opus_(streamInfo) {
    const Mp4Generator = shaka.util.Mp4Generator;
    const dopsBox = Mp4Generator.box('dOps', streamInfo.audioConfig);

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

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