[Bug 21431] Specify splicing behavior for text tracks

https://www.w3.org/Bugs/Public/show_bug.cgi?id=21431

David Singer <singer@apple.com> changed:

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--- Comment #8 from David Singer <singer@apple.com> ---
I think we have to be careful to distinguish to between editing operations:  I
want 30 seconds of this content appended after a 3-second green-screen, and
then after all that I need 2 minutes of this other content;  from
segmentation/delivery operations:  I want to deliver this content in roughly
5-second segments.

In the first, it's important that cues get truncated to match the edits.  This
is a content-level operation.

In the second, segmentation software typically doesn't look at or below the
content level.  If there are 'long duration' video frames (e.g. a slide-show, a
slow time-lapse), that's the way it is.

The VTT-in-MP4 work has focused on making it possible to random access, edit,
splice, fragment long cues to make segmentation easier, and so on, and know
whether some cue is still active.  What Silvia suggests -- a repetition that is
labelled as such -- is indeed possible.

The DASH work explicitly considered that segment boundaries may be 'ragged
edges' -- some tracks may have content that persists after the boundary. But
ideally the degree of raggedness is not 'large' (comparable to the segment
length).

Both are possible in MP4: if you're authoring for segmented delivery then I
would suggest segmenting cues also so that cues (and repetitions) are shorter
than the shortest expected segment length. Otherwise, you have a significant
ragged-edge issue.

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Received on Friday, 5 April 2013 17:32:27 UTC