trex_(streamInfo) {
    const Mp4Generator = shaka.util.Mp4Generator;
    const id = streamInfo.id + 1;
    const bytes = new Uint8Array([
      0x00, // version 0
      0x00, 0x00, 0x00, // flags
      ...this.breakNumberIntoBytes_(id, 4), // track_ID
      0x00, 0x00, 0x00, 0x01, // default_sample_description_index
      0x00, 0x00, 0x00, 0x00, // default_sample_duration
      0x00, 0x00, 0x00, 0x00, // default_sample_size
      0x00, 0x00, 0x00, 0x00, // default_sample_flags
    ]);
    return Mp4Generator.box('trex', bytes);
  }
Generate a TREX box

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