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

TASKS.md

@@ -200,7 +200,7 @@ 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 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)
@@ -390,6 +390,42 @@ Tests: `FfmpegEncoderTests` integration (probe → spawn with NVENC preferred
 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