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Dash-Industry-Forum / Guidelines-TimingModel

DASH-IF implementation guidelines: the DASH timing model
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Do not allow inaccuracy when using SegmentTimeline #20

Closed sandersaares closed 4 years ago

sandersaares commented 5 years ago

From IOP v4.3, section 4.3.3.4.1:

If the segment timeline is and the $Number$ template is used, then the MPD times shall at most deviate from the earliest presentation time documented in the MPD by 0.5sec.

This contradicts the below statement in 3.2.1 that inaccuracy is forbidden with SegmentTimeline:

If the SegmentTimeline element is used for the signaling of the Segment duration, the timing in the segment timeline shall be media time accurate and no constraints on segment duration deviation are added except the maximum segment duration as specified in the MPD

Note: I read "deviation" in this clause to mean "different segments have different durations" not "deviation from MPD".

This allowed deviation appears unnecessary and complicated the timing model. We should remove the statement allowing SegmentTimeline deviation from IOP v5 and constrain any inaccuracy to SegmentTemplate@duration addressing. This is already incorporated in the interoperable timing model in Dash-Industry-Forum/DASH-IF-IOP#210 but I raise it here as it was an unexpected find and may affect also the service type descriptions.

sandersaares commented 4 years ago

Closing as this is already addressed.