[Bug 691481] avidemux: a/v sync off on sample video when activated in push mode

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=691481
  GStreamer | gst-plugins-good | 1.x

--- Comment #15 from Matej Knopp <matej.knopp at gmail.com> 2013-02-17 18:58:22 UTC ---
I don't understand the very first paragraph; There is NO DTS on incoming
buffers in my case, only PTS. The PTS doesn't need to be picked, we already get
it from demuxer.

It's been a while since I was reading matroska specs, but IIRC matroska doesn't
store DTS, only PTS. At very least for video streams this is true, as the
timestamps from matroska are not monotonous (so it's easy to confirm).

I don't really understand the point of interpolating the DTS, especially from
segment start. Segment start does not guarantee that the incoming buffers are
within the segment boundaries. Also, if decoder really relies on having proper
DTS (i.e. for buffer under/overflow), the interpolated DTSs probably won't be
very helpful.

Just to recap, the problem in my case:

* Incoming buffers only have PTS (no DTS), matroska doesn't store DTS
* PTS gets interpolated from the PTS value of first buffer
* DTS gets interpolated from value of segment->start
* (segment->start) > (PTS of first buffer) because the seek goes 
   to last keyframe before segment start, thus on output, I get buffers
   with DTS > PTS, which breaks number of things

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