Duck the audio of other apps on Windows

Question

I am attempting to activate the Windows default automatic audio ducking: mmsys.cpl -> "Communications tab", inside my C++ desktop app so that I can duck only the audio of the rest of the applications but not that of mine so that any important audio is heard and not overlapped by a background such.

The problem is that I not only duck the audio of the rest of the applications - Spotify, browser's audio like YouTube, but also that of my application.

I have extracted the audio ducking functionality from this Microsoft example which can be downloaded from here.

The most obvious way to notice that the audio of the current application is also ducked is to set the audio ducking setting inside the Windows sound settings to "Mute all other sounds" as shown here.

The audio ducking example provided above simulates a communication session/activity as far as I know - a WASAPI chat. I presume this is the reason that my audio is ducked as well since despite being my app opens a communication stream still this sample communication activity from the Microsoft's example is probably overriding my app's audio in terms of priority. That is just a presumption/hypothesis. Presumably something should be changed in this part of the example's code.

I am open to all suggestions what should be fixed/changed/added. I confirm again that I want to use so-called "automatic" or I would say ready-made integrated audio ducking provided by Windows - the one shown on the screenshot above. I don't want to provide a custom ducking behavior by lowering the other apps volume to arbitrary levels.

There are two APIs that directly mention the audio ducking: IAudioSessionControl2::SetDuckingPreference IAudioClientDuckingControl::SetDuckingOptionsForCurrentStream

The first one only switches between the automatic ducking behavior and a custom one i.e. switch the automatic off. I am currently testing the second one. The problem with it is the minimum required Windows version.

Answer 1

Here's the minimal code that triggers the audio ducking:

CComPtr<IMMDeviceEnumerator> deviceEnumerator;
HRESULT hr = CoCreateInstance(
    __uuidof(MMDeviceEnumerator),
    nullptr,
    CLSCTX_ALL /* CLSCTX_INPROC_SERVER */,
    IID_PPV_ARGS(&deviceEnumerator));
if (FAILED(hr))
{
    return;
}

CComPtr<IMMDevice> communicationsDevice;
hr = deviceEnumerator->GetDefaultAudioEndpoint(
            eRender, // eCapture for microphone
            eCommunications,
            &communicationsDevice);
if (FAILED(hr))
{
    return;
}

CComPtr<IAudioClient3> audioClient;
hr = communicationsDevice->Activate(
        __uuidof(IAudioClient3),
        CLSCTX_ALL /* CLSCTX_INPROC_SERVER */,
        nullptr,
        reinterpret_cast<LPVOID*>(&audioClient));
if (FAILED(hr))
{
    return;
}

WAVEFORMATEX* mixFormat = nullptr;
hr = audioClient->GetMixFormat(&mixFormat);
if (FAILED(hr))
{
    return false;
}

hr = audioClient->Initialize(
        AUDCLNT_SHAREMODE_SHARED,
        AUDCLNT_SESSIONFLAGS_DISPLAY_HIDE
        | AUDCLNT_STREAMFLAGS_EVENTCALLBACK
        | AUDCLNT_STREAMFLAGS_NOPERSIST,
        500000,
        0,
        mixFormat,
        nullptr);
if (FAILED(hr))
{
    return;
}

CoTaskMemFree(mixFormat);
mixFormat = nullptr;

hr = audioClient->Start();
if (FAILED(hr))
{
    return;
}

Additionally, there are buffer manipulations - both initial and on a separate thread but they don't seem to be part of the minimum requirements to trigger the audio ducking.