TASK 51 slice 4: camera-path hookup — CameraManager renders per-scene effect variants (one segmentation per raw frame on a latest-frame-drop worker, raw path untouched), VM declares/adopts variants per config; separable upsampling cuts Remove 46->3 ms, Blur 80->18 ms (Debug, 720p) (Unit: bg-effects hookup)

ViewModels/MainViewModel.Sources.cs

@@ -252,6 +252,7 @@ public partial class MainViewModel
 
         if (element is WebcamSceneConfig)
         {
+            SyncWebcamEffects(); // drop a variant nobody shows any more
             OnPropertyChanged(nameof(CanAddWebcam));
             OnPropertyChanged(nameof(CanShowWebcamInStagedScene));
             OnPropertyChanged(nameof(WebcamAddToolTip));

ViewModels/MainViewModel.Webcam.cs

@@ -7,6 +7,7 @@ using ytLive;
 using ytLive.Helpers;
 using ytLive.Models;
 using ytLive.Services;
+using ytLive.Services.BackgroundEffects;
 
 namespace ytLive.ViewModels;
 
@@ -193,9 +194,8 @@ public partial class MainViewModel
         // A session already running (same device, or one that produced a first
         // frame) has its shared bitmap; freshly loaded configs must adopt it here,
         // because PreviewBitmapChanged never re-fires for an existing bitmap.
-        if (_cameraManager.GetPreviewBitmap(newDevice) is { } running)
-            foreach (var config in Scenes.SelectMany(s => s.Elements.OfType<WebcamSceneConfig>()))
-                config.VideoImageSource = running;
+        // SyncWebcamEffects also declares each config's background-effect variant.
+        SyncWebcamEffects();
     }
 
     // CameraManager creates the shared WriteableBitmap on the UI thread at the
@@ -209,7 +209,52 @@ public partial class MainViewModel
         RaiseWebcamGateChanged();
         foreach (var scene in Scenes)
             foreach (var config in scene.Elements.OfType<WebcamSceneConfig>())
+                if (EffectKeyFor(config).Effect == BackgroundEffect.None)
+                    config.VideoImageSource = bitmap;
+    }
+
+    // TASK 51: an effect variant's first processed frame created its bitmap — every config
+    // showing that variant adopts it (later frames write into it in place).
+    private void OnCameraEffectPreviewBitmapChanged(string deviceId, WebcamEffectKey key, WriteableBitmap bitmap)
+    {
+        if (_webcam?.DeviceId != deviceId) return;
+        foreach (var scene in Scenes)
+            foreach (var config in scene.Elements.OfType<WebcamSceneConfig>())
+                if (EffectKeyFor(config) == key)
+                    config.VideoImageSource = bitmap;
+    }
+
+    internal static WebcamEffectKey EffectKeyFor(WebcamSceneConfig config)
+        => WebcamEffectKey.For(config.BackgroundEffect, config.BackgroundStrength);
+
+    private readonly HashSet<WebcamSceneConfig> _effectWatchedConfigs = new();
+
+    /// <summary>TASK 51: declares the union of every scene's webcam effect variant to the camera
+    /// (unused variants stop costing CPU) and points each config's preview at its variant's
+    /// bitmap. An effect variant with no processed frame yet shows nothing rather than the raw
+    /// room. Re-run whenever a config is added/removed/loaded or its effect changes.</summary>
+    internal void SyncWebcamEffects()
+    {
+        if (_webcam == null || string.IsNullOrWhiteSpace(_webcam.DeviceId)) return;
+        var configs = Scenes.SelectMany(s => s.Elements.OfType<WebcamSceneConfig>()).ToList();
+        _cameraManager.SetRequestedEffects(_webcam.DeviceId, configs.Select(EffectKeyFor));
+        foreach (var config in configs)
+        {
+            if (_effectWatchedConfigs.Add(config))
+                config.PropertyChanged += OnWebcamConfigEffectChanged;
+            var key = EffectKeyFor(config);
+            var bitmap = _cameraManager.GetPreviewBitmap(_webcam.DeviceId, key);
+            if (bitmap != null || key.Effect != BackgroundEffect.None)
                 config.VideoImageSource = bitmap;
+        }
+    }
+
+    private void OnWebcamConfigEffectChanged(object? sender, System.ComponentModel.PropertyChangedEventArgs e)
+    {
+        if (e.PropertyName is not (nameof(WebcamSceneConfig.BackgroundEffect) or nameof(WebcamSceneConfig.BackgroundStrength)))
+            return;
+        SyncWebcamEffects();
+        ScheduleSave();
     }
 
     // The camera failed to start or died asynchronously (in use, offline, locked,
@@ -321,9 +366,9 @@ public partial class MainViewModel
 
         // PreviewBitmapChanged fires only on the camera's first frame, so a config
         // added while the session is already running must pick up the shared bitmap
-        // directly (it's written in place from then on).
-        if (_cameraManager.GetPreviewBitmap(_webcam.DeviceId) is { } running)
-            config.VideoImageSource = running;
+        // directly (it's written in place from then on) — SyncWebcamEffects does that,
+        // per the config's background-effect variant.
+        SyncWebcamEffects();
 
         var started = await _cameraManager.AcquireAsync(_webcam.DeviceId);
         if (!started)
@@ -346,6 +391,8 @@ public partial class MainViewModel
         if (!string.IsNullOrWhiteSpace(oldDevice) && oldDevice != device.Id)
             await _cameraManager.ReleaseAllAsync(oldDevice);
 
+        SyncWebcamEffects(); // the new device inherits the scenes' background effects
+
         foreach (var unused in Scenes.SelectMany(s => s.Elements.OfType<WebcamSceneConfig>()))
         {
             var started = await _cameraManager.AcquireAsync(device.Id);

ViewModels/MainViewModel.cs

@@ -276,8 +276,11 @@ public partial class MainViewModel : ViewModelBase
         _cameraManager = new CameraManager(
             _cameraEnumerator,
             CameraFrameSourceFactoryOverride ?? (id => new MediaCaptureFrameSource(id)),
-            System.Windows.Application.Current?.Dispatcher);
+            System.Windows.Application.Current?.Dispatcher,
+            effects: new Services.BackgroundEffects.BackgroundEffectProcessor(
+                PersonSegmenterOverride ?? new Services.BackgroundEffects.OnnxPersonSegmenter()));
         _cameraManager.PreviewBitmapChanged += OnCameraPreviewBitmapChanged;
+        _cameraManager.EffectPreviewBitmapChanged += OnCameraEffectPreviewBitmapChanged;
         _cameraManager.CameraFailed += OnCameraFailed;
 
         _microphoneEnumerator = new WinRtMicrophoneEnumerator();
@@ -384,6 +387,10 @@ public partial class MainViewModel : ViewModelBase
     internal static ICameraEnumerator? CameraEnumeratorOverride { get; set; }
     internal static Func<string, ICameraFrameSource>? CameraFrameSourceFactoryOverride { get; set; }
 
+    /// <summary>Test seam (TASK 51): a fake person segmenter so hermetic tests never load the
+    /// real ONNX model. Mirrors <see cref="CameraFrameSourceFactoryOverride"/>.</summary>
+    internal static Services.BackgroundEffects.IPersonSegmenter? PersonSegmenterOverride { get; set; }
+
     private void LoadLayout()
     {
         _isLoading = true;
@@ -570,7 +577,7 @@ public partial class MainViewModel : ViewModelBase
             // Looking up by the GUID returned null forever — the webcam was structurally
             // invisible on the output while the preview (bitmap path) looked fine
             // (caught by the resolver logging, 2026-09-01 take two).
-            WebcamSceneConfig webcam => _cameraManager.GetLatestFrame(DeviceKeyForWebcam(webcam.WebcamId)),
+            WebcamSceneConfig webcam => _cameraManager.GetLatestFrame(DeviceKeyForWebcam(webcam.WebcamId), EffectKeyFor(webcam)),
             Source { IsLiveCapture: true, CaptureKey: not null } live => _screenCaptureManager.GetLatestFrame(live.CaptureKey),
             Source { Type: SourceType.ChatBox } chatBox => RenderChatBox(chatBox),
             Source { Type: SourceType.AlertBox } alertBox => RenderAlertBox(alertBox),