Timestamp drift when using dmix/dsnoop plugins with alsasrc/sink

[Nox Deleo]

Hi all,

Not sure if this belongs on the alsa mailing list rather than here, but I'm
getting an interesting issue when using GStreamer with alsa dmix/dsnoop
plugins.

If I launch a pipeline that is simply alsasrc -> alsasink using
plughw:[device name] as the 'device' parameter of alsasrc/sink, everything
works as expected. However if I use dmix/dsnoop plugins instead, I get the
following errors:

0:00:01.391972927  3106      0x1cff450 WARN           audiobasesink
gstaudiobasesink.c:1273:gst_audio_base_sink_skew_slaving:<alsasink0>
correct clock skew 20310980 > 20000000
0:00:14.354153448  3106      0x1cff450 WARN           audiobasesink
gstaudiobasesink.c:1579:gst_audio_base_sink_get_alignment:<alsasink0>
Unexpected discontinuity in audio timestamps of +0:00:00.019342403,
resyncing
0:00:15.144134599  3106      0x1cff450 WARN           audiobasesink
gstaudiobasesink.c:1273:gst_audio_base_sink_skew_slaving:<alsasink0>
correct clock skew 20830214 > 20000000
0:00:15.144165855  3106      0x1cff450 WARN           audiobasesink
gstaudiobasesink.c:1579:gst_audio_base_sink_get_alignment:<alsasink0>
Unexpected discontinuity in audio timestamps of +0:00:00.040000000,
resyncing

If I then use some of the plug pcm's (layered on top of dmix/dsnoop) I
defined to split up the in and outs of my soundcard, there are even more of
these messages (more often), and I can actually hear the problem (audio
intermittently stuttering, and even sometimes dropping out altogether).

However, if I use any of the above devices with arecord -D [device name] -f
dat | aplay -D [device name], the audio is absolutely fine.

I've tried adjusting buffer/sample sizes in my .asoundrc, messing with
various options in alsasrc/sink, and even using a lowlatency kernel. These
don't seem to do anything to diminish this problem. I could introduce
latency problems by setting buffer/sample sizes too low, but this problem
never changed at all, which makes me think it's not a straight latency
issue.

Any ideas greatly appreciated.
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