@return {string}
@template T
Accepts either a StreamDB or Stream type.
@private