Writing on a bitmap not working for writing a frame with a forge

I need to output the video from a webcam to file with Aforge.

LocalWebCamsCollection = new FilterInfoCollection(FilterCategory.VideoInputDevice);
LocalWebCam = new VideoCaptureDevice(LocalWebCamsCollection[0].MonikerString);
LocalWebCam.NewFrame += LocalWebCam_NewFrame;
LocalWebCam.Start();

So when I get the frame I write it with:

private void LocalWebCam_NewFrame(object sender, AForge.Video.NewFrameEventArgs eventArgs)
{
    try
    {
        System.Drawing.Image img = (System.Drawing.Bitmap)eventArgs.Frame.Clone();
        MemoryStream ms = new MemoryStream();
        img.Save(ms, ImageFormat.Bmp);
        ms.Seek(0, SeekOrigin.Begin);
        bi = new BitmapImage();
        bi.BeginInit();
        bi.StreamSource = ms;
        bi.EndInit();
        bi.Freeze();

        Application.Current.Dispatcher.Invoke(() =>
        {
            var bmp2 = Helper.BitmapUtilities.BitmapImage2Bitmap(bi);
            FileWriter.WriteVideoFrame(bmp2);
        });     
    }
    catch (Exception ex)
    {
        
    }
}

That works but then if I try to write the timestamp I get the error: "parameter not valid" This is how I change it

System.Drawing.Bitmap bmpOut = null;
Application.Current.Dispatcher.Invoke(() =>
{
    var visual = new DrawingVisual();
    using (DrawingContext drawingContext = visual.RenderOpen())
    {
        drawingContext.DrawImage(bi, new Rect(0, 0, bi.Width, bi.Height));
        drawingContext.DrawText(new FormattedText(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss.fff"), CultureInfo.InvariantCulture, FlowDirection.LeftToRight, new Typeface("Segoe UI"), 32, Brushes.Red), new Point(0, 0));
    }
    var image = new DrawingImage(visual.Drawing);
    #endregion


    img_Webcam.Source = image;

    using (MemoryStream ms = new MemoryStream())
    {
        PngBitmapEncoder encoder = new PngBitmapEncoder();
        encoder.Frames.Add(BitmapFrame.Create(ToBitmapSource(image)));
        encoder.Save(ms);

        using (System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(ms))
        {
            bmpOut = new System.Drawing.Bitmap(bmp);
        }
    }


    FileWriter.WriteVideoFrame(bmpOut);<---here the error
});

Perhaps I have not followed the best strategy so I am open to any other solution: what I need is just to write a timestamp on the bitmap (or bitmapimage) to be written on the file

Thanks for any help

Patrick

--- ADD ---

public static BitmapSource ToBitmapSource(DrawingImage source)
{
    DrawingVisual drawingVisual = new DrawingVisual();
    DrawingContext drawingContext = drawingVisual.RenderOpen();
    drawingContext.DrawImage(source, new Rect(new Point(0, 0), new Size(source.Width, source.Height)));
    drawingContext.Close();

    RenderTargetBitmap bmp = new RenderTargetBitmap((int)source.Width, (int)source.Height, 96, 96, PixelFormats.Pbgra32);
    bmp.Render(drawingVisual);
    return bmp;
}