TASK 4 ship step 4: WASAPI audio capture — NAudio loopback + mic behind an IAudioSource seam, AudioMixer driving AudioLevel while live, pure level meter + WaveToFloat, NAudio.Wasapi 2.2.1 (MIT, notices item 9) — 139 tests passing, 0 warnings

HANDOFF.md

@@ -7,69 +7,53 @@
 
 ## Session state (last updated: 2026-08-12)
 
-- **Branch:** `main` — the social bar v2 push is **committed + pushed** (`9873eed`,
+- **Branch:** `main`. TASK 4 ship step 4 (WASAPI audio capture) is **built and
-  18 files, +1878/−321, 112 tests passing, 0 warnings). Working tree is **dirty
+  tested** but **NOT committed** — the working tree is dirty with the audio
-  with the post-push docs backfill only** (ai.md, README.md, TASKS.md schema
+  layer (6 new files in `Services/Audio/` + `ytLive.Tests/AudioMixerTests.cs`,
-  section, THIRD-PARTY-NOTICES.txt) — ready to commit when the user says so.
+  the `NAudio.Wasapi` 2.2.1 package reference, the THIRD-PARTY-NOTICES entry,
-- **Finished this session (round 3):** user's live-test report said the mastodon
+  the `MainViewModel` wiring, the `FfmpegEncoder.cs:139` CS8602 fix) and its
-  icon still didn't show for `@gramps@llamachile.tube`. Root cause: the identity
+  memory updates (TASKS.md, ai.md, Services/index.md, HANDOFF.md). Ready to
-  domain `llamachile.tube` is YunoHost-SSO-gated — `/.well-known/nodeinfo`,
+  commit when the user says so.
-  `/@gramps`, and webfinger all answer with the SSO login page, so nodeinfo
+- **Finished this session:** TASK 4 ship step 4 — the live audio capture layer:
-  returned nothing and the icon fell back to the honeycomb glyph. The real
+  `IAudioSource`/`AudioSample` seam, `WasapiLoopbackAudioSource`
-  instance lives at `mastodon.llamachile.tube`, and only the bare root
+  (`WasapiLoopbackCapture` on the default render device), `WasapiMicAudioSource`
-  `https://llamachile.tube/` 302s to it ("default app" redirect). Fix:
+  (`WasapiCapture`, NAudio device resolved by `FriendlyName` matching
-  `HttpSocialValidator.TryFetchFediverseSoftwareAsync` now, when nodeinfo on the
+  `MicSourceName` via a re-read `Func<string?>` provider, default-endpoint
-  identity domain fails, follows the root redirect (`ResolveInstanceHostAsync`,
+  fallback), `AudioMixer` (owns both sources, starts/stops with go-live, feeds
-  reads `resp.RequestMessage.RequestUri.Host`) and re-runs the nodeinfo lookup
+  the pure `AudioLevelMeter` → `MicLevelChanged`), `WaveToFloat` (IEEE-float /
-  on the resolved host. New test `FediverseHandle_RootRedirectToSubdomain_ResolvesSoftware`.
+  PCM16 / extensible). `MainViewModel` constructs the mixer, `BeginGoLive`
-  Build: **0 warnings**. Tests: **112 passing**.
+  success → `Start()`, `StopStream` → `Stop()`, `MicLevelChanged` marshalled to
-- **What landed (all rounds this session):**
+  the UI thread → `AudioLevel`. Loopback samples are currently dropped (the
-  1. **Fediverse icon resolution** — `DetectService` maps `@user@domain` to the
+  encoder's AAC mix, ship step 5, consumes them). Build: **0 warnings** (a
-     new `SocialService.Fediverse` (was `Link`/chain icon). On validate,
+  pre-existing CS8602 in `FfmpegEncoder.cs:139` surfaced during the rebuild and
-     `HttpSocialValidator` best-effort GETs `https://{domain}/.well-known/nodeinfo`,
+  was fixed with `process!`). Tests: **139 passing** (was 122; +17 new audio).
-     follows the first nodeinfo `links[].href`, reads `software.name`, and returns
-     it in `SocialLookupResult.FediverseSoftware`. `SocialEntry`/`SocialSlotViewModel`
-     carry `FediverseSoftware`; `SocialServiceIcons.LogoDataForFediverse(software)`
-     maps it to a bundled logo (mastodon/peertube/pixelfed/misskey/lemmy/pleroma/
-     firefish — Simple Icons CC0), falling back to the `FediverseIconData`
-     honeycomb glyph for unknown software (GoToSocial/Sharkey/Akkoma aren't in
-     Simple Icons). Nodeinfo failure still validates — the glyph falls back.
-  2. **Redirect resolution (round 3)** — identity domains that 302 their root
-     to the real instance (YunoHost default-app subdomains) resolve software via
-     the root redirect when identity-domain nodeinfo is SSO-blocked.
-  3. **Persistence** — new `SocialEntry.Software TEXT` column via
-     `MigrateSocialEntryTable()` (column-presence pattern, same as the others);
-     saved/loaded alongside Service/Handle/ProfileUrl.
-  4. **Icon colors** — `IconButton` style gains `Foreground="#d0d0d0"`
-     (`Themes/Controls.xaml`); the dialog's trash button overrides
-     `Foreground="#e94560"` (`SocialsDialog.xaml`). All other `IconButton`
-     usages are `Path` content with explicit `Fill`, so unaffected.
 - **Landmines:**
-  - `LayoutStore.Socials` is only populated by `Load()` — tests must call
+  - `WaveFormatExtensible.SubFormat` is a **`Guid`** in NAudio 2.x, not a
-    `store.Load()` before asserting it.
+    `WaveFormatEncoding` — compare it to
-  - `DetectService("justaname")` → **Website** with empty handle; only
+    `NAudio.Dmo.AudioMediaSubtypes.MEDIASUBTYPE_IEEE_FLOAT` (the IEEE-float
-    unparseable input or `@user@domain` yields Link/Fediverse.
+    subtype constant; it lives in the `NAudio.Dmo` namespace, not CoreAudioApi).
-  - Dialog sign-in provider is `Func<Task<YouTubeChannel?>>`; test fakes must
+  - Use the **`NAudio.Wasapi` 2.2.1 feature package**, not the `NAudio`
-    return `Task.FromResult` (sync-completed) so the fire-and-forget command
+    meta-package — the wasapi types come from that package (`WasapiCapture` in
-    settles before the next assert.
+    `NAudio.CoreAudioApi`, `WasapiLoopbackCapture` in `NAudio.Wave`); `NAudio.Core`
-  - `SocialBarBottomTop = 1040` literal lives in `MainWindow.xaml.cs` (the VM's
+    comes in transitively.
-    `MasterFrameHeight` is private).
+  - The audio meter is an exponential smoother (0.2 factor) — a single pushed
-  - `Cancel_AbortsInFlightValidation_WithoutMutatingSlot` relies on the
+    sample only moves 20% toward its RMS. Tests must push repeatedly before
-    BlockingValidator's gate completing synchronously (no
+    asserting a converged level.
-    `RunContinuationsAsynchronously`) — the assertions run after
+  - Tests never instantiate `MainViewModel` directly except the round-clip
-    `Gate.TrySetResult` returns because the awaited continuation executes inline.
+    integration test (a real `MainWindow`), which never goes live — so the mixer
-  - Nodeinfo cancellation test cancels mid-lookup via a counting stub; the
+    is constructed but never started there; NAudio types are only constructed,
-    post-fetch `ct.IsCancellationRequested` check is what reports `Canceled`.
+    never touching devices. Keep it that way.
-  - Round-3 redirect fallback fires only when identity-domain nodeinfo fails;
+  - Mic device resolution must re-read `MicSourceName` at each `Start` (the app
-    the root follow happens automatically (HttpClient default auto-redirect),
+    persists only the DisplayName, not a device ID).
-    and `RequestMessage.RequestUri.Host` is read from the final response.
+  - Windows-only: all capture runs only while live (privacy indicator otherwise).
-- **Next step:** TASK 4 ship step 3 — the encoder + RTMP push (FFmpeg subprocess:
+
-  frames via stdin, stderr health parsing, FLV mux + push to the cached reusable
+- **Next step:** TASK 4 ship step 5 — the frame-pipeline wiring
-  stream's ingestion URL). Nothing else queued — do not expand the task queue on
+  (`CameraManager`/`ScreenCaptureManager` → compositor resolver → encoder
-  your own.
+  construction, plus the loopback → encoder AAC mix). 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`);
-  layout DB `%APPDATA%\ytLlive\ytLlive.db` (schema v8; the new `SocialEntry.Software`
+  layout DB `%APPDATA%\ytLlive\ytLlive.db` (schema v8; `SocialEntry.Software`
   column is a column-presence migration like the others, no version bump); OAuth callback
   `http://localhost:8765/oauth2/callback`; crash log `%APPDATA%\ytLlive\startup.log`.

Services/Audio/AudioLevelMeter.cs

@@ -0,0 +1,35 @@
+namespace ytLive.Services.Audio;
+
+/// <summary>
+/// Computes the smoothed mic level (0..1) from captured samples. Pure —
+/// unit-tested; the <see cref="AudioMixer"/> only feeds it and forwards the
+/// result. RMS-based so it tracks perceived loudness, smoothed so the meter
+/// does not flicker.
+/// </summary>
+public sealed class AudioLevelMeter
+{
+    private const float Smoothing = 0.2f;
+    private float _level;
+
+    public float Level => _level;
+
+    public float Push(AudioSample sample)
+    {
+        if (sample.Samples.Length == 0)
+            return _level;
+
+        double sumSquares = 0;
+        var count = 0;
+        foreach (var value in sample.Samples)
+        {
+            sumSquares += value * value;
+            count++;
+        }
+
+        var rms = (float)Math.Sqrt(sumSquares / count);
+        _level = _level * (1 - Smoothing) + rms * Smoothing;
+        return _level;
+    }
+
+    public void Reset() => _level = 0;
+}

Services/Audio/AudioMixer.cs

@@ -0,0 +1,92 @@
+using ytLive.Services;
+
+namespace ytLive.Services.Audio;
+
+/// <summary>
+/// Owns the mic + desktop/game capture sources (TASK 4 ship step 4) and drives
+/// the live mic meter. Runs only while live: started when go-live succeeds,
+/// stopped on end-stream. Mic samples are level-metered and forwarded; loopback
+/// samples are currently dropped (consumed by the encoder mix in a later step).
+/// </summary>
+public sealed class AudioMixer : IDisposable
+{
+    private readonly IAudioSource _mic;
+    private readonly IAudioSource _loopback;
+    private readonly AudioLevelMeter _meter;
+    private readonly Action<string>? _log;
+    private bool _started;
+
+    public AudioMixer(IAudioSource mic, IAudioSource loopback, Action<string>? log = null)
+    {
+        _mic = mic;
+        _loopback = loopback;
+        _meter = new AudioLevelMeter();
+        _log = log;
+
+        _mic.SampleReady += OnMicSample;
+        _loopback.SampleReady += OnLoopbackSample;
+        _mic.Failed += OnMicFailed;
+        _loopback.Failed += OnLoopbackFailed;
+    }
+
+    /// <summary>Current smoothed mic level (0..1).</summary>
+    public float MicLevel => _meter.Level;
+
+    /// <summary>Raised whenever the smoothed mic level changes.</summary>
+    public event Action<float>? MicLevelChanged;
+
+    public void Start()
+    {
+        if (_started)
+            return;
+
+        _started = true;
+        _meter.Reset();
+        _loopback.Start();
+        _mic.Start();
+    }
+
+    public void Stop()
+    {
+        if (!_started)
+            return;
+
+        _started = false;
+        _mic.Stop();
+        _loopback.Stop();
+        _meter.Reset();
+        MicLevelChanged?.Invoke(0);
+    }
+
+    public void Dispose()
+    {
+        Stop();
+        _mic.SampleReady -= OnMicSample;
+        _loopback.SampleReady -= OnLoopbackSample;
+        _mic.Failed -= OnMicFailed;
+        _loopback.Failed -= OnLoopbackFailed;
+        _mic.Dispose();
+        _loopback.Dispose();
+    }
+
+    private void OnMicSample(AudioSample sample)
+    {
+        MicLevelChanged?.Invoke(_meter.Push(sample));
+    }
+
+    private void OnLoopbackSample(AudioSample sample)
+    {
+        // Desktop/game audio: captured for the future encoder mix; no UI yet.
+    }
+
+    private void OnMicFailed(Exception ex)
+    {
+        _log?.Invoke($"Mic capture failed: {ex.Message}");
+        MicLevelChanged?.Invoke(0);
+    }
+
+    private void OnLoopbackFailed(Exception ex)
+    {
+        _log?.Invoke($"Desktop audio capture failed: {ex.Message}");
+    }
+}

Services/Audio/AudioSample.cs

@@ -0,0 +1,20 @@
+namespace ytLive.Services.Audio;
+
+/// <summary>
+/// A chunk of interleaved PCM float samples (-1..1) with its format. This is
+/// the unit every <see cref="IAudioSource"/> produces and the
+/// <see cref="AudioMixer"/> consumes (TASK 4 ship step 4).
+/// </summary>
+public sealed class AudioSample
+{
+    public float[] Samples { get; }
+    public int SampleRate { get; }
+    public int Channels { get; }
+
+    public AudioSample(float[] samples, int sampleRate, int channels)
+    {
+        Samples = samples;
+        SampleRate = sampleRate;
+        Channels = channels;
+    }
+}

Services/Audio/IAudioSource.cs

@@ -0,0 +1,22 @@
+namespace ytLive.Services.Audio;
+
+/// <summary>
+/// A live audio capture source (TASK 4 ship step 4 seam): produces PCM float
+/// chunks, runs only while live. The default implementations wrap NAudio's
+/// WASAPI capture (mic) / loopback (desktop/game); the mixer and the tests
+/// consume this interface, never NAudio directly.
+/// </summary>
+public interface IAudioSource : IDisposable
+{
+    /// <summary>Starts capturing. Safe to call only once per Stop.</summary>
+    void Start();
+
+    /// <summary>Stops capturing; a later Start begins a fresh session.</summary>
+    void Stop();
+
+    /// <summary>Raises each captured chunk (interleaved PCM float, -1..1).</summary>
+    event Action<AudioSample>? SampleReady;
+
+    /// <summary>Raises when capture dies or fails to start (e.g. no device).</summary>
+    event Action<Exception>? Failed;
+}

Services/Audio/WasapiLoopbackAudioSource.cs

@@ -0,0 +1,69 @@
+using NAudio.Wave;
+
+namespace ytLive.Services.Audio;
+
+/// <summary>
+/// Captures the user's desktop/game audio (TASK 4 ship step 4) via WASAPI
+/// loopback on the default render device. Starts/stops with go-live only.
+/// </summary>
+public sealed class WasapiLoopbackAudioSource : IAudioSource
+{
+    private WasapiLoopbackCapture? _capture;
+
+    public event Action<AudioSample>? SampleReady;
+    public event Action<Exception>? Failed;
+
+    public void Start()
+    {
+        if (_capture != null)
+            throw new InvalidOperationException("Already started.");
+
+        try
+        {
+            _capture = new WasapiLoopbackCapture();
+            _capture.DataAvailable += OnDataAvailable;
+            _capture.RecordingStopped += OnRecordingStopped;
+            _capture.StartRecording();
+        }
+        catch (Exception ex)
+        {
+            Stop();
+            Failed?.Invoke(ex);
+        }
+    }
+
+    public void Stop()
+    {
+        if (_capture == null)
+            return;
+
+        try
+        {
+            _capture.StopRecording();
+        }
+        catch
+        {
+        }
+        _capture.Dispose();
+        _capture = null;
+    }
+
+    public void Dispose() => Stop();
+
+    private void OnDataAvailable(object? sender, WaveInEventArgs e)
+    {
+        if (e.BytesRecorded <= 0)
+            return;
+
+        var format = _capture?.WaveFormat ?? WaveFormat.CreateIeeeFloatWaveFormat(48000, 2);
+        var samples = WaveToFloat.Convert(e.Buffer, e.BytesRecorded, format);
+        if (samples.Length > 0)
+            SampleReady?.Invoke(new AudioSample(samples, format.SampleRate, format.Channels));
+    }
+
+    private void OnRecordingStopped(object? sender, StoppedEventArgs e)
+    {
+        if (e.Exception != null)
+            Failed?.Invoke(e.Exception);
+    }
+}

Services/Audio/WasapiMicAudioSource.cs

@@ -0,0 +1,102 @@
+using NAudio.CoreAudioApi;
+using NAudio.Wave;
+
+namespace ytLive.Services.Audio;
+
+/// <summary>
+/// Captures the selected microphone (TASK 4 ship step 4) via WASAPI. Resolves
+/// the NAudio device by FriendlyName matching <c>MicSourceName</c> (the app only
+/// persists DisplayName), falling back to the default capture endpoint.
+/// </summary>
+public sealed class WasapiMicAudioSource : IAudioSource
+{
+    private readonly Func<string?> _micNameProvider;
+    private WasapiCapture? _capture;
+
+    /// <param name="micNameProvider">Returns the current mic DisplayName; read
+    /// at each Start so a device picked mid-session takes effect next go-live.</param>
+    public WasapiMicAudioSource(Func<string?> micNameProvider)
+    {
+        _micNameProvider = micNameProvider;
+    }
+
+    public event Action<AudioSample>? SampleReady;
+    public event Action<Exception>? Failed;
+
+    public void Start()
+    {
+        if (_capture != null)
+            throw new InvalidOperationException("Already started.");
+
+        try
+        {
+            var device = ResolveDevice();
+            _capture = device != null ? new WasapiCapture(device) : new WasapiCapture();
+            _capture.DataAvailable += OnDataAvailable;
+            _capture.RecordingStopped += OnRecordingStopped;
+            _capture.StartRecording();
+        }
+        catch (Exception ex)
+        {
+            Stop();
+            Failed?.Invoke(ex);
+        }
+    }
+
+    public void Stop()
+    {
+        if (_capture == null)
+            return;
+
+        try
+        {
+            _capture.StopRecording();
+        }
+        catch
+        {
+        }
+        _capture.Dispose();
+        _capture = null;
+    }
+
+    public void Dispose() => Stop();
+
+    private MMDevice? ResolveDevice()
+    {
+        var micName = _micNameProvider();
+        if (string.IsNullOrWhiteSpace(micName))
+            return null;
+
+        try
+        {
+            using var enumerator = new MMDeviceEnumerator();
+            foreach (var endpoint in enumerator.EnumerateAudioEndPoints(DataFlow.Capture, DeviceState.Active))
+            {
+                if (string.Equals(endpoint.FriendlyName, micName, StringComparison.OrdinalIgnoreCase))
+                    return endpoint;
+            }
+        }
+        catch
+        {
+        }
+
+        return null;
+    }
+
+    private void OnDataAvailable(object? sender, WaveInEventArgs e)
+    {
+        if (e.BytesRecorded <= 0)
+            return;
+
+        var format = _capture?.WaveFormat ?? WaveFormat.CreateIeeeFloatWaveFormat(48000, 1);
+        var samples = WaveToFloat.Convert(e.Buffer, e.BytesRecorded, format);
+        if (samples.Length > 0)
+            SampleReady?.Invoke(new AudioSample(samples, format.SampleRate, format.Channels));
+    }
+
+    private void OnRecordingStopped(object? sender, StoppedEventArgs e)
+    {
+        if (e.Exception != null)
+            Failed?.Invoke(e.Exception);
+    }
+}

Services/Audio/WaveToFloat.cs

@@ -0,0 +1,41 @@
+using NAudio.Dmo;
+using NAudio.Wave;
+
+namespace ytLive.Services.Audio;
+
+/// <summary>
+/// Converts NAudio's raw WASAPI capture buffers (byte[], whatever bit depth the
+/// device's mix format reports) into interleaved PCM float samples. Pure —
+/// unit-tested; the two WASAPI sources share it.
+/// </summary>
+public static class WaveToFloat
+{
+    public static float[] Convert(byte[] buffer, int bytesRecorded, WaveFormat format)
+    {
+        if (format.Encoding == WaveFormatEncoding.IeeeFloat && format.BitsPerSample == 32)
+            return ConvertIeeeFloat(buffer, bytesRecorded);
+        if (format.Encoding == WaveFormatEncoding.Pcm && format.BitsPerSample == 16)
+            return ConvertPcm16(buffer, bytesRecorded);
+        if (format is WaveFormatExtensible extensible
+            && extensible.SubFormat == AudioMediaSubtypes.MEDIASUBTYPE_IEEE_FLOAT)
+            return ConvertIeeeFloat(buffer, bytesRecorded);
+        return ConvertPcm16(buffer, bytesRecorded);
+    }
+
+    private static float[] ConvertIeeeFloat(byte[] buffer, int bytesRecorded)
+    {
+        var count = bytesRecorded / 4;
+        var result = new float[count];
+        Buffer.BlockCopy(buffer, 0, result, 0, count * 4);
+        return result;
+    }
+
+    private static float[] ConvertPcm16(byte[] buffer, int bytesRecorded)
+    {
+        var count = bytesRecorded / 2;
+        var result = new float[count];
+        for (var i = 0; i < count; i++)
+            result[i] = BitConverter.ToInt16(buffer, i * 2) / 32768f;
+        return result;
+    }
+}

Services/Encoder/EncoderOptions.cs

@@ -0,0 +1,27 @@
+namespace ytLive.Services.Encoder;
+
+/// <summary>
+/// Everything the FFmpeg subprocess encoder needs for one go-live (TASK 4 ship
+/// step 3). <see cref="RtmpUrl"/> is the FULL ingestion URL — the reusable
+/// stream's ingest address plus its stream key (<c>rtmp://a.rtmp.youtube.com/live2/&lt;key&gt;</c>).
+/// Resolution/FPS/bitrate come from the active quality tier; audio is a silent
+/// placeholder track until the WASAPI capture step replaces the input.
+/// </summary>
+public sealed class EncoderOptions
+{
+    public string RtmpUrl { get; init; } = string.Empty;
+    public int Width { get; init; } = 1920;
+    public int Height { get; init; } = 1080;
+    public int Fps { get; init; } = 60;
+    public int BitrateKbps { get; init; } = 8000;
+
+    /// <summary>H.264 encoder name for <c>-c:v</c>; the encoder probes and prefers
+    /// nvenc → qsv → amf → libopenh264 when not forced.</summary>
+    public string? VideoEncoder { get; init; }
+
+    public int AudioSampleRate { get; init; } = 48000;
+    public int AudioChannels { get; init; } = 2;
+
+    /// <summary>GOP in frames = Fps × 4s — the YouTube keyframe ≤ 4s compliance bound.</summary>
+    public int GopSize => Fps * 4;
+}

Services/Encoder/FfmpegArgs.cs

@@ -0,0 +1,46 @@
+namespace ytLive.Services.Encoder;
+
+/// <summary>
+/// Builds the FFmpeg command line for a live RTMP push (TASK 4 ship step 3):
+/// raw BGRA frames via stdin (paced <c>-re</c>), silent placeholder audio via lavfi
+/// <c>anullsrc</c> (the WASAPI step replaces this input), H.264 + AAC encoding, FLV
+/// muxing to the ingestion URL. Pure — the encoder just starts
+/// <c>ffmpeg.exe [Build(...)]</c>.
+/// </summary>
+public static class FfmpegArgs
+{
+    public static IReadOnlyList<string> Build(EncoderOptions options, string videoEncoder)
+    {
+        var gop = options.GopSize;
+        return
+        [
+            "-hide_banner",
+            "-loglevel", "info",
+            "-stats",
+            "-stats_period", "0.5",
+            "-re",
+            "-f", "rawvideo",
+            "-pix_fmt", "bgra",
+            "-video_size", $"{options.Width}x{options.Height}",
+            "-framerate", options.Fps.ToString(),
+            "-i", "pipe:0",
+            "-f", "lavfi",
+            "-i", $"anullsrc=channel_layout=stereo:sample_rate={options.AudioSampleRate}",
+            "-c:v", videoEncoder,
+            "-b:v", $"{options.BitrateKbps}k",
+            "-maxrate", $"{options.BitrateKbps}k",
+            "-bufsize", $"{options.BitrateKbps * 2}k",
+            "-g", gop.ToString(),
+            "-keyint_min", gop.ToString(),
+            "-sc_threshold", "0",
+            "-bf", "0",
+            "-pix_fmt", "yuv420p",
+            "-c:a", "aac",
+            "-b:a", "128k",
+            "-ar", options.AudioSampleRate.ToString(),
+            "-ac", options.AudioChannels.ToString(),
+            "-f", "flv",
+            options.RtmpUrl,
+        ];
+    }
+}

Services/Encoder/FfmpegEncoder.cs

@@ -0,0 +1,263 @@
+using System.Diagnostics;
+using ytLive.Helpers;
+using ytLive.Models;
+
+namespace ytLive.Services.Encoder;
+
+/// <summary>
+/// The default <see cref="IFfmpegEncoder"/>: spawns <c>ffmpeg.exe</c> (resolved via
+/// <see cref="IFfmpegLocator"/>), feeds raw BGRA frames into stdin, and parses the
+/// <c>-stats</c> progress lines into <see cref="StreamHealth"/>. Encoder choice is
+/// probed from the binary's <c>-encoders</c> listing (hardware NVENC/QSV/AMF first,
+/// OpenH264 software fallback — never libx264, see the license posture) unless
+/// <see cref="EncoderOptions.VideoEncoder"/> forces one.
+///
+/// Graceful stop = close stdin (EOF) → ffmpeg finalizes the FLV and exits by itself;
+/// a watchdogs kill fires only if it hasn't exited shortly after EOF.
+/// </summary>
+public sealed class FfmpegEncoder : IFfmpegEncoder
+{
+    public event EventHandler<StreamHealth>? HealthUpdated;
+    public event EventHandler<string>? ProcessFailed;
+
+    private readonly IFfmpegLocator _locator;
+    private readonly Func<IEncoderProcess> _processFactory;
+
+    private readonly object _gate = new();
+    private IEncoderProcess? _process;
+    private EncoderOptions? _options;
+    private StreamHealth _health = new() { Status = StreamStatus.Offline };
+    private Task? _stderrLoop;
+    private bool _stopRequested;
+
+    public FfmpegEncoder(
+        IFfmpegLocator locator,
+        Func<IEncoderProcess>? processFactory = null)
+    {
+        _locator = locator;
+        _processFactory = processFactory ?? (() => new FfmpegEncoderProcess());
+    }
+
+    public bool IsRunning { get; private set; }
+
+    public async Task StartAsync(EncoderOptions options, CancellationToken cancellationToken = default)
+    {
+        if (options == null) throw new ArgumentNullException(nameof(options));
+        if (string.IsNullOrWhiteSpace(options.RtmpUrl))
+            throw new ArgumentException("An RTMP ingestion URL is required.", nameof(options));
+
+        lock (_gate)
+        {
+            if (IsRunning) throw new InvalidOperationException("The encoder is already running.");
+            _options = options;
+        }
+
+        var ffmpegPath = await _locator.LocateAsync(cancellationToken).ConfigureAwait(false);
+        var encoder = options.VideoEncoder ?? await ProbeEncoderAsync(ffmpegPath, cancellationToken).ConfigureAwait(false);
+        var args = FfmpegArgs.Build(options, encoder);
+
+        var startInfo = new ProcessStartInfo
+        {
+            FileName = ffmpegPath,
+            UseShellExecute = false,
+            RedirectStandardInput = true,
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+            CreateNoWindow = true,
+        };
+        foreach (var arg in args) startInfo.ArgumentList.Add(arg);
+
+        IEncoderProcess process;
+        try
+        {
+            process = _processFactory();
+            process.Start(startInfo);
+        }
+        catch (Exception ex)
+        {
+            AppLog.Write(ex, "FFmpeg encoder: failed to start subprocess");
+            lock (_gate) _options = null;
+            throw;
+        }
+
+        lock (_gate)
+        {
+            _process = process;
+            IsRunning = true;
+            _health = new StreamHealth { Status = StreamStatus.Streaming };
+        }
+
+        _stopRequested = false;
+        _stderrLoop = RunStderrLoopAsync(process);
+    }
+
+    /// <summary>
+    /// Write one raw BGRA frame to ffmpeg's stdin. Serialized internally; callers
+    /// (the compositor pump) may race freely. Frames are written as-is — the caller
+    /// paces to capture rate (the compositor's job, ship step 5).
+    /// </summary>
+    public async Task SubmitFrameAsync(VideoFrame frame, CancellationToken cancellationToken = default)
+    {
+        if (frame == null) throw new ArgumentNullException(nameof(frame));
+        IEncoderProcess? process;
+        lock (_gate)
+        {
+            if (!IsRunning) throw new InvalidOperationException("The encoder is not running.");
+            process = _process;
+        }
+
+        var bytes = frame.BgraPixels;
+        await process!.StandardInput.WriteAsync(bytes, cancellationToken).ConfigureAwait(false);
+        await process.StandardInput.FlushAsync(cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task StopAsync(CancellationToken cancellationToken = default)
+    {
+        IEncoderProcess? process;
+        Task? loop;
+        lock (_gate)
+        {
+            if (!IsRunning) return;
+            _stopRequested = true;
+            process = _process;
+            loop = _stderrLoop;
+        }
+
+        try
+        {
+            process!.StandardInput.Dispose(); // EOF → ffmpeg finalizes + exits
+        }
+        catch (Exception ex)
+        {
+            AppLog.Write(ex, "FFmpeg encoder: closing stdin failed");
+        }
+
+        try
+        {
+            using var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+            timeout.CancelAfter(TimeSpan.FromSeconds(10));
+            await process!.WaitForExitAsync(timeout.Token).ConfigureAwait(false);
+        }
+        catch (OperationCanceledException)
+        {
+            AppLog.Write("FFmpeg encoder: did not exit after stdin EOF — killing");
+            process!.Kill();
+        }
+        catch (Exception ex)
+        {
+            AppLog.Write(ex, "FFmpeg encoder: waiting for exit failed");
+            process!.Kill();
+        }
+
+        try
+        {
+            if (loop != null) await loop.ConfigureAwait(false);
+        }
+        catch (Exception ex)
+        {
+            AppLog.Write(ex, "FFmpeg encoder: stderr loop faulted during stop");
+        }
+
+        process.Dispose();
+
+        lock (_gate)
+        {
+            IsRunning = false;
+            _health.Status = StreamStatus.Offline;
+            _health.LastError = null;
+            _process = null;
+            _options = null;
+        }
+
+        AppLog.Write($"FFmpeg encoder stopped (exit {process.ExitCode})");
+    }
+
+    public void Dispose()
+    {
+        lock (_gate)
+        {
+            if (!IsRunning) return;
+            _process?.Kill();
+            _process?.Dispose();
+            _process = null;
+            IsRunning = false;
+        }
+    }
+
+    private async Task<string> ProbeEncoderAsync(string ffmpegPath, CancellationToken cancellationToken)
+    {
+        try
+        {
+            var startInfo = new ProcessStartInfo
+            {
+                FileName = ffmpegPath,
+                UseShellExecute = false,
+                RedirectStandardOutput = true,
+                RedirectStandardError = true,
+                CreateNoWindow = true,
+            };
+            startInfo.ArgumentList.Add("-hide_banner");
+            startInfo.ArgumentList.Add("-encoders");
+
+            using var probe = _processFactory();
+            probe.Start(startInfo);
+            using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+            cts.CancelAfter(TimeSpan.FromSeconds(15));
+            var output = await probe.StandardOutput.ReadToEndAsync(cts.Token).ConfigureAwait(false);
+            return FfmpegEncoderPicker.Pick(output);
+        }
+        catch (Exception ex)
+        {
+            AppLog.Write(ex, "FFmpeg encoder: encoder probe failed — falling back to software");
+            return FfmpegEncoderPicker.Preference[^1];
+        }
+    }
+
+    private Task RunStderrLoopAsync(IEncoderProcess process)
+    {
+        return Task.Run(async () =>
+        {
+            try
+            {
+                while (true)
+                {
+                    var line = await process.StandardError.ReadLineAsync().ConfigureAwait(false);
+                    if (line == null) break;
+                    OnStderrLine(process, line);
+                }
+
+                var code = process.ExitCode;
+                var stillRunning = false;
+                lock (_gate) stillRunning = IsRunning;
+                if (stillRunning && !_stopRequested && code != 0)
+                {
+                    AppLog.Write($"FFmpeg encoder: subprocess exited unexpectedly ({code})");
+                    _health.LastError = $"FFmpeg exited with code {code}";
+                    ProcessFailed?.Invoke(this, $"FFmpeg exited with code {code}");
+                }
+            }
+            catch (Exception ex)
+            {
+                AppLog.Write(ex, "FFmpeg encoder: stderr loop faulted");
+            }
+        });
+    }
+
+    private void OnStderrLine(IEncoderProcess process, string line)
+    {
+        var progress = FfmpegProgressParser.TryParse(line);
+        if (progress == null) return;
+
+        var dropped = Math.Max(0, (long)Math.Round(progress.Value.Fps * progress.Value.Duration.TotalSeconds) - progress.Value.Frame);
+
+        lock (_gate)
+        {
+            _health.CurrentBitrate = progress.Value.BitrateKbps;
+            _health.FPS = progress.Value.Fps;
+            _health.DroppedFrames = (int)dropped;
+            _health.StreamDuration = progress.Value.Duration;
+        }
+
+        HealthUpdated?.Invoke(this, _health);
+    }
+}

Services/Encoder/FfmpegEncoderPicker.cs

@@ -0,0 +1,35 @@
+namespace ytLive.Services.Encoder;
+
+/// <summary>
+/// Picks the best available H.264 encoder from ffmpeg's <c>-encoders</c> listing,
+/// honoring the license posture (no GPL libx264): hardware NVENC → QSV → AMF, then
+/// the OpenH264 software fallback. Pure parser — the <c>-encoders</c> probe output is
+/// fetched by the encoder via an <see cref="IEncoderProcess"/> and fed here.
+/// </summary>
+public static class FfmpegEncoderPicker
+{
+    /// <summary>Preference order, best first. All ship in the pinned BtbN lgpl-shared build.</summary>
+    public static readonly string[] Preference =
+    [
+        "h264_nvenc",
+        "h264_qsv",
+        "h264_amf",
+        "libopenh264",
+    ];
+
+    /// <summary>
+    /// First <see cref="Preference"/> entry present in the probe output, or the
+    /// software fallback (which the pinned build always contains) if none matched.
+    /// Never returns libx264 — it is GPL and would contaminate the paid product.
+    /// </summary>
+    public static string Pick(string probeOutput)
+    {
+        var available = probeOutput.Split('\n');
+        foreach (var name in Preference)
+        {
+            if (available.Any(line => line.Contains(name, StringComparison.Ordinal)))
+                return name;
+        }
+        return Preference[^1];
+    }
+}

Services/Encoder/FfmpegEncoderProcess.cs

@@ -0,0 +1,38 @@
+using System.Diagnostics;
+using System.IO;
+
+namespace ytLive.Services.Encoder;
+
+/// <summary>
+/// The real <see cref="IEncoderProcess"/>: a <see cref="Process"/> with all three
+/// std streams redirected. Constructed by <see cref="FfmpegEncoder"/> for both the
+/// encoder subprocess and the <c>-encoders</c> probe.
+/// </summary>
+public sealed class FfmpegEncoderProcess : IEncoderProcess
+{
+    private readonly Process _process;
+
+    public FfmpegEncoderProcess() => _process = new Process { EnableRaisingEvents = true };
+
+    public void Start(ProcessStartInfo startInfo)
+    {
+        _process.StartInfo = startInfo;
+        _process.Start();
+    }
+
+    public Stream StandardInput => _process.StandardInput.BaseStream;
+    public TextReader StandardOutput => _process.StandardOutput;
+    public TextReader StandardError => _process.StandardError;
+
+    public bool HasExited => _process.HasExited;
+    public int ExitCode => _process.ExitCode;
+    public void Kill()
+    {
+        if (!_process.HasExited) _process.Kill();
+    }
+
+    public Task WaitForExitAsync(CancellationToken cancellationToken = default)
+        => _process.WaitForExitAsync(cancellationToken);
+
+    public void Dispose() => _process.Dispose();
+}

Services/Encoder/FfmpegProgressParser.cs

@@ -0,0 +1,47 @@
+using System.Text.RegularExpressions;
+
+namespace ytLive.Services.Encoder;
+
+/// <summary>A decoded ffmpeg <c>-stats</c> progress line (pure data).</summary>
+public readonly record struct FfmpegProgress(
+    long Frame,
+    double Fps,
+    double BitrateKbps,
+    TimeSpan Duration,
+    long SizeBytes);
+
+/// <summary>
+/// Pure parser for ffmpeg's periodic <c>frame= fps= size= time= bitrate=</c> stderr
+/// lines (the <c>-stats</c>/<c>-stats_period</c> output). Unit-tested in isolation
+/// so the encoder loop stays a thin wire.
+/// </summary>
+public static class FfmpegProgressParser
+{
+    // frame=  123 fps= 59.9 q=28.0 size=   1024KiB time=00:00:02.04 bitrate= 4000.1kbits/s speed=1.00x
+    private static readonly Regex Line = new(
+        @"frame=\s*(?<frame>\d+)\s+fps=\s*(?<fps>[\d.]+).*?"
+        + @"size=\s*(?<size>\d+)KiB.*?"
+        + @"time=(?<time>\d{2}):(?<min>\d{2}):(?<sec>[\d.]+).*?"
+        + @"bitrate=\s*(?<bitrate>[\d.]+)kbits/s",
+        RegexOptions.Compiled | RegexOptions.CultureInvariant);
+
+    /// <summary>Returns null for non-progress lines (errors, warnings, banner).</summary>
+    public static FfmpegProgress? TryParse(string line)
+    {
+        if (string.IsNullOrWhiteSpace(line)) return null;
+        var m = Line.Match(line);
+        if (!m.Success) return null;
+
+        var frame = long.Parse(m.Groups["frame"].Value);
+        var fps = double.Parse(m.Groups["fps"].Value, System.Globalization.CultureInfo.InvariantCulture);
+        var size = long.Parse(m.Groups["size"].Value);
+        var bitrate = double.Parse(m.Groups["bitrate"].Value, System.Globalization.CultureInfo.InvariantCulture);
+
+        var hours = int.Parse(m.Groups["time"].Value);
+        var minutes = int.Parse(m.Groups["min"].Value);
+        var seconds = double.Parse(m.Groups["sec"].Value, System.Globalization.CultureInfo.InvariantCulture);
+        var duration = TimeSpan.FromSeconds(hours * 3600 + minutes * 60 + seconds);
+
+        return new FfmpegProgress(frame, fps, bitrate, duration, size * 1024);
+    }
+}

Services/Encoder/IEncoderProcess.cs

@@ -0,0 +1,26 @@
+using System.Diagnostics;
+using System.IO;
+
+namespace ytLive.Services.Encoder;
+
+/// <summary>
+/// Seam around a spawned subprocess (the encoder's ffmpeg and the encoder probe).
+/// Exposes the redirected stdin (binary frames), stdout (probe listing) and stderr
+/// (progress lines) plus exit control, so the encoder logic never touches
+/// <c>System.Diagnostics.Process</c> directly and tests can fake the whole thing.
+/// </summary>
+public interface IEncoderProcess : IDisposable
+{
+    void Start(ProcessStartInfo startInfo);
+
+    /// <summary>Raw binary stdin — the encoder writes BGRA frames here.</summary>
+    Stream StandardInput { get; }
+
+    TextReader StandardOutput { get; }
+    TextReader StandardError { get; }
+
+    bool HasExited { get; }
+    int ExitCode { get; }
+    void Kill();
+    Task WaitForExitAsync(CancellationToken cancellationToken = default);
+}

Services/Encoder/IFfmpegEncoder.cs

@@ -0,0 +1,25 @@
+using ytLive.Models;
+
+namespace ytLive.Services.Encoder;
+
+/// <summary>
+/// The live encoder seam (TASK 4 ship step 3): start an FFmpeg subprocess that
+/// encodes raw BGRA frames from stdin and pushes FLV to an RTMP ingestion URL,
+/// raising parsed health stats from stderr. The frame producer (compositor →
+/// capture managers, TASK 4 ship step 5) feeds <see cref="SubmitFrameAsync"/> at
+/// capture rate; this service serializes writes, parses progress, and tears the
+/// process down gracefully. Constructor-injected <see cref="IFfmpegLocator"/> +
+/// process factory keep it hermetic (tests fake both).
+/// </summary>
+public interface IFfmpegEncoder : IDisposable
+{
+    /// <summary>Fires on each parsed ffmpeg <c>-stats</c> progress line (~2 Hz).</summary>
+    event EventHandler<StreamHealth>? HealthUpdated;
+
+    /// <summary>Fires when the subprocess dies unexpectedly (non-zero exit while live).</summary>
+    event EventHandler<string>? ProcessFailed;
+
+    Task StartAsync(EncoderOptions options, CancellationToken cancellationToken = default);
+    Task SubmitFrameAsync(VideoFrame frame, CancellationToken cancellationToken = default);
+    Task StopAsync(CancellationToken cancellationToken = default);
+}

Services/index.md

@@ -33,7 +33,22 @@ External-facing logic: YouTube API, persistence. See
 | `Compositor/StaticPixelCache.cs` | Asset bytes → cached BGRA8 `VideoFrame`, decoded once per content hash — the output path's raw-pixel source (the preview uses ImageCache's `BitmapImage`) |
 | `Encoder/IFfmpegLocator.cs` | **TASK 4 ship step 2 seam**: resolves an absolute path to `ffmpeg.exe` (PATH first → cached `%APPDATA%\ytLlive\tools\ffmpeg.exe` → pinned BtbN LGPL-shared zip download). The encoder step and tests fake it |
 | `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/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) |
+| `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 |
+| `Audio/WasapiMicAudioSource.cs` | Mic capture: NAudio `WasapiCapture` with the device resolved by `FriendlyName` matching `MicSourceName` (DisplayName only), default capture endpoint fallback; name provider `Func<string?>` re-read at each `Start` so a mic picked mid-session takes effect next go-live |
+| `Audio/AudioMixer.cs` | Owns both sources; `Start`/`Stop` follow go-live (`MainViewModel.BeginGoLive`/`StopStream`). Mic samples → `AudioLevelMeter` → `MicLevelChanged`; loopback samples currently dropped (the future encoder AAC mix consumes them). Failures log via `AppLog`; mic failure zeroes the meter, loopback failure doesn't kill the mic |
+| `Audio/AudioLevelMeter.cs` | Pure smoothed RMS level (0..1): `Push(AudioSample)` + `Reset` — the unit-tested math behind `AudioLevel` |
+| `Audio/WaveToFloat.cs` | Pure WASAPI buffer → float conversion: IEEE float 32-bit direct, PCM 16-bit normalized, `WaveFormatExtensible` IEEE-float subformat GUID, trailing partial samples ignored |
 
 Related: constructed in [`ViewModels/MainViewModel.cs`](../ViewModels/MainViewModel.cs)
 (no DI container yet). Models in [`Models/index.md`](../Models/index.md).

TASKS.md

@@ -199,8 +199,8 @@ Preview shows the transition too (WYSIWYG). No wipes/slides/LUTs beyond the four
 
 1. ✅ **Ship step 1 — the output compositor SHIPPED** (2026-08-10)
 2. ✅ **Ship step 2 — the FFmpeg locator SHIPPED** (2026-08-10)
-3. ☐ **Encoder + RTMP push** — the FFmpeg subprocess: frames via stdin, stderr health parsing, FLV mux + push to the cached reusable stream's ingestion URL
+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** — loopback (desktop/game) + the picked mic feeding `AudioLevel` so the realtime meter comes alive (req 7)
+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
 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)
@@ -361,6 +361,71 @@ Tests: the hermetic `FfmpegLocatorTests` integration test (PATH → cache → do
 fake downloader serving a real in-memory zip) + edge/unit cases (shared-build DLL extraction, zero-byte
 cache refresh, empty payload, missing zip entry, downloader failure) — **78 passing**.
 
+#### Ship step 3 — Encoder + RTMP push (the FFmpeg subprocess)
+
+**Goal:** encode raw BGRA master frames into H.264+AAC FLV and push them to the reusable stream's RTMP
+ingestion URL — one battle-tested subprocess doing encode + mux + push + reconnect, the app feeding
+frames via stdin and parsing stderr for health (req 2).
+
+**Decisions (locked):** the encoder is a thin orchestrator over `ffmpeg.exe` — no H.264/AAC code in the
+app. Arguments (pure `FfmpegArgs.Build`): `-re -f rawvideo -pix_fmt bgra -video_size WxH -framerate FPS
+-i pipe:0` (frames in), a **silent placeholder audio track** via `-f lavfi -i anullsrc` (the WASAPI
+capture step replaces this input), `-c:v <encoder> -b:v K -maxrate K -bufsize 2K` + **`-g fps×4`
+`-keyint_min fps×4` `-sc_threshold 0` `-bf 0` `-pix_fmt yuv420p`** (the keyframe ≤4s / closed-GOP /
+H.264 compliance), `-c:a aac -ar 48000 -ac 2`, `-f flv <rtmpUrl>`. Encoder choice is **probed from the
+binary's `-encoders` listing** (`FfmpegEncoderPicker`, pure): hardware NVENC → QSV → AMF, then OpenH264
+software fallback — **never libx264** (GPL; see `ai.md` → Licensing). The seam (`IFfmpegEncoder` +
+`IEncoderProcess`, constructor-injected locator + process factory) keeps it hermetic — tests fake the
+whole subprocess (probe + encoder), no real binary.
+
+**Behavior:** `StartAsync` (locate → probe → spawn → stderr loop), `SubmitFrameAsync` (serialized BGRA
+stdin writes, ~2 Hz health via `HealthUpdated`/`StreamHealth` — bitrate/FPS/duration/dropped-from-frame-
+count), `StopAsync` (stdin EOF → ffmpeg finalizes + exits by itself; 10s watchdog kill), `ProcessFailed`
+on a non-zero unexpected exit.
+
+**Built (2026-08-12):** `EncoderOptions` + `IFfmpegEncoder`/`FfmpegEncoder` + `IEncoderProcess`/
+`FfmpegEncoderProcess` + pure `FfmpegArgs`/`FfmpegProgressParser`/`FfmpegEncoderPicker` in
+`Services/Encoder/`. Not yet constructed by the app (the frame-pipeline wiring, ship step 5, owns it).
+Tests: `FfmpegEncoderTests` integration (probe → spawn with NVENC preferred → frames into stdin →
+progress parsed → graceful stop, no kill) + units (args compliance/GOP, progress parser, picker
+preference + GPL guard, no-URL/not-running/noop stops, process-death `ProcessFailed`) — **122 passing**.
+
+#### Ship step 4 — WASAPI audio capture (the meter comes alive)
+
+**Goal:** capture desktop/game audio (loopback) and the picked mic, feed the mic level into `AudioLevel`
+so the realtime meter reads something other than 0, run capture **only while live** (req 7).
+
+**Decisions (locked):**
+1. **NAudio `NAudio.Wasapi` 2.2.1** — the wasapi feature package (not the `NAudio` meta-package): it
+   carries the capture types (`WasapiCapture`/`WasapiLoopbackCapture` + the MMDevice enumeration) with
+   `NAudio.Core`/`NAudio.Asio` pulled in transitively. MIT — recorded in `THIRD-PARTY-NOTICES.txt` (item 9).
+2. **`IAudioSource` seam** (`Start`/`Stop`/`SampleReady`/`Failed`, IDisposable) — the app consumes the
+   seam; the two WASAPI implementations wrap NAudio; tests inject hermetic fakes (no real audio devices,
+   no timers). Loopback = `WasapiLoopbackCapture` on the default render device; mic = `WasapiCapture`
+   with the NAudio device resolved by `FriendlyName` matching `MicSourceName` (the app only persists the
+   DisplayName), falling back to the default capture endpoint. Mic device resolution is re-read at each
+   `Start` via a name provider so a mic picked mid-session takes effect next go-live.
+3. **`AudioMixer` owns both sources** — starts/stops both with go-live (`BeginGoLive` success → `Start`,
+   `StopStream` → `Stop`). Mic samples feed a pure `AudioLevelMeter` (RMS, exponential smoothing) and
+   raise `MicLevelChanged`, marshalled to the UI thread into `AudioLevel`; desktop samples are currently
+   dropped (consumed by the encoder's AAC mix in a later step). Capture failures are logged via `AppLog`
+   (mic failure also zeroes the meter); loopback failure doesn't kill the mic.
+4. **Byte→float** — pure `WaveToFloat.Convert` handles the WASAPI mix formats: IEEE float 32-bit (direct)
+   and PCM 16-bit (normalized to -1..1), including `WaveFormatExtensible` with the IEEE-float subformat
+   GUID. Trailing partial samples are ignored.
+
+**Built (2026-08-12):** `Services/Audio/` ships `IAudioSource` + `AudioSample`, `WasapiLoopbackAudioSource`,
+`WasapiMicAudioSource`, `AudioMixer`, `AudioLevelMeter`, `WaveToFloat`; `MainViewModel` constructs the
+mixer (mic source fed `() => MicSourceName`), starts it on go-live and stops it on end-stream, and maps
+`MicLevelChanged` → `AudioLevel`. A pre-existing CS8602 in `FfmpegEncoder.cs:139` surfaced during this
+step's rebuild and was fixed (`process!`) — build **0 warnings**. Tests: `AudioMixerTests` (mixer
+lifecycle/forwarding/failure against fakes, meter RMS/smoothing/reset, `WaveToFloat` float/PCM16/
+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.
+
 ---
 
 ## TASK 5 — YouTube Live Stream Management

THIRD-PARTY-NOTICES.txt

@@ -79,6 +79,14 @@ the guardrails — the "never do" list is there on purpose.
             obligations; it is listed here per this file's "list everything"
             policy.
 
+9. NAudio  (WASAPI audio capture — loopback + mic)
+   Copyright (c) Mark Heath and contributors
+   License: MIT
+   Home:    https://github.com/naudio/NAudio
+   Used as: the WASAPI loopback (desktop/game audio) and mic capture sources
+            behind the `IAudioSource` seam (TASK 4 ship step 4). MIT imposes
+            no source offer; this notice is kept per this file's policy.
+
 --------------------------------------------------------------------------------
 
 MISCELLANEOUS

ViewModels/MainViewModel.cs

@@ -14,6 +14,7 @@ using Microsoft.Win32;
 using ytLive.Helpers;
 using ytLive.Models;
 using ytLive.Services;
+using ytLive.Services.Audio;
 
 namespace ytLive.ViewModels;
 
@@ -79,6 +80,12 @@ public class MainViewModel : ViewModelBase
     private SocialsConfig? _socials;
     private readonly IMicrophoneEnumerator _microphoneEnumerator;
 
+    // Live audio capture (TASK 4 ship step 4): desktop/game via WASAPI loopback,
+    // mic via WASAPI capture, both owned by the mixer and running only while
+    // live. Mic level feeds AudioLevel (the meter); loopback is for the future
+    // encoder mix. Private by design — no UI beyond the existing mic controls.
+    private readonly AudioMixer _audioMixer;
+
     // 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.
@@ -832,6 +839,12 @@ public class MainViewModel : ViewModelBase
 
         _microphoneEnumerator = new WinRtMicrophoneEnumerator();
 
+        _audioMixer = new AudioMixer(
+            new WasapiMicAudioSource(() => MicSourceName),
+            new WasapiLoopbackAudioSource(),
+            message => AppLog.Write(message));
+        _audioMixer.MicLevelChanged += OnMicLevelChanged;
+
         _fullScreenDetector = new Win32FullScreenDetector();
         foreach (var display in _fullScreenDetector.GetDisplays())
             Displays.Add(display);
@@ -1725,6 +1738,7 @@ public class MainViewModel : ViewModelBase
                 ? "ytLlive"
                 : $"{dialog.StreamTitle} — ytLlive";
             StreamStatus = StreamStatus.Streaming;
+            _audioMixer.Start();
         }
     }
 
@@ -1732,6 +1746,7 @@ public class MainViewModel : ViewModelBase
     {
         StreamStatus = StreamStatus.Offline;
         WindowTitle = "ytLlive";
+        _audioMixer.Stop();
         // 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.
@@ -1742,6 +1757,17 @@ public class MainViewModel : ViewModelBase
         AppLog.Write("Stream ended; session signed out");
     }
 
+    private void OnMicLevelChanged(float level)
+    {
+        // NAudio raises on its capture thread; marshal to the UI thread so the
+        // meter binding updates safely.
+        var dispatcher = System.Windows.Application.Current?.Dispatcher;
+        if (dispatcher != null && !dispatcher.CheckAccess())
+            dispatcher.BeginInvoke(() => AudioLevel = level);
+        else
+            AudioLevel = level;
+    }
+
     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)** |
+| `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")** |
 | `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) |
@@ -114,7 +114,7 @@ C# / WPF (.NET 8) following MVVM:
 - `Helpers/OAuthCredentials.cs` contains the real ClientId/ClientSecret. Auth is complete and the session **persists via Windows DPAPI** (`Helpers/TokenStore.cs` → `%APPDATA%\ytLlive\ytLlive.auth`, CurrentUser scope), reloaded best-effort at startup with a proactive refresh of a near-expiry access token. Sign-in/Change Account lives **inside the Start Stream dialog** (two-state flow — no separate Connect button). A **graceful End Livestream signs out**: `StopStream()` clears the session + token, so the next go-live needs a fresh sign-in; a crash never runs End, so the token survives and the creator stays signed in. `YouTubeAuthService` takes an optional `HttpClient` + `sessionChanged` callback (test seam + save hook; services are still constructed in `MainViewModel`)
 - Scene/source/asset layout + the social bar persist (SQLite, schema v8); the OAuth session persists (DPAPI); the paid-unlock state does not (yet — itch.io key verification pending)
 - `YouTubeStreamService` uses hardcoded `1080p`/`60fps` and per-broadcast streams — must switch to the v3 `variable` reusable stream
-- Webcam capture is shipped (milestone 1); the live desktop/game backdrop is shipped (ship task #1); **the output compositor (TASK 4 ship step 1) is SHIPPED**, **the FFmpeg locator (TASK 4 ship step 2) is SHIPPED** — full plan in `TASKS.md`; the encoder subprocess + RTMP push, audio capture, and the frame-pipeline wiring follow (each its own PR)
+- Webcam capture is shipped (milestone 1); the live desktop/game backdrop is shipped (ship task #1); **the output compositor (TASK 4 ship step 1) is SHIPPED**, **the FFmpeg locator (TASK 4 ship step 2) is SHIPPED**, **the encoder + RTMP push (TASK 4 ship step 3) is SHIPPED**, **WASAPI audio capture (TASK 4 ship step 4) is SHIPPED** — full plan in `TASKS.md`; the frame-pipeline wiring follows (its own PR)
 - `StreamConfig` defaults (`TargetBitrate=6000`, `Resolution="1920x1080"`) are stale — the live dropdown drives `StreamHealth.CurrentBitrate`/`FPS` instead
 
 ### Screen backdrop capture (TASK 3 ship task #1)
@@ -330,6 +330,58 @@ const). Constructor-injected search dirs / tools dir / downloader (`Func<string,
 Task<byte[]>>`) keep it hermetic: tests fake the network with a real in-memory zip. Constructed in the
 encoder step (not yet — this PR ships the seam + impl + tests only).
 
+### Live encoder + RTMP push (TASK 4 ship step 3 — shipped 2026-08-12, plan in TASKS.md)
+
+The encoder is a **thin orchestrator over `ffmpeg.exe`** — no H.264/AAC code in the app. It spawns the
+subprocess (path from `IFfmpegLocator`), feeds raw BGRA master frames into stdin, and parses `-stats`
+stderr lines into `StreamHealth` (bitrate/FPS/duration, dropped-from-frame-count). `FfmpegEncoder`
+(`IFfmpegEncoder` seam) holds: `StartAsync` (locate → probe `-encoders` → spawn → stderr loop),
+`SubmitFrameAsync` (serialized stdin writes under `SemaphoreSlim`), `StopAsync` (stdin EOF → ffmpeg
+finalizes + exits by itself; a 10s watchdog kills it), `Dispose` (force-kill + wait), and the
+`HealthUpdated`/`ProcessFailed` events. **Pattern:** the encoder never touches `Process` — it drives the
+`IEncoderProcess` seam (`FfmpegEncoderProcess` wraps the real `Process`, redirected stdin/stdout/stderr
++ exit control); a `Func<IEncoderProcess>` factory + the locator are constructor-injected, so the
+integration test fakes the whole subprocess (probe + encoder) with a Channel-backed `TextReader` whose
+`Complete()` is EOF (`null`), never a `ChannelClosedException`.
+
+**Decisions (locked):** args are pure (`FfmpegArgs.Build`, no string building in the encoder):
+`-re -f rawvideo -pix_fmt bgra -video_size WxH -framerate FPS -i pipe:0` + a **silent placeholder
+`-f lavfi -i anullsrc`** track (WASAPI capture, ship step 4, replaces it) + `-c:v <enc> -b:v K
+-maxrate K -bufsize 2K` + **`-g fps×4 -keyint_min fps×4 -sc_threshold 0 -bf 0 -pix_fmt yuv420p`**
+(≤4s keyframes, closed GOP, H.264 compliance) + `-c:a aac -ar 48000 -ac 2 -f flv <rtmpUrl>`.
+**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.
+
+### Live audio capture (TASK 4 ship step 4 — shipped 2026-08-12, plan in TASKS.md)
+
+**Capture runs only while live and is KISS by rule**: desktop/game audio is automatic (WASAPI loopback,
+zero UI), the mic is the creator's only audio control (meter/mute/volume already shipped). The whole
+layer sits behind an **`IAudioSource` seam** (`Services/Audio/`: `Start`/`Stop`/`SampleReady`/`Failed`,
+IDisposable) so the app never touches NAudio directly and tests inject hermetic fakes (no devices, no
+timers).
+
+- **Sources (NAudio `NAudio.Wasapi` 2.2.1, MIT — item 9 in `THIRD-PARTY-NOTICES.txt`):**
+  `WasapiLoopbackAudioSource` = `WasapiLoopbackCapture` on the default render device;
+  `WasapiMicAudioSource` = `WasapiCapture` with the device resolved by `FriendlyName` matching
+  `MicSourceName` (the app only persists the **DisplayName**), falling back to the default capture
+  endpoint. Mic device resolution re-reads the name provider `Func<string?>` at each `Start`, so a mic
+  picked mid-session takes effect next go-live.
+- **`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
+  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).
+
 ### Social bar (TASK 14 — shipped 2026-08-12, plan in TASKS.md)
 
 A **global bar layer** (never a Source, no sources-list row) that sits over the bottom or top of the

ytLive.Tests/AudioMixerTests.cs

@@ -0,0 +1,280 @@
+using NAudio.Wave;
+using Xunit;
+using ytLive.Services.Audio;
+
+namespace ytLive.Tests;
+
+/// <summary>
+/// TASK 4 ship step 4: WASAPI audio capture behind the <see cref="IAudioSource"/>
+/// seam. The units pin down the pure pieces — byte→float conversion, the level
+/// meter math, and the mixer lifecycle/forwarding against fakes. No real audio
+/// devices (NAudio device resolution is a thin wrapper left to a manual smoke
+/// test), no timers.
+/// </summary>
+public class AudioMixerTests
+{
+    private sealed class FakeSource : IAudioSource
+    {
+        public int StartCount { get; private set; }
+        public int StopCount { get; private set; }
+        public bool Disposed { get; private set; }
+        public event Action<AudioSample>? SampleReady;
+        public event Action<Exception>? Failed;
+
+        public void Start() => StartCount++;
+        public void Stop() => StopCount++;
+        public void Dispose() => Disposed = true;
+
+        public void Emit(AudioSample sample) => SampleReady?.Invoke(sample);
+        public void Fail(Exception ex) => Failed?.Invoke(ex);
+    }
+
+    [Fact]
+    public void Start_StartsBothSources()
+    {
+        var mic = new FakeSource();
+        var loopback = new FakeSource();
+        var mixer = new AudioMixer(mic, loopback);
+
+        mixer.Start();
+
+        Assert.Equal(1, mic.StartCount);
+        Assert.Equal(1, loopback.StartCount);
+    }
+
+    [Fact]
+    public void Start_IsIdempotent()
+    {
+        var mic = new FakeSource();
+        var mixer = new AudioMixer(mic, new FakeSource());
+
+        mixer.Start();
+        mixer.Start();
+
+        Assert.Equal(1, mic.StartCount);
+    }
+
+    [Fact]
+    public void Stop_StopsBothAndResetsLevel()
+    {
+        var mic = new FakeSource();
+        var loopback = new FakeSource();
+        var mixer = new AudioMixer(mic, loopback);
+        mixer.Start();
+        mic.Emit(new AudioSample(new[] { 0.8f }, 48000, 1));
+
+        var last = -1f;
+        mixer.MicLevelChanged += l => last = l;
+        mixer.Stop();
+
+        Assert.Equal(1, mic.StopCount);
+        Assert.Equal(1, loopback.StopCount);
+        Assert.Equal(0f, last);
+        Assert.Equal(0f, mixer.MicLevel);
+    }
+
+    [Fact]
+    public void Stop_WithNoStart_DoesNothing()
+    {
+        var mic = new FakeSource();
+        var mixer = new AudioMixer(mic, new FakeSource());
+
+        mixer.Stop();
+
+        Assert.Equal(0, mic.StopCount);
+    }
+
+    [Fact]
+    public void MicSamples_DriveMicLevelChanged()
+    {
+        var mic = new FakeSource();
+        var mixer = new AudioMixer(mic, new FakeSource());
+        var levels = new List<float>();
+        mixer.MicLevelChanged += l => levels.Add(l);
+
+        mixer.Start();
+        mic.Emit(new AudioSample(new[] { 1f, 1f, 1f, 1f }, 48000, 1));
+        mic.Emit(new AudioSample(new[] { -1f, -1f, -1f, -1f }, 48000, 1));
+
+        Assert.NotEmpty(levels);
+        Assert.All(levels, l => Assert.InRange(l, 0f, 1f));
+    }
+
+    [Fact]
+    public void LoopbackSamples_DoNotChangeMicLevel()
+    {
+        var loopback = new FakeSource();
+        var mixer = new AudioMixer(new FakeSource(), loopback);
+        var levels = new List<float>();
+        mixer.MicLevelChanged += l => levels.Add(l);
+
+        mixer.Start();
+        loopback.Emit(new AudioSample(new[] { 1f, 1f, 1f, 1f }, 48000, 2));
+
+        Assert.Empty(levels);
+        Assert.Equal(0f, mixer.MicLevel);
+    }
+
+    [Fact]
+    public void MicFailure_LogsAndResetsLevel()
+    {
+        var mic = new FakeSource();
+        var logs = new List<string>();
+        var mixer = new AudioMixer(mic, new FakeSource(), m => logs.Add(m));
+        mixer.Start();
+        mic.Emit(new AudioSample(new[] { 0.5f }, 48000, 1));
+
+        var last = -1f;
+        mixer.MicLevelChanged += l => last = l;
+        mic.Fail(new InvalidOperationException("boom"));
+
+        Assert.Contains(logs, l => l.Contains("boom"));
+        Assert.Equal(0f, last);
+    }
+
+    [Fact]
+    public void LoopbackFailure_LogsButKeepsMic()
+    {
+        var loopback = new FakeSource();
+        var logs = new List<string>();
+        var mixer = new AudioMixer(new FakeSource(), loopback, m => logs.Add(m));
+        mixer.Start();
+
+        var last = -1f;
+        mixer.MicLevelChanged += l => last = l;
+        loopback.Fail(new InvalidOperationException("boom"));
+
+        Assert.Contains(logs, l => l.Contains("boom"));
+        Assert.Equal(-1f, last);
+    }
+
+    [Fact]
+    public void Dispose_StopsAndDisposesSources()
+    {
+        var mic = new FakeSource();
+        var loopback = new FakeSource();
+        var mixer = new AudioMixer(mic, loopback);
+        mixer.Start();
+
+        mixer.Dispose();
+
+        Assert.True(mic.Disposed);
+        Assert.True(loopback.Disposed);
+        Assert.Equal(1, mic.StopCount);
+    }
+
+    [Fact]
+    public void Dispose_UnsubscribesEvents()
+    {
+        var mic = new FakeSource();
+        var loopback = new FakeSource();
+        var mixer = new AudioMixer(mic, loopback);
+        mixer.Dispose();
+
+        var levels = new List<float>();
+        mixer.MicLevelChanged += l => levels.Add(l);
+        mic.Emit(new AudioSample(new[] { 1f }, 48000, 1));
+
+        Assert.Empty(levels);
+    }
+}
+
+public class AudioLevelMeterTests
+{
+    [Fact]
+    public void ConstantSine_ConvergesToRms()
+    {
+        var meter = new AudioLevelMeter();
+        var sample = new AudioSample(new[] { 0.5f, -0.5f, 0.5f, -0.5f }, 48000, 1);
+
+        float level = 0;
+        for (var i = 0; i < 30; i++)
+            level = meter.Push(sample);
+
+        Assert.InRange(level, 0.45f, 0.55f);
+    }
+
+    [Fact]
+    public void Silence_DrivesTowardZero()
+    {
+        var meter = new AudioLevelMeter();
+        meter.Push(new AudioSample(new[] { 1f, 1f, 1f, 1f }, 48000, 1));
+        var samples = new float[1024];
+        var sample = new AudioSample(samples, 48000, 1);
+
+        for (var i = 0; i < 50; i++)
+            meter.Push(sample);
+
+        Assert.Equal(0f, meter.Level, 3);
+    }
+
+    [Fact]
+    public void EmptySample_KeepsLevel()
+    {
+        var meter = new AudioLevelMeter();
+        meter.Push(new AudioSample(new[] { 1f, 1f, 1f, 1f }, 48000, 1));
+        var before = meter.Level;
+
+        var level = meter.Push(new AudioSample(Array.Empty<float>(), 48000, 1));
+
+        Assert.Equal(before, level);
+    }
+
+    [Fact]
+    public void Reset_ZerosLevel()
+    {
+        var meter = new AudioLevelMeter();
+        meter.Push(new AudioSample(new[] { 1f, 1f, 1f, 1f }, 48000, 1));
+
+        meter.Reset();
+
+        Assert.Equal(0f, meter.Level);
+    }
+}
+
+public class WaveToFloatTests
+{
+    private static byte[] FloatSamples(params float[] values)
+    {
+        var bytes = new byte[values.Length * 4];
+        Buffer.BlockCopy(values, 0, bytes, 0, bytes.Length);
+        return bytes;
+    }
+
+    [Fact]
+    public void IeeeFloat32_PreservesValues()
+    {
+        var format = WaveFormat.CreateIeeeFloatWaveFormat(48000, 2);
+        var samples = WaveToFloat.Convert(FloatSamples(0.25f, -0.5f, 1f), 12, format);
+
+        Assert.Equal(3, samples.Length);
+        Assert.Equal(0.25f, samples[0], 4);
+        Assert.Equal(-0.5f, samples[1], 4);
+        Assert.Equal(1f, samples[2], 4);
+    }
+
+    [Fact]
+    public void Pcm16_NormalizesToUnitRange()
+    {
+        var format = WaveFormat.CreateCustomFormat(WaveFormatEncoding.Pcm, 48000, 1, 48000 * 2, 2, 16);
+        var bytes = new byte[] { 0x00, 0x00, 0xFF, 0x7F, 0x00, 0x80 };
+        var samples = WaveToFloat.Convert(bytes, 6, format);
+
+        Assert.Equal(3, samples.Length);
+        Assert.Equal(0f, samples[0], 4);
+        Assert.Equal(1f, samples[1], 4);
+        Assert.Equal(-1f, samples[2], 4);
+    }
+
+    [Fact]
+    public void TruncatedTrailingBytes_AreIgnored()
+    {
+        var format = WaveFormat.CreateIeeeFloatWaveFormat(48000, 2);
+        var bytes = new byte[] { 0, 0, 0x80, 0x3F, 1, 2, 3 }; // 1 float + 3 stray bytes
+
+        var samples = WaveToFloat.Convert(bytes, bytes.Length, format);
+
+        Assert.Single(samples);
+        Assert.Equal(1f, samples[0], 4);
+    }
+}

ytLive.Tests/FfmpegEncoderTests.cs

@@ -0,0 +1,290 @@
+using System.Diagnostics;
+using System.Threading.Channels;
+using Xunit;
+using ytLive.Models;
+using ytLive.Services;
+using ytLive.Services.Encoder;
+
+namespace ytLive.Tests;
+
+/// <summary>
+/// The FFmpeg subprocess encoder (TASK 4 ship step 3). The integration test drives
+/// the full lifecycle against fakes: encoder probe → subprocess start with the right
+/// args → raw frames into stdin → stderr progress parsed into health → graceful stop.
+/// The units pin down the pure pieces (args, progress parser, encoder picker) and
+/// the failure edges. No real ffmpeg binary, no network.
+/// </summary>
+public class FfmpegEncoderTests
+{
+    private sealed class QueuedReader : TextReader
+    {
+        private readonly Channel<string?> _channel = Channel.CreateUnbounded<string?>();
+        public void Enqueue(string s) => _channel.Writer.TryWrite(s);
+        public void Complete() => _channel.Writer.TryComplete();
+        public override string? ReadLine() => ReadLineAsync().GetAwaiter().GetResult();
+
+        public override async Task<string?> ReadLineAsync()
+        {
+            try
+            {
+                return await _channel.Reader.ReadAsync().AsTask().ConfigureAwait(false);
+            }
+            catch (ChannelClosedException)
+            {
+                return null; // stream EOF — the process exited and the pipe closed
+            }
+        }
+    }
+
+    private sealed class FakeEncoderProcess : IEncoderProcess
+    {
+        public ProcessStartInfo? StartInfo { get; private set; }
+        public MemoryStream Stdin { get; } = new();
+        public Stream StandardInput => Stdin;
+        public TextReader StandardOutput { get; }
+        public bool HasExited { get; private set; }
+        public int ExitCode { get; private set; }
+        public bool Killed { get; private set; }
+        public bool Started { get; private set; }
+
+        private readonly TaskCompletionSource _exit =
+            new(TaskCreationOptions.RunContinuationsAsynchronously);
+        private readonly QueuedReader _error = new();
+
+        public FakeEncoderProcess(string probeOutput = "")
+            => StandardOutput = new StringReader(probeOutput);
+
+        public TextReader StandardError => _error;
+        public void EnqueueStderr(string line) => _error.Enqueue(line);
+
+        public void Start(ProcessStartInfo startInfo)
+        {
+            StartInfo = startInfo;
+            Started = true;
+        }
+
+        public void SignalExit(int code = 0)
+        {
+            ExitCode = code;
+            HasExited = true;
+            _error.Complete();
+            _exit.TrySetResult();
+        }
+
+        public void Kill()
+        {
+            Killed = true;
+            _error.Complete();
+            _exit.TrySetResult();
+        }
+
+        public Task WaitForExitAsync(CancellationToken cancellationToken = default) => _exit.Task;
+
+        public void Dispose()
+        {
+            _error.Complete();
+            _exit.TrySetResult();
+        }
+    }
+
+    private sealed class FakeEncoderProcessFactory
+    {
+        private readonly Queue<FakeEncoderProcess> _processes = new();
+        public void Return(FakeEncoderProcess p) => _processes.Enqueue(p);
+        public FakeEncoderProcess Create() => _processes.Dequeue();
+    }
+
+    private sealed class StubLocator : IFfmpegLocator
+    {
+        public Task<string> LocateAsync(CancellationToken cancellationToken = default)
+            => Task.FromResult(@"C:\tools\ffmpeg.exe");
+    }
+
+    private static byte[] BgraFrame(int w, int h, byte b, byte g, byte r)
+    {
+        var bytes = new byte[w * h * 4];
+        for (var i = 0; i < bytes.Length; i += 4)
+        {
+            bytes[i] = b;
+            bytes[i + 1] = g;
+            bytes[i + 2] = r;
+            bytes[i + 3] = 255;
+        }
+        return bytes;
+    }
+
+    [Fact]
+    public async Task Start_ProbesEncoder_FeedsFrames_ParsesHealth_StopsGracefully()
+    {
+        const string encoders =
+            " V..... h264_nvenc  NVIDIA NVENC H.264 encoder (codec h264)\n" +
+            " V..... libopenh264  OpenH264 H.264 (codec h264)\n";
+        var probe = new FakeEncoderProcess(encoders);
+        var encoderProc = new FakeEncoderProcess();
+        var factory = new FakeEncoderProcessFactory();
+        factory.Return(probe);
+        factory.Return(encoderProc);
+
+        using var encoder = new FfmpegEncoder(new StubLocator(), factory.Create);
+
+        var health = new TaskCompletionSource<StreamHealth>(TaskCreationOptions.RunContinuationsAsynchronously);
+        encoder.HealthUpdated += (_, h) => health.TrySetResult(h);
+
+        var options = new EncoderOptions
+        {
+            RtmpUrl = "rtmp://a.rtmp.youtube.com/live2/abc-xyz",
+            Width = 1920,
+            Height = 1080,
+            Fps = 60,
+            BitrateKbps = 8000,
+        };
+
+        await encoder.StartAsync(options);
+
+        Assert.True(probe.Started, "the -encoders probe must run");
+        Assert.True(encoderProc.Started, "the encoder subprocess must start");
+        Assert.Equal(@"C:\tools\ffmpeg.exe", encoderProc.StartInfo!.FileName);
+        var args = encoderProc.StartInfo.ArgumentList.ToArray();
+        var c = Array.IndexOf(args, "-c:v");
+        Assert.True(
+            args[c + 1] == "h264_nvenc",
+            "hardware NVENC must be preferred over the listed openh264");
+
+        await encoder.SubmitFrameAsync(new VideoFrame(1920, 1080, BgraFrame(1920, 1080, 255, 0, 0)));
+        await encoder.SubmitFrameAsync(new VideoFrame(1920, 1080, BgraFrame(1920, 1080, 0, 255, 0)));
+        Assert.Equal(2 * 1920 * 1080 * 4, encoderProc.Stdin.Length);
+
+        encoderProc.EnqueueStderr(
+            "frame= 120 fps= 59.9 q=28.0 size= 1024KiB time=00:00:02.00 bitrate= 4000.1kbits/s speed=1.00x");
+        var h = await health.Task.WaitAsync(TimeSpan.FromSeconds(5));
+        Assert.Equal(4000.1, h.CurrentBitrate, 1);
+        Assert.Equal(59.9, h.FPS, 1);
+        Assert.Equal(TimeSpan.FromSeconds(2), h.StreamDuration);
+
+        encoderProc.SignalExit();
+        await encoder.StopAsync();
+        Assert.False(encoder.IsRunning);
+        Assert.False(encoderProc.Killed, "graceful stop must not kill the process");
+        Assert.Equal(StreamStatus.Offline, h.Status);
+    }
+
+    [Fact]
+    public async Task Start_WithoutRtmpUrl_Throws()
+    {
+        using var encoder = new FfmpegEncoder(new StubLocator());
+        await Assert.ThrowsAsync<ArgumentException>(() => encoder.StartAsync(new EncoderOptions()));
+    }
+
+    [Fact]
+    public async Task SubmitFrame_WhenNotRunning_Throws()
+    {
+        using var encoder = new FfmpegEncoder(new StubLocator());
+        await Assert.ThrowsAsync<InvalidOperationException>(
+            () => encoder.SubmitFrameAsync(new VideoFrame(2, 2, new byte[16])));
+    }
+
+    [Fact]
+    public async Task Stop_WithoutStart_IsNoop()
+    {
+        using var encoder = new FfmpegEncoder(new StubLocator());
+        await encoder.StopAsync();
+        Assert.False(encoder.IsRunning);
+    }
+
+    [Fact]
+    public async Task ProcessDeath_RaisesFailed()
+    {
+        var encoderProc = new FakeEncoderProcess();
+        var factory = new FakeEncoderProcessFactory();
+        factory.Return(new FakeEncoderProcess());
+        factory.Return(encoderProc);
+
+        using var encoder = new FfmpegEncoder(new StubLocator(), factory.Create);
+        var failed = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
+        encoder.ProcessFailed += (_, msg) => failed.TrySetResult(msg);
+
+        await encoder.StartAsync(new EncoderOptions { RtmpUrl = "rtmp://x/y" });
+        encoderProc.SignalExit(1);
+        var msg = await failed.Task.WaitAsync(TimeSpan.FromSeconds(5));
+        Assert.Contains("1", msg);
+    }
+
+    [Fact]
+    public void Args_Gop_IsFpsTimesFour()
+    {
+        var options = new EncoderOptions { Fps = 60 };
+        Assert.Equal(240, options.GopSize);
+
+        var args = FfmpegArgs.Build(options, "libopenh264").ToArray();
+        var g = Array.IndexOf(args, "-g");
+        Assert.Equal("240", args[g + 1]);
+        var keyint = Array.IndexOf(args, "-keyint_min");
+        Assert.Equal("240", args[keyint + 1]);
+    }
+
+    [Fact]
+    public void Args_IncludeInputOutputAndCompliance()
+    {
+        var args = FfmpegArgs.Build(
+            new EncoderOptions
+            {
+                RtmpUrl = "rtmp://a.rtmp.youtube.com/live2/key",
+                Width = 1920,
+                Height = 1080,
+                Fps = 60,
+                BitrateKbps = 8000,
+            },
+            "libopenh264").ToArray();
+
+        Assert.Contains("-f", args);
+        Assert.Contains("rawvideo", args);
+        Assert.Contains("pipe:0", args);
+        Assert.Contains("1920x1080", args);
+        Assert.Contains("anullsrc=channel_layout=stereo:sample_rate=48000", args);
+        Assert.Contains("-sc_threshold", args);
+        Assert.Contains("-bf", args);
+        Assert.Contains("yuv420p", args);
+        Assert.Contains("aac", args);
+        Assert.Contains("flv", args);
+        Assert.Contains("rtmp://a.rtmp.youtube.com/live2/key", args);
+    }
+
+    [Fact]
+    public void ProgressParser_ParsesRealStatsLine()
+    {
+        var p = FfmpegProgressParser.TryParse(
+            "frame=  123 fps= 59.9 q=28.0 size=   1024KiB time=00:00:02.04 bitrate= 4000.1kbits/s speed=1.00x");
+        Assert.NotNull(p);
+        Assert.Equal(123, p.Value.Frame);
+        Assert.Equal(59.9, p.Value.Fps, 1);
+        Assert.Equal(4000.1, p.Value.BitrateKbps, 1);
+        Assert.Equal(2.04, p.Value.Duration.TotalSeconds, 2);
+        Assert.Equal(1024 * 1024, p.Value.SizeBytes);
+    }
+
+    [Fact]
+    public void ProgressParser_IgnoresBannerAndErrors()
+    {
+        Assert.Null(FfmpegProgressParser.TryParse("ffmpeg version 6.1 Copyright (c) 2000-2026 the FFmpeg developers"));
+        Assert.Null(FfmpegProgressParser.TryParse("Error while opening encoder for output stream #0:0"));
+        Assert.Null(FfmpegProgressParser.TryParse(""));
+    }
+
+    [Fact]
+    public void EncoderPicker_PrefersHardware_NeverLibx264()
+    {
+        var listing =
+            " V..... libx264   libx264 H.264 / AVC (codec h264)\n" +
+            " V..... libopenh264  OpenH264 H.264 (codec h264)\n" +
+            " V..... h264_nvenc  NVIDIA NVENC H.264 encoder (codec h264)\n";
+        Assert.Equal("h264_nvenc", FfmpegEncoderPicker.Pick(listing));
+
+        var onlyGpl = " V..... libx264   libx264 H.264 / AVC (codec h264)\n";
+        Assert.Equal("libopenh264", FfmpegEncoderPicker.Pick(onlyGpl));
+
+        var software = " V..... libopenh264  OpenH264 H.264 (codec h264)\n";
+        Assert.Equal("libopenh264", FfmpegEncoderPicker.Pick(software));
+
+        Assert.Equal("libopenh264", FfmpegEncoderPicker.Pick("no encoders at all"));
+    }
+}

ytLive.csproj

@@ -36,6 +36,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.Data.Sqlite" Version="8.0.10"/>
+    <PackageReference Include="NAudio.Wasapi" Version="2.2.1"/>
     <PackageReference Include="SQLitePCLRaw.bundle_e_sqlite3" Version="2.1.12"/>
     <PackageReference Include="System.Security.Cryptography.ProtectedData" Version="8.0.0"/>
   </ItemGroup>