[pulseaudio-discuss] Issue connecting a null-sink to a tunnel sink

[Olivier Delbeke]

Hi all,

I'm struggling with a pulseaudio configuration that I expected to be
working out-of-the box (as it seems very simple).

I have :
 * a null-sink "mynullsink"
 * a tunnel-sink "mytunnel"
 * a module-loopback to connect "mynullsink.monitor" to "mytunnel"

Content of /etc/pulse/default.pa is here (full content):
  load-module
module-native-protocol-unix

  load-module
module-suspend-on-idle

  load-module module-null-sink
sink_name=mynullsink

  load-module module-tunnel-sink sink_name=mytunnel server=tcp:
192.168.100.3:4713 sink=remotesink

Playing a wav file directly to the tunnel works fine, all the time :
  paplay sample1.wav -d mytunnel
  => audio sent correctly through the tunnel
     However, I can see with "pacmd list-sinks" that "mytunnel" has a
"current latency" of 0ms. Normal ?

To connect the null-sink and the tunnel, I do this (with either pactl or
pacmd) :
  pacmd load-module module-loopback source=mynullsink.monitor sink=mytunnel
  => The module is correctly loaded (as I can see with "pacmd list-modules")

But playing audio to the null-sink does not work (i.e., no sound is
forwarded to the tunnel by the loopback) :
  paplay sample1.wav -d mynullsink
  => NO AUDIO. NO ERROR MESSAGE. VOLUMES AT 100%. STATE RUNNING

With pulseaudio 6.0, I see that the latency calculated by the
module-loopback is increased by 10s every 10s :
D: [pulseaudio] module-loopback.c: Loopback overall latency is 21552.00 ms
+ 0.00 ms + 0.00 ms = 21552.00 ms
D: [pulseaudio] module-loopback.c: Should buffer 0 bytes, buffered at
minimum 0 bytes
D: [pulseaudio] module-loopback.c: [mytunnel] Updated sampling rate to
48000 Hz.
D: [pulseaudio] module-loopback.c: Loopback overall latency is 31524.00 ms
+ 0.00 ms + 0.00 ms = 31524.00 ms
D: [pulseaudio] module-loopback.c: Should buffer 0 bytes, buffered at
minimum 0 bytes
D: [pulseaudio] module-loopback.c: [mytunnel] Updated sampling rate to
48000 Hz.

With pulseaudio 4.0, the latency moves around 250ms, but there is also no
audio.

There seems to be a very unexpected workaround : loading the loopback
module twice ! When I do that, I get audio, but it's slightly disturbed
(sounds like an old vinyl record).

What is happening ? Does anyone have a hint ?
Why can't I chain a null sink to a tunnel sink using a loopback module ?

Thank you and best regards,

Olivier
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