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I want to list all connected webcams (USB-webcams and internal webcams), using C++, OpenCV 2.4.11, Windows 8.1 and Qt Creator 3.4.2. For me it is enough to get the number of accessible webcams in the following way:

VideoCapture videoCapture(0); // Will access my internal laptop webcam.
VideoCapture videoCapture(1); // Will access the first connected usb webcam.

Here is my code:

// Following procedure detects, how many webcams are accessible from 0 on upwards.
numberOfDevices = 0;
bool noError = true;

while (noError)
{
    try
    {
        // Check if camera is available.
        VideoCapture videoCapture(numberOfDevices); // Will crash if not available, hence try/catch.

        // ...
    }
    catch (...)
    {
        noError = false;
    }

    // If above call worked, we have found another camera.
    numberOfDevices++;
}

The code in the try-block works if I have activated my internal webcam. The call fails when I deactivate the internal camera in the hardware manager (and no other camera is attached to my laptop) with the following error message (debug mode):

Exception Triggered
---------------------------
The inferior stopped because it triggered an exception.<p>Stopped in thread 0 by: 
Exception at 0x7ff8533d9090, code: 0xc0000005: read access violation at: 0x0, flags=0x0 (first chance).

and the following 2 build problems: 

Exception at 0x7ff871af8b9c, code: 0xa1a01db1: , flags=0x0 (first chance)

Exception at 0x7ff8533d9090, code: 0xc0000005: read access violation at: 0x0, flags=0x0 (first chance)

How can I fetch the occuring error? As you see, try/catch does not work.

Or is there a method where I can access all available webcams in OpenCV without such a dirty loop?

m0nhawk
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Loomis
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    I didn't observe crashes on Windows, when doing something very similar... – Micka Dec 10 '15 at 09:24
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    ok, this seems to depend on the installed device drivers. I had no problems testing inexistent devices by just trying to open them until I installed a GigE camera... – Micka Dec 10 '15 at 09:41
  • There is a similar thread [link](http://stackoverflow.com/questions/7322939/how-to-count-cameras-in-opencv-2-3). The commenters had different results. :/ – Loomis Dec 10 '15 at 09:41
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    I would encourage you to use VideoInput library (used by openCV internally anyways): https://github.com/ofTheo/videoInput – Micka Dec 10 '15 at 09:52

2 Answers2

5

There is still no any functionality related to camera count in OpenCV at the current moment (3.0.0 version) - see corresponding ticket.

Proper camera handling seems like OpenCV internal problem (for example, described here or here). Usually it appears in capture code after physically disabling camera while it is still opened in OpenCV (when we try to read destroyed file descriptor).

Generally you can even implement your own handler for access violations (please look into this thread), but it's really dirty trick.

Community
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avtomaton
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  • Thank you for your effort. I search for something else so that I can avoid above dirty trick. I will update this topic if I find a sufficient solution. – Loomis Dec 17 '15 at 11:23
3

I created this C++ class that allows enumerating devices (including the ID) to be used inside OpenCV. It is hosted on GitHub.

https://github.com/studiosi/OpenCVDeviceEnumerator

The idea is to use DirectShow to get all the devices that have the category with GUID CLSID_VideoInputDeviceCategory, and then, through an enumerator, you get in which order they appear on the system, which is the ID you need to open them on OpenCV by creating a VideoCapture object (by using the constructor that receives the ID, which would be the index of the device on the enumeration). Obviously, this approach only works on Windows.

dagilpe
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    Please consider to explain the solution the original question, instead of linking to other classes and resources. – Tim Visée Jan 16 '18 at 09:30
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    Added explanation. Still recommend to see the code. – dagilpe Jan 16 '18 at 09:44
  • This used to work in v3, but v4, seems like the order doesn't match up. Any one got any idea how to map the index to the camera name? – rukiman Jul 18 '19 at 03:48
  • I don't see a reason that the OpenCV version interferes with device enumeration, what do you mean? – dagilpe Jul 19 '19 at 06:39