QT OpenCV Play Pause and Stop Video

[jsulm]

@Stevendragoes As I said already: in the slot connected to the timer you get next frame and show it. You need to implement this to make it work.

[Stevendragoes]

Yeap. I think I figured it out.
I shifted the initialisation of the timer in the MainWindow.

MainWindow::MainWindow(QWidget *parent): QMainWindow(parent), ui(new Ui::MainWindow)
{
    timer = new QTimer(this);
    connect(timer,SIGNAL(timeout()),this,SLOT(getNextFrame()));
    ui->setupUi(this);
}

and I used the cShowVideo Class to start the timer when I load the video from the FileDialog

cShowVideo::cShowVideo(Ui::MainWindow& ui, std::string& path, QString& qpath, MainWindow &parent) : MainWindow()
{
    parent.timer->start(1000);
    ui.textEdit->append(qpath);
}

and it works, it is appending every second.

[Stevendragoes]

@jsulm
From what I saw in the QTimer Class, there is no such thing as pause the timer?

[jsulm]

@Stevendragoes This is not good design - child should not access parent members directly. And this timer does not belong to MainWindow but to cShowVideo. Move timer again to cShowVideo.
I just noticed that cShowVideo is a local variable in on_actionLoad_Video_triggered(). That means it is destroyed as soon as on_actionLoad_Video_triggered() finishes - that's why your timer is not working. Make sure cShowVideo instance lives as long as it is playing video.
Also another note regarding design: your cShowVideo should not know anything about the MainWindow UI. This issue is called tight coupling and makes the maintenance of your software harder. In cShowVideo you should only get next frame and send it to MainWindow via a slot, MainWindow knows better how to use its UI to show the frames.

[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.