c++ builder: convert video to png-snapshots with directshow - directshow

Question

Thanks to your help I was able to search for the right words to use directshow a bit better.
I found a tutorial how to use the SampleGrabber-object here:
http://msdn.microsoft.com/en-us/library/windows/desktop/dd407288%28v=vs.85%29.aspx
I could implement it and modified it a bit so it isn't just saving the first frame, but every Frame to a PNG. For that I use corona.
However, I just guessed something around and don't quite know which buffers are containing my data and in which form.
So, I have basically 3 questions:
Am I using SavePNG right? the resulting Images are upside-down!
Can I replace the BaseFilter for the video with one that is connected to a camera?
Contains pBuffer my Imagedata so I can get rgb-byte-informations by simply type pBuffer[123]?
I'm using embarcadero's C++-Builder (XE2 16).
Here is the code I found at the website, a bit modified (error-handling removed for better view. after each hr=... there is a Failed-check):
void __fastcall TForm1::btn_kameraClick(TObject *Sender)
{
HRESULT hr = S_OK;
IGraphBuilder *pGraph = NULL;
IMediaControl *pControl = NULL;
IMediaEventEx *pEvent = NULL;
IBaseFilter *pGrabberF = NULL;
ISampleGrabber *pGrabber = NULL;
IBaseFilter *pSourceF = NULL;
IEnumPins *pEnum = NULL;
IPin *pPin = NULL;
IBaseFilter *pNullF = NULL;
BYTE *pBuffer = NULL;
hr = CoCreateInstance(CLSID_FilterGraph, NULL,CLSCTX_INPROC_SERVER,IID_PPV_ARGS(&pGraph));
hr = pGraph->QueryInterface(IID_PPV_ARGS(&pControl));
hr = pGraph->QueryInterface(IID_PPV_ARGS(&pEvent));
hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER,IID_PPV_ARGS(&pGrabberF));
hr = pGraph->AddFilter(pGrabberF, L"Sample Grabber");
hr = pGrabberF->QueryInterface(IID_PPV_ARGS(&pGrabber));
AM_MEDIA_TYPE mt;
ZeroMemory(&mt, sizeof(mt));
mt.majortype = MEDIATYPE_Video;
mt.subtype = MEDIASUBTYPE_RGB24;
hr = pGrabber->SetMediaType(&mt);
hr = pGraph->AddSourceFilter(L"C:/Users/Julian/Desktop/homogenität/1,1x_2,7y.mpg", L"Source", &pSourceF);
hr = pSourceF->EnumPins(&pEnum);
while (S_OK == pEnum->Next(1, &pPin, NULL))
{
hr = ConnectFilters(pGraph, pPin, pGrabberF);
SafeRelease(&pPin);
if (SUCCEEDED(hr))break;
}
hr = CoCreateInstance(CLSID_NullRenderer, NULL, CLSCTX_INPROC_SERVER,IID_PPV_ARGS(&pNullF));
hr = pGraph->AddFilter(pNullF, L"Null Filter");
hr = ConnectFilters(pGraph, pGrabberF, pNullF);
hr = pGrabber->SetOneShot(TRUE);
hr = pGrabber->SetBufferSamples(TRUE);
long evCode=0;
long cbBuffer=0;
hr = pControl->Run();
hr = pEvent->WaitForCompletion(INFINITE, &evCode);
hr = pGrabber->GetCurrentBuffer(&cbBuffer, NULL);
pBuffer = (BYTE*)CoTaskMemAlloc(cbBuffer);
hr = pGrabber->GetConnectedMediaType(&mt);
CComQIPtr< IMediaSeeking, &IID_IMediaSeeking > pSeeking( pGraph );
// for(int i=0;i<10;i++){
bool hui=true;int i=0;
while(hui){
REFERENCE_TIME Start = i * UNITS;
hr = pSeeking->SetPositions( &Start, AM_SEEKING_AbsolutePositioning,NULL, AM_SEEKING_NoPositioning );
// Sleep(10);
hr = pEvent->WaitForCompletion(INFINITE,&evCode);
if(hr!=0)hui=false;
hr = pGrabber->GetCurrentBuffer(&cbBuffer, (long*)pBuffer);
if ((mt.formattype == FORMAT_VideoInfo) &&(mt.cbFormat >= sizeof(VIDEOINFOHEADER)) &&(mt.pbFormat != NULL))
{
VIDEOINFOHEADER *pVih = (VIDEOINFOHEADER*)mt.pbFormat;
// hr = WriteBitmap(("hui"+(String)i+".bmp").c_str(), &pVih->bmiHeader, mt.cbFormat - SIZE_PREHEADER, pBuffer, cbBuffer);
hr = SavePNG(i,pBuffer, pVih->bmiHeader.biWidth, pVih->bmiHeader.biHeight);
}
else hr = VFW_E_INVALIDMEDIATYPE;
i++;
}
FreeMediaType(mt);
done:
CoTaskMemFree(pBuffer);
SafeRelease(&pPin);
SafeRelease(&pEnum);
SafeRelease(&pNullF);
SafeRelease(&pSourceF);
SafeRelease(&pGrabber);
SafeRelease(&pGrabberF);
SafeRelease(&pControl);
SafeRelease(&pEvent);
SafeRelease(&pGraph);
}
bool SavePNG(int i, Byte* m_pImageData,long m_Width,long m_Height)
{
// Make sure there is image data
if (!m_pImageData)
return false;
stringstream FilePath;
FilePath << "hui"<< i<<".png";
// Create a corona image
corona::Image* pImage = corona::CreateImage(m_Width, m_Height, corona::PF_R8G8B8, m_pImageData);
// Make sure the image was created
if (!pImage)
return false;
// Save the image to a PNG file
corona::SaveImage(FilePath.str().c_str(), corona::FF_PNG, pImage);
// Delete the corona image
delete pImage;
// Nothing went wrong
return true;
}
I hope I have done nothing horribly wrong... I really tried to research everything^^
Does somebody knows about my 3 questions above?
I you found something really wrong here, I would also appreciate for you to tell me, so I can fix and improve.
Regards,
Julian

Answer 1

Now when you have a video frame in 24-bit RGB format, all you need is to compress to PNG. You have choices here:
libpng
GDI+
WIC
Possibly, C++ bulder has native classes to cover PNG as well.
P.S. DirectShow API you are using is not DirectX, it is a part of Windows core SDK.