Add chapters display, gray out fixed tracks, spacebar preview

MainWindow.xaml.cs

@@ -1,5 +1,6 @@
 using System.Collections.ObjectModel;
 using System.ComponentModel;
+using System.Diagnostics;
 using System.IO;
 using System.Threading;
 using System.Windows;
@@ -357,6 +358,13 @@ public partial class MainWindow : FluentWindow
     /// </summary>
     private void FileQueueList_PreviewKeyDown(object sender, System.Windows.Input.KeyEventArgs e)
     {
+        if (e.Key == System.Windows.Input.Key.Space)
+        {
+            OpenSelectedFileInDefaultPlayer();
+            e.Handled = true;
+            return;
+        }
+
         if (e.Key != System.Windows.Input.Key.Delete) return;
 
         var selected = FileQueueList.SelectedItems.Cast<QueuedFileItem>().ToList();
@@ -371,6 +379,25 @@ public partial class MainWindow : FluentWindow
         e.Handled = true;
     }
 
+    /// <summary>
+    /// Opens the currently-selected queue item with whatever application
+    /// Windows has associated with .mkv files (typically the default video
+    /// player), so the user can quickly preview a file without leaving the app.
+    /// </summary>
+    private void OpenSelectedFileInDefaultPlayer()
+    {
+        if (FileQueueList.SelectedItem is not QueuedFileItem item) return;
+
+        try
+        {
+            Process.Start(new ProcessStartInfo(item.FilePath) { UseShellExecute = true });
+        }
+        catch (Exception ex)
+        {
+            StatusText.Text = $"Couldn't open {item.FileName}: {ex.Message}";
+        }
+    }
+
     private void ClearQueueButton_Click(object sender, RoutedEventArgs e)
     {
         foreach (var item in _fileQueue)