Fix the bug that UTCTiming is ignored even when autoCorrectDrift is off

[thmatuza]

This is the fix for this issue.
#2411

shaka.dash.DashParser.processManifest is using the presentationTimeline.usingPresentationStartTime() to determine if it parses UTCTiming or not.

The usingPresentationStartTime always returns the false when maxSegmentEndTime_ is not null.

When the manifest has SegmentTimeline, it seems always setting a value to maxSegmentEndTime_.

I added the code not to set maxSegmentEndTime_ when autoCorrectDrift is false.

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[thmatuza]

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[joeyparrish]

Thanks for fixing this! I would like to see a slightly different fix, though.

[joeyparrish]

I don't think this is the right fix. See this code in lib/dash/dash_parser.js:

      // We only need to do clock sync when we're using presentation start
      // time. This condition also excludes VOD streams.
      if (presentationTimeline.usingPresentationStartTime()) {
        const timingElements = XmlUtils.findChildren(mpd, 'UTCTiming');
        const offset = await this.parseUtcTiming_(baseUris, timingElements);
        // Detect calls to stop().
        if (!this.playerInterface_) {
          return;
        }
        presentationTimeline.setClockOffset(offset);
      }

Your fix works by changing the results of usingPresentationStartTime(), but it's indirect. The real bug seems to be this condition in usingPresentationStartTime():

    // If we have explicit segment times, we're not using the presentation
    // start time.
    if (this.maxSegmentEndTime_ != null) {
      return false;
    }

Rather that avoid computing maxSegmentEndTime_, you should require both maxSegmentEndTime_ and autoCorrectDrift_ in that condition.

[thmatuza]

Make sense.
I changed my fix.
ee5c071

[joeyparrish]

Looks good! Thanks for the help!

I'll ask the build bot to test it now.

[shaka-bot]

All tests passed!

[joeyparrish]

Thanks for your contribution!