windwos系统抓取声卡音频

参考：https://msdn.microsoft.com/en-us/library/windows/desktop/dd316551%28v=vs.85%29.aspx

因为一个我的需求须要抓取声卡音频数据，可是找了一圈好像都是麦克风录音的，而后发现Potplayer里面的声音抓取用wasapi，因而就找了了微软这个msdn文档，根据例子看起来很简单。直接上我修改后的代码。

依赖头文件及库：

#include <mmdeviceapi.h>
#include <Audioclient.h>
#include <Functiondiscoverykeys_devpkey.h>

-lole32 -lmmdevapi

请先初始化com库，CoInitializeEx( NULL, COINIT_MULTITHREADED );

IMMDeviceEnumerator *pEnumerator = NULL;
    IMMDevice *pEndpoint = NULL;
    IAudioClient* pAudioClient = NULL;
    IAudioCaptureClient* pAudioCaptureClient = NULL;
    WAVEFORMATEX* pwfx = NULL;

    pEnumerator->GetDefaultAudioEndpoint(eRender,eConsole,&pEndpoint);
    HRESULT hr = pEndpoint->Activate(__uuidof(IAudioClient),CLSCTX_ALL,NULL,(void**)&pAudioClient);
    hr = pAudioClient->GetMixFormat(&pwfx);
    hr = pAudioClient->Initialize(AUDCLNT_SHAREMODE_SHARED,
                             AUDCLNT_STREAMFLAGS_LOOPBACK,
                             0,
                             0,
                             pwfx,
                             NULL);
    hr = pAudioClient->GetService(__uuidof(IAudioCaptureClient),(void**)&pAudioCaptureClient);
    pAudioClient->Start();
    for(;;)
    {
        uchar* data = NULL;
        uint packetLength = 0,numFramesAvailable = 0;
        ulong flags;
        hr = pAudioCaptureClient->GetNextPacketSize(&packetLength);
        if(packetLength == 0)
        {
            Sleep(1);
            continue;
        }
        hr = pAudioCaptureClient->GetBuffer(
                              &data,
                              &numFramesAvailable,
                              &flags, NULL, NULL);

        if (flags & AUDCLNT_BUFFERFLAGS_SILENT)
        {
            data = NULL;
        }
        if(data != NULL)
        {
            //这里data就是捕获到的pcm数据,大小为numFramesAvailable*pwfx->nBlockAlign
            //注意pcm的格式,在我电脑上是signed float 32bit
        }

        pAudioCaptureClient->ReleaseBuffer(numFramesAvailable);
    }