C# Atualizar valor de TextBlock num documento XAML com C#

[Joel Martins]

Olá, Estou a tentar mudar o valor de texto de um bloco de texto de um documento XAML mas sem sucesso.
Código XAML atual:

        <TextBlock
            HorizontalAlignment="Left"
            Margin="198,86,0,0"
            TextWrapping="Wrap"
            Text="{Binding SetRecordStatusTxt}"
            VerticalAlignment="Top" Foreground="Red"/>

Código C# atual:

/*
 * 
 * 
 * 
 * 
 * ESTE FOI O ULTIMO
 * 
 * 
 * 
 * 
 */
using System;
using System.Collections.ObjectModel;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Security.Principal;
using System.Windows;
using System.Windows.Forms;
using System.Windows.Input;
using System.Windows.Media.Imaging;
using System.Windows.Threading;
using Accord.vídeo.FFMPEG;
using AForge.vídeo;
using AForge.vídeo.DirectShow;
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.CommandWpf;
using Microsoft.Win32;
using static System.Windows.Forms.VisualStyles.VisualStyleElement.Window;
using MessageBox = System.Windows.Forms.MessageBox;
using SaveFileDialog = System.Windows.Forms.SaveFileDialog;

namespace VideoRecorder
{
    internal class MainWindowViewModel : ObservableObject, IDisposable
    {
        #region Private fields

        private FilterInfo _currentDevice;

        private String _txtBox = "";
        private String _statTxt = "PAUSE";

        private BitmapImage _image;

        private IVideoSource _videoSource;
        private VideoFileWriter _writer;
        private bool _recording;
        private DateTime? _firstFrameTime;

        #endregion

        #region Constructor

        public MainWindowViewModel()
        {
            VideoDevices = new ObservableCollection<FilterInfo>();
            GetVideoDevices();
            StartRecordingCommand = new RelayCommand(StartRecording);
        }

        #endregion

        #region Properties

        public ObservableCollection<FilterInfo> VideoDevices { get; set; }
        public BitmapImage Image
        {
            get { return _image; }
            set { Set(ref _image, value); }
        }
        public FilterInfo CurrentDevice
        {
            get { return _currentDevice; }
            set { Set(ref _currentDevice, value); }
        }
        public string ValueText
        {
            get { return ""; }
            set { _txtBox = value; }
        }

        public string SetRecordStatusTxt
        {
            get { return _statTxt; }
            set { _statTxt = value; }
        }
        public ICommand StartRecordingCommand { get; private set; }

        public ICommand StopRecordingCommand { get; private set; }

        public ICommand StartSourceCommand { get; private set; }

        public ICommand StopSourceCommand { get; private set; }

        #endregion

        #region Full Program
        private void GetVideoDevices()
        {
            var devices = new FilterInfoCollection(FilterCategory.VideoInputDevice);
            foreach (FilterInfo device in devices)
            {
                VideoDevices.Add(device);
            }
            if (VideoDevices.Any())
            {
                CurrentDevice = VideoDevices[0];
                this.StartCamera();
            }
            else
            {
                MessageBox.Show("No webcam found");
            }
        }

        private void StartCamera()
        {
            if (CurrentDevice != null)
            {
                _videoSource = new VideoCaptureDevice(CurrentDevice.MonikerString);
                _videoSource.NewFrame += video_NewFrame;
                _videoSource.Start();
            }
            else
            {
                MessageBox.Show("Current device can't be null");
            }
        }

        private void video_NewFrame(object sender, NewFrameEventArgs eventArgs)
        {
            try
            {
                if (_recording)
                {
                    using (var bitmap = (Bitmap)eventArgs.Frame.Clone())
                    {
                        if (_firstFrameTime != null)
                        {
                            _writer.WriteVideoFrame(bitmap, DateTime.Now - _firstFrameTime.Value);
                        }
                        else
                        {
                            _writer.WriteVideoFrame(bitmap);
                            _firstFrameTime = DateTime.Now;
                        }
                    }
                }
                using (var bitmap = (Bitmap)eventArgs.Frame.Clone())
                {
                    var bi = bitmap.ToBitmapImage();
                    bi.Freeze();
                    Dispatcher.CurrentDispatcher.Invoke(() => Image = bi);
                }
            }
            catch (Exception exc)
            {
                MessageBox.Show("Error on _videoSource_NewFrame:\n" + exc.Message, "Error", (MessageBoxButtons)MessageBoxButton.OK,
                    (MessageBoxIcon)MessageBoxImage.Error);
            }
        }

        System.Windows.Forms.Timer timer = new System.Windows.Forms.Timer();

        private void StatusTXT()
        {
            if (_recording == true)
            {
                _statTxt = "Recording...";
            }
            else
            {
                if (_recording == false)
                {
                    _statTxt = "PAUSE";
                }
            }
        }
        private void StartRecording()
        {

            if (_txtBox == "")
            {
                MessageBox.Show("Insert vídeo name please!");
                return;
            }
            _firstFrameTime = null;
            _writer = new VideoFileWriter();
            _writer.Open("C:\\Users\\SCHOOL ACCOUNT\\Videos\\trys\\" + _txtBox + ".avi", (int)Math.Round(Image.Width, 0), (int)Math.Round(Image.Height, 0));
            _recording = true;
            StatusTXT();
            timer.Interval = 5000; // here time in milliseconds 1000 milisegundos = 1 segundo
            timer.Tick += timer_Tick;
            timer.Start();
        }

        void timer_Tick(object sender, System.EventArgs e)
        {
            _recording = false;
            _writer.Close();
            _writer.Dispose();
            timer.Stop();
            _txtBox = "";
            StatusTXT();
        }

        public void Dispose()
        {
            if (_videoSource != null && _videoSource.IsRunning)
            {
                _videoSource.SignalToStop();
            }
            _writer?.Dispose();
        }
        #endregion
    }
}

Eu acho que o "problema" esteja nos getters e setters desta propriedade: "SetRecordStatusTxt";

e nesta classe "StatusTXT".

E o objetivo é sempre que a classe "StartRecording()" comece, chamar a classe StatusTXT e defenir o valor do campo TextBlock como "Recording..." e depois quando a classe TimerTick() for chamada defenir o valor do campo como "PAUSED".