Trouble simply recording mono audio from IP camera!

[Shervin Emami]

Hi,

For weeks I've been having trouble combining 2 audio streams into a single
stream, but I narrowed the problem down as much as possible and now I
realize I can't even record mono audio from a single IP camera to disk
without significant audio loss!

Here is my pipeline, the generated AVI file has roughly 1 audio drop per
second, even when running on an x86 Core i7 PC using today's Git "master"
branch of Gstreamer built from source:

gst-launch-1.0 -e  rtspsrc location=rtsp://cam protocols=tcp latency=2000 !
queue ! application/x-rtp, media=audio ! rtppcmudepay ! mulawdec !
audiorate silent=false ! avimux ! filesink location=out.avi

I looked at the Gstreamer source and tried to figure out if Gstreamer is
getting correct timestamps from my IP camera but due to the complexity of
timestamps in the code I couldn't figure out anything useful. I did notice
a large number of log messages that I think indicate that perhaps
timestamps weren't obtained from the camera:

GST_SCHEDULING
gstpad.c:4194:gst_pad_chain_data_unchecked:<rtpsession0:recv_rtp_sink>
calling chainfunction &0x7f3018aad5e0 with buffer buffer: 0x7f3014060060,
pts 99:99:99.999999999, dts 99:99:99.999999999, dur 99:99:99.999999999,
size 1472, offset none, offset_end none, flags 0x4000

But I don't understand the code well enough to know if this really means
Gstreamer couldn't get correct timestamps from my camera or if those
messages are normal.

I ran a full GST_DEBUG=5 to get all log messages, that I've uploaded some
of it to "https://db.tt/lE3U4f5G", surrounding the audio drop that occurred
at time "0:00:08.183688522". (Indicated in the log by
"gstaudiorate.c:551:gst_audio_rate_chain:<audiorate0> inserting 342
samples")

Note that the audio is PCM mulaw format G.711 (Mono, 8KHz sampling rate,
16-bit samples compressed as 8-bit data). I get the same results when using
Gstreamer 1.2.4, Gstreamer 1.8.2 or today's Gstreamer git "master", and the
same results whether I run it on an x86 or a Jetson TK1 ARM CPU, and I get
the same results with my 2 different brands of IP cameras. So I get the
impression that either I'm simply not using Gstreamer correctly, or
Gstreamer doesn't know how to get timestamps from IP cameras.

And note that if I remove the "audiorate" element from the pipeline, there
aren't any audio drops at all, but the audio is grossly out-of-sync with
any other stream I integrate to the pipeline.

Cheers,
Shervin Emami.
http://www.shervinemami.info/Robotics_Engineer.html
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/gstreamer-devel/attachments/20160630/edee36cd/attachment.html>