[gst-devel] Audio/video sync problems

[Daniel Drake]

On 28 April 2010 16:13, Daniel Drake <dsd at laptop.org> wrote:
> 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.

Thanks for the suggestions!

I didn't get around to trying AIFF, but I did try speex + theora
on-the-fly, writing to an oggmux. The resultant file was unplayable.
Possible bug there.

Uncompressed AVI on-the-fly recording worked quite well, as did
on-the-fly recording to vorbis + theora using 2 very large queue
buffers.

But in the end, I solved the problem and obtained the best sync simply
by sticking with the 2-pass technique, but adding a queue buffer in
the audio recording path, after alsasrc. It seems like the queue is
able to smooth out the overruns/underruns that occur at the start of
recording, which was throwing off the sync for the whole recording
session.

I think this indicates a bug somewhere in gstreamer or alsa -- if the
audio recording can't keep up for whatever reason, I feel like it
should resync later on, but that's not working well.

Due to time pressures I think this is the "solution" we'll go with for now.

cheers,
Daniel