I've been using cvcam for some time but in my case processor load goes
to 100% after a few minutes. This allways happens if the callback
function is too time consuming (lets say above 30% processor load).
Strange. So I switched to highgui and was surprised that there is no
way to adjust the capturing dimensions. Argh!

I just added a way to set the capture width and hight within highgui:

To set format directly, put width and hight in one integer and use
CV_CAP_PROP_FRAME_WIDTH_HEIGHT:

cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_WIDTH_HEIGHT, 640480 )
or
cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_WIDTH_HEIGHT, 320280 )
...

Or to use the built in dialogs:
cvSetCaptureProperty(capture, CV_CAP_PROP_DIALOG_COMPRESSION, 0 );
cvSetCaptureProperty(capture, CV_CAP_PROP_DIALOG_SOURCE, 0 );
cvSetCaptureProperty(capture, CV_CAP_PROP_DIALOG_DISPLAY, 0 );
cvSetCaptureProperty(capture, CV_CAP_PROP_DIALOG_FORMAT, 0 );

---------------------------
What you have to do:

Add to highgui.h:

#define CV_CAP_PROP_DIALOG_DISPLAY 8
#define CV_CAP_PROP_DIALOG_FORMAT 9
#define CV_CAP_PROP_DIALOG_SOURCE 10
#define CV_CAP_PROP_DIALOG_COMPRESSION 11
#define CV_CAP_PROP_FRAME_WIDTH_HEIGHT 12

Add the function icvSetPropertyCAM_VFW to cvcap.cpp:

static int icvSetPropertyCAM_VFW( CvCaptureCAM_VFW* capture, int
property_id, double value )
{
int result = -1;
CAPSTATUS capstat;
CAPTUREPARMS capparam;
BITMAPINFO btmp;

switch( property_id ) {
case CV_CAP_PROP_DIALOG_DISPLAY:
result = capDlgVideoDisplay(capture->capWnd);
//SendMessage(capture->capWnd,WM_CAP_DLG_VIDEODISPLAY,0,0);
break;
case CV_CAP_PROP_DIALOG_FORMAT:
result = capDlgVideoFormat(capture->capWnd);
//SendMessage(capture->capWnd,WM_CAP_DLG_VIDEOFORMAT,0,0);
break;
case CV_CAP_PROP_DIALOG_SOURCE:
result = capDlgVideoSource(capture->capWnd);
//SendMessage(capture->capWnd,WM_CAP_DLG_VIDEOSOURCE,0,0);
break;
case CV_CAP_PROP_DIALOG_COMPRESSION:
result = capDlgVideoCompression(capture->capWnd);
break;
case CV_CAP_PROP_FRAME_WIDTH_HEIGHT:
capGetVideoFormat(capture->capWnd, &btmp, sizeof(BITMAPINFO));
btmp.bmiHeader.biWidth = floor(value/1000);
btmp.bmiHeader.biHeight = value-floor(value/1000)*1000;
btmp.bmiHeader.biSizeImage = btmp.bmiHeader.biHeight *
btmp.bmiHeader.biWidth * btmp.bmiHeader.biPlanes *
btmp.bmiHeader.biBitCount / 8;
capSetVideoFormat(capture->capWnd, &btmp, sizeof(BITMAPINFO));
break;
default:
break;
}

return result;
}


and edit captureCAM_VFW_vtable as following:


static CvCaptureVTable captureCAM_VFW_vtable =
{
6,
(CvCaptureCloseFunc)icvCloseCAM_VFW,
(CvCaptureGrabFrameFunc)icvGrabFrameCAM_VFW,
(CvCaptureRetrieveFrameFunc)icvRetrieveFrameCAM_VFW,
(CvCaptureGetPropertyFunc)icvGetPropertyCAM_VFW,
(CvCaptureSetPropertyFunc)icvSetPropertyCAM_VFW, // was NULL
(CvCaptureGetDescriptionFunc)0
};
-----------------------------------

Now rebuilt highgui.dll.