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QT OpenCV Play Pause and Stop Video

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  • S Stevendragoes

    @jsulm and I am guessing getNewFrame is the function that I have to implement so that I get the new frame?

    jsulmJ Offline
    jsulmJ Offline
    jsulm
    Lifetime Qt Champion
    wrote on last edited by
    #7

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

    and I am guessing getNewFrame is the function that I have to implement so that I get the new frame?

    Yes

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

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    • S Offline
      S Offline
      Stevendragoes
      wrote on last edited by
      #8

      Hello @jsulm
      When I implement getNewFrame, I can't even get the path to print on the text edit. Any Reason why? I know it is triggering every 1 second, and I am trying to append every one second as well?

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      • S Offline
        S Offline
        Stevendragoes
        wrote on last edited by
        #9

        @jsulm
        db330cbf-9dbb-474f-982d-59344137290a-image.png

        qpath is loaded into by FileDialog

        jsulmJ 1 Reply Last reply
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        • S Stevendragoes

          @jsulm
          db330cbf-9dbb-474f-982d-59344137290a-image.png

          qpath is loaded into by FileDialog

          jsulmJ Offline
          jsulmJ Offline
          jsulm
          Lifetime Qt Champion
          wrote on last edited by
          #10

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

          qpath

          Do you assign the path selected in the file dialog to it? Please show your code, else I can only guess.

          "I know it is triggering every 1 second, and I am trying to append every one second as well?" - if you did not change the timeout period then yes it is triggered once each second.

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

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          • S Offline
            S Offline
            Stevendragoes
            wrote on last edited by
            #11

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

            Do you assign the path selected in the file dialog to it?

            Hello @jsulm
            6c06a870-02f9-4a11-b478-622f8ca6e627-image.png

            I assighed the qpath after I pressed Load PushButton in the UI

            jsulmJ 1 Reply Last reply
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            • S Stevendragoes

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

              Do you assign the path selected in the file dialog to it?

              Hello @jsulm
              6c06a870-02f9-4a11-b478-622f8ca6e627-image.png

              I assighed the qpath after I pressed Load PushButton in the UI

              jsulmJ Offline
              jsulmJ Offline
              jsulm
              Lifetime Qt Champion
              wrote on last edited by
              #12

              @Stevendragoes Are you sure your timer is actually running? And are you sure you connected the slot for the timer properly?

              Please post your code as text, not as screen shot, then it is easier to others to change it if there is something wrong.

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

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              • S Offline
                S Offline
                Stevendragoes
                wrote on last edited by
                #13
                cShowVideo::cShowVideo(Ui::MainWindow& ui, std::string& path, QString& qpath, MainWindow &parent) : MainWindow()
                {
                    timer = new QTimer(this);
                    connect(timer,SIGNAL(timeout()),this,SLOT(getNextFrame()));
                    //ui.textEdit->setText(qpath);
                    timer->start(1000);
                    DisplayVideo(ui,path,parent);
                

                this is my timer code. It starts properly.
                when i used qDebug, it shows the text in 1 second which means that the Timer function is working?
                However, when I change it to the text edit, as shown below, the text is not appearing as intended
                The code printing is as follows:

                void MainWindow::getNextFrame()
                {
                    qDebug("Get Next Frame is working");
                    ui->textEdit->append("GetNextFrame");
                }
                
                

                To show its working, the "Get Next Frame is working" is printing every second
                cc2daa6d-75d7-42d1-9596-5e7fe43a2ce7-image.png

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                • S Offline
                  S Offline
                  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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                    • S Offline
                      S Offline
                      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
                        jsulmJ Offline
                        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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                        • S Offline
                          S Offline
                          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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                            • S Offline
                              S Offline
                              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
                                jsulmJ Offline
                                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.

                                  jsulmJ 1 Reply Last reply
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                                  • S Offline
                                    S Offline
                                    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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                                      • S Offline
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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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                                        • S Offline
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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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