Question

I’m going to run this really simple cod that will be compiled in visual studio and opencv libraries are used in.

 #include <opencv2/opencv.hpp>

int main()
{
    CvCapture *capture=cvCaptureFromFile("sample_1.avi");
    IplImage *FirstFrame=cvQueryFrame(capture);
    cvShowImage("first",FirstFrame);
    cvWaitKey();
}

The compile process is OK But when debugger reaches

IplImage *FirstFrame=cvQueryFrame(capture);

the following exception is ocurred :

Unhandled exception at 0x715f6a7e in VideoTest.exe: 0xC0000005: Access violation reading location 0x01bc4000.

How can I fix this problem ?
Thanks!

Answer 1

cvQueryFrame() crashes because cvCaptureFromFile() is probably failing. That happens when it can’t open/find the file or when OpenCV doesn’t support the container/codec of the video.

Whenever a function returns something is good practice to test the validity of what was returned, in this case since it’s a pointer you should do:

CvCapture *capture=cvCaptureFromFile("sample_1.avi");
if (!capture)  // same as: if (capture == NULL)
{
  // print error message and abort execution
}