Refactor webcam initialization and camera change handling

Co-authored-by: toniolo.luca <toniolo.luca@outlook.com>

Author: cursoragent

src/Captura/Pages/WebcamPlacementPreviewPage.xaml.cs

@@ -76,14 +76,7 @@ void SetupPreview()
             {
                 if (IsVisible && _webcamCapture == null)
                 {
-                    _webcamCapture = _webcamModel.InitCapture();
-
-                    if (_webcamCapture.Value is { } capture)
-                    {
-                        _reactor.WebcamSize.OnNext(new WSize(capture.Width, capture.Height));
-
-                        UpdateWebcamPreview();
-                    }
+                    InitializeWebcam();
                 }
                 else if (!IsVisible && _webcamCapture != null)
                 {
@@ -104,7 +97,16 @@ void OnRegionChange()
 
             _webcamModel
                 .ObserveProperty(M => M.SelectedCam)
-                .Subscribe(M => UpdateWebcamPreview());
+                .Subscribe(M =>
+                {
+                    // Release previous capture and reinitialize when camera changes
+                    if (_webcamCapture != null && IsVisible)
+                    {
+                        _webcamModel.ReleaseCapture();
+                        _webcamCapture = null;
+                        InitializeWebcam();
+                    }
+                });
 
             _reactor.Location
                 .CombineLatest(_reactor.Size, (M, N) =>
@@ -114,7 +116,26 @@ void OnRegionChange()
                 })
                 .Subscribe();
 
-            UpdateWebcamPreview();
+            // If page is already visible, initialize webcam immediately
+            if (IsVisible)
+            {
+                InitializeWebcam();
+            }
+        }
+
+        void InitializeWebcam()
+        {
+            if (_webcamCapture != null)
+                return;
+
+            _webcamCapture = _webcamModel.InitCapture();
+
+            if (_webcamCapture.Value is { } capture)
+            {
+                _reactor.WebcamSize.OnNext(new WSize(capture.Width, capture.Height));
+
+                UpdateWebcamPreview();
+            }
         }
 
         Rectangle GetPreviewWindowRect()