TASK 51 jitter fix: temporal mask smoothing. MaskSmoother blends each raw segmentation 0.75xnew + 0.25xprevious at the one CameraManager worker (state per CameraSession, not in the shared segmenter); null resets history, first frame passes through, input array never aliased, ping-pong buffers (no LOH alloc for a 147KB 256x144 mask). Creator's real-camera check: Remove was 'jittery' (per-frame independent segmentation). Weights from the OBS/Jitsi consensus. One integration test asserts the second frame keeps partial alpha (x=6 -> 58) where the raw mask cuts to 0. 416 pass / 2 known env flakes. Refs: https://deepwiki.com/royshil/obs-backgroundremoval/2-core-features https://github.com/jitsi/jitsi-meet/issues/17080 (Unit: bg-removal jitter fix)

Services/CameraManager.cs

@@ -26,8 +26,9 @@ namespace ytLive.Services;
 ///
 /// Background effects (TASK 51) are the ONE processing point on the camera path: per device,
 /// the set of requested <see cref="WebcamEffectKey"/>s (<see cref="SetRequestedEffects"/>) is
-/// rendered from each raw frame on a background worker — one segmentation per frame, shared by
-/// every variant, latest-frame-drop when the worker is busy — and each variant keeps its own
+/// rendered from each raw frame on a background worker — one segmentation per frame, smoothed
+/// per camera across frames (see <see cref="MaskSmoother"/>) and shared by every variant,
+/// latest-frame-drop when the worker is busy — and each variant keeps its own
 /// latest frame (the compositor) and shared WriteableBitmap (the preview). The raw path is
 /// untouched, so a slow or failing model never stalls the plain webcam.
 /// </summary>
@@ -55,6 +56,7 @@ public sealed class CameraManager : IDisposable
         public readonly Dictionary<WebcamEffectKey, EffectVariant> Effects = new();
         public bool EffectWorkerRunning;
         public VideoFrame? LastEffectSource;
+        public readonly MaskSmoother Smoother = new();
 
         public CameraSession(string deviceId, ICameraFrameSource source)
         {
@@ -436,7 +438,7 @@ public sealed class CameraManager : IDisposable
                 }
 
                 var started = System.Diagnostics.Stopwatch.GetTimestamp();
-                var mask = _effects!.TrySegment(source);
+                var mask = session.Smoother.Smooth(_effects!.TrySegment(source));
                 var rendered = new List<(WebcamEffectKey Key, VideoFrame Frame)>(keys.Count);
                 if (mask != null)
                     foreach (var key in keys)