Capture specific process with WasapiLoopbackCapture

[joseluisct]

Hello,

I would like to use NAudio WasapiLoopbackCapture with the new possibility of capture loopback audio from (or excluding) a specific process. This requires Win 10 20348 or later.

There is a new initialization structure of the ActivateAudioInterfaceAsync Win32 API that allows you to pass a process to be included or excluded (and it's children).

I have been playing with the sample code on the docs and it's working OK but I would like to use it from my .Net apps that use NAudio. It would be a very good opportunity for audio apps. https://docs.microsoft.com/en-us/samples/microsoft/windows-classic-samples/applicationloopbackaudio-sample/

AUDIOCLIENT_ACTIVATION_PARAMS audioclientActivationParams = {};
audioclientActivationParams.ActivationType = AUDIOCLIENT_ACTIVATION_TYPE_PROCESS_LOOPBACK;
       audioclientActivationParams.ProcessLoopbackParams.ProcessLoopbackMode = includeProcessTree ?
       PROCESS_LOOPBACK_MODE_INCLUDE_TARGET_PROCESS_TREE : PROCESS_LOOPBACK_MODE_EXCLUDE_TARGET_PROCESS_TREE;
audioclientActivationParams.ProcessLoopbackParams.TargetProcessId = processId;
PROPVARIANT activateParams = {};
activateParams.vt = VT_BLOB;
activateParams.blob.cbSize = sizeof(audioclientActivationParams);
activateParams.blob.pBlobData = (BYTE*)&audioclientActivationParams;
wil::com_ptr_nothrow<IActivateAudioInterfaceAsyncOperation> asyncOp;
RETURN_IF_FAILED(ActivateAudioInterfaceAsync(VIRTUAL_AUDIO_DEVICE_PROCESS_LOOPBACK, __uuidof(IAudioClient), 
        &activateParams, this, &asyncOp));
// Wait for activation completion
m_hActivateCompleted.wait();

Thanks.

[markheath]

This is really cool. I don't have much time for working on NAudio these days but I'd love to get this in. Will have to find some time for experimenting with it

[markheath]

I gave this a good try, but something isn't quite working. I think I'm close, but the IAudioClient I end up creating fails with weird COM errors. Here's what I tried: https://github.com/naudio/NAudio/commit/446096a0495950342a3594bb57bea00bfdbad44e

[TomieAi]

someone did a c# version of that Microsoft sample about AUDIOCLIENT_ACTIVATION_PARAMS or ApplicationLoopback. and it's kind of working.. but yeah it's friendly to have it built inside naudio best library ever.

https://github.com/ShortDevelopment/VB-Audio-Router/blob/main/VBAudioRouter.Capture/ProcessAudioCapture.cs

[FactoryXCode]

I'd discover that IActivateAudioInterfaceAsyncOperation::GetActivateResult only returns IAudioClient but not IAudioClient2 or IAudioClient3. Calls on the latter always return E_NOINTERFACE or E_NOT_IMPLEMENTED when calling methods like IsFormatSupported or GetDevicePeriod etc. On samples that are using IMMDevice, those interfaces and methods are working as expected. Why is that?

[joseluisct]

It seems that IAudioClient.GetMixFormat() and IsFormatSupported() are not supported on this scenario and we should use hardcoded format as in the Microsoft example. This is an answer from Microsoft. https://learn.microsoft.com/en-us/answers/questions/1125409/loopbackcapture-(-activateaudiointerfaceasync-with

This is an issue of win-capture-audio plugin C++ implementation https://github.com/bozbez/win-capture-audio/issues/14

[joseluisct]

I have been trying to port the Microsoft C++ Sample to C# but I had no luck because I don´t know how to Pinvoke/port the WIL library that they are using. I think everything should work if the calls to native methods from C# are done in the same way. I hope that someone can help on this task to finally make it available in NAudio.

At the moment, I have made a tiny wrapper dll to call StartCapture and StopCapture of their class, to test it from C#. The code is here: https://github.com/joseluisct/AppLoopback