traf_(streamInfo) {
    const Mp4Generator = shaka.util.Mp4Generator;
    const sampleDependencyTable = this.sdtp_(streamInfo);
    const offset = sampleDependencyTable.length +
          32 + // tfhd
          20 + // tfdt
          8 + // traf header
          16 + // mfhd
          8 + // moof header
          8; // mdat header;
    return Mp4Generator.box('traf',
        this.tfhd_(streamInfo),
        this.tfdt_(streamInfo),
        this.trun_(streamInfo, offset),
        sampleDependencyTable);
  }
Generate a TRAF box

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