TASK 4 ship step 5: live frame pipeline — FramePump paces the active scene's composite into the encoder, ScreenCaptureManager.GetLatestFrame, MainViewModel resolver/option-builder/pump wiring, FramePumpTests (7) + GetLatestFrame test — 147 tests passing, 0 warnings

ViewModels/MainViewModel.cs

@@ -15,6 +15,8 @@ using ytLive.Helpers;
 using ytLive.Models;
 using ytLive.Services;
 using ytLive.Services.Audio;
+using ytLive.Services.Compositor;
+using ytLive.Services.Encoder;
 
 namespace ytLive.ViewModels;
 
@@ -86,6 +88,12 @@ public class MainViewModel : ViewModelBase
     // encoder mix. Private by design — no UI beyond the existing mic controls.
     private readonly AudioMixer _audioMixer;
 
+    // Live frame pipeline (TASK 4 ship step 5): composites the active scene at the
+    // tier's FPS and paces frames into the encoder. The RTMP URL seam stays null
+    // until the live-stream create flow (TASK 5) supplies the reusable stream URL.
+    private readonly Func<string?> _rtmpUrlProvider;
+    private readonly FramePump _framePump;
+
     // Screen backdrop: a permanent live capture (desktop/game) that every scene
     // shows at the bottom layer. One shared capture session per key — the
     // ScreenCaptureManager refcounts by key, mirroring CameraManager.
@@ -857,6 +865,16 @@ public class MainViewModel : ViewModelBase
         _screenCaptureManager.CaptureFailed += (key, message) =>
             AppLog.Write($"ScreenCaptureManager: capture '{key}' failed: {message}");
 
+        _rtmpUrlProvider = () => null; // TASK 5: the reusable stream's ingest URL
+        _framePump = new FramePump(
+            sceneProvider: () => ActiveScene,
+            frameResolver: ResolveOutputFrame,
+            compositorOptions: BuildCompositorOptions,
+            encoderOptions: BuildEncoderOptions,
+            encoderFactory: () => new FfmpegEncoder(new FfmpegLocator()),
+            log: message => AppLog.Write(message));
+        _framePump.Failed += OnFramePumpFailed;
+
         LoadLayout();
         _ = LoadSavedSessionAsync();
         AppLog.Write("MainViewModel ctor end");
@@ -1169,6 +1187,7 @@ public class MainViewModel : ViewModelBase
     {
         _saveDebounce?.Stop();
         SaveLayoutNow();
+        _framePump.Dispose();
         _cameraManager.Dispose();
         _screenCaptureManager.Dispose();
         _layoutStore.Dispose();
@@ -1739,6 +1758,7 @@ public class MainViewModel : ViewModelBase
                 : $"{dialog.StreamTitle} — ytLlive";
             StreamStatus = StreamStatus.Streaming;
             _audioMixer.Start();
+            _ = _framePump.StartAsync(); // never throws; failures log + surface via Failed
         }
     }
 
@@ -1747,6 +1767,7 @@ public class MainViewModel : ViewModelBase
         StreamStatus = StreamStatus.Offline;
         WindowTitle = "ytLlive";
         _audioMixer.Stop();
+        _ = _framePump.StopAsync();
         // Graceful end completes the session = signs out (the DPAPI token is
         // cleared so the next Start Stream requires a fresh sign-in). A crash
         // never runs this, so the token survives and the creator stays signed in.
@@ -1768,6 +1789,59 @@ public class MainViewModel : ViewModelBase
             AudioLevel = level;
     }
 
+    // Scene-element → latest frame, for the live compositor. The map mirrors the
+    // preview: webcam by DeviceId, live captures (the backdrop) by CaptureKey,
+    // images/background by AssetId. A null frame leaves the element transparent.
+    private VideoFrame? ResolveOutputFrame(SceneElement element)
+    {
+        return element switch
+        {
+            WebcamSceneConfig webcam => _cameraManager.GetLatestFrame(webcam.WebcamId),
+            Source { IsLiveCapture: true, CaptureKey: not null } live => _screenCaptureManager.GetLatestFrame(live.CaptureKey),
+            Source { AssetId: not null } image => StaticPixelCache.Get(image.AssetId),
+            _ => null,
+        };
+    }
+
+    // The tier's crop rect over the 1920x1080 master, integer-aligned (the VM's
+    // OutputRect* are doubles — the vertical 607.5 half-pixel crop rounds to 608).
+    private CompositorOptions BuildCompositorOptions()
+    {
+        var quality = SelectedQuality;
+        return new CompositorOptions
+        {
+            SourceRectX = (int)Math.Round(OutputRectX),
+            SourceRectY = (int)Math.Round(OutputRectY),
+            SourceRectWidth = (int)Math.Round(OutputRectWidth),
+            SourceRectHeight = (int)Math.Round(OutputRectHeight),
+            OutputWidth = quality.Width,
+            OutputHeight = quality.Height,
+        };
+    }
+
+    // Full encoder options for the current tier, or null when no RTMP URL is
+    // available — the pump then skips the encoder entirely (TASK 5 fills the seam).
+    private EncoderOptions? BuildEncoderOptions()
+    {
+        var url = _rtmpUrlProvider();
+        if (string.IsNullOrWhiteSpace(url)) return null;
+        var quality = SelectedQuality;
+        return new EncoderOptions
+        {
+            RtmpUrl = url,
+            Width = quality.Width,
+            Height = quality.Height,
+            Fps = quality.Fps,
+            BitrateKbps = (int)Math.Round(quality.Bitrate * 1000),
+        };
+    }
+
+    private void OnFramePumpFailed(object? sender, string message)
+    {
+        AppLog.Write($"Frame pump failed: {message}");
+        if (IsLive) StreamStatus = StreamStatus.Error;
+    }
+
     private void UpdateLiveVisuals()
     {
         var live = IsLive;