mdia_(streamInfo) {
    const Mp4Generator = shaka.util.Mp4Generator;
    return Mp4Generator.box('mdia', this.mdhd_(streamInfo),
        this.hdlr_(streamInfo), this.minf_(streamInfo));
  }
Generate a MDIA box

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