Getting a still picture with SampleGrabber

SampleGrabber

SampleGrabber is a transform filter. To use SampleGrabber, you must add SampleGrabber filter into the Graph. Since SampleGrabber grabs a frame directly, it has much versatility than IBasicVideo::GetCurrentImage.

To use SampleGrabber, your DirectX version must use at least DirectX8.

Sample code

The following sample code shows how to use SampleGrabber. This sample saves the grabbed video frame as a bitmap file. Please note that saving the video frame is in this sample just to make it easily understandable, and it is not a required function to use SampleGrabber.

#include <stdio.h>

#include <dshow.h>
#include <qedit.h> // for SampleGrabber

#define	FILENAME L"C:\\DXSDK\\Samples\\Media\\butterfly.mpg"

int
main()
{
 IGraphBuilder *pGraphBuilder;
 IMediaControl *pMediaControl;

 IBaseFilter *pSampleGrabberFilter;
 ISampleGrabber *pSampleGrabber;
 AM_MEDIA_TYPE am_media_type;

 // initialize COM
 CoInitialize(NULL);

 // create FilterGraph
 CoCreateInstance(CLSID_FilterGraph,
	NULL,
	CLSCTX_INPROC,
	IID_IGraphBuilder,
	(LPVOID *)&pGraphBuilder);

 // create SampleGrabber(Filter)
 CoCreateInstance(CLSID_SampleGrabber,
	 NULL,
	 CLSCTX_INPROC,
	 IID_IBaseFilter,
	 (LPVOID *)&pSampleGrabberFilter);

 // get ISampleGrabber interface from the Filter
 pSampleGrabberFilter->QueryInterface(IID_ISampleGrabber,
	 (LPVOID *)&pSampleGrabber);

 // determine the format for connecting SampleGrabber.
 // You can configure the SampleGrabber insertion place
 // by changing the values in this structure.
 // If you use the values in this sample,
 // you can get the video frame data right before
 // it is displayed.
 ZeroMemory(&am_media_type, sizeof(am_media_type));
 am_media_type.majortype = MEDIATYPE_Video;
 am_media_type.subtype = MEDIASUBTYPE_RGB24;
 am_media_type.formattype = FORMAT_VideoInfo;
 pSampleGrabber->SetMediaType(&am_media_type);

 // add SampleGrabber Filter to the Graph
 pGraphBuilder->AddFilter(pSampleGrabberFilter,
	 L"Sample Grabber");

 // get MediaControl
 pGraphBuilder->QueryInterface(IID_IMediaControl,
	(LPVOID *)&pMediaControl);

 // create Graph.
 // Graph that contains SampleGrabber
 // will be created automatically.
 pMediaControl->RenderFile(FILENAME);

 // Get connection information.
 // This must be done after the Graph is created
 // by RenderFile.
 pSampleGrabber->GetConnectedMediaType(&am_media_type);
 VIDEOINFOHEADER *pVideoInfoHeader =
     (VIDEOINFOHEADER *)am_media_type.pbFormat;

 // Print the width and height of the image.
 // This is just to make the sample understandable.
 // This is not a required feature.
 printf("size = %dx%d\n",
	 pVideoInfoHeader->bmiHeader.biWidth,
	 pVideoInfoHeader->bmiHeader.biHeight);

 // Print the data size.
 // This is just for understanding too.
 printf("sample size = %d\n",
	 am_media_type.lSampleSize);

 // Configure SampleGrabber to do grabbing.
 // Buffer data can not be obtained if you
 // do not use SetBufferSamples.
 // You can use SetBufferSamples after Run() too.
 pSampleGrabber->SetBufferSamples(TRUE);

 // Start playing
 pMediaControl->Run();

 // Block execution
 MessageBox(NULL,
	"Block Execution",
	"Block",
	MB_OK);

 // BITMAP will be saved after OK is pressed

 // prepare buffer
 long nBufferSize = am_media_type.lSampleSize;
 long *pBuffer = (long *)malloc(nBufferSize);

 // grab image data.
 pSampleGrabber->GetCurrentBuffer(&nBufferSize,
     pBuffer);

 //
 // Save image data as Bitmap.
 // This is just to make this sample easily understandable.
 //
 HANDLE fh;
 BITMAPFILEHEADER bmphdr;
 DWORD nWritten;

 memset(&bmphdr, 0, sizeof(bmphdr));

 bmphdr.bfType = ('M' << 8) | 'B';
 bmphdr.bfSize = sizeof(bmphdr) + sizeof(BITMAPINFOHEADER) + nBufferSize;
 bmphdr.bfOffBits = sizeof(bmphdr) + sizeof(BITMAPINFOHEADER);

 fh = CreateFile("result.bmp",
	 GENERIC_WRITE, 0, NULL,
	 CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
 WriteFile(fh, &bmphdr, sizeof(bmphdr), &nWritten, NULL);
 WriteFile(fh,
     &pVideoInfoHeader->bmiHeader,
     sizeof(BITMAPINFOHEADER), &nWritten, NULL);
 WriteFile(fh, pBuffer, nBufferSize, &nWritten, NULL);
 CloseHandle(fh);

 free(pBuffer);

 // Release
 pSampleGrabber->Release();
 pSampleGrabberFilter->Release();
 pMediaControl->Release();
 pGraphBuilder->Release();

 // finish COM
 CoUninitialize();

 return 0;
}

This sample saves the video frame as a bitmap file named "result.bmp". Please check the created bitmap file when you try this sample. The bitmap file format is explained here.