AudioDriverKit IOUserAudioIOOperationWriteEnd avoid for input loopback

Question

JFreyberger OP

Created Feb ’24

Replies 2

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Dear Sirs,

I've written an audio driver based on AudioDriverKit.

In my audio callback function I'm receiving calls with io operation IOUserAudioIOOperationWriteEnd and IOUserAudioIOOperationBeginRead as expected which means I see IOUserAudioIOOperationWriteEnd operations during a playback in an application like VLC or the browser and I see IOUserAudioIOOperationBeginRead when recording in Audacity etc..

But when I open the SystemSettings and goto Sound and I select my driver as input I also see calls with IOUserAudioIOOperationWriteEnd which seem to be the just read input data. I can also watch this when starting up Teams. I think the purpose is to add the (mic) input also to the output so you have the chance to listen to yourself.

Nevertheless I'd like to fully avoid this but I don't see a way to distinguish between the playback audio data and the input audio data inside this callback. How could I do this?

Or even better is there a switch which would completely switch off these callbacks which forward the input to the output?

Thanks and best regards, Johannes

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Answer 1

JFreyberger OP

Feb ’24

P.S.: This happens when I have my audio device selected as the default playback device.

In addition I just noticed that there seems to be a little step back back in the audio from the playback application at the moment my device is selected as input device in the SystemSettings.So a small part of the audio (est. 0.3 secs) from the playing application is transferred twice while the same amount of audio is skipped when I switch back to a different audio device as input device. Looking at the in_sample_time of the audio callback with io operation IOUserAudioIOOperationWriteEnd this seems to increase just steadily and according to the previous callbacks for my playback audio data. So I cannot see any jump backward or forward in the in_sample_time.

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Answer 2

bsc1234 OP

Aug ’24

Please file a Feedback for this and post the FB number in the thread. Might be useful to grab a sysdiagnose and also capture a ktrace when this issue occurs.

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