[gstreamer-bugs] [Bug 570378] New: Weird bus messages after calling gst_mixer_set_volume()

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | gst-plugins-base | Ver: 0.10.21
           Summary: Weird bus messages after calling gst_mixer_set_volume()
           Product: GStreamer
           Version: 0.10.21
          Platform: Other
        OS/Version: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-base
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: jannis at xfce.org
         QAContact: gstreamer-bugs at lists.sourceforge.net
     GNOME version: Unspecified
   GNOME milestone: Unspecified


Please describe the problem:
I'm the author of xfce4-mixer which uses the GstMixer interface of GStreamer.
Ever since I started working on it, one bug annoyed the hell out of me.

It appears in at least two variants:

1. 
After a call to gst_mixer_set_volume(), I receive a volume change message from
the bus which belongs to the track I just changed. Let (10,10) be the volumes
I've set with gst_mixer_set_volume(), then the message I receive would be
something like (0,10). One channel is dropped to zero and I have no idea why.
This only happens sometimes but often enough to be annoying. In xfce4-mixer it
makes GtkScales jump around like crazy.

2. 
After a call to gst_mixer_set_volume() of a capture track and recording on that
track is disabled, I suddenly receive a record toggled message which tells me
that recording was enabled. Weird.

I've written a small test program for scenario 1 in order to make sure it's not
a bug in xfce4-mixer and it's not caused by a race condition between the faders
and the GstBus. I'll attach it to this bug report.

Steps to reproduce:
1. Call gst_mixer_set_volume() on a playback or capture track

Actual results:
The volume is applied but suddenly GStreamer freaks out,  drops some of the
channels of the track (playback) or activates recording (capture) and sends out
a bus message reflecting its weird behaviour.

Expected results:
The volume is applied inside GStreamer and no bus messages are sent back to the
application that changed the volume.

Does this happen every time?
No, but quite often.

Other information:
I'm using gst-plugins-base 0.10.21 with the ALSA driver.


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