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QT OpenCV Play Pause and Stop Video

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  • S Offline
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    Stevendragoes
    wrote on last edited by
    #14

    @jsulm Sorry forgot to tag you

    jsulmJ 1 Reply Last reply
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    • S Stevendragoes

      @jsulm Sorry forgot to tag you

      jsulmJ Offline
      jsulmJ Offline
      jsulm
      Lifetime Qt Champion
      wrote on last edited by
      #15

      @Stevendragoes Do you still have the loop in DisplayVideo?

      https://forum.qt.io/topic/113070/qt-code-of-conduct

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        Stevendragoes
        wrote on last edited by
        #16

        @jsulm Yes I do have the loop, Should I take it out first?

        jsulmJ 1 Reply Last reply
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        • S Stevendragoes

          @jsulm Yes I do have the loop, Should I take it out first?

          jsulmJ Offline
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          jsulm
          Lifetime Qt Champion
          wrote on last edited by
          #17

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

          Should I take it out first?

          Of course. As I said before this loop is blocking the event loop, so UI does not work properly.

          https://forum.qt.io/topic/113070/qt-code-of-conduct

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            Stevendragoes
            wrote on last edited by
            #18

            @jsulm When I commented out the loop, the timer doesn't run anymore.

            jsulmJ 1 Reply Last reply
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            • S Stevendragoes

              @jsulm When I commented out the loop, the timer doesn't run anymore.

              jsulmJ Offline
              jsulmJ Offline
              jsulm
              Lifetime Qt Champion
              wrote on last edited by
              #19

              @Stevendragoes Please comment out DisplayVideo call in cShowVideo

              https://forum.qt.io/topic/113070/qt-code-of-conduct

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                Stevendragoes
                wrote on last edited by
                #20

                I have commented it out also.
                However, what I want is that when I load the video, the timer to start. So, I initialised the timer in the cShowvideo which is a class inherited from the MainWindow().
                Is that an incorrect way of doing so?

                jsulmJ 1 Reply Last reply
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                • S Stevendragoes

                  I have commented it out also.
                  However, what I want is that when I load the video, the timer to start. So, I initialised the timer in the cShowvideo which is a class inherited from the MainWindow().
                  Is that an incorrect way of doing so?

                  jsulmJ Offline
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                  jsulm
                  Lifetime Qt Champion
                  wrote on last edited by
                  #21

                  @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.

                  https://forum.qt.io/topic/113070/qt-code-of-conduct

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                    Stevendragoes
                    wrote on last edited by
                    #22

                    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.

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                      Stevendragoes
                      wrote on last edited by
                      #23

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

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                      • S 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.

                        jsulmJ Offline
                        jsulmJ Offline
                        jsulm
                        Lifetime Qt Champion
                        wrote on last edited by
                        #24

                        @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.

                        https://forum.qt.io/topic/113070/qt-code-of-conduct

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                          Stevendragoes
                          wrote on last edited by
                          #25

                          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.

                          ac96b437-ad70-4103-b8b4-efab7b6c279a-image.png

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                            Stevendragoes
                            wrote on last edited by
                            #26

                            maybe @J.Hilk could help me?

                            jsulmJ 1 Reply Last reply
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                            • S Stevendragoes

                              maybe @J.Hilk could help me?

                              jsulmJ Offline
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                              jsulm
                              Lifetime Qt Champion
                              wrote on last edited by
                              #27

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

                              https://forum.qt.io/topic/113070/qt-code-of-conduct

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                                Stevendragoes
                                wrote on last edited by
                                #28

                                @jsulm this is my destructor

                                MainWindow::~MainWindow()
                                {
                                    cap.release();
                                    delete ui;
                                }
                                
                                
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                                  Stevendragoes
                                  wrote on last edited by
                                  #29

                                  @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();
                                      }
                                  }
                                  
                                  jsulmJ 1 Reply Last reply
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                                  • S 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();
                                        }
                                    }
                                    
                                    jsulmJ Offline
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                                    jsulm
                                    Lifetime Qt Champion
                                    wrote on last edited by
                                    #30

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

                                    https://forum.qt.io/topic/113070/qt-code-of-conduct

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                                      Stevendragoes
                                      wrote on last edited by
                                      #31

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

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                                        Stevendragoes
                                        wrote on last edited by
                                        #32

                                        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.

                                        jsulmJ 2 Replies Last reply
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                                        • S 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.

                                          jsulmJ Offline
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                                          jsulm
                                          Lifetime Qt Champion
                                          wrote on last edited by
                                          #33

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

                                          w.setAttribute

                                          What is w? Maybe it was double delete?

                                          https://forum.qt.io/topic/113070/qt-code-of-conduct

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