windwos系統抓取聲卡音頻

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

因爲一個我的需求須要抓取聲卡音頻數據，可是找了一圈好像都是麥克風錄音的，而後發現Potplayer裏面的聲音抓取用wasapi，因而就找了了微軟這個msdn文檔，根據例子看起來很簡單。直接上我修改後的代碼。

依賴頭文件及庫：

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

-lole32 -lmmdevapi

請先初始化com庫，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)
        {
            //這裏data就是捕獲到的pcm數據,大小爲numFramesAvailable*pwfx->nBlockAlign
            //注意pcm的格式,在我電腦上是signed float 32bit
        }

        pAudioCaptureClient->ReleaseBuffer(numFramesAvailable);
    }