IPCamAppBar/CameraView.cs

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;
using DateTime = System.DateTime;

namespace IPCamAppBar
{
    public partial class CameraView : UserControl
    {
        private DateTime lastFrameTime;
        private Timer noDataTimer;


        public CameraView(string url)
        {
            InitializeComponent();

            var cameraStream = new CameraMJPEGStream();
            cameraStream.Frame += CameraStreamOnFrame;
            cameraStream.Start(url);

            noDataTimer = new Timer
            {
                Interval = 1000
            };
            noDataTimer.Tick += CheckNoData;

            Disposed += (sender, args) =>
            {
                noDataTimer?.Dispose();
                cameraStream?.Dispose();
            };
        }


        private void CameraStreamOnFrame(object sender, FrameEventArgs args)
        {
            // The event comes from a background thread, so if needed invoke it on the main thread
            if (InvokeRequired)
            {
                Invoke(new Action(() => { CameraStreamOnFrame(sender, args); }));
                return;
            }

            ConnectingLabel.Visible = false;
            StreamView.Visible = true;
            NoDataLabel.Visible = false;

            lastFrameTime = DateTime.Now;
            noDataTimer.Start();

            var viewImage = new Bitmap(Width, Height);
            using (var graphics = Graphics.FromImage(viewImage))
            {
                graphics.SmoothingMode = SmoothingMode.AntiAlias;
                graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
                graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;

                graphics.DrawImage(args.Image, 0, 0, viewImage.Width, viewImage.Height);

                using (var path = new GraphicsPath())
                {
                    path.AddString(
                        lastFrameTime.ToString("G"), 
                        FontFamily.GenericSansSerif, 
                        (int)FontStyle.Regular,
                        graphics.DpiY * 14 / 72,
                        Rectangle.Inflate(new Rectangle(0, 0, viewImage.Width, viewImage.Height), -4, -4),
                        new StringFormat
                        {
                            Alignment = StringAlignment.Far,
                            LineAlignment = StringAlignment.Far
                        });

                    graphics.DrawPath(new Pen(Color.Black, 3), path);
                    graphics.FillPath(Brushes.White, path);
                }

                graphics.Flush();
            }

            var oldImage = StreamView.Image;
            StreamView.Image = viewImage;
            oldImage?.Dispose();
        }


        private void CheckNoData(object sender, EventArgs e)
        {
            var timeSinceLastFrame = DateTime.Now - lastFrameTime;
            if (timeSinceLastFrame.TotalSeconds < 10)
                return;

            NoDataLabel.Text = $@"No data for {timeSinceLastFrame.TotalSeconds} seconds";
            NoDataLabel.Visible = true;
        }
    }
}