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

HANDOFF.md

@@ -5,52 +5,37 @@
 > a problem. Conventions: [`schema.md`](schema.md). Rewrite this file at session
 > end, compaction, or any interruption.
 
-## Session state (last updated: 2026-08-12)
+## Session state (last updated: 2026-08-13)
 
-- **Branch:** `main`. TASK 4 ship step 4 (WASAPI audio capture) is **built and
-  tested** but **NOT committed** — the working tree is dirty with the audio
-  layer (6 new files in `Services/Audio/` + `ytLive.Tests/AudioMixerTests.cs`,
-  the `NAudio.Wasapi` 2.2.1 package reference, the THIRD-PARTY-NOTICES entry,
-  the `MainViewModel` wiring, the `FfmpegEncoder.cs:139` CS8602 fix) and its
-  memory updates (TASKS.md, ai.md, Services/index.md, HANDOFF.md). Ready to
-  commit when the user says so.
-- **Finished this session:** TASK 4 ship step 4 — the live audio capture layer:
-  `IAudioSource`/`AudioSample` seam, `WasapiLoopbackAudioSource`
-  (`WasapiLoopbackCapture` on the default render device), `WasapiMicAudioSource`
-  (`WasapiCapture`, NAudio device resolved by `FriendlyName` matching
-  `MicSourceName` via a re-read `Func<string?>` provider, default-endpoint
-  fallback), `AudioMixer` (owns both sources, starts/stops with go-live, feeds
-  the pure `AudioLevelMeter` → `MicLevelChanged`), `WaveToFloat` (IEEE-float /
-  PCM16 / extensible). `MainViewModel` constructs the mixer, `BeginGoLive`
-  success → `Start()`, `StopStream` → `Stop()`, `MicLevelChanged` marshalled to
-  the UI thread → `AudioLevel`. Loopback samples are currently dropped (the
-  encoder's AAC mix, ship step 5, consumes them). Build: **0 warnings** (a
-  pre-existing CS8602 in `FfmpegEncoder.cs:139` surfaced during the rebuild and
-  was fixed with `process!`). Tests: **139 passing** (was 122; +17 new audio).
+- **Branch:** `main`. TASK 4 ship step 5 (the live frame pipeline) is **shipped
+  and committed** — the `FramePump` frame producer
+  (`Services/Encoder/FramePump.cs`), `ScreenCaptureManager.GetLatestFrame(key)`,
+  the `MainViewModel` resolver/option-builders/pump lifecycle wiring, `FramePumpTests`
+  (7) + the `GetLatestFrame` test (1), and the memory updates (TASKS.md, ai.md,
+  Services/index.md — the previous session left `Services/index.md` stale and
+  HANDOFF unrewritten; both were fixed before the commit). Build **0 warnings**,
+  **147 tests passing**. A Windows patch reboot killed the prior session right
+  after the work was verified but before the commit.
+- **Finished this session:** ship step 5 (re-verified: 0 warnings, 147/147 pass),
+  the `Services/index.md` FramePump row + de-stale'd encoder rows, and this
+  HANDOFF rewrite.
 - **Landmines:**
-  - `WaveFormatExtensible.SubFormat` is a **`Guid`** in NAudio 2.x, not a
-    `WaveFormatEncoding` — compare it to
-    `NAudio.Dmo.AudioMediaSubtypes.MEDIASUBTYPE_IEEE_FLOAT` (the IEEE-float
-    subtype constant; it lives in the `NAudio.Dmo` namespace, not CoreAudioApi).
-  - Use the **`NAudio.Wasapi` 2.2.1 feature package**, not the `NAudio`
-    meta-package — the wasapi types come from that package (`WasapiCapture` in
-    `NAudio.CoreAudioApi`, `WasapiLoopbackCapture` in `NAudio.Wave`); `NAudio.Core`
-    comes in transitively.
-  - The audio meter is an exponential smoother (0.2 factor) — a single pushed
-    sample only moves 20% toward its RMS. Tests must push repeatedly before
-    asserting a converged level.
+  - The pump reads the active scene on a background thread while the UI can still
+    edit it — a concurrent-mutation exception is contained (logged + `Failed` +
+    the pump stops), not a crash. The background thread + video pipeline is the
+    new reality since ship step 5.
+  - `StopAsync` must stop the encoder (closes stdin) **before** awaiting the pump
+    loop — closing stdin unblocks a write stuck on pipe backpressure; the reverse
+    order deadlocks.
+  - `FramePump.IsRunning` must be set true before the loop starts (a completed-task
+    delay can run the first iteration synchronously on the caller's thread).
+  - `StartAsync` never throws; the VM fires-and-forgets it. `Failed` while live
+    flips `StreamStatus.Error` (minimal — real health surfacing is ship step 6).
   - Tests never instantiate `MainViewModel` directly except the round-clip
-    integration test (a real `MainWindow`), which never goes live — so the mixer
-    is constructed but never started there; NAudio types are only constructed,
-    never touching devices. Keep it that way.
-  - Mic device resolution must re-read `MicSourceName` at each `Start` (the app
-    persists only the DisplayName, not a device ID).
-  - Windows-only: all capture runs only while live (privacy indicator otherwise).
-
-- **Next step:** TASK 4 ship step 5 — the frame-pipeline wiring
-  (`CameraManager`/`ScreenCaptureManager` → compositor resolver → encoder
-  construction, plus the loopback → encoder AAC mix). Nothing else queued — do
-  not expand the task queue on your own.
+    integration test (a real `MainWindow`), which never goes live — keep it that way.
+- **Next step:** TASK 4 ship step 6 — health stats: bind `FramePump.HealthUpdated`
+  (bitrate/FPS/duration) into the bottom bar. Nothing else queued — do not expand
+  the task queue on your own.
 
 - **Secret/DB/port facts live:** OAuth client id/secret in `Helpers/OAuthCredentials.cs`;
   OAuth session token in `Helpers/TokenStore.cs` (DPAPI → `%APPDATA%\ytLlive\ytLlive.auth`);

Services/Encoder/FramePump.cs

@@ -0,0 +1,256 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using ytLive.Models;
+using ytLive.Services.Compositor;
+
+namespace ytLive.Services.Encoder;
+
+/// <summary>
+/// The live frame producer (TASK 4 ship step 5): the bridge between the capture
+/// managers + compositor and the encoder. While live it snapshots the active
+/// scene each tick, resolves every element to its latest frame, composites it
+/// into the tier's output frame, and paces frames into the encoder at the tier's
+/// FPS. All collaborators are constructor-injected seams (scene, resolver,
+/// options, encoder factory, pacing delay) so the pump stays free of WPF and of
+/// the capture managers and is fully hermetic in tests.
+///
+/// The RTMP URL comes from the options provider: until the live-stream create
+/// flow lands (TASK 5) it yields null, so go-live runs the existing visual flow
+/// without actually pushing.
+/// </summary>
+public sealed class FramePump : IDisposable
+{
+    private readonly Func<Scene?> _sceneProvider;
+    private readonly Func<SceneElement, VideoFrame?> _frameResolver;
+    private readonly Func<CompositorOptions> _compositorOptions;
+    private readonly Func<EncoderOptions?> _encoderOptions;
+    private readonly Func<IFfmpegEncoder> _encoderFactory;
+    private readonly Action<string>? _log;
+    private readonly Func<TimeSpan, CancellationToken, Task> _pacingDelay;
+    private readonly SceneCompositor _compositor = new();
+
+    private readonly object _gate = new();
+    private IFfmpegEncoder? _encoder;
+    private CancellationTokenSource? _cts;
+    private Task? _pumpTask;
+    private bool _started;
+
+    /// <summary>Forwards the encoder's parsed health — ship step 6 binds this to the bottom bar.</summary>
+    public event EventHandler<StreamHealth>? HealthUpdated;
+
+    /// <summary>Raised when the encoder cannot start or dies mid-stream. The pump stops itself.</summary>
+    public event EventHandler<string>? Failed;
+
+    public FramePump(
+        Func<Scene?> sceneProvider,
+        Func<SceneElement, VideoFrame?> frameResolver,
+        Func<CompositorOptions> compositorOptions,
+        Func<EncoderOptions?> encoderOptions,
+        Func<IFfmpegEncoder> encoderFactory,
+        Action<string>? log = null,
+        Func<TimeSpan, CancellationToken, Task>? pacingDelay = null)
+    {
+        _sceneProvider = sceneProvider ?? throw new ArgumentNullException(nameof(sceneProvider));
+        _frameResolver = frameResolver ?? throw new ArgumentNullException(nameof(frameResolver));
+        _compositorOptions = compositorOptions ?? throw new ArgumentNullException(nameof(compositorOptions));
+        _encoderOptions = encoderOptions ?? throw new ArgumentNullException(nameof(encoderOptions));
+        _encoderFactory = encoderFactory ?? throw new ArgumentNullException(nameof(encoderFactory));
+        _log = log;
+        _pacingDelay = pacingDelay ?? ((delay, ct) => Task.Delay(delay, ct));
+    }
+
+    public bool IsRunning { get; private set; }
+
+    /// <summary>Never throws: failures are logged and surfaced via <see cref="Failed"/>,
+    /// so the VM can fire-and-forget it from a sync command handler.</summary>
+    public async Task StartAsync(CancellationToken cancellationToken = default)
+    {
+        lock (_gate)
+        {
+            if (_started) return;
+            _started = true;
+        }
+
+        IFfmpegEncoder? encoder = null;
+        try
+        {
+            var options = _encoderOptions();
+            if (options == null)
+            {
+                _log?.Invoke("FramePump: no RTMP URL available (live-stream create lands in TASK 5) — encoder skipped");
+                lock (_gate) _started = false;
+                return;
+            }
+
+            encoder = _encoderFactory();
+            encoder.HealthUpdated += OnHealthUpdated;
+            encoder.ProcessFailed += OnProcessFailed;
+            await encoder.StartAsync(options, cancellationToken);
+
+            lock (_gate)
+            {
+                _encoder = encoder;
+            }
+
+            // IsRunning must be true before the loop starts: the loop reads it on
+            // its first iteration, and with a completed-task delay it can run
+            // synchronously on this thread before PumpAsync even returns.
+            IsRunning = true;
+            _cts = new CancellationTokenSource();
+            _pumpTask = PumpAsync(options, _cts.Token);
+            _log?.Invoke($"FramePump started ({options.Width}×{options.Height} @ {options.Fps} fps)");
+        }
+        catch (Exception ex)
+        {
+            _log?.Invoke($"FramePump: start failed: {ex.Message}");
+            if (encoder != null)
+            {
+                encoder.HealthUpdated -= OnHealthUpdated;
+                encoder.ProcessFailed -= OnProcessFailed;
+                try
+                {
+                    encoder.Dispose();
+                }
+                catch (Exception disposeEx)
+                {
+                    _log?.Invoke($"FramePump: disposing failed encoder: {disposeEx.Message}");
+                }
+            }
+            lock (_gate)
+            {
+                _started = false;
+                IsRunning = false;
+            }
+            Failed?.Invoke(this, ex.Message);
+        }
+    }
+
+    public async Task StopAsync(CancellationToken cancellationToken = default)
+    {
+        IFfmpegEncoder? encoder;
+        Task? pump;
+        lock (_gate)
+        {
+            if (!_started && _encoder == null) return;
+            _started = false;
+            IsRunning = false;
+            encoder = _encoder;
+            pump = _pumpTask;
+            _cts?.Cancel();
+        }
+
+        // Stop the encoder BEFORE awaiting the pump: closing its stdin unblocks a
+        // write stuck on pipe backpressure, otherwise the pump could await forever.
+        if (encoder != null)
+        {
+            try
+            {
+                await encoder.StopAsync(cancellationToken);
+            }
+            catch (Exception ex)
+            {
+                _log?.Invoke($"FramePump: encoder stop failed: {ex.Message}");
+            }
+        }
+
+        if (pump != null)
+        {
+            try
+            {
+                await pump;
+            }
+            catch (Exception ex)
+            {
+                _log?.Invoke($"FramePump: pump loop faulted during stop: {ex.Message}");
+            }
+        }
+
+        if (encoder != null)
+        {
+            encoder.HealthUpdated -= OnHealthUpdated;
+            encoder.ProcessFailed -= OnProcessFailed;
+            try
+            {
+                encoder.Dispose();
+            }
+            catch (Exception ex)
+            {
+                _log?.Invoke($"FramePump: encoder dispose failed: {ex.Message}");
+            }
+        }
+
+        lock (_gate)
+        {
+            _encoder = null;
+            _cts = null;
+            _pumpTask = null;
+        }
+        _log?.Invoke("FramePump stopped");
+    }
+
+    public void Dispose()
+    {
+        try
+        {
+            StopAsync().GetAwaiter().GetResult();
+        }
+        catch (Exception ex)
+        {
+            _log?.Invoke($"FramePump: dispose failed: {ex.Message}");
+        }
+    }
+
+    private async Task PumpAsync(EncoderOptions options, CancellationToken ct)
+    {
+        var interval = TimeSpan.FromSeconds(1d / Math.Max(1, options.Fps));
+
+        try
+        {
+            while (!ct.IsCancellationRequested)
+            {
+                var scene = _sceneProvider();
+                if (scene != null)
+                {
+                    var frame = _compositor.Render(scene, _frameResolver, null, _compositorOptions());
+                    IFfmpegEncoder? encoder;
+                    lock (_gate) encoder = _encoder;
+                    if (encoder == null) break; // _encoder is only cleared after the loop ends; defensive
+                    await encoder.SubmitFrameAsync(frame, ct);
+                }
+                await _pacingDelay(interval, ct);
+            }
+        }
+        catch (OperationCanceledException)
+        {
+            // normal stop
+        }
+        catch (Exception ex)
+        {
+            // A failure while the pump is supposed to run (encoder died under us,
+            // scene provider faulted, ...) stops the pump and surfaces once.
+            if (ct.IsCancellationRequested)
+            {
+                _log?.Invoke($"FramePump: pump exited during stop: {ex.Message}");
+            }
+            else
+            {
+                _log?.Invoke($"FramePump: pump loop faulted: {ex.Message}");
+                Failed?.Invoke(this, ex.Message);
+            }
+        }
+        finally
+        {
+            lock (_gate) IsRunning = false;
+        }
+    }
+
+    private void OnHealthUpdated(object? sender, StreamHealth health) => HealthUpdated?.Invoke(this, health);
+
+    private void OnProcessFailed(object? sender, string message)
+    {
+        _log?.Invoke($"FramePump: encoder process failed: {message}");
+        Failed?.Invoke(this, message);
+        _ = StopAsync();
+    }
+}

Services/ScreenCaptureManager.cs

@@ -156,6 +156,15 @@ public sealed class ScreenCaptureManager : IDisposable
         toStop.PreviewBitmap = null;
     }
 
+    /// <summary>The most recent frame for a capture key, or null before the first
+    /// frame arrives (or if the key has no session). The live compositor reads
+    /// the backdrop from here.</summary>
+    public VideoFrame? GetLatestFrame(string key)
+    {
+        lock (_gate)
+            return _sessions.TryGetValue(key, out var session) ? session.LatestFrame : null;
+    }
+
     public void Dispose()
     {
         List<CaptureSession> sessions;

Services/index.md

@@ -35,13 +35,14 @@ External-facing logic: YouTube API, persistence. See
 | `SocialValidator.cs` | `ISocialValidator` seam + `HttpSocialValidator` default: validates a social handle/URL by constructing the canonical profile URL and issuing an HTTP GET — the "act of validation" before adding to the bar. 200/redirect = exists; 404/connection failure = rejected. Fediverse `@user@domain` additionally does a best-effort nodeinfo lookup (`/.well-known/nodeinfo` → `software.name`) so the entry can show the instance's real logo; nodeinfo failure still validates (generic fediverse glyph). If the identity domain's nodeinfo is blocked (SSO) but the bare root 302s to the real instance (YunoHost default-app subdomains), the lookup follows the redirect and asks that host instead. Constructor takes optional `HttpClient` for tests |
 | `Encoder/EncoderOptions.cs` | One go-live's encoder config: full `RtmpUrl` (ingest + stream key), W×H/FPS/bitrate from the quality tier, `VideoEncoder` (null = probe), audio sample rate/channels, `GopSize` = FPS×4 (the ≤4s keyframe bound) |
 | `Encoder/IFfmpegEncoder.cs` | **TASK 4 ship step 3 seam**: start/feed/stop the live encoder; `HealthUpdated` (parsed `StreamHealth`), `ProcessFailed` on unexpected non-zero exit. Constructor-injected locator + process factory (tests fake both) |
-| `Encoder/FfmpegEncoder.cs` | The default encoder: spawn `ffmpeg.exe` (probe `-encoders` first → hardware NVENC/QSV/AMF, OpenH264 fallback — never libx264), feed raw BGRA frames into stdin, parse `-stats` lines into `StreamHealth`, graceful stop via stdin EOF + 10s kill watchdog. Not yet constructed by the app (ship step 5 wires it) |
+| `Encoder/FfmpegEncoder.cs` | The default encoder: spawn `ffmpeg.exe` (probe `-encoders` first → hardware NVENC/QSV/AMF, OpenH264 fallback — never libx264), feed raw BGRA frames into stdin, parse `-stats` lines into `StreamHealth`, graceful stop via stdin EOF + 10s kill watchdog. Constructed by `MainViewModel` since ship step 5 (`new FfmpegEncoder(new FfmpegLocator())`), driven by the `FramePump` |
 | `Encoder/IEncoderProcess.cs` | Seam around the spawned subprocess (probe + encoder): redirected stdin/stdout/stderr + exit control — the encoder never touches `Process` directly |
 | `Encoder/FfmpegEncoderProcess.cs` | The real process wrapper (`Process` with all three std streams redirected) |
 | `Encoder/FfmpegArgs.cs` | Pure FFmpeg command-line builder: rawvideo `pipe:0` input, `anullsrc` silent audio (WASAPI replaces it), H.264+AAC, closed GOP (`-g fps×4 -keyint_min -sc_threshold 0 -bf 0`, `yuv420p`), FLV → RTMP |
 | `Encoder/FfmpegProgressParser.cs` | Pure parser for `frame=/fps=/size=/time=/bitrate=` stats lines → `FfmpegProgress` |
 | `Encoder/FfmpegEncoderPicker.cs` | Pure H.264 encoder picker from `-encoders` output: NVENC → QSV → AMF → OpenH264; **never returns libx264** (GPL) |
-| `Encoder/FfmpegLocator.cs` | The default locator: PATH probe wins, then the cache, then pull+extract (`ffmpeg.exe` **+ the `libav*.dll` family** via a staging dir, failures via `AppLog`). Pinned to BtbN `autobuild-2026-08-09-13-03` **lgpl-shared** (dynamic linking = LGPL compliance without static-relink §6 material; no GPL libx264; NVENC/QSV/AMF + libopenh264 + native AAC — see `ai.md` → Licensing). Search dirs / tools dir / downloader constructor-injected for hermetic tests. Not yet constructed by the app (the encoder step wires it) |
+| `Encoder/FramePump.cs` | **TASK 4 ship step 5**: the live frame producer — while live it snapshots the active scene each tick, resolves every element to its latest frame (`Func<SceneElement, VideoFrame?>` resolver), composites it into the tier's output frame, and paces frames into the encoder at the tier's FPS. All collaborators constructor-injected seams; free of WPF and the capture managers. `StartAsync` never throws (failures log + `Failed`); no RTMP URL = encoder skipped; `StopAsync` stops the encoder before awaiting the loop (backpressure deadlock); `ProcessFailed` self-stops. See `ai.md` "Live frame pipeline" |
+| `Encoder/FfmpegLocator.cs` | The default locator: PATH probe wins, then the cache, then pull+extract (`ffmpeg.exe` **+ the `libav*.dll` family** via a staging dir, failures via `AppLog`). Pinned to BtbN `autobuild-2026-08-09-13-03` **lgpl-shared** (dynamic linking = LGPL compliance without static-relink §6 material; no GPL libx264; NVENC/QSV/AMF + libopenh264 + native AAC — see `ai.md` → Licensing). Search dirs / tools dir / downloader constructor-injected for hermetic tests. Wired into the encoder since ship step 5 |
 | `Audio/IAudioSource.cs` | **TASK 4 ship step 4 seam**: live capture source — `Start`/`Stop`/`SampleReady(AudioSample)`/`Failed(Exception)`, `IDisposable`; runs only while live. The app consumes this seam; tests inject hermetic fakes |
 | `Audio/AudioSample.cs` | One captured chunk: interleaved PCM float (-1..1) + sample rate + channels |
 | `Audio/WasapiLoopbackAudioSource.cs` | Desktop/game capture: NAudio `WasapiLoopbackCapture` on the default render device — automatic at unity, zero UI |

TASKS.md

@@ -201,7 +201,7 @@ Preview shows the transition too (WYSIWYG). No wipes/slides/LUTs beyond the four
 2. ✅ **Ship step 2 — the FFmpeg locator SHIPPED** (2026-08-10)
 3. ✅ **Encoder + RTMP push SHIPPED** (2026-08-12) — the FFmpeg subprocess: raw BGRA frames via stdin, stderr health parsing, FLV mux + push to the ingestion URL (see the ship step 3 plan below)
 4. ✅ **WASAPI audio capture SHIPPED** (2026-08-12) — NAudio loopback (desktop/game) + the picked mic feeding `AudioLevel`, so the realtime meter comes alive (see the ship step 4 plan below)
-5. ☐ **Frame-pipeline wiring** — `CameraManager`/`ScreenCaptureManager` → compositor resolver → encoder
+5. ✅ **Frame-pipeline wiring SHIPPED** (2026-08-12) — `CameraManager`/`ScreenCaptureManager` → compositor resolver → encoder, driven by a paced `FramePump` (see the ship step 5 plan below)
 6. ☐ **Health stats** — bitrate, FPS, dropped frames reported live in the bottom bar (req 5)
 7. ☐ **One-click go live + private-only enforcement** — Go Live always creates/updates the broadcast with `privacyStatus = "private"` + PRIVATE badge (req 8, test-verifiable)
 
@@ -423,8 +423,57 @@ lifecycle/forwarding/failure against fakes, meter RMS/smoothing/reset, `WaveToFl
 extensible/truncation) — **139 passing**.
 
 **Deferred (later ship steps):** wiring the desktop-capture samples into the encoder's AAC mix (replaces
-the `-f lavfi -i anullsrc` placeholder; ship step 5 owns the encoder construction), WASAPI capture while
-not live, and any audio UI beyond the existing mic controls.
+the `-f lavfi -i anullsrc` placeholder; the encoder construction itself shipped in ship step 5), WASAPI
+capture while not live, and any audio UI beyond the existing mic controls.
+
+#### Ship step 5 — Frame-pipeline wiring (the encoder gets a frame source)
+
+**Goal:** the chain `CameraManager`/`ScreenCaptureManager` → compositor resolver → encoder, driven while
+live by a paced frame pump: snapshot the active scene → resolve each element to its latest frame →
+composite into the tier's output frame → pace into the encoder's stdin at the tier's FPS.
+
+**Decisions (locked via user Q&A, 2026-08-12):**
+1. **Video pipeline first** — the `-f lavfi -i anullsrc` silent track stays; mixing the loopback/mic
+   WASAPI samples into the encoder's AAC track is its own later step.
+2. **RTMP URL via a provider seam** — `MainViewModel._rtmpUrlProvider` is a `Func<string?>` returning
+   null today (the reusable stream's ingest URL lands with TASK 5); when it yields null the pump logs
+   and skips the encoder entirely, so go-live runs the existing visual flow without pushing.
+
+**Design:**
+1. `Services/Encoder/FramePump.cs` — the frame producer. All collaborators constructor-injected seams
+   (`Func<Scene?>`, `Func<SceneElement, VideoFrame?>` resolver, `Func<CompositorOptions>`,
+   `Func<EncoderOptions?>`, `Func<IFfmpegEncoder>`, `Action<string>` log, injectable pacing delay) so it
+   stays free of WPF and of the capture managers and is hermetic in tests. `StartAsync` never throws
+   (failures log + surface via `Failed` — the VM fires-and-forgets from the sync command handler);
+   loop = snapshot → render → `SubmitFrameAsync`, paced at `1/options.Fps` (default `Task.Delay`; tests
+   inject `Task.Yield`). `StopAsync` stops the encoder (closes stdin) BEFORE awaiting the loop — closing
+   stdin unblocks a write stuck on pipe backpressure, so stop can't deadlock on the pump. `ProcessFailed`
+   self-stops the pump. `HealthUpdated` forwards the encoder's stats (ship step 6 binds the bottom bar).
+2. `ScreenCaptureManager.GetLatestFrame(key)` — mirrors `CameraManager.GetLatestFrame(deviceId)`; the
+   backdrop's live frame for the compositor.
+3. `MainViewModel` — owns the resolver (`WebcamSceneConfig` → `GetLatestFrame(WebcamId)`;
+   `Source.IsLiveCapture` → `GetLatestFrame(CaptureKey)`; image/background → `StaticPixelCache.Get(AssetId)`),
+   builds `CompositorOptions` from the tier + `OutputRect*` (doubles rounded to ints — the vertical
+   607.5 half-pixel crop rounds to a perfectly-centered 608), builds `EncoderOptions` from the tier when
+   the URL provider returns one, constructs the real `FfmpegEncoder(new FfmpegLocator())`, starts the
+   pump on go-live, stops it on end-stream, disposes in `Shutdown`, and flips `StreamStatus.Error` when
+   the pump fails while live (minimal — detailed health surfacing is ship step 6).
+
+**Test plan (Good Dog Rule — ONE integration test):** `FramePumpTests.Start_CompositesScene_FeedsEncoder_StopsCleanly`
+drives the full lifecycle against fakes — real `SceneCompositor` + real `FramePump`, fake `IFfmpegEncoder`
+— asserting the composited red backdrop frame actually reaches the encoder at the tier size and that stop
+tears everything down. Units: no-URL start skips the encoder, re-entrant start/stop no-ops, encoder
+start-failure raises `Failed` + disposes, `ProcessFailed` self-stops the pump, `HealthUpdated` forwards.
+`ScreenCaptureManagerTests.GetLatestFrame_ReturnsLatestPump_UntilReleased` pins the new accessor.
+
+**Out of scope (later ship steps):** the loopback/mic → AAC mix (replaces `anullsrc`), health stats in the
+bottom bar (ship step 6), scene-switching transitions, and any flash-frame wiring.
+
+**Built (2026-08-12):** `FramePump` shipped in `Services/Encoder/`, `ScreenCaptureManager.GetLatestFrame`
+added, `MainViewModel` wired end-to-end (resolver + both option builders + pump lifecycle), `FramePumpTests`
+(7) + `GetLatestFrame` test (1) added — build **0 warnings**, **147 tests passing**. Known consideration:
+the pump reads the active scene on a background thread while the UI can still edit it; a concurrent-mutation
+exception is contained (logged + `Failed` + pump stops) rather than crashing.
 
 ---
 

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;

ai.md

@@ -91,7 +91,7 @@ C# / WPF (.NET 8) following MVVM:
 |------|------|
 | `Models/` | Plain data types — Scene, Source (incl. `ClipShape`, `IsMirrored`, `VideoImageSource`), QualityOption, StreamConfig, StreamHealth, YouTubeChannel, ChatMessage, **Socials (`SocialService` enum + `SocialEntry`/`SocialsConfig` + `SocialServiceIcons`) — the social bar** |
 | `ViewModels/` | MainViewModel — exposes collections + commands for the UI; GoLiveViewModel, ReuseImageViewModel, CameraPickerViewModel, **SocialsDialogViewModel** |
-| `Services/` | YouTube OAuth2, stream/broadcast management, live chat polling, LayoutStore (SQLite), **SocialValidator (`ISocialValidator` seam + `HttpSocialValidator` default)**, **webcam: `VideoFrame` seam + `CameraDeviceInfo`/`ICameraEnumerator`/`ICameraFrameSource` interfaces + `MediaCaptureCameraEnumerator`/`MediaCaptureFrameSource` (WinRT) + `CameraManager`**, **screen capture: `IFullScreenDetector`/`Win32FullScreenDetector` + `IScreenCaptureSource`/`ScreenCaptureFrameSource` (WinRT GraphicsCapture) + `ScreenCaptureManager` + `ScreenCaptureSourceFactory` + `Direct3D11Helper`/`CaptureInterop` (COM bridges)**, **audio: `IAudioSource` seam + `WasapiLoopbackAudioSource`/`WasapiMicAudioSource` (NAudio WASAPI) + `AudioMixer` + pure `AudioLevelMeter`/`WaveToFloat` (see "Live audio capture")** |
+| `Services/` | YouTube OAuth2, stream/broadcast management, live chat polling, LayoutStore (SQLite), **SocialValidator (`ISocialValidator` seam + `HttpSocialValidator` default)**, **webcam: `VideoFrame` seam + `CameraDeviceInfo`/`ICameraEnumerator`/`ICameraFrameSource` interfaces + `MediaCaptureCameraEnumerator`/`MediaCaptureFrameSource` (WinRT) + `CameraManager`**, **screen capture: `IFullScreenDetector`/`Win32FullScreenDetector` + `IScreenCaptureSource`/`ScreenCaptureFrameSource` (WinRT GraphicsCapture) + `ScreenCaptureManager` + `ScreenCaptureSourceFactory` + `Direct3D11Helper`/`CaptureInterop` (COM bridges)**, **compositor: `SceneCompositor` + `CompositorOptions` + pure `StretchMath` + `StaticPixelCache` (see "Scene compositor")**, **audio: `IAudioSource` seam + `WasapiLoopbackAudioSource`/`WasapiMicAudioSource` (NAudio WASAPI) + `AudioMixer` + pure `AudioLevelMeter`/`WaveToFloat` (see "Live audio capture")**, **encoder: `IFfmpegEncoder`/`FfmpegEncoder` + `IEncoderProcess`/`FfmpegEncoderProcess` + `IFfmpegLocator`/`FfmpegLocator` + pure `FfmpegArgs`/`FfmpegProgressParser`/`FfmpegEncoderPicker` + the `FramePump` frame producer (see "Live encoder" + "Live frame pipeline")** |
 | `Helpers/` | ViewModelBase (INotifyPropertyChanged), RelayCommand, ImageCache, AppLog (file logger), FocusPreservingListBox, OAuthCredentials, **TokenStore (DPAPI session persistence)**, visibility converters |
 | `Themes/` | `Controls.xaml` — the single dark-theme source, merged once in `App.xaml` (see `Themes/index.md`) |
 | `MainWindow.xaml` | Dark theme; layout: top bar (controls), center (preview), left (scenes/sources), right (chat), bottom (health) |
@@ -352,7 +352,8 @@ integration test fakes the whole subprocess (probe + encoder) with a Channel-bac
 **Encoder choice is probed from the binary's `-encoders` listing** (`FfmpegEncoderPicker`, pure):
 NVENC → QSV → AMF → OpenH264 fallback, **never libx264** (GPL; see Licensing). `EncoderOptions.VideoEncoder`
 forces one and skips the probe. `EncoderOptions` also carries W×H/FPS/bitrate from the quality tier and
-`GopSize` = FPS×4. Not yet constructed by the app — the frame-pipeline wiring (ship step 5) owns it.
+`GopSize` = FPS×4. Constructed by `MainViewModel` since ship step 5 (`new FfmpegEncoder(new FfmpegLocator())`),
+driven by the `FramePump` below.
 
 ### Live audio capture (TASK 4 ship step 4 — shipped 2026-08-12, plan in TASKS.md)
 
@@ -371,16 +372,44 @@ timers).
 - **`AudioMixer`** owns both sources; `Start`/`Stop` follow go-live (`MainViewModel.BeginGoLive` success
   → `_audioMixer.Start()`, `StopStream` → `Stop()`). Mic samples feed a pure **`AudioLevelMeter`** (RMS
   with 0.2 exponential smoothing) → `MicLevelChanged` → marshalled to the UI thread → `AudioLevel`.
-  Desktop samples are currently **dropped** — the future encoder's AAC mix (ship step 5) consumes them,
-  replacing the `-f lavfi -i anullsrc` placeholder. Failures log via `AppLog`; a mic failure zeroes the
+  Desktop samples are currently **dropped** — a later step's AAC mix consumes them, replacing the
+  `-f lavfi -i anullsrc` placeholder (the encoder construction itself shipped in ship step 5). Failures log via `AppLog`; a mic failure zeroes the
   meter, a loopback failure never kills the mic.
 - **`WaveToFloat`** (pure, shared): WASAPI mix formats → interleaved float — IEEE float 32-bit direct,
   PCM 16-bit normalized to -1..1, `WaveFormatExtensible` with the IEEE-float subformat GUID
   (`NAudio.Dmo.AudioMediaSubtypes.MEDIASUBTYPE_IEEE_FLOAT`), trailing partial samples ignored.
 - `FfmpegEncoder.cs:139` pre-existing CS8602 fixed (`process!`) — build **0 warnings**; **139 passing**.
 
-**Deferred:** loopback→encoder mix wiring and the encoder construction (ship step 5); capture while not
-live is deliberately not shipped (privacy indicator otherwise).
+**Deferred:** the loopback→encoder AAC mix wiring (a later step — the encoder construction + frame
+pipeline shipped in ship step 5); capture while not live is deliberately not shipped (privacy indicator
+otherwise).
+
+### Live frame pipeline (TASK 4 ship step 5 — shipped 2026-08-12, plan in TASKS.md)
+
+The **`FramePump`** (`Services/Encoder/`) is the live frame producer: while live it snapshots the active
+scene each tick, resolves every element to its latest frame, composites it into the tier's output frame,
+and paces frames into the encoder at the tier's FPS. **Pattern — everything is a constructor-injected
+seam:** `Func<Scene?>`, `Func<SceneElement, VideoFrame?>` resolver, `Func<CompositorOptions>`,
+`Func<EncoderOptions?>`, `Func<IFfmpegEncoder>`, `Action<string>` log, and an injectable pacing delay
+(default `Task.Delay`; tests inject `Task.Yield`). The pump is free of WPF and of the capture managers.
+
+- **`StartAsync` never throws** — the VM fires-and-forgets it from the sync command handler; failures log
+  + surface via the `Failed` event. `EncoderOptions == null` means "no RTMP URL": the pump logs and skips
+  the encoder entirely. `MainViewModel._rtmpUrlProvider` is that seam — a `Func<string?>` returning null
+  until TASK 5 supplies the reusable stream's ingest URL, so go-live runs the current visual flow.
+- **Stop ordering matters:** `StopAsync` stops the encoder (closes stdin → EOF → ffmpeg finalizes+exits)
+  **before** awaiting the loop, because closing stdin unblocks a write stuck on pipe backpressure — the
+  reverse order would deadlock. `ProcessFailed` self-stops the pump. `HealthUpdated` is forwarded
+  (ship step 6 binds it to the bottom bar); `Failed` while live flips `StreamStatus.Error` (minimal).
+- **`MainViewModel` owns the resolver** (`ResolveOutputFrame`): `WebcamSceneConfig` →
+  `CameraManager.GetLatestFrame(WebcamId)`, `Source { IsLiveCapture, CaptureKey }` →
+  `ScreenCaptureManager.GetLatestFrame(CaptureKey)` (the new accessor mirroring `CameraManager`), image/
+  background → `StaticPixelCache.Get(AssetId)`. `BuildCompositorOptions` rounds the VM's `OutputRect*`
+  doubles to ints — the vertical 607.5 half-pixel crop rounds to a perfectly-centered **608** (`Math.Round`,
+  ToEven); `BuildEncoderOptions` fills W×H/FPS/bitrate from the tier once the URL provider yields one.
+- Known consideration: the pump reads the active scene on a background thread while the UI can still edit
+  it; a concurrent-mutation exception is contained (logged + `Failed` + the pump stops) rather than
+  crashing. The background thread + video pipeline is the new reality since this step.
 
 ### Social bar (TASK 14 — shipped 2026-08-12, plan in TASKS.md)
 

ytLive.Tests/FramePumpTests.cs

@@ -0,0 +1,221 @@
+using Xunit;
+using ytLive.Models;
+using ytLive.Services;
+using ytLive.Services.Compositor;
+using ytLive.Services.Encoder;
+
+namespace ytLive.Tests;
+
+/// <summary>
+/// The live frame producer (TASK 4 ship step 5): composites the active scene at
+/// the tier's FPS and paces frames into the encoder. The integration test drives
+/// the full lifecycle against fakes — real SceneCompositor + real FramePump, fake
+/// IFfmpegEncoder — proving the composite frame actually reaches the encoder and
+/// that stop tears the pump down cleanly. The units pin the failure edges: the
+/// no-URL skip (the TASK 5 seam), re-entrancy, and encoder death.
+/// </summary>
+public class FramePumpTests
+{
+    private sealed class FakeEncoder : IFfmpegEncoder
+    {
+        public readonly List<VideoFrame> Frames = new();
+        public int StartCount;
+        public int StopCount;
+        public bool Disposed;
+        public EncoderOptions? LastOptions;
+        public Exception? StartError;
+        public TaskCompletionSource FrameArrived = new(TaskCreationOptions.RunContinuationsAsynchronously);
+
+        public event EventHandler<StreamHealth>? HealthUpdated;
+        public event EventHandler<string>? ProcessFailed;
+
+        public Task StartAsync(EncoderOptions options, CancellationToken cancellationToken = default)
+        {
+            StartCount++;
+            LastOptions = options;
+            if (StartError != null) throw StartError;
+            return Task.CompletedTask;
+        }
+
+        public Task SubmitFrameAsync(VideoFrame frame, CancellationToken cancellationToken = default)
+        {
+            Frames.Add(frame);
+            FrameArrived.TrySetResult();
+            return Task.CompletedTask;
+        }
+
+        public Task StopAsync(CancellationToken cancellationToken = default)
+        {
+            StopCount++;
+            return Task.CompletedTask;
+        }
+
+        public void Dispose() => Disposed = true;
+
+        public void RaiseProcessFailed(string message) => ProcessFailed?.Invoke(this, message);
+
+        public void RaiseHealth(StreamHealth health) => HealthUpdated?.Invoke(this, health);
+    }
+
+    private static Scene BackdropScene()
+    {
+        var scene = new Scene { Name = "Live" };
+        scene.Elements.Add(new Source { Type = SourceType.DisplayCapture, IsBackdrop = true, CaptureKey = "monitor:0" });
+        return scene;
+    }
+
+    private static FramePump NewPump(FakeEncoder encoder, Func<EncoderOptions?>? options = null,
+        Func<Scene?>? scene = null, Func<SceneElement, VideoFrame?>? resolve = null,
+        List<string>? log = null)
+    {
+        return new FramePump(
+            sceneProvider: scene ?? (() => BackdropScene()),
+            frameResolver: resolve ?? (_ => null),
+            compositorOptions: () => new CompositorOptions
+            {
+                SourceRectX = 0, SourceRectY = 0, SourceRectWidth = 64, SourceRectHeight = 48,
+                OutputWidth = 64, OutputHeight = 48,
+            },
+            encoderOptions: options ?? (() => new EncoderOptions
+            {
+                RtmpUrl = "rtmp://a.rtmp.youtube.com/live2/abc",
+                Width = 64, Height = 48, Fps = 60,
+            }),
+            encoderFactory: () => encoder,
+            log: log != null ? m => log.Add(m) : null,
+            pacingDelay: async (_, _) => await Task.Yield()); // deterministic: no real waits
+    }
+
+    private static void AssertColor(VideoFrame frame, int x, int y, byte r, byte g, byte b)
+    {
+        var i = (y * frame.Width + x) * 4;
+        var br = frame.BgraPixels[i + 2];
+        var bg = frame.BgraPixels[i + 1];
+        var bb = frame.BgraPixels[i];
+        Assert.True(
+            Math.Abs(br - r) <= 2 && Math.Abs(bg - g) <= 2 && Math.Abs(bb - b) <= 2,
+            $"pixel ({x},{y}): expected rgb({r},{g},{b}), got rgb({br},{bg},{bb})");
+    }
+
+    [Fact]
+    public async Task Start_CompositesScene_FeedsEncoder_StopsCleanly()
+    {
+        var red = SceneCompositorTests.Solid(64, 48, 255, 0, 0);
+        var encoder = new FakeEncoder();
+        using var pump = NewPump(encoder,
+            resolve: e => e is Source { IsBackdrop: true } ? red : null);
+
+        await pump.StartAsync();
+        Assert.True(pump.IsRunning);
+        Assert.Equal(1, encoder.StartCount);
+
+        await encoder.FrameArrived.Task.WaitAsync(TimeSpan.FromSeconds(5));
+        Assert.NotEmpty(encoder.Frames);
+        var frame = encoder.Frames[0];
+        Assert.Equal(64, frame.Width);
+        Assert.Equal(48, frame.Height);
+        AssertColor(frame, 0, 0, 255, 0, 0); // the backdrop really was composited in
+
+        await pump.StopAsync();
+        Assert.False(pump.IsRunning);
+        Assert.Equal(1, encoder.StopCount);
+        Assert.True(encoder.Disposed);
+    }
+
+    [Fact]
+    public async Task Start_WithoutRtmpUrl_SkipsEncoder()
+    {
+        var encoder = new FakeEncoder();
+        var log = new List<string>();
+        using var pump = NewPump(encoder, options: () => null, log: log);
+
+        await pump.StartAsync();
+
+        Assert.False(pump.IsRunning);
+        Assert.Equal(0, encoder.StartCount);
+        Assert.Contains(log, m => m.Contains("RTMP"));
+
+        await pump.StopAsync(); // no-op after a skipped start
+        Assert.Equal(0, encoder.StopCount);
+    }
+
+    [Fact]
+    public async Task Start_WhileRunning_IsNoop()
+    {
+        var encoder = new FakeEncoder();
+        using var pump = NewPump(encoder);
+
+        await pump.StartAsync();
+        await pump.StartAsync();
+
+        Assert.Equal(1, encoder.StartCount);
+    }
+
+    [Fact]
+    public async Task Stop_WithoutStart_IsNoop()
+    {
+        var encoder = new FakeEncoder();
+        using var pump = NewPump(encoder);
+
+        await pump.StopAsync();
+
+        Assert.Equal(0, encoder.StopCount);
+        Assert.False(pump.IsRunning);
+    }
+
+    [Fact]
+    public async Task Start_EncoderThrows_RaisesFailed_AndDisposes()
+    {
+        var encoder = new FakeEncoder { StartError = new InvalidOperationException("access denied") };
+        var failed = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
+        using var pump = NewPump(encoder);
+        pump.Failed += (_, m) => failed.TrySetResult(m);
+
+        await pump.StartAsync();
+
+        Assert.False(pump.IsRunning);
+        var message = await failed.Task.WaitAsync(TimeSpan.FromSeconds(5));
+        Assert.Contains("access denied", message);
+        Assert.True(encoder.Disposed);
+    }
+
+    [Fact]
+    public async Task ProcessDeath_StopsPump_AndRaisesFailed()
+    {
+        var encoder = new FakeEncoder();
+        var failed = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
+        using var pump = NewPump(encoder);
+        pump.Failed += (_, m) => failed.TrySetResult(m);
+
+        await pump.StartAsync();
+        encoder.RaiseProcessFailed("FFmpeg exited with code 1");
+
+        var message = await failed.Task.WaitAsync(TimeSpan.FromSeconds(5));
+        Assert.Contains("1", message);
+
+        // The pump self-stops (fire-and-forget); poll the definitive teardown
+        // marker — the encoder's disposal — rather than the IsRunning flag, which
+        // StopAsync clears before the loop has fully drained.
+        var deadline = DateTime.UtcNow.AddSeconds(5);
+        while (!encoder.Disposed && DateTime.UtcNow < deadline)
+            await Task.Delay(10);
+        Assert.True(encoder.Disposed);
+        Assert.False(pump.IsRunning);
+    }
+
+    [Fact]
+    public async Task HealthUpdated_ForwardsEncoderHealth()
+    {
+        var encoder = new FakeEncoder();
+        var health = new TaskCompletionSource<StreamHealth>(TaskCreationOptions.RunContinuationsAsynchronously);
+        using var pump = NewPump(encoder);
+        pump.HealthUpdated += (_, h) => health.TrySetResult(h);
+
+        await pump.StartAsync();
+        encoder.RaiseHealth(new StreamHealth { Status = StreamStatus.Streaming, FPS = 59.9 });
+
+        var h = await health.Task.WaitAsync(TimeSpan.FromSeconds(5));
+        Assert.Equal(StreamStatus.Streaming, h.Status);
+        Assert.Equal(59.9, h.FPS, 1);
+    }
+}

ytLive.Tests/ScreenCaptureManagerTests.cs

@@ -145,6 +145,28 @@ public class ScreenCaptureManagerTests
         Assert.False(await manager.AcquireAsync(" "));
     }
 
+    [Fact]
+    public async Task GetLatestFrame_ReturnsLatestPump_UntilReleased()
+    {
+        FakeScreenSource? captured = null;
+        var manager = new ScreenCaptureManager(key => captured = new FakeScreenSource(key));
+
+        Assert.Null(manager.GetLatestFrame("monitor:0"));
+
+        Assert.True(await manager.AcquireAsync("monitor:0"));
+        Assert.Null(manager.GetLatestFrame("monitor:0")); // nothing pumped yet
+
+        var first = new VideoFrame(2, 2, Pixels(1, 0, 0, 255, 2, 0, 0, 255, 3, 0, 0, 255, 4, 0, 0, 255));
+        var second = new VideoFrame(2, 2, Pixels(5, 0, 0, 255, 6, 0, 0, 255, 7, 0, 0, 255, 8, 0, 0, 255));
+        captured!.Pump(first);
+        captured.Pump(second);
+
+        Assert.Same(second, manager.GetLatestFrame("monitor:0"));
+
+        await manager.ReleaseAsync("monitor:0");
+        Assert.Null(manager.GetLatestFrame("monitor:0"));
+    }
+
     // The one integration test for this branch: one target creates one shared
     // WriteableBitmap, published once, and back-to-back frames coalesce to the
     // latest (a single pending UI copy per session).