[gstreamer-bugs] [Bug 539858] not enough NEWSEGMENT events from matroskademux

[GStreamer (bugzilla.gnome.org) <bug...@bu...>]

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  GStreamer | gst-plugins-good | Ver: HEAD CVS

Evgeniy Stepanov changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEEDINFO                    |UNCONFIRMED




------- Comment #3 from Evgeniy Stepanov  2008-06-24 10:19 UTC -------
(In reply to comment #2)
> Why is it necessary to send the NEWSEGMENT events for overlapping buffers? What
> happens without them?

Textoverlay can push video buffer only if it is sure that it has seen all the
subtitle buffers with the less or equal timestamps. This is the case (or so it
thinks) if either there is a buffer with end point in the future, or there was
a NEWSEGMENT for text stream with start point in the future.

With overlapping buffers, the first condition is incorrect. It results in lost
subtitles. We can only be sure that we have seen all the subtitles from the
past if the _start_ of some subtitle is in the future, or the same NEWSEGMENT
condition. For example, if there were two subtitles with time intervals [0, 10]
and [1, 2], the second one may never be displayed.

This is not that important for textoverlay, because it does not support
overlapping subtitles at all. In fact, the second buffer ([1, 2]) would be
locked in text_chain until the end of the first one.

I'm writing an overlay that supports overlapping subtitles. For this reason I
can only rely on start points of text buffers to decide when to push the video
frame. If I get a long subtitle buffer, only NEWSEGMENT events (starting from
start of the buffer + 0.5 seconds) can tell me that video stream can progress.


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