如何检测默认音频 output 设备更改 Windows

Question

I am developing an audio recording program in C++ (I use OpenAL and ImGui with OpenGL if that helps) and i want to know if i can detect if my default audio output device changes without running a loop that blocks my program. Is there a way for me to detect it like with callbacks maybe?

I tried using

alcGetString(device, ALC_DEFAULT_DEVICE_SPECIFIER);

function to get the name of the default device and compare it with last one i used in a loop on another thread. It did the job but it cost me lots of performance.

Answer 1

Thanks to @PaulSanders i have found a solution. It is not what i was looking for but i think it is still a good one. Here is the code:

#include <Windows.h>
#include <mmdeviceapi.h>
#include <endpointvolume.h>

// The notification client class
class NotificationClient : public IMMNotificationClient {
public:
    // IUnknown methods
    HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, void** ppvObject) {
        if (riid == IID_IUnknown || riid == __uuidof(IMMNotificationClient)) {
            *ppvObject = this;
            AddRef();
            return S_OK;
        }
        *ppvObject = NULL;
        return E_NOINTERFACE;
    }
    ULONG STDMETHODCALLTYPE AddRef() { return InterlockedIncrement(&m_cRef); }
    ULONG STDMETHODCALLTYPE Release() {
        ULONG ulRef = InterlockedDecrement(&m_cRef);
        if (ulRef == 0)
            delete this;
        return ulRef;
    }

    // IMMNotificationClient methods
    HRESULT STDMETHODCALLTYPE OnDefaultDeviceChanged(EDataFlow flow, ERole role, LPCWSTR pwstrDeviceId) {
        // The default audio output device has changed
        // Handle the device change event
        // ...
        return S_OK;
    }
    HRESULT STDMETHODCALLTYPE OnDeviceAdded(LPCWSTR pwstrDeviceId) { return S_OK; }
    HRESULT STDMETHODCALLTYPE OnDeviceRemoved(LPCWSTR pwstrDeviceId) { return S_OK; }
    HRESULT STDMETHODCALLTYPE OnDeviceStateChanged(LPCWSTR pwstrDeviceId, DWORD dwNewState) { return S_OK; }
    HRESULT STDMETHODCALLTYPE OnPropertyValueChanged(LPCWSTR pwstrDeviceId, const PROPERTYKEY key) { return S_OK; }

    // Constructor and destructor
    NotificationClient() : m_cRef(1) {}
    ~NotificationClient() {}

private:
    long m_cRef;
};

class AudioDeviceNotificationListener
{
public:
    AudioDeviceNotificationListener() = default;
    ~AudioDeviceNotificationListener() { Close(); }

    bool Start()
    {
        // Initialize the COM library for the current thread
        HRESULT hr = CoInitialize(NULL);
        if (FAILED(hr)) {
            return false;
        }

        // Create the device enumerator
        hr = CoCreateInstance(__uuidof(MMDeviceEnumerator), NULL, CLSCTX_ALL, __uuidof(IMMDeviceEnumerator), (void**)&pEnumerator);
        if (FAILED(hr)) {
            CoUninitialize();
            return false;
        }

        // Create the notification client object
        pNotificationClient = new NotificationClient();

        // Register the notification client
        hr = pEnumerator->RegisterEndpointNotificationCallback(pNotificationClient);
        if (FAILED(hr)) {
            pEnumerator->Release();

            pNotificationClient->Release();
            pNotificationClient = nullptr;

            CoUninitialize();
            return false;
        }

        // Create the notification thread
        hNotificationThread = CreateThread(NULL, 0, &AudioDeviceNotificationListener::NotificationThreadProc, pNotificationClient, 0, NULL);
        if (hNotificationThread == NULL) {
            pEnumerator->UnregisterEndpointNotificationCallback(pNotificationClient);
            pEnumerator->Release();

            pNotificationClient->Release();
            pNotificationClient = nullptr;

            CoUninitialize();
            return false;
        }

        bDidStart = true;
    }

    void Close()
    {
        if (bDidStart)
        {
            // Clean up

            /* Not happy with TerminateThread but until another solution i will use this */
            TerminateThread(hNotificationThread, 0);

            pEnumerator->UnregisterEndpointNotificationCallback(pNotificationClient);
            pEnumerator->Release();

            pNotificationClient->Release();
            pNotificationClient = nullptr;

            CoUninitialize();
            bDidStart = false;
        }
    }

private:
    // Thread Function
    static DWORD WINAPI NotificationThreadProc(LPVOID lpParameter)
    {
        // Run the message loop
        MSG msg;
        while (true) {
            // Check for a message
            if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {
                // A message was received. Process it.
                TranslateMessage(&msg);
                DispatchMessage(&msg);
            }
            else {
                // No message was received. Suspend the thread until a message is received.
                WaitMessage();
            }
        }
    }

private:
    bool bDidStart = false;

    NotificationClient* pNotificationClient = nullptr;

    IMMDeviceEnumerator* pEnumerator = NULL;
    HANDLE hNotificationThread = NULL;
};

NotificationClient class inherits IMMNotificationClient so i can override its functions for custom handling its events. This code generates a thread to check if default device is changed, AudioDeviceNotificationListener::Start will start the thread and AudioDeviceNotificationListener::Close will terminate it. I am not happy with TerminateThread function but it didn't create a problem for me so i will use it for now. This thread checks for a device change message and if it doesn't receive any message the thread is suspended until a message is received so this solves busy-looping which has caused my problem of performance.