debugging a/v-sync issues, possibly inter*-element related

[Peter Körner]

Hi

I'm writing a Videomixer-Application written in python, based on
gsteamer. I'm using an uninstalled git-master build for my tests.

My pipelines look somewhat like this (there are multiple of these
sources and sinks):
<https://gist.github.com/MaZderMind/ad4699906c946be5bd3a>


Tests revealed, that after 15-30 Minutes of Playback, The output-audio
drifts by 30-50ms with regard to the video (the audio is late wrt. to
the video).

Here is a comparison of a 15 Minute Test-Clip, on the top is the
input, on the bottom the output:
Minute  0: http://pasteboard.co/VeEzzF0.png
Minute 20: http://pasteboard.co/VeHxCU0.png

The Test-Clip can be found here:
<http://c3voc.mazdermind.de/avsync-30min.mp4>

Results vary a little from Machine to Machine and test to test but
they are constant, in that always the audio gets late wrt. the video.

I was able to reproduce the issue with a simple set of pipelines like
this:
<https://github.com/voc/voctomix/blob/117354649fc8e27a5ad5d1b158b4ce9f49114027/voctocore/experiments/avsync.py>

although the effect seems to be smaller (I see a drift of 40ms over 30
Minutes) here.

I am ready to spend as much time and effort as needed to debug this
problem, but I get the feeling that simply restructuring the pipelines
and waiting 30 minutes, over and over again, won't help, so I'm asking
you what options I have to debug this further and possibly help fixing it.

My guess is, that there may be a truncation error or sth. the like in
the inter* elements, but I may be wrong here. I'm happy to accept
Ideas on how to debug this further.


Regards,
Peter


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