Aren't there applications like Skype that mess with volume settings, wouldn't that cause annoying sounds everytime?

Ping. The issue pointed by @broulik have now been fixed, it only plays feedback for volume changes made by the applet.

Is the onVolumeChange call delayed? I'm not sure if it's fired when we set it, or PulseAudio gets back to us.

Does this fire onVolumeChange immediately?

sinkModel.preferredSink.volume = volume;

If so, you're currently calling

playFeedback(); // feedback.sinkIndex = sinkModel.preferredSink.index;

after you change the volume. Which means feedback.sinkIndex isn't set the first volume change, but it is still set until the next time you change the volume. Since it's not -1 after the first "volume change", it will play feedback, even if it's from something else.

If this is so, then we probably want to move the call before we assign the volume. Maybe even rename the function to playFeedbackNextVolumeChange() as well.

diff --git a/applet/contents/ui/main.qml b/applet/contents/ui/main.qml
index 1c9b759..cf58149 100644
--- a/applet/contents/ui/main.qml
+++ b/applet/contents/ui/main.qml
@@ -78,10 +78,10 @@ Item {
         }
         var volume = boundVolume(sinkModel.preferredSink.volume + volumeStep);
         var percent = volumePercent(volume, maxVolumeValue);
+        playFeedbackNextVolumeChange();
         sinkModel.preferredSink.muted = percent == 0;
         sinkModel.preferredSink.volume = volume;
         osd.show(percent);
-        playFeedback();
     }
 
     function decreaseVolume() {

Also, does sinkModel.preferredSink.volume = sinkModel.preferredSink.volume fire onVolumeChange too?

Eg: increaseVolume() setting it to 100% when it's already at 100%.

In D4140#188956, @Zren wrote:

Is the onVolumeChange call delayed? I'm not sure if it's fired when we set it, or PulseAudio gets back to us.

Does this fire onVolumeChange immediately?

sinkModel.preferredSink.volume = volume;

No. All signals are delayed by design because they are emitted only when changes are signaled from pulseaudio.

Also, does sinkModel.preferredSink.volume = sinkModel.preferredSink.volume fire onVolumeChange too?

Eg: increaseVolume() setting it to 100% when it's already at 100%.

Most likely no, unless it actually did change volume on pulseaudio side.

Could we maybe accept this?

BUG: 393931

In D4140#259101, @apol wrote:

Could we maybe accept this?

Not as is, because after D9755 this would need duplicated SinkModel (or revert D9755).