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alsasink does not synchronise properly with a live streaming source, yet (timing skew)

Submitted by Thomas DEBESSE

Link to original bug (#692953)

Description

Hi, alsa modules (alsasrc, alsasink) become silent when used for several hours.
The time before become silent or noisy depend on the whole pipeline.

A pipeline like "udpsrc ! … ! alsasink" breaks after 3 ou 4 hours.
A pipeline like "alsasrc ! … ! alsasink" does the same.
A pipeline like "jackaudiosrc ! … ! alsasink" breaks after 14 hours.

I have tried different uses case, sometimes it's the alsasrc module that become silent, sometimes it's the alsasink module.

On some use case, I get noise instead of silence.

This is a complete pipeline that breaks :
gst-launch-0.10 jackaudiosrc ! "audio/x-raw-float" ! audioconvert ! audioresample ! "audio/x-raw-int, rate=44100, width=16" ! alsasink device="hw:1" sync=0

And another pipeline that breaks :
gst-launch-0.10 -v alsasrc device="hw:0" audioconvert ! audioresample ! "audio/x-raw-int,rate=44100,width=16,channels=2" ! alsasink device="hw:1" sync=false

And another pipeline (Gst 1.0) that breaks :
gst-launch-1.0 alsasrc device="hw:0 ! 'audio/x-raw, format=S16LE' ! audioconvert ! audioresample ! 'audio/x-raw, format=F32LE, channels=2' ! jackaudiosink sync=0

I have some other examples with "alsasrc ! … ! udpsink" or "udpsrc ! … ! alsasink".

Good to know :

  • I don't get this problem on other Gstreamer modules.
  • This bug affect both Gstreamer 0.10 and Gstreamer 1.0
  • The bug appears every time an alsa module (alsasrc or alsasink) is used, just wait long.
  • The time before become silent depend on the whole pipeline.
  • The fact of getting noise or silence depend on the whole pipeline.
  • I use soundcards directly without alsa modules (no 'plug', no 'dmix', no 'dsnoop') or with alsa modules (that changes nothing)

How to reproduce :

  • build a pipeline using alsasrc or alsasink
  • let the pipeline running a complete day to be sure to get the bug
    Note : pipelining alsasrc with alsasink is one of the faster way to get a bug, only 3 or 4 hours instead of more than 12 hours.

Some details :

  • gst-inspect with -v option said nothing about any problem.
  • GST_DEBUG=3 said nothing about any problem.
  • The pipeline isn't broken, state is always Gst.State.PLAYING and the pipeline seems functionnal
  • Nothing seems broken, there is no sound so people could say "I got the bug" but software does'nt know there is a bug.
  • Some pipeline get noise instead of silent.
  • Restarting the pipeline without destroying it (set Gst.State.NULL then set Gst.State.PLAYING) fix it. So you can restart the pipeline every 3 hours to have sound several days dealing with some milliseconds of silence every 3 hours)

The bug was tested and confirmed on :

  • several computers
  • several soundcards (usb Muse Pocket LT3, pci Audigy CA0106, internal Intel 82801, Nvidia MCP51, some Realtek chip)
  • several alsa build
  • several linux build (2.6.32 → 3.2.0), rt-kernels or not rt-kernels
  • several Gstreamer versions (0.10 → 1.0)
  • some distros (Debian Squeeze, Wheezy, Sid, Ubuntu 12.10)

There is a discussion about this bug on the mailing list :

Version: 1.0.10

See also