Endpoint Volume Controls

本次使用win32 api的Endpoint Volume Controls实现当系统音量变化时程序收到通知，环境为win10 64位。

[1] 实现IAudioEndpointVolumeCallback接口

实现IAudioEndpointVolumeCallback接口，重点是OnNotify方法。

/*  Epvolume.h   */
#include <windows.h>
#include <mmdeviceapi.h>
#include <endpointvolume.h>

// Client's proprietary event-context GUID
extern GUID g_guidMyContext;

class CAudioEndpointVolumeCallback : public IAudioEndpointVolumeCallback
{
    LONG _cRef;
public:
    CAudioEndpointVolumeCallback() :
        _cRef(1)
    {
    }
    ~CAudioEndpointVolumeCallback()
    {
    }

    // IUnknown methods -- AddRef, Release, and QueryInterface
    ULONG STDMETHODCALLTYPE AddRef()    //增加引用计数
    {
        return InterlockedIncrement(&_cRef);
    }
    ULONG STDMETHODCALLTYPE Release()   //减少引用计数
    {
        ULONG ulRef = InterlockedDecrement(&_cRef);
        if (0 == ulRef)
        {
            delete this;
        }
        return ulRef;
    }
    HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, VOID** ppvInterface)//查询组件实现接口
    {
        if (IID_IUnknown == riid)
        {
            AddRef();
            *ppvInterface = (IUnknown*)this;
        }
        else if (__uuidof(IAudioEndpointVolumeCallback) == riid)
        {
            AddRef();
            *ppvInterface = (IAudioEndpointVolumeCallback*)this;
        }
        else
        {
            *ppvInterface = NULL;
            return E_NOINTERFACE;
        }
        return S_OK;
    }
    // Callback method for endpoint-volume-change notifications.
    //接口 - 通知方法实现
    HRESULT STDMETHODCALLTYPE OnNotify(PAUDIO_VOLUME_NOTIFICATION_DATA pNotify)
    {
        if (pNotify == NULL)
        {
            return E_INVALIDARG;
        }
        if (pNotify->guidEventContext != g_guidMyContext)
        {
            float fVolume = pNotify->fMasterVolume; //主音量级别
        }
        return S_OK;
    }
};

[2] 主函数

主函数作用是创建实例，初始化，注册事件和注销。

#include <windows.h>
#include <mmdeviceapi.h>
#include <endpointvolume.h>
#include "Epvolume.h"

GUID g_guidMyContext = GUID_NULL;
static IAudioEndpointVolume* g_pEndptVol = NULL;

#define SAFE_RELEASE(punk)  if((punk) != NULL){ (punk)->Release(); (punk) = NULL; }

int main()
{
	HRESULT hr = S_OK;
	IMMDeviceEnumerator* pEnumerator = NULL;
	IMMDevice* pDevice = NULL;
	CAudioEndpointVolumeCallback EPVolEvents;

	//初始化
	CoInitialize(NULL);
	//创建GUID
	hr = CoCreateGuid(&g_guidMyContext);
	// Get enumerator for audio endpoint devices.
	hr = CoCreateInstance(__uuidof(MMDeviceEnumerator), NULL, CLSCTX_INPROC_SERVER,	__uuidof(IMMDeviceEnumerator), (void**)&pEnumerator);
	// Get default audio-rendering device.
	hr = pEnumerator->GetDefaultAudioEndpoint(eRender, eConsole, &pDevice);
	//激活
	hr = pDevice->Activate(__uuidof(IAudioEndpointVolume), CLSCTX_ALL, NULL, (void**)&g_pEndptVol);
	//注册控件变化通知
	hr = g_pEndptVol->RegisterControlChangeNotify((IAudioEndpointVolumeCallback*)&EPVolEvents);

	//消息循环
	MSG msg;
	while (GetMessage(&msg, NULL, 0, 0))	 //从消息队列中取消息 
	{
		TranslateMessage(&msg);              //转换消息
		DispatchMessage(&msg);               //派发消息
	}
	//释放
	SAFE_RELEASE(pEnumerator)
	SAFE_RELEASE(pDevice)
	SAFE_RELEASE(g_pEndptVol)
	CoUninitialize();
	
	return 0;
}

总结

总的来说，我们实现了利用Endpoint Volume Controls来监控系统音量的功能，但实际上该控件并不知有这一个功能，还可以用来做一个音量控制面板实现调节音量的功能。阅读官方文档，学习更多知识。

参考

Microsoft Core Audio APIs- Endpoint Volume Controls