c++ - Detecting an unplugged capture device (OpenCV)

Question

I'm attempting to detect if my capture camera gets unplugged. My assumption was that a call to cvQueryFrame would return NULL, however it continues to return the last valid frame.

Does anyone know of how to detect camera plug/unplug events with OpenCV? This seems so rudimentary...what am I missing?

Answer 1

There is no API function to do that, unfortunately.

However, my suggestion is that you create another thread that simply calls cvCaptureFromCAM() and check it's result (inside a loop). If the camera get's disconnected then it should return NULL.

I'll paste some code just to illustrate my idea:

// This code should be executed on another thread!
while (1)
{
  CvCapture* capture = NULL;
  capture = cvCaptureFromCAM(-1); // or whatever parameter you are already using
  if (!capture)
  {
    std::cout << "!!! Camera got disconnected !!!!" << std::endl;
    break;
  }

  // I'm not sure if releasing it will have any affect on the other thread
  cvReleaseCapture(&capture); 
}