QT OpenCV Play Pause and Stop Video

Stevendragoes

Hi All, I want to add Play Pause and Stop ToolButtons to my current code shown below. Any idea how?

void MainWindow::DisplayVideo(Ui::MainWindow& ui, std::string& path, MainWindow &parent){

    cv::VideoCapture cap(path);
    int frameRate = (int) cap.get(cv::CAP_PROP_FPS);
    
    cv::Mat frame;
    ui.textEdit->append("Display Video Called");
    parent.on_actionPlay_triggered();
    while(!stop)
    {
        ui.textEdit->append("While loop called");
       cap >> frame;
       if(!cap.read(frame))
       {
           stop = true;
       }
       if(frame.channels() == 3)
       {
           cv::Mat dest;
           cv::cvtColor(frame,  dest, cv::COLOR_BGR2RGB);
           cv::resize(dest, dest, cv::Size(900,700), 0, 0, cv::INTER_AREA);
           QImage imdisplay((uchar*)dest.data, dest.cols, dest.rows, dest.step, QImage::Format_RGB888);
           ui.display_image->setPixmap(QPixmap::fromImage(imdisplay));
       }
       else
       {
           QImage imdisplay = QImage((const unsigned char*)(frame.data),
                                            frame.cols,frame.rows,QImage::Format_Indexed8);
           ui.display_image->setPixmap(QPixmap::fromImage(imdisplay));
       }
       QApplication::processEvents();
    }

}

possibly logic controls? to pause the video frames from displaying when the Pause ToolButton is clicked.

jsulm

@Stevendragoes This is not how event driven applications are implemented.
Do not implement endless loops!
If there is no callback in OpenCV which is called when a new frame is available (I'm not an OpenCV expert) I suggest to use a QTimer to call a slot regularly where you fetch the next frame. Then it is easy to implement stop/pause: call stop() on the timer and start when user wants to start play back again.

Stevendragoes

Hi @jsulm

I am not implementing endless loops. I have a button that makes "stop" to true when the stop button is pressed. Alright. Any examples on the QTimer so that I can try it out in my code?

jsulm

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

I am not implementing endless loops. I have a button that makes "stop" to true when the stop button is pressed

I know, but this is still not how you should implement event driven applications.

You can find examples here: https://doc.qt.io/qt-5/qtimer.html

QTimer *timer = new QTimer(this);
connect(timer, &QTimer::timeout, this, &getNewFrame);
timer->start(1000); // Change the interval to a value matching your framerate

Here getNewFrame is a lot where you read one frame.

Stevendragoes

Alright @jsulm, I will try it out and Will update accordingly. Thank you for your assistance

Stevendragoes

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

jsulm

@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

Stevendragoes

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?

Stevendragoes

@jsulm

qpath is loaded into by FileDialog

jsulm

@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.

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

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

jsulm

@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.

Stevendragoes

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

Stevendragoes

@jsulm Sorry forgot to tag you

jsulm

@Stevendragoes Do you still have the loop in DisplayVideo?

Stevendragoes

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

jsulm

@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.

Stevendragoes

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

jsulm

@Stevendragoes Please comment out DisplayVideo call in cShowVideo

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?