[gst-devel] Audio/video sync problems

[Arnout Vandecappelle]

 To facilitate debugging, you can insert identities in the audio and video 
pipelines, and compare the timestamps reported by them (when using gst-
launch -v or displaying the messages in your messagecb).  That could help to 
identify where the wrong timestamps are created.

 Regards,
 Arnout

On Wednesday 28 April 2010 21:13:07, Daniel Drake wrote:
> Hi,
> 
> I'm diagnosing a bug in OLPC's Record activity. We use gstreamer to
> capture audio and video from the microphone and webcam, allowing the
> laptop to be used like a camcorder.
> 
> The problem is that the A/V sync on the output file is really bad.
> 
> I'm wondering if anyone can suggest a place to start investigating
> this, or anything else to try. Happy to jump into the code, but would
> love to have some suggestion of where to start.
> 
> This is brand new hardware (new "1.5" version of the laptop) so
> unfortunately we don't have a prior baseline to be working towards.
> 
> Environment:
> Fedora 11
> gstreamer-0.10.25
> gstreamer-plugins-base-0.10.25
> gstreamer-plugins-good-0.10.16
> No PulseAudio
> alsa-lib-1.0.23
> Linux 2.6.31
> XO-1.5 laptop (VIA 1ghz CPU, HDA sound with Conexant codec)
> 
> I've narrowed down the problem to a simple pygst test program. The
> program encodes the webcam input on-the-fly to theora, while recording
> audio to a .wav file.
> After recording for a few seconds, it runs a 2nd pipeline which
> transcodes the .wav into vorbis, and muxes it with the .ogg theora
> file, resulting in a vorbis+theora .ogg output file
> 
> (the reason for doing it in 2 passes is that the system is not capable
> of recording smooth video while encoding to both theora and vorbis
> simultaneously)
> 
> Test program:
> http://dev.laptop.org/~dsd/20100428/record.py
> 
> Intermediate theora:
> http://dev.laptop.org/~dsd/20100428/video.ogg
> 
> Intermediate .wav:
> http://dev.laptop.org/~dsd/20100428/audio.wav
> 
> Resultant file with obvious bad sync:
> http://dev.laptop.org/~dsd/20100428/output.ogg
> 
> Logs from running with GST_DEBUG=2
> http://dev.laptop.org/~dsd/20100428/log2
> 
> Logs from running with GST_DEBUG=4
> http://dev.laptop.org/~dsd/20100428/log4.gz
> 
> Any tips appreciated
> 
> cheers
> Daniel
> 
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-- 
Arnout Vandecappelle                               arnout at mind be
Senior Embedded Software Architect                 +32-16-286540
Essensium/Mind                                     http://www.mind.be
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