Fix: Allow the playback whenever the t attribute is missing in the SegmentTimeline elements

[dario-fiore]

Hello team, I would like to submit some changes to add support for the playback of dynamic manifests whenever the t attribute is missing in the SegmentTimeline elements.

With this change, the player now handles the case when segments[0].t is NaN and calculates the timeshift window using the default range.start and the timeShiftBufferDepth attribute of the manifest.

This update could also improve the reliability of the player and align the behavior with all the other commercial players. Please review and provide your feedback. Thank you!

[dsilhavy]

@dario-fiore Thanks for your PR. Following our contribution guidelines, and since this seems to be your first PR, could you please send me a signed copy of dash.js feedback agreement?

[dsilhavy]

Thanks @dario-fiore .

We should indeed cover the case when S@t is missing. From 23009-1: If not present, then the value shall be assumed to be zero for the first S element.

In _calcRangeForTimeline we avoid using the timeshiftBufferDepth on purpose. The goal is to use the Segments in SegmentTimeline to determine the DVR window.

I think we can still use the summed duration here:

 if(!isNaN(segmentTime)) {
    range.end = calcPresentationTimeFromMediaTime((segmentTime + d) / timescale, voRepresentation);
} else {
     range.end = timeShiftBufferDepth;
}

So instead of using timeShiftBufferDepth we set segmentTime to 0 if it is NaN (due to missing @t).

What do you think? Also do you have a testvector you can share?

[dario-fiore]

Yes, it makes sense (definitely better to use the segments in the timeline). I just pushed the updated version.

Regarding the testvector here you can find a sample: https://gist.github.com/dario-fiore/709c1c71f6a25a174a8d3df1dd1ee739. Unfortunately, I can't share the whole stream.

Do you think it is possible to include this change in 4.7.0?