shaka prft mp4 box surfacing proposal

shaka-prft-changes.js

// file: streaming_engine.js
// The _append method will call this method

  /**
   * Parse PRFT box.
   * @param {!shaka.media.SegmentReference} reference
   * @param {!shaka.extern.ParsedBox} box
   * @private
   */
  parsePrft_(reference, box) {
    if (this.parsedPrftEventRaised) {
      return;
    }
    box.reader.readUint32(); // Ignore referenceTrackId
    const ntpTimestampSec = box.reader.readUint32();
    const ntpTimestampFrac = box.reader.readUint32();
    const ntpTimestamp = ntpTimestampSec * 1000 + ntpTimestampFrac / 2**32;

    let mediaTime;
    if ( box.version === 0) {
      mediaTime = box.reader.readUint32();
    } else {
      mediaTime = box.reader.readUint64();
    }

    const wallClockTime = this.convertNtp(ntpTimestamp);
    const eventName = shaka.Player.EventName.Prft;
    const event = new shaka.util.FakeEvent(
        eventName, {
          wallClockTime,
          mediaTime,
          timescale: reference.timescale, //timescale added to segment reference
        });
    this.playerInterface_.onEvent(event);
    this.parsedPrftEventRaised = true;
  }

  /**
   * Convert Ntp ntpTimeStamp to UTC Time
   *
   * @param {number} ntpTimeStamp
   * @return {number} utcTime
   */
  convertNtp(ntpTimeStamp) {
    const start = new Date(Date.UTC(1900, 0, 1, 0, 0, 0));
    return new Date(start.getTime() + ntpTimeStamp).getTime();
  }