[gst-devel] Audio/video sync problems

[Stefan Kost]

Am 28.04.2010 22:13, schrieb Daniel Drake:
> 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)

I was recently suggesting someone working on OLPC to record in one pass, but use
speex instead of vorbis and he reported that this makes it work fine.

You could try to replace wavenc/wavparse with aiffmux/aiffparse to check if its
wav plugin related.

Stefan

> 
> 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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