Video not playing continuously - qt

Question

I am playing video in Qt using opencv. I am having 6 tiled view cameras from which I am playing video. The problem is if one of the videos is not playing i.e finishes then the GUI freezes and exits. The error I get is you must reimplement QApplication::notify() and catch the exceptions there. How to do this?
The code I am using is as follows.
Somewhere in a function
void MainWindow::ActivateWindow()
{
//Some part of code to set Index for stacked widget
if(stackWidget->currentIndex()==9)
{
const int imagePeriod == 1000/25;
imageTimer->setInterval(imagePeriod);
connect(imageTimer,SIGNAL(timeout()),this,SLOT(demoSlot());
imageTimer->start();
}
}
In slot demoSlot
void MainWindow::demoSlot()
{
captureCamera1 cvCaptureFromFile("/root/mp.mp4");
captureCamera2 cvCaptureFromFile("/root/mp.mp4");
captureCamera3 cvCaptureFromFile("/root/mp.mp4");
while(imageTimer->isActive())
{
frameCamera1 = cvQueryFrame(captureCamera1);
frameCamera2 = cvQueryFrame(captureCamera2);
frameCamera3 = cvQueryFrame(captureCamera2);
sourceImageCam1 = frameCamera1;
sourceImageCam2 = frameCamera2;
sourceImageCam3 = frameCamera3;
cv::resize(sourceImageCam1,sourceImageCam1,cv::size(400,100),0,0);
cv::resize(sourceImageCam1,sourceImageCam1,cv::size(400,100),0,0);
cv::resize(sourceImageCam1,sourceImageCam1,cv::size(400,100),0,0);
cv::cvtColor(sourceImageCam1,sourceImageCam2,CV_BGR2RGB);
cv::cvtColor(sourceImageCam2,sourceImageCam2,CV_BGR2RGB);
cv::cvtColor(sourceImageCam2,sourceImageCam2,CV_BGR2RGB);
QImage tempImage1 = QImage((const unsigned char* sourceImageCam1.data,sourceImageCam1.cols,sourceImageCam2.rows,QImage::Format_RG888);
QImage tempImage2 = QImage((const unsigned char* sourceImageCam2.data,sourceImageCam2.cols,sourceImageCam2.rows,QImage::Format_RG888);
QImage tempImage3 = QImage((const unsigned char* sourceImageCam3.data,sourceImageCam3.cols,sourceImageCam3.rows,QImage::Format_RG888);
labelCameraCapture1->setPixmap(QPixmap::fromImage(tempImage1)); //label to display video
labelCameraCapture2->setPixmap(QPixmap::fromImage(tempImage2));
labelCameraCapture3->setPixmap(QPixmap::fromImage(tempImage3));
lblCameraCapture1->resize(lblCameraCapture1->Pixmap->size());
lblCameraCapture1->resize(lblCameraCapture1->Pixmap->size());
lblCameraCapture1->resize(lblCameraCapture1->Pixmap->size());
cvWaitkey(20);
qApp->processEvents();
}
if(imageTimer->isActive())
{
imageTimer->stop();
}
else
{
imageTimer->start();
}
}
In header file
cvCapture *captureCamera1;
cvCapture *captureCamera1;
cvCapture *captureCamera1;
IplImage frameCamera1;
IplImage frameCamera2;
IplImage frameCamera3;
cv::Mat sourceImageCam1;
cv::Mat sourceImageCam2;
cv::Mat sourceImageCam3;

Answer 1

This will do the trick changing that to 3 movies is simple.
class MainWindow : public QMainWindow {
Q_OBJECT
explicit QMainWindow(QWidget *parent) ....
// prepare timer and so on
public slots:
void startVideo() {
vid1.close();
vid1.open("/root/mp.mp4");
imageTimer->start();
}
void demoSlot() {
cv::Mat frame;
vid1 >> frame;
cv::cvtColor(frame,frame,CV_BGR2RGB);
QImage img((uchar*) frame.data, frame.cols, frame.rows, frame.step, QImage::Format_RGB888);
label1->setPixmap(QPixmap::fromImage(img));
}
private:
...
QTimer *imageTimer;
cv::VideoCapture vid1;
};

Answer 2

Check if frame captured from camera is NULL. Then simply skip processing steps for this camera.
And it'll be better to not mix C++ and C interfaces (I mean cv::Mat and IplImage).