mp4a_(streamInfo) {
    const Mp4Generator = shaka.util.Mp4Generator;
    let esdsBox;
    if (streamInfo.audioConfig.byteLength > 0) {
      esdsBox = Mp4Generator.box('esds', streamInfo.audioConfig);
    } else {
      esdsBox = Mp4Generator.box('esds', this.esds_(streamInfo));
    }

    let boxName = 'mp4a';
    let sinfBox = new Uint8Array([]);
    if (streamInfo.encrypted) {
      sinfBox = this.sinf(streamInfo.stream, streamInfo.codecs);
      boxName = 'enca';
    }
    return Mp4Generator.box(boxName,
        this.audioStsd_(streamInfo), esdsBox, sinfBox);
  }
Generate a MP4A box

@param {shaka.util.Mp4Generator.StreamInfo} streamInfo
@return {!Uint8Array}
@private