DASH - Understanding MPD at availabilityStartTime

[Arjen Veenhuizen]

Timing is still a heavily discussed topic in the DASH standardisation
organisation but I'll try to answer your question. It depends on the profile
you use but assuming MP4 or MPEG-2 TS profile in MPEG DASH :

“When the MPD is updated, the value of MPD at availabilityStartTime shall be
the same in the original and the updated MPD.”

So when it updates the MPD by removing or adding stuff you shouldn’t update
this value.

Also, If I understand you correctly, you assume that Segment availability
Start time = MPD at availabilityStartTime. But it is a bit more complex. It is
actually :

Segment availability start time = MPD at availabilityStartTime + PeriodStart +
MediaSegment[i].startTime + MediaSegment[i].duration

Basically, this means that you can access a segment before the content it
describes in UTC time is over, aka you can look into the future:).

I hope this answers your questions at least a little bit.



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