Opencv_ffmpeg module crash (IP camera)

Question

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I'm using IP webcam android app(It converts mobile camera into IP web camera).
I'm running below code in Visual Studio 2015 with OpenCV 3.1.

C++

VideoCapture cap; Mat img;
    cap.open("http://192.168.0.101:8080/video?x.mjpeg");
    while(waitKey(33)!=27)
    {
        try{
            cap>>img;  //code crashes here
            if(img.empty())
            {
             cout<<"camera Closed"<<endl;
             break;
            }
             imshow("Video",img);
          } catch(...{}    
    }

Getting below error.cIf the internet connection is slow or if the Wi-Fi is disconnected in my android device the program crashes

Error:

Exception thrown at 0x0BF2F6F0 (opencv_ffmpeg310.dll) in test.exe:<br />
 0xC0000005: Access violation reading location 0x00000020.<br />
 <br />
 If there is a handler for this exception, the program may be safely<br />
 continued.

even if the code is wrapped within try catch block, it crashes!

Should I use try {} catch (...) block in source file, if yes, then where should I use this?

What I have tried:

I referred this link link but did not find the right answer.

Posted 25-Nov-16 2:37am

Member 12761317

Updated 27-Nov-16 18:56pm

Richard MacCutchan

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Arthur V. Ratz 28-Nov-16 0:33am

I hope that using try {} catch(...) exception handling mechanism will not help you in this case. Read my solution below.

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Arthur V. Ratz · Answer 1 · 2016-11-27T18:56:00

Normally, in this code, at the beginning, you declare two variables:

C++

VideoCapture cap; Mat img;

You normally open the camera by invoking

C++

cap.open("http://192.168.0.101:8080/video?x.mjpeg");

method and then perform a loop to retrieve each frame from the camera device storing them into a frame matrix represented by

C++

Mat img

object. During the first iteration of the following loop you just normally retrieve the first frame from the camera stream by using

C++

cap

object handle and store it into the matrix

C++

img

. *BUT* for the next iterations you use the same object

C++

img

which is not empty containing the previous frame's matrix. That's actually why, in my opinion, your application crashes since you need to an empty matrix for each frame fetch during the loop execution. Try to declare the

C++

Mat img

object in the scope of the following loop the way I've shown below:

C++

VideoCapture cap;
    cap.open("http://192.168.0.101:8080/video?x.mjpeg");
    while(waitKey(33)!=27)
    {
        try{
            Mat img;
            cap>>img;  //code crashes here
            if(img.empty())
            {
             cout<<"camera Closed"<<endl;<!-- newline="" --="">             break;
            }
             imshow("Video",img);
          } catch(...{}    
    }</endl;<!-->