parsePrft_(timescale, box) {
    goog.asserts.assert(
        box.version == 0 || box.version == 1,
        'PRFT version can only be 0 or 1');
    const parsed = shaka.util.Mp4BoxParsers.parsePRFTInaccurate(
        box.reader, box.version);

    const wallClockTime = shaka.util.TimeUtils.convertNtp(parsed.ntpTimestamp);
    const programStartDate = new Date(wallClockTime -
      (parsed.mediaTime / timescale) * 1000);
    /** @type {shaka.extern.ProducerReferenceTime} */
    const prftInfo = {
      wallClockTime,
      programStartDate,
    };

    const eventName = shaka.util.FakeEvent.EventName.Prft;
    const data = (new Map()).set('detail', prftInfo);
    const event = new shaka.util.FakeEvent(
        eventName, data);
    this.playerInterface_.onEvent(event);
  }
Parse PRFT box.
@param {number} timescale
@param {!shaka.extern.ParsedBox} box
@private