I’m trying to get notifications whenever the master volume changes on Windows Vista/7. This

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Asked: May 13, 20262026-05-13T16:47:28+00:00 2026-05-13T16:47:28+00:00

I’m trying to get notifications whenever the master volume changes on Windows Vista/7. This

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I’m trying to get notifications whenever the master volume changes on Windows Vista/7. This is the code I’m using:

#include <audiopolicy.h>
#include <audioclient.h>
#include <mmdeviceapi.h>
#include <endpointvolume.h>
#include <windows.h>
#include <shlwapi.h>
#include <iostream>
#include <Tchar.h>

static const GUID AudioSessionVolumeCtx = { 0x2715279f, 0x4139, 0x4ba0, { 0x9c, 0xb1, 0xb3, 0x51, 0xf1, 0xb5, 0x8a, 0x4a } };

template <class T> void SafeRelease(T **ppT)
{
    if (*ppT)
    {
        (*ppT)->Release();
        *ppT = NULL;
    }
}

class CAudioSessionVolume : public IAudioSessionEvents
{
public:
    static HRESULT CreateInstance( UINT uNotificationMessage, HWND hwndNotification, CAudioSessionVolume **ppAudioSessionVolume )
    {
        CAudioSessionVolume *pAudioSessionVolume = new (std::nothrow) 
            CAudioSessionVolume(uNotificationMessage, hwndNotification);

        if (pAudioSessionVolume == NULL)
        {
            return E_OUTOFMEMORY;
        }

        HRESULT hr = pAudioSessionVolume->Initialize();
        if (SUCCEEDED(hr))
        {
            *ppAudioSessionVolume = pAudioSessionVolume;
        }
        else
        {
            pAudioSessionVolume->Release();
        }

        return hr;
    }

    // IUnknown methods.
    STDMETHODIMP QueryInterface(REFIID riid, void **ppv)
    {
        static const QITAB qit[] = 
        {
            QITABENT(CAudioSessionVolume, IAudioSessionEvents),
            { 0 },
        };
        return QISearch(this, qit, riid, ppv);
    }

    STDMETHODIMP_(ULONG) AddRef()
    {
        return InterlockedIncrement(&m_cRef);
    }

    STDMETHODIMP_(ULONG) Release()
    {
        LONG cRef = InterlockedDecrement( &m_cRef );
        if (cRef == 0)
        {
            delete this;
        }
        return cRef;
    }

    STDMETHODIMP OnSimpleVolumeChanged( float NewVolume, BOOL NewMute, LPCGUID EventContext )
    {
        MessageBox(NULL, _T("vol changed"), _T("test"), MB_OK);
        return S_OK;
    }

    // The remaining audio session events do not require any action.
    STDMETHODIMP OnDisplayNameChanged(LPCWSTR,LPCGUID)
    {
        return S_OK;
    }

    STDMETHODIMP OnIconPathChanged(LPCWSTR,LPCGUID)
    {
        return S_OK;
    }

    STDMETHODIMP OnChannelVolumeChanged(DWORD,float[],DWORD,LPCGUID)
    {
        return S_OK;
    }

    STDMETHODIMP OnGroupingParamChanged(LPCGUID,LPCGUID)
    {
        return S_OK;
    }

    STDMETHODIMP OnStateChanged(AudioSessionState)
    {
        return S_OK;
    }

    STDMETHODIMP OnSessionDisconnected(AudioSessionDisconnectReason)
    {
        return S_OK;
    }

    // Other methods
    HRESULT EnableNotifications(BOOL bEnable)
    {
        HRESULT hr = S_OK;

        if (bEnable)
        {
            hr = m_pAudioSession->RegisterAudioSessionNotification(this);
        }
        else
        {
            hr = m_pAudioSession->UnregisterAudioSessionNotification(this);
        }

        return hr;
    }

    HRESULT SetDisplayName(const WCHAR *wszName)
    {
        if (m_pAudioSession == NULL)
        {
            return E_FAIL;
        }
        else
        {
            return m_pAudioSession->SetDisplayName(wszName, NULL);
        }
    }

protected:
    CAudioSessionVolume( UINT uNotificationMessage, HWND hwndNotification ) :
        m_cRef(1), m_pAudioSession(NULL), m_pSimpleAudioVolume(NULL)
    {
    }

    ~CAudioSessionVolume()
    {
        EnableNotifications(FALSE);

        SafeRelease(&m_pAudioSession);
        SafeRelease(&m_pSimpleAudioVolume);
    }

    HRESULT Initialize()
    {
        HRESULT hr = S_OK;

        IMMDeviceEnumerator *pDeviceEnumerator = NULL;
        IMMDevice *pDevice = NULL;
        IAudioSessionManager *pAudioSessionManager = NULL;

        // Get the enumerator for the audio endpoint devices.
        hr = CoCreateInstance(__uuidof(MMDeviceEnumerator), NULL,
            CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pDeviceEnumerator));

        if (FAILED(hr)) 
        { 
            goto done; 
        }

        // Get the default audio endpoint that the SAR will use.
        hr = pDeviceEnumerator->GetDefaultAudioEndpoint(eRender, eConsole,
            &pDevice);

        if (FAILED(hr)) 
        { 
            goto done; 
        }

        // Get the session manager for this device.
        hr = pDevice->Activate(__uuidof(IAudioSessionManager), 
            CLSCTX_INPROC_SERVER, NULL, (void**) &pAudioSessionManager);

        if (FAILED(hr)) 
        { 
            goto done; 
        }

        // Get the audio session. 
        hr = pAudioSessionManager->GetAudioSessionControl( 
            &GUID_NULL,     // Get the default audio session. 
            FALSE,          // The session is not cross-process.
            &m_pAudioSession);


        if (FAILED(hr)) 
        { 
            goto done; 
        }

        hr = pAudioSessionManager->GetSimpleAudioVolume(&GUID_NULL, 0,
            &m_pSimpleAudioVolume);

    done:
        SafeRelease(&pDeviceEnumerator);
        SafeRelease(&pDevice);
        SafeRelease(&pAudioSessionManager);
        return hr;
    }

private:
    LONG m_cRef;

    IAudioSessionControl    *m_pAudioSession;
    ISimpleAudioVolume      *m_pSimpleAudioVolume;
};

int main()
{
    CoInitialize(NULL);
    CAudioSessionVolume *asv;
    CAudioSessionVolume::CreateInstance(0, NULL, &asv);
    asv->EnableNotifications(true);

    char s;
    gets(&s);
}

I was expecting to get a message box saying “vol changed” when the system volume changes, but I never get a message box.

I got most of the code from http://msdn.microsoft.com/en-us/library/dd374921(VS.85).aspx

What am I doing wrong?

EDIT: I do get notifications when changing the volume for my application (thanks @nobugz). But I want notification when changing the master volume. (Listed as “Device” in Win7’s Volume Mixers dialog)

EDIT 2: Larry Osterman has a series of blog posts about the volume in Vista/7. This one in particular is interesting: http://blogs.msdn.com/larryosterman/archive/2007/03/22/fun-with-the-endpoint-volume-interfaces-closing-the-loop.aspx I’ll try the code out tomorrow to see if I can get what I want. Now it’s time for bed.

EDIT 3: This is the complete code from Larry’s blog posts up to and including the link posted above. It does what I need and then some. I’ll try to trim the features I don’t need.

#include <windows.h>
#include <mmdeviceapi.h>
#include <endpointvolume.h>
#include <Tchar.h>
#include <strsafe.h>

class CVolumeNotification : public IAudioEndpointVolumeCallback 
{ 
    LONG m_RefCount; 
    ~CVolumeNotification(void) {}; 
public: 
    CVolumeNotification(void) : m_RefCount(1) 
    { 
    } 
    STDMETHODIMP_(ULONG)AddRef() { return InterlockedIncrement(&m_RefCount); } 
    STDMETHODIMP_(ULONG)Release()  
    { 
        LONG ref = InterlockedDecrement(&m_RefCount);  
        if (ref == 0) 
            delete this; 
        return ref; 
    } 
    STDMETHODIMP QueryInterface(REFIID IID, void **ReturnValue) 
    { 
        if (IID == IID_IUnknown || IID== __uuidof(IAudioEndpointVolumeCallback))  
        { 
            *ReturnValue = static_cast<IUnknown*>(this); 
            AddRef(); 
            return S_OK; 
        } 
        *ReturnValue = NULL; 
        return E_NOINTERFACE; 
    } 

    STDMETHODIMP OnNotify(PAUDIO_VOLUME_NOTIFICATION_DATA NotificationData) 
    { 
        wchar_t outputString[256]; 
        DWORD written; 
        COORD writeCoord; 
        StringCbPrintf(outputString, sizeof(outputString), L"Volume Changed: %f", NotificationData->fMasterVolume); 

        writeCoord.X = 0; 
        writeCoord.Y = 3; 
        WriteConsoleOutputCharacter(GetStdHandle(STD_OUTPUT_HANDLE), outputString, (DWORD)wcslen(outputString), writeCoord, &written); 
        return S_OK; 
    } 
}; 

struct TimerContext 
{ 
    IAudioMeterInformation *_Meter; 
}; 

const int TimerPeriodicityMS = 100; 
void CALLBACK TimerMeterCallback(PTP_CALLBACK_INSTANCE CallbackInstance, PVOID Context, PTP_TIMER Timer) 
{
    TimerContext *timerContext = (TimerContext *)Context; 
    wchar_t outputString[256]; 
    float peakValue; 
    DWORD written; 
    COORD writeCoord; 
    StringCbCopy(outputString, sizeof(outputString), L"Meter: "); 

    timerContext->_Meter->GetPeakValue(&peakValue); 
    for (size_t i = 0 ; i < peakValue*100; i += 1) 
    { 
        StringCbCat(outputString, sizeof(outputString), L"*"); 
    } 
    for (size_t i = (size_t)(peakValue*100) ; i < 100; i += 1) 
    { 
        StringCbCat(outputString, sizeof(outputString), L"."); 
    } 
    writeCoord.X = 0; 
    writeCoord.Y = 1; 
    WriteConsoleOutputCharacter(GetStdHandle(STD_OUTPUT_HANDLE), outputString, (DWORD)wcslen(outputString), writeCoord, &written); 
} 

int _tmain(int argc, _TCHAR* argv[])
{
    CoInitialize(NULL);
    HRESULT hr;
    IMMDeviceEnumerator *deviceEnumerator = NULL;;
    HANDLE handle; 
    TP_CALLBACK_ENVIRON callbackEnvironment; 
    PTP_CLEANUP_GROUP cleanupGroup; 
    PTP_TIMER timer; 
    TimerContext context; 

    InitializeThreadpoolEnvironment(&callbackEnvironment); 
    cleanupGroup = CreateThreadpoolCleanupGroup(); 
    SetThreadpoolCallbackCleanupGroup(&callbackEnvironment, cleanupGroup, NULL); 

    timer = CreateThreadpoolTimer(TimerMeterCallback, &context, &callbackEnvironment); 

    //
    //    Clear the screen.  Code stolen from: http://support.microsoft.com/kb/319257.
    //
    handle = GetStdHandle(STD_OUTPUT_HANDLE);
    DWORD writtenChars = 0;
    CONSOLE_SCREEN_BUFFER_INFO consoleInfo;
    COORD home;
    home.X = home.Y = 0;
    GetConsoleScreenBufferInfo(handle, &consoleInfo);
    FillConsoleOutputCharacter(handle, L' ', consoleInfo.dwSize.X * consoleInfo.dwSize.Y, home, &writtenChars);
    SetConsoleCursorPosition(handle, home);

    //
    //    Set the console to raw mode. 
    //
    DWORD oldMode;
    GetConsoleMode(GetStdHandle(STD_INPUT_HANDLE), &oldMode);
    SetConsoleMode(GetStdHandle(STD_INPUT_HANDLE), oldMode & ~(ENABLE_LINE_INPUT | ENABLE_ECHO_INPUT));

    // 
    //    Instantiate an endpoint volume object.
    //
    hr = CoCreateInstance(__uuidof(MMDeviceEnumerator), NULL, CLSCTX_INPROC_SERVER, __uuidof(IMMDeviceEnumerator), (LPVOID *)&deviceEnumerator);
    IMMDevice *defaultDevice = NULL;

    hr = deviceEnumerator->GetDefaultAudioEndpoint(eRender, eConsole, &defaultDevice);
    deviceEnumerator->Release();
    deviceEnumerator = NULL;

    IAudioEndpointVolume *endpointVolume = NULL;
    hr = defaultDevice->Activate(__uuidof(IAudioEndpointVolume), CLSCTX_INPROC_SERVER, NULL, (LPVOID *)&endpointVolume);
    CVolumeNotification *volumeNotification = new CVolumeNotification(); 
    hr = endpointVolume->RegisterControlChangeNotify(volumeNotification); 
    hr = defaultDevice->Activate(__uuidof(IAudioMeterInformation), CLSCTX_INPROC_SERVER, NULL, (LPVOID *)&context._Meter); 
    defaultDevice->Release(); 
    defaultDevice = NULL; 
    // Set a 100 millisecond timer. 
    LARGE_INTEGER timerPeriodicityLI; 
    FILETIME timerPeriodicity; 
    timerPeriodicityLI.QuadPart = -1*(TimerPeriodicityMS* 10000 ); 

    timerPeriodicity.dwLowDateTime = timerPeriodicityLI.LowPart; 
    timerPeriodicity.dwHighDateTime = timerPeriodicityLI.HighPart; 

    SetThreadpoolTimer(timer, &timerPeriodicity, TimerPeriodicityMS, 10); 

    wchar_t inputChar = '\0';
    while (inputChar != '\r')
    {
        UINT currentStep, stepCount;
        DWORD read, written;
        COORD writeCoord;
        wchar_t outputString[256];
        StringCbCopy(outputString, sizeof(outputString), L"Volume: ");

        // 
        //    Calculate the cheesy OSD.
        //
        endpointVolume->GetVolumeStepInfo(&currentStep, &stepCount);
        for (size_t i = 0 ; i < stepCount ; i += 1)
        {
            if (i <= currentStep)
            {
                StringCbCat(outputString, sizeof(outputString), L"=");
            }
            else
            {
                StringCbCat(outputString, sizeof(outputString), L"-");
            }
        }
        writeCoord.X = 0;
        writeCoord.Y = 0;
        WriteConsoleOutputCharacter(handle, outputString, (DWORD)wcslen(outputString), writeCoord, &written);

        ReadConsole(GetStdHandle(STD_INPUT_HANDLE), &inputChar, 1, &read, NULL);
        if (inputChar == '+')
        {
            endpointVolume->VolumeStepUp(NULL);
        }
        else if (inputChar == '-')
        {
            endpointVolume->VolumeStepDown(NULL);
        }
    }

    // 
    //    Remove our notification. 
    // 
    endpointVolume->UnregisterControlChangeNotify(volumeNotification); 

    endpointVolume->Release(); 
    volumeNotification->Release(); 
    SetConsoleMode(GetStdHandle(STD_INPUT_HANDLE), oldMode);

    CloseThreadpoolCleanupGroupMembers(cleanupGroup, FALSE, NULL); 
    CloseThreadpoolCleanupGroup(cleanupGroup); 
    cleanupGroup = NULL; 
    DestroyThreadpoolEnvironment(&callbackEnvironment); 

    context._Meter->Release(); 

    CoUninitialize();

    return 0;
}

EDIT 4: This is a stripped down version of Larry’s code.

#include <windows.h>
#include <mmdeviceapi.h>
#include <endpointvolume.h>
#include <iostream>
#include <Tchar.h>

class CVolumeNotification : public IAudioEndpointVolumeCallback 
{ 
    LONG m_RefCount; 
    ~CVolumeNotification(void) {}; 
public: 
    CVolumeNotification(void) : m_RefCount(1) 
    { 
    } 
    STDMETHODIMP_(ULONG)AddRef() { return InterlockedIncrement(&m_RefCount); } 
    STDMETHODIMP_(ULONG)Release()  
    { 
        LONG ref = InterlockedDecrement(&m_RefCount);  
        if (ref == 0) 
            delete this; 
        return ref; 
    } 
    STDMETHODIMP QueryInterface(REFIID IID, void **ReturnValue) 
    { 
        if (IID == IID_IUnknown || IID== __uuidof(IAudioEndpointVolumeCallback))  
        { 
            *ReturnValue = static_cast<IUnknown*>(this); 
            AddRef(); 
            return S_OK; 
        } 
        *ReturnValue = NULL; 
        return E_NOINTERFACE; 
    } 

    STDMETHODIMP OnNotify(PAUDIO_VOLUME_NOTIFICATION_DATA NotificationData) 
    { 
        std::cout << NotificationData->fMasterVolume << _T(" ");

        return S_OK; 
    } 
}; 

int _tmain(int argc, _TCHAR* argv[])
{
    CoInitialize(NULL);
    HRESULT hr;
    IMMDeviceEnumerator *deviceEnumerator = NULL;;

    // 
    //    Instantiate an endpoint volume object.
    //
    hr = CoCreateInstance(__uuidof(MMDeviceEnumerator), NULL, CLSCTX_INPROC_SERVER, __uuidof(IMMDeviceEnumerator), (LPVOID *)&deviceEnumerator);
    IMMDevice *defaultDevice = NULL;

    hr = deviceEnumerator->GetDefaultAudioEndpoint(eRender, eConsole, &defaultDevice);
    deviceEnumerator->Release();
    deviceEnumerator = NULL;

    IAudioEndpointVolume *endpointVolume = NULL;
    hr = defaultDevice->Activate(__uuidof(IAudioEndpointVolume), CLSCTX_INPROC_SERVER, NULL, (LPVOID *)&endpointVolume);
    CVolumeNotification *volumeNotification = new CVolumeNotification(); 
    hr = endpointVolume->RegisterControlChangeNotify(volumeNotification); 
    defaultDevice->Release(); 
    defaultDevice = NULL; 

    wchar_t inputChar = '\0';
    while (inputChar != '\r')
    {
        DWORD read;
        ReadConsole(GetStdHandle(STD_INPUT_HANDLE), &inputChar, 1, &read, NULL);
    }

    // 
    //    Remove our notification. 
    // 
    endpointVolume->UnregisterControlChangeNotify(volumeNotification); 
    endpointVolume->Release(); 
    volumeNotification->Release(); 

    CoUninitialize();

    return 0;
}

I still haven’t looked at the SDK example. I now know how this stuff works well enough to add what I need to my application. Thanks for everyones help!

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1 Answer

Editorial Team · Answer 1 · 2026-05-13T16:47:28+00:00

Editorial Team

2026-05-13T16:47:28+00:00Added an answer on May 13, 2026 at 4:47 pm

It works fine when I try it. Be sure to click on the volume control tray icon, click Mixer and modify the volume for your app.

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