read successive frames OpenCV using cvQueryframe

Question

I have a basic question in regards to cvQueryFrame() in OpenCV.

I have the following code:

IplImage *frame1,*frame2;
frame1 = cvQueryFrame(capture         


        

Answer 1

Ok !

You have to make a copy of your frame. frame1 = cvQueryFrame(capture); is a pointer as you said.

The code i found is :

IplImage* img1(null), img2(null);
CvCapture* cap = cvCaptureFromAVI("mavideo.avi");
img2 = cvQueryFrame( cap );
img1 = cvCloneImage( img2 ); // on alloue une nouvelle image

while( cvGrabFrame( cap ) )
{
    cvCopy( img2, img1 ); // copie de l'image, pas du pointeur
    img2 = cvRetrieveFrame( cap );
} 

cvReleaseCapture( &cap );
cvReleaseImage( &img1 );

You can replace the while by a waitkey or anything but if you do that use

img2 = cvQueryFrame( cap ); 

instead of

img2 = cvRetrieveFrame( cap );

cause you'll not have the

cvGrabFrame( cap )

anymore

I don't know if i'm clear so... i stay here ^^

Enjoy ;)

Laurent