QT OpenCV Play Pause and Stop Video

Stevendragoes

Hello @jsulm
I have FINALLY made it work already. Thank you for your guidance, it was good to drop the cShowVideo Completely. This is the following codes. However, there are a few issues when I try to close the program

Loading the Video and Starting the Timer so that it gets the next frame.

void MainWindow::on_actionLoad_Video_triggered()
{
    QMessageBox::StandardButton loadBtn = QMessageBox::question( this, "MainWindow",tr("Load Video? \n"), QMessageBox::No | QMessageBox::Yes,QMessageBox::Yes);
    if (loadBtn == QMessageBox::Yes)
    {
        qpath = QFileDialog::getOpenFileName(this, "Load Video File"); //Input code to skip the event when cancel is pressed
        if (qpath.isNull())
        {
            ui->textEdit->append("Cannot get file, user cancelled while choosing file");
        }
        else
        {
            path = qpath.toLocal8Bit().constData();\
            ui->textEdit->append("cShowVideo is called");
            //cShowVideo(*ui, path, qpath, *this);                        //For OPENCV analysis and filtering
            cap.open(path);
            vwidth = ui->display_image->height();
            vheight = ui->display_image->width();
            timer->start(30);                                           //this can set the frame rate
            cap >> frame;
        }
    }
    else
    {
        ui->textEdit->setText("User Cancelled");
    }
}

This is the getNextFrame() function to get the next frame after every timeout() event from the timer

void MainWindow::getNextFrame()
{
    cap.read(frame);
    if(frame.empty()==true) return;
    cv::cvtColor(frame,  frame, cv::COLOR_BGR2RGB);
    cv::resize(frame, frame, cv::Size(vheight,vwidth), 0, 0, cv::INTER_AREA);
    QImage imdisplay((uchar*)frame.data, frame.cols, frame.rows, frame.step, QImage::Format_RGB888);
    ui->display_image->setPixmap(QPixmap::fromImage(imdisplay));
}

I have also implemented 3 pushbuttons to play, pause and stop

void MainWindow::on_Play_clicked()
{
    if(timer->isActive() == true){
        return;
    }
    else {
        timer->start(30);
    }
}

void MainWindow::on_Pause_clicked()
{
    if(timer->isActive() == true)
    {
        timer->stop();
    }
    else{
        return;
    }
}

void MainWindow::on_Stop_clicked()
{
    if(timer->isActive()==true)
    {
        timer->stop();
        cap.release();
    }
}

However, when I try to close it, the program finishes unexpectedly and crashed unexpectedly.
This is the screenshot when i try to use the debugger to trace where it went wrong.

Stevendragoes

maybe @J.Hilk could help me?

jsulm

@Stevendragoes Can you show the destructor of your MainWindow?
Also, when closing your app you should first stop the playback if active.

Stevendragoes

@jsulm this is my destructor

MainWindow::~MainWindow()
{
    cap.release();
    delete ui;
}

Stevendragoes

@jsulm I have also attached the close event captured for reference

void MainWindow::closeEvent(QCloseEvent *event)    //To confirm that the user really wants to quit the application
{
    QMessageBox::StandardButton exitBtn = QMessageBox::question( this, "MainWindow",tr("Are you sure you want to exit?\n"), QMessageBox::Cancel | QMessageBox::No | QMessageBox::Yes,QMessageBox::Yes);
    if (exitBtn == QMessageBox::Yes) {
        event->accept();
    } else {
        event->ignore();
    }
}

jsulm

@Stevendragoes I would stop the timer in closeEvent if it is running and user wants to quit.

Stevendragoes

Hi @jsulm I have implemented timer->stop() but it still gives me the same error. I am not too sure why.

Stevendragoes

Hi @jsulm
I think i have solved the problem

w.setAttribute(Qt::WA_DeleteOnClose, true);

this was inside the main.cpp. I am not sure why this happens.

jsulm

@Stevendragoes said in QT OpenCV Play Pause and Stop Video:

w.setAttribute

What is w? Maybe it was double delete?

jsulm

@Stevendragoes said in QT OpenCV Play Pause and Stop Video:

w.set

Now I see the problem: w is allocated on the stack and there is no need to delete it explicitly (what Qt::WA_DeleteOnClose does), so it was double delete.

Stevendragoes

@jsulm I suspect is double delete. w is the MainWindow Setup in the main.cpp
The Code is as follows

#include "mainwindow.h"
#include <QApplication>                                         //Widgets Events Handling, Mouse Movements


int main(int argc, char *argv[])                                //All Executions are going to begin
{
    QApplication a(argc, argv);                                 //Create the QApplication Object to Handle Events etc.
    MainWindow w;
    w.showMaximized();
    w.show();
    return a.exec();
}

on other hand, do u mind if use my solution to mark it as solved?

Stevendragoes

@jsulm
Thank you so much for your assistance in these few days. Now I need to move on to interfacing with an inbuilt camera or USB connected camera to do my object tracking.

jsulm

@Stevendragoes There is no need for Qt::WA_DeleteOnClose, see my previous comment.