OpenCV - Error in Displaying Webcam Video

Question

I'm pretty new to OpenCV and I'm trying to get my bearings by looking at, and running, sample code.

One of the sample programs that I was looking at is a program for displaying webcam video. Here are the important lines (the program doesn't execute farther than this):

// Make frame.
CvCapture* capture = cvCaptureFromCAM(0);

if(!capture) {
    printf("Webcam not initialized....");
}
// Display video in frame.

Unfortunately, the if statement always executes. For some reason, capture is not initialized.

Even stranger, when I run the program, it even gives me a GUI to select the webcam that I want to use:

However, even after I select the webcam, capture is not initialized!

What does this mean? How do I fix this?

Thanks for any suggestions.

Answer 1

It is possible that OpenCV cannot access the webcam until after you select it. In that case, try looping until the webcam is available:

CvCapture *capture = NULL;
do {
    // you could also try passing in CV_CAP_ANY or -1 instead of 0
    capture = cvCaptureFromCAM(0);
} while (!capture);

If this still doesn't work, call cvErrorStr(cvGetErrStatus()) to get a string explaining the error.