[gst-devel] async Audio/Video

Stefan Kost ensonic at hora-obscura.de
Tue Mar 18 14:19:37 CET 2008


Quoting Matthias Rolf <mrolf at techfak.uni-bielefeld.de>:

> Hi all,
> I'm using gstreamer for realizing an audio/video-synchrony-detection
> algorithm and having the following problem:  using the following
> test-script causes audio and video to go out of sync:

What format are the files in. A demuxer pipleine is prefferably  
working so that the demuxer pulls from its source (the filesrc) and  
pushes on the decoders. Adding a queue after filesrc forces the  
demuxer into streaming mode (push based parsing). Thats separate  
codepath in the demxer and maybe you see a bug there.


> gst-launch-0.10 \
>     filesrc location=$1 ! queue ! decodebin2 name=dec \
>     dec. ! queue ! identity check-perfect=true ! \
>        videorate ! ffmpegcolorspace ! ximagesink \
>     dec. ! queue ! audiorate ! \
>        audioconvert ! alsasink \
>     --gst-debug=videorate:3,identity:4,audiorate:4
> The impact highly depends on the concrete video, but I can reproduce it
> across several test-videos. You can hear/see the asynchrony and it is
> reflected in my computation results from my orignal (very large)
> pipeline (thats my pain-point!).
> My observation is: when removing the queue between filesrc and decodebin
> both streams get synchronized again. Though seeming to solve the problem
> in this special case that knowledge is not sufficient to me, since the
> reliability of my results depends on whether this effect can also impact
> in other situations.
> Note: audiorate and videorate are necessary for my purpose since I have
> to compute precise timing relations between audio and video and thus
> need an absolute high-quality streams.
> Does anybody have an explanation or at least a hypothesis for that
> phenomenon?
> Thanks in advance,
> Matthias
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