directShow 摄像头截图,位图文件内容是黑屏？

int captureMap(IBasicVideo *pBasicVideo)
{

// get width and height
long height, width;
pBasicVideo->get_VideoHeight(&height);
pBasicVideo->get_VideoWidth(&width);
long bufSize;
long *imgData;
HRESULT hr;

hr = pBasicVideo->GetCurrentImage(&bufSize, NULL);
if (FAILED(hr)) {
printf("GetCurrentImage failed\n");
return 1;
}
if (bufSize < 1) {
printf("failed to get data size\n");
return 1;
}
imgData = (long *)malloc(bufSize);
// The data will be in DIB format
pBasicVideo->GetCurrentImage(&bufSize, imgData);


// save DIB file as Bitmap.
// This sample saves image as bitmap to help
// understanding the sample.
HANDLE fh;
BITMAPFILEHEADER bmphdr;
BITMAPINFOHEADER bmpinfo;
DWORD nWritten;
memset(&bmphdr, 0, sizeof(bmphdr));
memset(&bmpinfo, 0, sizeof(bmpinfo));
bmphdr.bfType = ('M' << 8) | 'B';
bmphdr.bfSize = sizeof(bmphdr) + sizeof(bmpinfo) + bufSize;
bmphdr.bfOffBits = sizeof(bmphdr) + sizeof(bmpinfo);
bmpinfo.biSize = sizeof(bmpinfo);
bmpinfo.biWidth = width;
bmpinfo.biHeight = height;
bmpinfo.biPlanes = 1;
bmpinfo.biBitCount =24;
fh = CreateFile(L"d:\\donaldo.bmp",
GENERIC_WRITE, 0, NULL,
CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
WriteFile(fh, &bmphdr, sizeof(bmphdr), &nWritten, NULL);
WriteFile(fh, &bmpinfo, sizeof(bmpinfo), &nWritten, NULL);
WriteFile(fh, imgData, bufSize, &nWritten, NULL);
CloseHandle(fh);

free(imgData);



CoUninitialize();
return 0;
}