init a video file and starting a timer:

private void InitVideoFile(string videoFileName)
{
    _videoCapture = new VideoCapture(videoFileName);
    _totalFrames = _videoCapture.FrameCount;

    // Configure the trackBarFrames
    trackBarFrames.Minimum = 0;
    trackBarFrames.Maximum = _totalFrames - 1;
    trackBarFrames.TickFrequency = 1;
    trackBarFrames.Value = 0;

    // Display the first frame for drawing the ROI
    _firstFrame = new Mat();
    if (_videoCapture.Read(_firstFrame))
    {
        Bitmap bitmap = BitmapConverter.ToBitmap(_firstFrame);
        UpdateControl(bitmap.Width, bitmap.Height);
        pictureBoxFrames.Image = bitmap;
        labelFrames.Text = $"Displaying frame 1/{_totalFrames}"; // Show 1 as the first frame
    }

    _timer = new System.Windows.Forms.Timer();
    _timer.Interval = 30; // Adjust as needed
    _timer.Tick += ProcessFrame;
}

then on a stop button click event i stop the timer:

private void buttonStop_Click(object sender, EventArgs e)
{
    _timer.Stop();
    trackBarFrames.Value = 0;
    buttonStart.Enabled = true;
    buttonStop.Enabled = false;
    btnLoadVideo.Enabled = true;
    trackBarFrames.Enabled = true;
    progressBarAnalysis.Value = 0;
    labelStatus.Text = "Ready";
    
    if (_firstFrame != null)
    {
        pictureBoxFrames.Image = BitmapConverter.ToBitmap(_firstFrame);
        labelFrames.Text = $"Displaying frame 1/{_totalFrames}"; // Show 1 as the first frame
    }
}

then in the Process event sometimes it stops but sometimes after stopping the timer the code in the event is keep running like finish if it was in the middle of a task and then i see the progressBarAnalysis.Value raising a bit again after it was reset to 0 and then it stops and the progressBarAnalysis.Value stay on the last value it was.

how can i stop the process in the async ProcessFrame event? stop it completely when clicking the stop button.

private async void ProcessFrame(object sender, EventArgs e)
{
    using (Mat frame = new Mat())
    {
        if (_videoCapture.Read(frame))
        {
            // Update the ROI if tracking is enabled
            if (_tracking && _firstFrame != null)
            {
                _roiPictureboxFrames = UpdateROI(_firstFrame, frame, _roiPictureboxFrames);
            }

            // Ensure ROI is within frame bounds
            _roiPictureboxFrames = EnsureROIWithinBounds(frame, _roiPictureboxFrames);

            // Display each frame in pictureBoxFrame
            pictureBoxFrames.Image = BitmapConverter.ToBitmap(frame);

            // Process and analyze the frame
            (Mat analyzedFrame, bool segmentDetected, bool blinkDetected) = await Task.Run(() => AnalyzeFrame(frame, _currentFrame));
            if (analyzedFrame != null)
            {
                pictureBoxPoints.Image = BitmapConverter.ToBitmap(analyzedFrame);
                labelStatus.Text = $"Segment detected in frame {_currentFrame}.";
            }
            else
            {
                pictureBoxPoints.Image = null; // Clear the PictureBox if no segments are detected
                labelStatus.Text = $"Processing frame {_currentFrame}/{_totalFrames}.";
            }

            // Update progress
            trackBarFrames.Value = _currentFrame;
            _videoCapture.Set(VideoCaptureProperties.PosFrames, _currentFrame);
            pictureBoxFrames.Image = BitmapConverter.ToBitmap(frame);
            labelFrames.Text = $"Displaying frame {_currentFrame + 1}/{_totalFrames}"; // Add 1 to display the frame number starting from 1

            progressBarAnalysis.Value = (int)((double)_currentFrame / _totalFrames * 100);
            _currentFrame++;
            // Update status label
            labelStatus.Text = segmentDetected ? $"Segment detected in frame {_currentFrame}." : $"Processing frame {_currentFrame}/{_totalFrames}";

            if (_currentFrame >= _totalFrames)
            {
                progressBarAnalysis.Value = 100;
                _timer.Stop();
                labelStatus.Text = "Analysis complete.";
            }

            // Store the current frame as the previous frame for the next iteration
            _firstFrame = frame.Clone();
        }
        else
        {
            _timer.Stop();
            labelStatus.Text = "Error reading video file.";
        }
    }
}

i tried to add at the top of the ProcessFrame event code this two lines:

if (!_timer.Enabled)
    return;

but it didn’t help much.