[vorbis-dev] granulepos start/end revisited

[Conrad Parker]

On Fri, May 21, 2004 at 10:53:45AM -0400, Arc Riley wrote:
> On Fri, May 21, 2004 at 04:27:08PM +1000, Andr? Pang wrote:
> > 
> > for a description of how to implement SMIL's durations.  I'm not 
> > implying that the Writ's implementation will end up being that complex, 
> > of course: my point is that there's more logic needed just to make sure 
> > that your table, which tells you when to turn off subtitles, is 
> > correct, especially once seeking comes into play.  How is this any 
> > simpler than turning subtitles off/on via state changes?
> 
> I think you're confused, so here's a walk-through..

No, I have it on good authority that Andr? isn't confused :)

Your argument is irrelevent to the discussion of Ogg page granulepos. The
presentation duration of subtitle packet is of course specified within the
subtitle data, not in the Ogg framing. 

The only relevent difference between the two schemes is that the state-change
style injects an extra packet at the end-time of the subtitle's presentation.
All subtitle buffering features that you discuss are identical, however
by going from a state-change style to a duration-only style you've lost
end-confirmation packets.

Of course, in the not-uncommon case where subtitles follow directly one after
another (AAAABBBCCCCDDDD), the two schemes are similar, as a state-change
from A to B does not require an end-confirmation for A, just a state change
to B. However in the general case, the added robustness of end-confirmations
ensures that blind seeks (ie. those without foreknowledge of active
subtitles) can operate efficiently in both demux and decode.

Conrad.
--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/
To unsubscribe from this list, send a message to 'vorbis-dev-request at xiph.org'
containing only the word 'unsubscribe' in the body.  No subject is needed.
Unsubscribe messages sent to the list will be ignored/filtered.