docs(android): add audio-capture design + missing-functionality review

- android-audio-capture-plan.md — design behind the merged on-device audio
  capture feature (487259a).
- android-missing-functionality.md — Android missing-feature review notes.

ANDROID-REVIEW/android-audio-capture-plan.md

@@ -0,0 +1,308 @@
+# Plan: Android on-device audio capture
+
+> Status: proposed plan (not yet approved). No code changes. Last updated 2026-06-01.
+
+## Context
+
+LedGrab's audio-reactive features (music analyzer, audio value sources, band filters)
+depend on capturing an audio stream and running it through `AudioAnalyzer`
+(`server/src/ledgrab/core/audio/analysis.py`). On desktop this is fed by **WASAPI**
+(Windows) or **Sounddevice/PortAudio** (cross-platform). On the **experimental
+Android-TV build** neither is available — `sounddevice` has no Chaquopy wheel and PortAudio
+isn't bundled — so `core/audio/__init__.py` registers only `DemoAudioEngine`, and
+audio-reactive lighting is effectively dead on Android.
+
+Android does not need PortAudio: the platform exposes **`AudioPlaybackCapture`** (API 29+),
+which captures system playback audio and **takes a `MediaProjection` token — the very token
+the app already obtains for screen capture** (`ScreenCapture(projection, …)`). This plan adds
+a push-based Android audio engine so the TV box can drive sound-reactive lighting from its own
+media playback, at parity with how desktop audio feeds the analyzer.
+
+The design mirrors the working screen-capture bridge
+(`mediaprojection_engine.py` ↔ `ScreenCapture.kt` ↔ `PythonBridge`) and the existing audio
+engine abstraction (`AudioCaptureEngine` / `AudioCaptureStreamBase` /
+`AudioEngineRegistry`). **No new Python dependencies** (`numpy` is already bundled) → no
+Chaquopy / `build.gradle.kts` `pip {}` changes.
+
+---
+
+## Approach
+
+A new **push-based** audio engine registered in the existing `AudioEngineRegistry`:
+
+- **Python:** `AndroidAudioEngine` + `AndroidAudioCaptureStream` mirroring `SounddeviceEngine`,
+  but `read_chunk()` pops PCM from a module-level queue that **Kotlin fills** (mirror of
+  `mediaprojection_engine.push_frame`). High `ENGINE_PRIORITY` so
+  `AudioEngineRegistry.get_best_available_engine()` selects it on Android. The existing
+  `ManagedAudioStream` capture loop and `AudioAnalyzer` consume `read_chunk()` unchanged.
+- **Android:** an `AudioCapture` helper using `AudioRecord` + `AudioPlaybackCaptureConfiguration`
+  (reusing `CaptureService`'s `MediaProjection`), pushing float32 PCM to Python. Mic
+  (`AudioSource.MIC`) fallback. Wired into `CaptureService` next to `ScreenCapture`.
+
+```
+[media playback] → AudioRecord (AudioPlaybackCapture, reuses MediaProjection)
+   → AudioCapture.kt → PythonBridge.pushAudio(pcmFloat32, frames, channels)
+   → android_audio_engine.push_samples()  [module-level queue]
+   → AndroidAudioCaptureStream.read_chunk()  → ManagedAudioStream → AudioAnalyzer  [unchanged]
+```
+
+---
+
+## Part A — Python (server)
+
+**New file: `server/src/ledgrab/core/audio/android_audio_engine.py`** — mirror
+`mediaprojection_engine.py` (queue + configure + push) and `sounddevice_engine.py` (engine/stream shape):
+
+```python
+import queue
+import numpy as np
+from typing import Any, Dict, List
+from ledgrab.core.audio.base import AudioCaptureEngine, AudioCaptureStreamBase, AudioDeviceInfo
+from ledgrab.utils import get_logger
+
+logger = get_logger(__name__)
+
+_pcm_queue: "queue.Queue[np.ndarray]" = queue.Queue(maxsize=8)
+_sample_rate = 48000
+_channels = 2
+_chunk_size = 1024
+_active = False
+
+def configure(sample_rate: int, channels: int, chunk_size: int) -> None:
+    """Called from Kotlin before audio frames start flowing. Drains stale PCM."""
+    global _sample_rate, _channels, _chunk_size, _active
+    while not _pcm_queue.empty():
+        try: _pcm_queue.get_nowait()
+        except queue.Empty: break
+    _sample_rate, _channels, _chunk_size = sample_rate, channels, chunk_size
+    _active = True
+
+def push_samples(pcm_float32: bytes) -> None:
+    """Push one interleaved float32 PCM chunk from Kotlin. Drops oldest if full."""
+    samples = np.frombuffer(pcm_float32, dtype=np.float32)
+    try:
+        _pcm_queue.put_nowait(samples)
+    except queue.Full:
+        try: _pcm_queue.get_nowait()
+        except queue.Empty: pass
+        try: _pcm_queue.put_nowait(samples)
+        except queue.Full: pass
+
+def shutdown() -> None:
+    global _active
+    _active = False
+
+
+class AndroidAudioCaptureStream(AudioCaptureStreamBase):
+    @property
+    def channels(self) -> int: return _channels
+    @property
+    def sample_rate(self) -> int: return _sample_rate
+    @property
+    def chunk_size(self) -> int: return _chunk_size
+    def initialize(self) -> None:
+        if not _active:
+            raise RuntimeError("Android audio engine not configured (only valid in-app).")
+        self._initialized = True
+    def cleanup(self) -> None:
+        self._initialized = False
+    def read_chunk(self) -> np.ndarray | None:
+        try:
+            return _pcm_queue.get(timeout=0.1)  # 1-D float32 interleaved
+        except queue.Empty:
+            return None
+
+
+class AndroidAudioEngine(AudioCaptureEngine):
+    ENGINE_TYPE = "android_playback"
+    ENGINE_PRIORITY = 100  # highest on Android (demo is lower)
+    @classmethod
+    def is_available(cls) -> bool:
+        from ledgrab.utils.platform import is_android
+        return is_android() and _active
+    @classmethod
+    def get_default_config(cls) -> Dict[str, Any]:
+        return {"sample_rate": _sample_rate, "channels": _channels, "chunk_size": _chunk_size}
+    @classmethod
+    def enumerate_devices(cls) -> List[AudioDeviceInfo]:
+        if not cls.is_available(): return []
+        return [AudioDeviceInfo(index=0, name="Android playback (system audio)",
+                                is_input=True, is_loopback=True,
+                                channels=_channels, default_samplerate=float(_sample_rate))]
+    @classmethod
+    def create_stream(cls, device_index, is_loopback, config) -> AndroidAudioCaptureStream:
+        return AndroidAudioCaptureStream(device_index, is_loopback, {**cls.get_default_config(), **config})
+```
+
+**Modify `server/src/ledgrab/core/audio/__init__.py`** — register behind a guarded import,
+matching the existing `_has_wasapi` / `_has_sounddevice` pattern:
+
+```python
+try:
+    from ledgrab.core.audio.android_audio_engine import AndroidAudioEngine
+    _has_android_audio = True
+except ImportError:
+    _has_android_audio = False
+...
+if _has_android_audio:
+    AudioEngineRegistry.register(AndroidAudioEngine)
+```
+
+**Reused, unchanged:** `AudioEngineRegistry.get_best_available_engine()` (picks by priority),
+`ManagedAudioStream._capture_loop()` (`audio_capture.py`), `AudioAnalyzer`, the audio value
+sources, and the device-enumeration endpoints. The Android engine appears as one loopback
+device named "Android playback (system audio)".
+
+---
+
+## Part B — Android (Kotlin + manifest)
+
+**New file: `android/app/src/main/java/com/ledgrab/android/AudioCapture.kt`**
+
+Mirrors `ScreenCapture.kt`, taking the same `MediaProjection`:
+
+```kotlin
+class AudioCapture(
+    private val projection: MediaProjection,
+    private val bridge: PythonBridge,
+    private val sampleRate: Int = 48000,
+    private val channels: Int = 2,
+    private val chunkFrames: Int = 1024,
+)
+```
+
+- `start()` (API 29+, MediaProjection mode):
+  - Build `AudioPlaybackCaptureConfiguration(projection)` adding usages
+    `USAGE_MEDIA`, `USAGE_GAME`, `USAGE_UNKNOWN` (the capturable set).
+  - `AudioRecord.Builder().setAudioPlaybackCaptureConfig(cfg)` with
+    `AudioFormat(ENCODING_PCM_FLOAT, sampleRate, CHANNEL_IN_STEREO)`.
+  - On a dedicated `HandlerThread`, loop `audioRecord.read(floatBuf, …, READ_BLOCKING)` →
+    wrap into a little-endian float32 `ByteArray` (reusable buffer, like `ScreenCapture`'s
+    `frameBuffer`) → `bridge.pushAudio(bytes, framesRead, channels)`.
+- `stop()`: stop/release `AudioRecord`, quit the thread.
+- **Mic fallback** (`startMic()`): `AudioSource.MIC` for root mode (no MediaProjection) or
+  API < 29. Used only when playback capture is unavailable.
+
+**Modify `android/app/src/main/java/com/ledgrab/android/PythonBridge.kt`** — add the audio
+push path (same shape as `pushFrame`, with a cached PyObject handle):
+
+```kotlin
+@Volatile private var androidAudioEngine: PyObject? = null
+
+fun configureAudio(sampleRate: Int, channels: Int, chunkFrames: Int) {
+    val engine = Python.getInstance().getModule("ledgrab.core.audio.android_audio_engine")
+    engine.callAttr("configure", sampleRate, channels, chunkFrames)
+    androidAudioEngine = engine
+}
+fun pushAudio(pcmFloat32: ByteArray, frames: Int, channels: Int) {
+    if (!running) return
+    androidAudioEngine?.let {
+        try { it.callAttr("push_samples", pcmFloat32) }
+        catch (e: Exception) { Log.w(TAG, "pushAudio failed: ${e.message}") }
+    }
+}
+```
+
+**Modify `android/app/src/main/java/com/ledgrab/android/CaptureService.kt`** — in the
+MediaProjection start path (where `ScreenCapture` is created with the projection), if
+`RECORD_AUDIO` is granted and API ≥ 29, also `bridge.configureAudio(...)` and start an
+`AudioCapture(projection, bridge)`. Stop/release it in `onDestroy` alongside `ScreenCapture`.
+Root path → optional mic fallback (or skip; see Risks).
+
+**Modify `android/app/src/main/AndroidManifest.xml`:**
+```xml
+<uses-permission android:name="android.permission.RECORD_AUDIO" />
+<!-- For mic-mode foreground capture on API 34+ (playback capture is covered by the
+     existing mediaProjection FGS type): -->
+<uses-permission android:name="android.permission.FOREGROUND_SERVICE_MICROPHONE" />
+```
+The existing `CaptureService` already declares `foregroundServiceType="mediaProjection|specialUse"`
+and holds `FOREGROUND_SERVICE_MEDIA_PROJECTION`; add `microphone` to the type only if mic
+fallback is implemented.
+
+**Modify `MainActivity.kt`** — request `RECORD_AUDIO` at runtime alongside the existing
+`ensureNotificationPermission()` (POST_NOTIFICATIONS) flow, before starting capture. Capture
+proceeds without audio if denied (graceful degradation).
+
+---
+
+## Orchestration decision (the main trade-off)
+
+Desktop starts audio capture **on demand** when an audio-reactive source is acquired
+(`AudioCaptureManager.acquire`). On Android, PCM only flows if Kotlin has set up `AudioRecord`.
+
+- **MVP (recommended):** start `AudioCapture` when `CaptureService` starts (if `RECORD_AUDIO`
+  granted + MediaProjection mode + API ≥ 29) and push continuously; the bounded queue drops
+  frames when no audio source consumes them. Simplest; modest extra CPU.
+- **Future optimization:** on-demand start/stop signaled Python→Kotlin (Chaquopy can call
+  Kotlin, as `BleBridge`/`UsbSerialBridge` show) so `AudioRecord` runs only while an
+  audio-reactive source is active. Defer unless CPU/battery on low-end boxes warrants it.
+
+---
+
+## What does NOT change
+
+- **Frontend / API** — audio engine + device selection, the music analyzer UI, and audio value
+  sources are engine-agnostic; the Android engine shows up via the existing device enumeration.
+- **`build.gradle.kts` / Chaquopy pip block** — no new Python packages.
+- **Audio analysis pipeline** — `AudioAnalyzer`, band filters, `ManagedAudioStream` untouched.
+
+---
+
+## Files
+
+**Create**
+- `server/src/ledgrab/core/audio/android_audio_engine.py`
+- `android/app/src/main/java/com/ledgrab/android/AudioCapture.kt`
+- `server/tests/core/audio/test_android_audio_engine.py`
+
+**Modify**
+- `server/src/ledgrab/core/audio/__init__.py` — guarded import + registry registration.
+- `android/app/src/main/java/com/ledgrab/android/PythonBridge.kt` — `configureAudio` + `pushAudio`.
+- `android/app/src/main/java/com/ledgrab/android/CaptureService.kt` — start/stop `AudioCapture`.
+- `android/app/src/main/java/com/ledgrab/android/MainActivity.kt` — request `RECORD_AUDIO`.
+- `android/app/src/main/AndroidManifest.xml` — `RECORD_AUDIO` (+ mic FGS if mic fallback).
+
+---
+
+## Tests (Python — run on desktop CI, no Android device needed)
+
+New `server/tests/core/audio/test_android_audio_engine.py`:
+
+- `configure()` then `push_samples()` → `read_chunk()` returns the same float32 samples;
+  queue drops oldest when full (push > maxsize).
+- `AndroidAudioEngine.is_available()` is `False` until `configure()` and only on Android
+  (monkeypatch `ledgrab.utils.platform.is_android`); `True` after.
+- `enumerate_devices()` returns exactly one loopback device when active, `[]` otherwise.
+- Integration: with `is_android()` patched true + `configure()`, `get_best_available_engine()`
+  returns `"android_playback"` (priority beats demo), and a stream created via
+  `AudioEngineRegistry.create_stream("android_playback", 0, True, {})` yields pushed chunks.
+- Registry isolation: use `AudioEngineRegistry.clear_registry()` / re-register in fixtures so
+  desktop engines aren't disturbed.
+
+## Verification
+
+1. **Python:** `py -3.13 -m pytest tests/core/audio/test_android_audio_engine.py --no-cov -q`
+   (from `server/`), then the full suite.
+2. **Lint:** `ruff check src/ tests/ --fix` (from `server/`).
+3. **Android build:** `./gradlew :app:assembleDebug` (from `android/`).
+4. **On device/emulator (manual):** install APK → grant `RECORD_AUDIO` + screen-capture consent
+   → start capture → play non-DRM media (e.g. a local video / YouTube web) → create an
+   audio-reactive value source bound to a strip → confirm the LEDs react to the audio, and the
+   Android playback device appears in audio device enumeration.
+
+## Risks / notes
+
+- **DRM opt-out:** Netflix/Disney+/etc. set audio as non-capturable; `AudioPlaybackCapture`
+  yields silence for them. Works for non-DRM media and the device's own audio. Document in UI.
+- **API 29 minimum** for playback capture (minSdk is 24). API 24–28 and root mode (no
+  MediaProjection) → mic fallback only, or audio unsupported. Gate cleanly + log.
+- **`RECORD_AUDIO`** is a runtime "dangerous" permission — must be requested; capture must
+  degrade gracefully when denied.
+- **Format:** request `ENCODING_PCM_FLOAT` so Kotlin pushes float32 matching
+  `read_chunk()`'s contract (1-D interleaved float32, length = frames × channels). If a device
+  rejects float, capture 16-bit PCM and convert (`/32768.0`) before pushing.
+- **Latency/CPU:** small `chunkFrames` (e.g. 1024 @ 48 kHz ≈ 21 ms) keeps reactivity tight;
+  continuous capture (MVP) adds modest CPU on low-end boxes — see the orchestration trade-off.
+- **R8/ProGuard:** minify is disabled and the Python module is resolved by string from Kotlin;
+  no new keep-rules needed.

ANDROID-REVIEW/android-missing-functionality.md

@@ -0,0 +1,153 @@
+# Android (TV) — Missing Functionality Assessment
+
+> Status: review/feasibility document. No code changes. Last updated 2026-06-01.
+
+## Context
+
+LedGrab ships an **experimental on-device Android-TV build**: a Kotlin shell that
+embeds the Python FastAPI server via **Chaquopy**, with Kotlin↔Python **bridges**
+(`PythonBridge`, `BleBridge`, `UsbSerialBridge`). Several desktop features are
+unavailable on this build because their Python backends rely on native libraries
+that have no Android/Chaquopy wheels (`mss`, `dxcam`, `sounddevice`/PortAudio,
+`opencv`, `nvidia-ml-py`, `winrt`, `dbus-next`), or on OS facilities Android
+sandboxes differently.
+
+The README "Feature support by OS" table now carries an Android column reflecting
+this. This document assesses **whether each missing feature can be added**, how, and
+whether it's worth it.
+
+### The enabling pattern (why most of this is feasible)
+
+Every desktop capability that's "missing" on Android is missing only because of a
+*native dependency*, not because the capability is impossible. Android exposes the
+same capability through a platform API, and the codebase already has the bridge
+shape to plug it in:
+
+> **Bridge pattern:** a Kotlin component captures an event/buffer → pushes it across
+> the Chaquopy JNI boundary into a **module-level receiver** in a small Python engine
+> → an existing engine/stream consumes it unchanged.
+
+Reference implementation: `server/src/ledgrab/core/capture_engines/mediaprojection_engine.py`
+(`configure()` + `push_frame()` + a bounded `queue.Queue`) ↔
+`android/app/src/main/java/com/ledgrab/android/ScreenCapture.kt` ↔
+`PythonBridge.pushFrame()`. Screen capture already works on Android this exact way.
+
+So for most missing features the work is: **add a Kotlin capture source + a thin
+Python receiver engine mirroring that pattern.**
+
+---
+
+## Current Android capability matrix
+
+| Feature | Desktop | Android (TV) today | Missing? |
+| ------- | ------- | ------------------ | -------- |
+| Screen capture | DXCam/WGC/MSS | ✅ MediaProjection + root `screenrecord` | No |
+| LED transports (network/USB-serial/BLE) | ✅ | ✅ (USB via Android driver, BLE via Android bridge) | No |
+| System metrics | psutil | ✅ CPU/RAM/battery/thermal via `/proc`, `/sys` (`AndroidMetricsProvider`) | No |
+| **Audio capture** | WASAPI / Sounddevice | ❌ no PortAudio | **Yes** |
+| **Notification capture** | WinRT / D-Bus | ❌ listener only Win/Linux | **Yes** |
+| Webcam capture | OpenCV | ❌ no OpenCV wheel | Yes (niche) |
+| GPU monitoring | NVML | ❌ no NVIDIA GPU | Marginal |
+| Capture from *another* Android phone | scrcpy/ADB | ❌ | Skip (redundant) |
+| Automation: window/process conditions | Windows ctypes | ❌ sandboxed | Partial |
+| Monitor names / multi-display | WMI / generic | Single built-in display | Low value |
+
+---
+
+## Per-feature feasibility
+
+### 🔊 Audio capture — **FEASIBLE, HIGH VALUE** ⭐ (detailed plan exists)
+
+- **Blocker:** only `sounddevice`/PortAudio is missing — not the capability.
+- **Android path:** `AudioPlaybackCapture` (API 29+) captures system playback audio and
+  **takes a `MediaProjection` token — which the app already obtains for screen capture.**
+  Kotlin `AudioRecord` → push PCM (float32) → a new push-based `AndroidAudioEngine`
+  mirroring `mediaprojection_engine.py`, registered in `core/audio/__init__.py`, feeding
+  the existing `AudioAnalyzer` unchanged. Mic (`AudioSource.MIC`) is the fallback.
+- **Effort:** moderate. **Value:** high — music/sound-reactive lighting is a flagship use
+  on a TV box. **No new Python deps.**
+- ⚠️ DRM-protected apps (Netflix etc.) opt out of playback capture; works for non-DRM
+  media and the device's own audio. Root mode (no MediaProjection) → mic-only.
+- 📄 **See `android-audio-capture-plan.md`** for the full implementation plan.
+
+### 🔔 Notification capture — **FEASIBLE, HIGH VALUE** ⭐ (planned)
+
+- **Android is the *best* platform for this:** `NotificationListenerService` is the native,
+  event-push mechanism (no polling).
+- **Path:** a `NotificationListenerService` resolves the posting app's display label and
+  pushes it via a module-level `push_notification()` into the existing
+  `os_notification_listener.py` pipeline (a new push-based `_AndroidBackend` alongside
+  `_WindowsBackend`/`_LinuxBackend`). Existing `NotificationColorStripSource` filters,
+  per-app colors/sounds, and the history endpoint all work unchanged. **No new Python deps.**
+- **Permission:** user enables "Notification access" in Settings (`ACTION_NOTIFICATION_LISTENER_SETTINGS`);
+  no runtime-permission popup.
+- **Effort:** moderate. **Value:** high.
+- 📄 **Plan approved & detailed** — see `C:\Users\Alexei\.claude\plans\deep-enchanting-muffin.md`
+  (app-name parity; prompt-once permission UX).
+
+### 📷 Webcam capture — **FEASIBLE, LOW VALUE**
+
+- **Blocker** is `opencv-python-headless` (no Chaquopy cp311 wheel) — but capture doesn't
+  *need* OpenCV. Use **CameraX / Camera2** + `ImageReader` in Kotlin and push frames through
+  the same bridge as MediaProjection into a new `CameraBridgeEngine`.
+- **Effort:** moderate. **Value:** low — TVs rarely have cameras; USB-UVC webcams need extra
+  device handling. Recommend deferring unless a concrete use case appears.
+
+### 🎮 GPU monitoring — **MARGINAL, SKIP FOR NOW**
+
+- NVML is desktop-NVIDIA only. Android GPU load lives in **vendor-specific sysfs**
+  (Adreno `/sys/class/kgsl/kgsl-3d0/gpubusy`, Mali `/sys/class/devfreq/*.mali/...`),
+  inconsistent and often root-only.
+- CPU/RAM/battery/thermal are **already** covered by `AndroidMetricsProvider`. A best-effort
+  GPU-load reader could be added to that provider, but reliability is poor and value is low.
+
+### 🪟 Automation: window/process conditions — **PARTIAL**
+
+- Android forbids full window/process enumeration (`getRunningTasks` restricted since API 21+).
+- **Obtainable:** the *current foreground app package* via `UsageStatsManager` (needs the
+  `PACKAGE_USAGE_STATS` special access) or an `AccessibilityService`.
+- So "when <app> is in the foreground → scene X" is feasible (mirrors
+  `automations/platform_detector.py`, which currently returns empty off-Windows); full
+  window-title matching is **not**. **Effort:** moderate. **Value:** moderate (per-app scenes
+  on a TV box).
+
+### 📱 Capture from *another* Android phone (scrcpy/ADB) — **SKIP**
+
+- Impractical and redundant: no `adb` binary in Chaquopy, TV boxes can't reliably host an
+  adb server, and the device already captures its **own** screen via MediaProjection.
+
+### 🖥️ Monitor names / multi-display — **LOW VALUE**
+
+- `DisplayManager` can report a better display name and enumerate secondary (HDMI) displays,
+  but MediaProjection captures the default display; capturing a secondary display is more
+  involved and rarely useful on a single-screen box.
+
+---
+
+## Prioritization
+
+| Priority | Feature | Effort | Value | New Python deps | Status |
+| -------- | ------- | ------ | ----- | --------------- | ------ |
+| 1 | Notification capture | Moderate | High | None | **Plan approved** |
+| 2 | Audio capture | Moderate | High | None | **Plan written** (this folder) |
+| 3 | Automation: foreground-app condition | Moderate | Moderate | None | Idea |
+| 4 | Webcam capture (CameraX) | Moderate | Low | None | Idea |
+| — | GPU load (vendor sysfs) | Low–Med | Low | None | Not recommended |
+| — | Capture from another phone | — | — | — | Won't do |
+| — | Multi-display / monitor names | Low | Low | None | Not recommended |
+
+**Recommended order:** ship notifications → ship audio → reassess. Both reuse existing
+infrastructure (bridge pattern, the MediaProjection consent token, the audio/notification
+pipelines) and add **zero** Python dependencies, so neither risks the Chaquopy
+`--no-deps` build constraint documented in `CLAUDE.md`.
+
+## Cross-cutting notes
+
+- **No `build.gradle.kts` / Chaquopy pip impact** for notifications or audio — both use Android
+  platform APIs (Kotlin) + stdlib/`numpy` (already bundled) on the Python side.
+- **Per-instance `PythonBridge`:** `PythonBridge` is created per `CaptureService` instance, so
+  system-bound services (e.g. a `NotificationListenerService`) call Python via the
+  process-global `Python.getInstance()` rather than borrowing that bridge.
+- **Permissions are the recurring friction**, not the capture: audio needs `RECORD_AUDIO` +
+  (for playback capture) a MediaProjection token; notifications need the "Notification access"
+  settings toggle; foreground-app automation needs `PACKAGE_USAGE_STATS`.

android/app/src/main/AndroidManifest.xml

@@ -39,6 +39,14 @@
     <!-- POST_NOTIFICATIONS for Android 13+ foreground service notification -->
     <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
 
+    <!-- RECORD_AUDIO for on-device system-playback capture (AudioPlaybackCapture,
+         API 29+) feeding audio-reactive lighting. Runtime "dangerous" permission,
+         requested in MainActivity; capture degrades gracefully when denied.
+         Playback capture runs under the existing mediaProjection FGS type, so no
+         FOREGROUND_SERVICE_MICROPHONE / microphone FGS type is needed (that would
+         only be required if the mic-fallback path ran inside the service). -->
+    <uses-permission android:name="android.permission.RECORD_AUDIO" />
+
     <!-- Autostart on boot — BootReceiver spawns CaptureService in root
          mode so capture resumes without the user touching the remote. -->
     <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />

android/app/src/main/java/com/ledgrab/android/AudioCapture.kt

@@ -0,0 +1,234 @@
+package com.ledgrab.android
+
+import android.annotation.SuppressLint
+import android.media.AudioAttributes
+import android.media.AudioFormat
+import android.media.AudioPlaybackCaptureConfiguration
+import android.media.AudioRecord
+import android.media.MediaRecorder
+import android.media.projection.MediaProjection
+import android.os.Build
+import android.util.Log
+import java.nio.ByteBuffer
+import java.nio.ByteOrder
+
+/**
+ * Captures audio with [AudioRecord] and pushes interleaved float32 PCM to
+ * the LedGrab Python server via [PythonBridge], where the
+ * `android_audio_engine` feeds it into the unchanged audio-analysis
+ * pipeline.
+ *
+ * Two sources:
+ *  - [start] — system playback capture via `AudioPlaybackCapture` (API 29+),
+ *    reusing the same [MediaProjection] token the app already holds for
+ *    screen capture. This is the primary path on the consent flow.
+ *  - [startMic] — microphone fallback (`AudioSource.MIC`) for paths with no
+ *    MediaProjection (root mode) or API < 29.
+ *
+ * Mirrors [ScreenCapture]'s shape: a dedicated capture thread, a single
+ * reusable cross-JNI buffer (no per-block allocation → no GC churn on
+ * low-end TV boxes), and graceful teardown in [stop].
+ *
+ * The capture format is negotiated by [AudioRecord]; the **actual**
+ * channel count and sample rate are read back and forwarded to
+ * `configureAudio` so the Python analyzer's interleaving matches the bytes
+ * we push (e.g. a stereo request that the device satisfies as mono).
+ */
+class AudioCapture(
+    private val projection: MediaProjection?,
+    private val bridge: PythonBridge,
+    private val sampleRate: Int = 48000,
+    private val channels: Int = 2,
+    private val chunkFrames: Int = 1024,
+) {
+    companion object {
+        private const val TAG = "AudioCapture"
+        private const val BYTES_PER_FLOAT = 4
+    }
+
+    private var audioRecord: AudioRecord? = null
+    private var captureThread: Thread? = null
+    @Volatile private var running = false
+
+    /**
+     * Start system playback capture (API 29+). Requires the app to hold
+     * RECORD_AUDIO and a valid [projection]. Returns true if capture began.
+     */
+    @SuppressLint("MissingPermission")
+    fun start(): Boolean {
+        if (running) return true
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q) {
+            Log.i(TAG, "Playback capture needs API 29+; skipping (have ${Build.VERSION.SDK_INT})")
+            return false
+        }
+        val proj = projection
+        if (proj == null) {
+            Log.i(TAG, "No MediaProjection; playback capture unavailable")
+            return false
+        }
+
+        val config = AudioPlaybackCaptureConfiguration.Builder(proj)
+            .addMatchingUsage(AudioAttributes.USAGE_MEDIA)
+            .addMatchingUsage(AudioAttributes.USAGE_GAME)
+            .addMatchingUsage(AudioAttributes.USAGE_UNKNOWN)
+            .build()
+
+        val record = try {
+            AudioRecord.Builder()
+                .setAudioFormat(audioFormat())
+                .setBufferSizeInBytes(bufferBytes())
+                .setAudioPlaybackCaptureConfig(config)
+                .build()
+        } catch (e: Exception) {
+            Log.e(TAG, "Failed to build playback AudioRecord: ${e.message}")
+            return false
+        }
+        return begin(record, "playback")
+    }
+
+    /**
+     * Start microphone capture (fallback). Works on API 24+ and needs no
+     * MediaProjection. Requires RECORD_AUDIO. Returns true if capture began.
+     *
+     * ⚠️ SECURITY/POLICY: currently UNWIRED (no caller). Microphone capture is
+     * a materially different posture than playback capture — it records real
+     * room audio (bystander voices). Before wiring this into [CaptureService]:
+     *  - add FOREGROUND_SERVICE_MICROPHONE permission + the `microphone` FGS
+     *    type (on API 34+ the service is killed without it), and
+     *  - add the Play Store privacy disclosure for microphone use,
+     *  - re-trigger a security review.
+     * Do NOT call this from inside the foreground service without the above.
+     */
+    @SuppressLint("MissingPermission")
+    fun startMic(): Boolean {
+        if (running) return true
+        val record = try {
+            AudioRecord.Builder()
+                .setAudioSource(MediaRecorder.AudioSource.MIC)
+                .setAudioFormat(audioFormat())
+                .setBufferSizeInBytes(bufferBytes())
+                .build()
+        } catch (e: Exception) {
+            Log.e(TAG, "Failed to build mic AudioRecord: ${e.message}")
+            return false
+        }
+        return begin(record, "mic")
+    }
+
+    /** Stop capturing and release all resources. Idempotent. */
+    fun stop() {
+        running = false
+        // AudioRecord.stop() unblocks a pending READ_BLOCKING read within
+        // milliseconds, so the loop sees running=false and returns well inside
+        // the 500ms join window — release() below won't race a live read.
+        // (Mirrors ScreenCapture's bounded join.)
+        runCatching { audioRecord?.stop() }
+        captureThread?.let { runCatching { it.join(500) } }
+        captureThread = null
+        runCatching { audioRecord?.release() }
+        audioRecord = null
+        runCatching { bridge.shutdownAudio() }
+        Log.i(TAG, "Audio capture stopped")
+    }
+
+    // ── internals ──────────────────────────────────────────────────────
+
+    private fun begin(record: AudioRecord, mode: String): Boolean {
+        if (record.state != AudioRecord.STATE_INITIALIZED) {
+            Log.e(TAG, "AudioRecord ($mode) failed to initialize")
+            runCatching { record.release() }
+            return false
+        }
+        val actualChannels = record.channelCount.coerceAtLeast(1)
+        val actualRate = record.sampleRate
+
+        // Confirm recording actually started before reporting success —
+        // startRecording() can throw (exclusive-capture contention) or
+        // leave the record in a non-recording state, in which case read()
+        // would only ever return errors.
+        val started = runCatching { record.startRecording() }.isSuccess &&
+            record.recordingState == AudioRecord.RECORDSTATE_RECORDING
+        if (!started) {
+            Log.e(TAG, "AudioRecord ($mode) failed to start recording")
+            runCatching { record.release() }
+            return false
+        }
+
+        // Recording confirmed — tell Python the real negotiated format
+        // before frames flow, so the analyzer's channel/sample-rate match
+        // the interleaving we push.
+        bridge.configureAudio(actualRate, actualChannels, chunkFrames)
+
+        audioRecord = record
+        running = true
+        captureThread = Thread(
+            { captureLoop(record, actualChannels) },
+            "LedGrab-AudioCapture",
+        ).also { it.start() }
+        Log.i(TAG, "Audio capture started ($mode, sr=$actualRate ch=$actualChannels chunk=$chunkFrames)")
+        return true
+    }
+
+    /**
+     * Blocking read loop. Accumulates into fixed `chunkFrames * channels`
+     * float blocks and pushes only COMPLETE blocks — [AudioRecord.read]
+     * returns a variable count, so partial reads are stitched here rather
+     * than handed to Python as ragged chunks (the analyzer requires
+     * whole-frame, ≤ chunk-size blocks).
+     */
+    private fun captureLoop(record: AudioRecord, actualChannels: Int) {
+        val blockFloats = chunkFrames * actualChannels
+        val floatBuf = FloatArray(blockFloats)
+        // Reusable little-endian byte buffer — Python copies on push, so the
+        // same backing array is safe to overwrite next block. Default
+        // ByteBuffer order is BIG_ENDIAN, which would corrupt every sample;
+        // LITTLE_ENDIAN matches numpy's native float32 on all Android ABIs.
+        val byteBuf = ByteArray(blockFloats * BYTES_PER_FLOAT)
+        val floatView = ByteBuffer.wrap(byteBuf).order(ByteOrder.LITTLE_ENDIAN).asFloatBuffer()
+
+        var filled = 0
+        while (running) {
+            val n = record.read(floatBuf, filled, blockFloats - filled, AudioRecord.READ_BLOCKING)
+            if (n < 0) {
+                if (running) {
+                    // A negative read (e.g. ERROR_DEAD_OBJECT after an audio-route
+                    // change, ERROR_INVALID_OPERATION) means this AudioRecord is
+                    // finished. Deactivate the Python engine so is_available() stops
+                    // advertising a dead stream and the audio-reactive consumer isn't
+                    // left polling an empty queue forever. We're on the capture thread,
+                    // so we can't call stop() (it would self-join) — just flip running
+                    // and shut the engine down; onDestroy's stop() releases the record.
+                    Log.w(TAG, "AudioRecord.read error: $n — stopping audio capture")
+                    running = false
+                    runCatching { bridge.shutdownAudio() }
+                }
+                break
+            }
+            filled += n
+            if (filled < blockFloats) continue
+
+            floatView.clear()
+            floatView.put(floatBuf, 0, blockFloats)
+            bridge.pushAudio(byteBuf)
+            filled = 0
+        }
+    }
+
+    private fun channelMask(): Int =
+        if (channels >= 2) AudioFormat.CHANNEL_IN_STEREO else AudioFormat.CHANNEL_IN_MONO
+
+    private fun audioFormat(): AudioFormat =
+        AudioFormat.Builder()
+            .setEncoding(AudioFormat.ENCODING_PCM_FLOAT)
+            .setSampleRate(sampleRate)
+            .setChannelMask(channelMask())
+            .build()
+
+    private fun bufferBytes(): Int {
+        val minBuf = AudioRecord.getMinBufferSize(sampleRate, channelMask(), AudioFormat.ENCODING_PCM_FLOAT)
+        // A few blocks of headroom so a slow consumer doesn't overrun the
+        // hardware buffer between reads.
+        val want = chunkFrames * channels * BYTES_PER_FLOAT * 4
+        return if (minBuf > 0) maxOf(minBuf, want) else want
+    }
+}

android/app/src/main/java/com/ledgrab/android/CaptureService.kt

@@ -4,9 +4,11 @@ import android.app.Notification
 import android.app.NotificationChannel
 import android.app.NotificationManager
 import android.app.PendingIntent
+import android.Manifest
 import android.app.Service
 import android.content.Context
 import android.content.Intent
+import android.content.pm.PackageManager
 import android.content.pm.ServiceInfo
 import android.media.projection.MediaProjection
 import android.media.projection.MediaProjectionManager
@@ -85,6 +87,7 @@ class CaptureService : Service() {
     private var bridge: PythonBridge? = null
     private var screenCapture: ScreenCapture? = null
     private var rootCapture: RootScreenrecord? = null
+    private var audioCapture: AudioCapture? = null
     private var mediaProjection: MediaProjection? = null
 
     // Service-scoped coroutine scope for the root-capture watchdog.
@@ -338,6 +341,25 @@ class CaptureService : Service() {
             onProjectionStopped = { stopSelf() },
         ).also { it.start() }
 
+        // Reuse the same projection to capture system playback audio so
+        // audio-reactive lighting works on-device (API 29+, RECORD_AUDIO
+        // granted). Best-effort: screen capture and the server keep running
+        // if audio is unavailable. Started AFTER ScreenCapture so the
+        // projection's callback is already registered.
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q &&
+            checkSelfPermission(Manifest.permission.RECORD_AUDIO) ==
+            PackageManager.PERMISSION_GRANTED
+        ) {
+            audioCapture = AudioCapture(projection, newBridge).also { ac ->
+                if (!ac.start()) {
+                    Log.i(TAG, "Playback audio capture unavailable — continuing without audio")
+                    audioCapture = null
+                }
+            }
+        } else {
+            Log.i(TAG, "RECORD_AUDIO not granted or API < 29 — audio-reactive capture disabled")
+        }
+
         Log.i(TAG, "LedGrab service started (MediaProjection) — web UI at $url")
     }
 
@@ -351,6 +373,10 @@ class CaptureService : Service() {
         screenCapture?.stop()
         screenCapture = null
 
+        // Stop audio before the server: stop() calls bridge.shutdownAudio().
+        audioCapture?.stop()
+        audioCapture = null
+
         rootCapture?.stop()
         rootCapture = null
 

android/app/src/main/java/com/ledgrab/android/MainActivity.kt

@@ -53,6 +53,7 @@ class MainActivity : Activity() {
         private const val SERVER_PORT = 8080
         private const val REQUEST_MEDIA_PROJECTION = 1001
         private const val REQUEST_POST_NOTIFICATIONS = 1002
+        private const val REQUEST_RECORD_AUDIO = 1003
         private const val QR_SIZE_PX = 560
     }
 
@@ -215,6 +216,7 @@ class MainActivity : Activity() {
 
     private fun startCaptureService(resultCode: Int, resultData: Intent) {
         ensureNotificationPermission()
+        ensureAudioPermission()
         val intent = CaptureService.createIntent(this, resultCode, resultData)
         ContextCompat.startForegroundService(this, intent)
         updateUI()
@@ -471,4 +473,24 @@ class MainActivity : Activity() {
             }
         }
     }
+
+    /**
+     * Request RECORD_AUDIO (API 29+) so the capture service can capture
+     * system playback audio for audio-reactive lighting.  Fire-and-forget,
+     * like [ensureNotificationPermission]: capture still works without it
+     * (just no audio), so we don't block on the result.  If first granted
+     * here, audio becomes available on the next Start.
+     */
+    private fun ensureAudioPermission() {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q) return
+        if (checkSelfPermission(Manifest.permission.RECORD_AUDIO)
+            != PackageManager.PERMISSION_GRANTED
+        ) {
+            @Suppress("DEPRECATION")
+            requestPermissions(
+                arrayOf(Manifest.permission.RECORD_AUDIO),
+                REQUEST_RECORD_AUDIO,
+            )
+        }
+    }
 }

android/app/src/main/java/com/ledgrab/android/PythonBridge.kt

@@ -28,6 +28,7 @@ class PythonBridge(private val context: Context) {
     // single-writer/single-reader pattern we have here.
     @Volatile private var mediaProjectionEngine: PyObject? = null
     @Volatile private var rootEngine: PyObject? = null
+    @Volatile private var androidAudioEngine: PyObject? = null
 
     /**
      * Configure the MediaProjection engine with screen dimensions.
@@ -53,6 +54,49 @@ class PythonBridge(private val context: Context) {
         Log.i(TAG, "Root screenrecord engine configured: ${width}x${height}")
     }
 
+    /**
+     * Configure the Android playback-capture audio engine with the format
+     * actually negotiated by [AudioCapture]'s `AudioRecord`. Must be called
+     * before [pushAudio]. Caches the module handle for the per-block fast
+     * path (same pattern as [configureCapture]).
+     */
+    fun configureAudio(sampleRate: Int, channels: Int, chunkFrames: Int) {
+        val py = Python.getInstance()
+        val engine = py.getModule("ledgrab.core.audio.android_audio_engine")
+        engine.callAttr("configure", sampleRate, channels, chunkFrames)
+        androidAudioEngine = engine
+        Log.i(TAG, "Android audio engine configured: sr=$sampleRate ch=$channels chunk=$chunkFrames")
+    }
+
+    /**
+     * Push one interleaved little-endian float32 PCM block to the Python
+     * audio engine. Called from [AudioCapture]'s capture thread. The byte
+     * array crosses the JNI boundary; Python copies it on receipt, so the
+     * caller may reuse the same buffer for the next block.
+     */
+    fun pushAudio(pcmFloat32: ByteArray) {
+        if (!running) return
+        val engine = androidAudioEngine ?: return
+        try {
+            engine.callAttr("push_samples", pcmFloat32)
+        } catch (e: Exception) {
+            Log.w(TAG, "Failed to push audio: ${e.message}")
+        }
+    }
+
+    /**
+     * Deactivate the Python audio engine. Called from [AudioCapture.stop].
+     */
+    fun shutdownAudio() {
+        val engine = androidAudioEngine ?: return
+        try {
+            engine.callAttr("shutdown")
+        } catch (e: Exception) {
+            Log.w(TAG, "Failed to shut down audio engine: ${e.message}")
+        }
+        androidAudioEngine = null
+    }
+
     /**
      * Start the LedGrab FastAPI server on a background thread.
      *

server/src/ledgrab/core/audio/__init__.py

@@ -38,6 +38,19 @@ try:
 except ImportError:
     _has_sounddevice = False
 
+# Android playback-capture engine — pure Python (numpy only), but the
+# guard keeps the registration pattern uniform and tolerant of any future
+# import-time dependency.
+try:
+    from ledgrab.core.audio.android_audio_engine import (
+        AndroidAudioEngine,
+        AndroidAudioCaptureStream,
+    )
+
+    _has_android_audio = True
+except ImportError:
+    _has_android_audio = False
+
 from ledgrab.core.audio.demo_engine import DemoAudioEngine, DemoAudioCaptureStream
 
 # Auto-register available engines
@@ -45,6 +58,8 @@ if _has_wasapi:
     AudioEngineRegistry.register(WasapiEngine)
 if _has_sounddevice:
     AudioEngineRegistry.register(SounddeviceEngine)
+if _has_android_audio:
+    AudioEngineRegistry.register(AndroidAudioEngine)
 AudioEngineRegistry.register(DemoAudioEngine)
 
 __all__ = [
@@ -65,3 +80,5 @@ if _has_wasapi:
     __all__ += ["WasapiEngine", "WasapiCaptureStream"]
 if _has_sounddevice:
     __all__ += ["SounddeviceEngine", "SounddeviceCaptureStream"]
+if _has_android_audio:
+    __all__ += ["AndroidAudioEngine", "AndroidAudioCaptureStream"]

server/src/ledgrab/core/audio/android_audio_engine.py

@@ -0,0 +1,229 @@
+"""Android playback-capture audio engine.
+
+Receives PCM pushed from Kotlin (via Chaquopy) through a module-level
+sample queue.  The Kotlin layer captures system playback audio with
+``AudioRecord`` + ``AudioPlaybackCaptureConfiguration`` (reusing the
+app's ``MediaProjection`` token) and calls :func:`push_samples` with
+interleaved float32 PCM for each fixed-size block.
+
+Mirrors the screen-capture bridge
+(``core/capture_engines/mediaprojection_engine.py``): a module-level
+queue plus ``configure`` / ``push_samples`` / ``shutdown`` filled by
+Kotlin, consumed through the standard :class:`AudioCaptureStreamBase`
+interface so :class:`~ledgrab.core.audio.audio_capture.ManagedAudioStream`
+and :class:`~ledgrab.core.audio.analysis.AudioAnalyzer` work unchanged.
+
+This engine is only available when running inside the LedGrab Android
+app, which has set up the sample queue via :func:`configure`.
+"""
+
+import queue
+from typing import Any, Dict, List
+
+import numpy as np
+
+from ledgrab.core.audio.base import (
+    AudioCaptureEngine,
+    AudioCaptureStreamBase,
+    AudioDeviceInfo,
+)
+from ledgrab.utils import get_logger
+from ledgrab.utils.platform import is_android
+
+logger = get_logger(__name__)
+
+# ---------------------------------------------------------------------------
+# Sample queue — the bridge between Kotlin and Python
+# ---------------------------------------------------------------------------
+
+_pcm_queue: "queue.Queue[np.ndarray]" = queue.Queue(maxsize=8)
+_sample_rate = 48000
+_channels = 2
+_chunk_size = 1024
+_active = False
+_frames_received = 0
+
+
+def configure(sample_rate: int, channels: int, chunk_size: int) -> None:
+    """Set the stream format.  Called from Kotlin before frames flow.
+
+    Drains any stale PCM from a previous capture session so the first
+    chunk after a restart is actually current.  ``channels`` /
+    ``sample_rate`` should be the values the Kotlin ``AudioRecord``
+    actually negotiated (which can differ from the requested values,
+    e.g. a stereo request that falls back to mono) — the analyzer keys
+    off these, so they must match the interleaving of pushed samples.
+    """
+    global _sample_rate, _channels, _chunk_size, _active, _frames_received
+    while not _pcm_queue.empty():
+        try:
+            _pcm_queue.get_nowait()
+        except queue.Empty:
+            break
+    _sample_rate = sample_rate
+    _channels = max(1, channels)
+    _chunk_size = max(1, chunk_size)
+    _frames_received = 0
+    _active = True
+    logger.info(
+        "Android audio engine configured: sr=%d channels=%d chunk=%d",
+        _sample_rate,
+        _channels,
+        _chunk_size,
+    )
+
+
+def push_samples(pcm_float32: bytes) -> None:
+    """Push one interleaved float32 PCM block from Kotlin.
+
+    The byte buffer is interpreted as native-endian float32 (Kotlin
+    packs little-endian; all Android ABIs are little-endian).  Drops the
+    oldest queued block if the consumer is slow (non-blocking).
+
+    Defensive framing: the downstream :class:`AudioAnalyzer` reshapes to
+    ``(-1, channels)`` and copies into ``chunk_size``-sized scratch
+    buffers, so it raises on a block whose length is not a whole number
+    of frames or that exceeds ``chunk_size`` frames.  We trim to a whole
+    multiple of ``_channels`` and clamp to ``_chunk_size`` frames so a
+    malformed push can never crash the capture thread.
+    """
+    global _frames_received
+    # np.frombuffer raises if the length isn't a whole number of float32s.
+    # Kotlin always pushes complete blocks, but guard so a malformed buffer is
+    # dropped here rather than surfacing as an exception across the JNI bridge.
+    if len(pcm_float32) % 4 != 0:
+        return
+    samples = np.frombuffer(pcm_float32, dtype=np.float32)
+
+    # Trim to whole frames, then clamp to chunk_size frames.
+    frames = len(samples) // _channels
+    if frames <= 0:
+        return
+    frames = min(frames, _chunk_size)
+    usable = frames * _channels
+
+    # Copy out of the read-only frombuffer view so the queued block owns its
+    # memory.  This lets the Kotlin side push from a reusable buffer (low GC on
+    # low-end TV boxes) without the not-yet-consumed queued block aliasing
+    # bytes Kotlin is about to overwrite.  Mirrors mediaprojection_engine's
+    # push_frame .copy().
+    block = samples[:usable].copy()
+
+    _frames_received += 1
+    if _frames_received == 1 or _frames_received % 100 == 0:
+        logger.info("Android audio: received %d blocks", _frames_received)
+
+    try:
+        _pcm_queue.put_nowait(block)
+    except queue.Full:
+        try:
+            _pcm_queue.get_nowait()
+        except queue.Empty:
+            pass
+        try:
+            _pcm_queue.put_nowait(block)
+        except queue.Full:
+            pass
+
+
+def shutdown() -> None:
+    """Deactivate the engine.  Called when the Android app stops audio."""
+    global _active
+    _active = False
+    logger.info("Android audio engine shut down")
+
+
+# ---------------------------------------------------------------------------
+# CaptureStream
+# ---------------------------------------------------------------------------
+
+
+class AndroidAudioCaptureStream(AudioCaptureStreamBase):
+    """Reads PCM blocks pushed by Kotlin from the module-level queue."""
+
+    @property
+    def channels(self) -> int:
+        return _channels
+
+    @property
+    def sample_rate(self) -> int:
+        return _sample_rate
+
+    @property
+    def chunk_size(self) -> int:
+        return _chunk_size
+
+    def initialize(self) -> None:
+        if self._initialized:
+            return
+        if not _active:
+            raise RuntimeError(
+                "Android audio engine not configured. "
+                "This engine is only available inside the Android app."
+            )
+        self._initialized = True
+        logger.info("Android audio capture stream initialized")
+
+    def cleanup(self) -> None:
+        self._initialized = False
+        logger.info("Android audio capture stream cleaned up")
+
+    def read_chunk(self) -> np.ndarray | None:
+        try:
+            return _pcm_queue.get(timeout=0.1)  # 1-D float32 interleaved
+        except queue.Empty:
+            return None
+
+
+# ---------------------------------------------------------------------------
+# CaptureEngine
+# ---------------------------------------------------------------------------
+
+
+class AndroidAudioEngine(AudioCaptureEngine):
+    """Android playback-capture audio engine.
+
+    Only available when running inside the LedGrab Android app, which
+    calls :func:`configure` once audio capture is set up.  Exposes a
+    single loopback "device" representing the system audio mix.
+    """
+
+    ENGINE_TYPE = "android_playback"
+    ENGINE_PRIORITY = 100  # highest on a real Android device (demo only wins in demo mode)
+
+    @classmethod
+    def is_available(cls) -> bool:
+        return is_android() and _active
+
+    @classmethod
+    def get_default_config(cls) -> Dict[str, Any]:
+        return {
+            "sample_rate": _sample_rate,
+            "channels": _channels,
+            "chunk_size": _chunk_size,
+        }
+
+    @classmethod
+    def enumerate_devices(cls) -> List[AudioDeviceInfo]:
+        if not cls.is_available():
+            return []
+        return [
+            AudioDeviceInfo(
+                index=0,
+                name="Android playback (system audio)",
+                is_input=True,
+                is_loopback=True,
+                channels=_channels,
+                default_samplerate=float(_sample_rate),
+            )
+        ]
+
+    @classmethod
+    def create_stream(
+        cls,
+        device_index: int,
+        is_loopback: bool,
+        config: Dict[str, Any],
+    ) -> AndroidAudioCaptureStream:
+        merged = {**cls.get_default_config(), **config}
+        return AndroidAudioCaptureStream(device_index, is_loopback, merged)

server/tests/core/test_android_audio_engine.py

@@ -0,0 +1,253 @@
+"""Tests for the Android playback-capture audio engine.
+
+These run on desktop CI (no Android device needed): ``is_android`` is
+monkeypatched and PCM is pushed directly into the module-level queue,
+exactly as the Kotlin bridge would.
+"""
+
+import queue
+
+import numpy as np
+import pytest
+
+# Importing the package triggers auto-registration of AndroidAudioEngine.
+import ledgrab.core.audio  # noqa: F401
+from ledgrab.core.audio import android_audio_engine as eng
+from ledgrab.core.audio.analysis import AudioAnalysis, AudioAnalyzer
+from ledgrab.core.audio.audio_capture import AudioCaptureManager
+from ledgrab.core.audio.factory import AudioEngineRegistry
+
+ENGINE_MOD = "ledgrab.core.audio.android_audio_engine"
+SAMPLE_RATE = 48000
+CHANNELS = 2
+CHUNK = 1024
+
+
+# ---------------------------------------------------------------------------
+# Helpers / fixtures
+# ---------------------------------------------------------------------------
+
+
+def _drain() -> None:
+    while not eng._pcm_queue.empty():
+        try:
+            eng._pcm_queue.get_nowait()
+        except queue.Empty:
+            break
+
+
+def _block(marker: float = 0.0, frames: int = CHUNK, channels: int = CHANNELS) -> np.ndarray:
+    """A float32 interleaved block whose first sample is ``marker``."""
+    data = np.zeros(frames * channels, dtype=np.float32)
+    data[0] = marker
+    return data
+
+
+@pytest.fixture
+def reset_engine():
+    """Reset module-global engine state; snapshot/restore the registry.
+
+    The engine keeps its queue + format in module globals and the registry
+    is a class-level singleton — both must be restored so this test file
+    never disturbs the desktop engines other tests rely on.
+    """
+    saved_engines = dict(AudioEngineRegistry._engines)
+    eng.shutdown()
+    _drain()
+    eng._sample_rate = SAMPLE_RATE
+    eng._channels = CHANNELS
+    eng._chunk_size = CHUNK
+    eng._frames_received = 0
+
+    yield eng
+
+    eng.shutdown()
+    _drain()
+    AudioEngineRegistry._engines.clear()
+    AudioEngineRegistry._engines.update(saved_engines)
+
+
+@pytest.fixture
+def on_android(monkeypatch, reset_engine):
+    """Engine fixture with ``is_android`` forced True and demo mode off."""
+    monkeypatch.setattr(f"{ENGINE_MOD}.is_android", lambda: True)
+    monkeypatch.setattr("ledgrab.core.audio.factory.is_demo_mode", lambda: False)
+    return reset_engine
+
+
+# ---------------------------------------------------------------------------
+# Queue / push contract
+# ---------------------------------------------------------------------------
+
+
+def test_configure_then_push_round_trips_samples(reset_engine):
+    # Arrange
+    eng.configure(SAMPLE_RATE, CHANNELS, CHUNK)
+    samples = np.arange(CHUNK * CHANNELS, dtype=np.float32)
+
+    # Act
+    eng.push_samples(samples.tobytes())
+    stream = eng.AndroidAudioEngine.create_stream(0, True, {})
+    stream.initialize()
+    got = stream.read_chunk()
+
+    # Assert
+    assert got is not None
+    np.testing.assert_array_equal(got, samples)
+
+
+def test_queue_drops_oldest_when_full(reset_engine):
+    # Arrange
+    eng.configure(SAMPLE_RATE, CHANNELS, CHUNK)
+    maxsize = eng._pcm_queue.maxsize  # 8
+
+    # Act — push more blocks than the queue can hold, each tagged 0..N-1
+    total = maxsize + 2
+    for i in range(total):
+        eng.push_samples(_block(marker=float(i)).tobytes())
+
+    drained = []
+    while True:
+        try:
+            drained.append(eng._pcm_queue.get_nowait())
+        except queue.Empty:
+            break
+
+    # Assert — only the newest `maxsize` blocks survived, oldest dropped
+    assert len(drained) == maxsize
+    markers = [int(b[0]) for b in drained]
+    assert markers == list(range(total - maxsize, total))
+
+
+def test_initialize_raises_when_not_configured(reset_engine):
+    # Arrange — fixture left the engine inactive
+    stream = eng.AndroidAudioEngine.create_stream(0, True, {})
+
+    # Act / Assert
+    with pytest.raises(RuntimeError):
+        stream.initialize()
+
+
+def test_read_chunk_returns_none_when_empty(reset_engine):
+    eng.configure(SAMPLE_RATE, CHANNELS, CHUNK)
+    stream = eng.AndroidAudioEngine.create_stream(0, True, {})
+    stream.initialize()
+    assert stream.read_chunk() is None
+
+
+# ---------------------------------------------------------------------------
+# Availability / enumeration (platform-gated)
+# ---------------------------------------------------------------------------
+
+
+def test_is_available_requires_android_and_active(monkeypatch, reset_engine):
+    # Not configured yet → inactive → unavailable even on Android.
+    monkeypatch.setattr(f"{ENGINE_MOD}.is_android", lambda: True)
+    assert eng.AndroidAudioEngine.is_available() is False
+
+    # Configured → active + Android → available.
+    eng.configure(SAMPLE_RATE, CHANNELS, CHUNK)
+    assert eng.AndroidAudioEngine.is_available() is True
+
+    # Active but not on Android → unavailable.
+    monkeypatch.setattr(f"{ENGINE_MOD}.is_android", lambda: False)
+    assert eng.AndroidAudioEngine.is_available() is False
+
+
+def test_enumerate_devices(on_android):
+    # Inactive → no devices.
+    assert eng.AndroidAudioEngine.enumerate_devices() == []
+
+    # Active → exactly one loopback device.
+    eng.configure(SAMPLE_RATE, CHANNELS, CHUNK)
+    devices = eng.AndroidAudioEngine.enumerate_devices()
+    assert len(devices) == 1
+    dev = devices[0]
+    assert dev.is_loopback is True
+    assert dev.is_input is True
+    assert "Android playback" in dev.name
+    assert dev.channels == CHANNELS
+
+
+# ---------------------------------------------------------------------------
+# Regression guard — the analyzer must never crash on a malformed block
+# (over-length or non-frame-divisible). This is the on-device failure the
+# plan review surfaced; the desktop suite must catch it.
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "raw_floats",
+    [
+        (CHUNK + 100) * CHANNELS,  # over-length (more frames than chunk_size)
+        CHUNK * CHANNELS + 1,  # not a whole number of stereo frames
+        3,  # tiny + odd
+        CHUNK * CHANNELS,  # exact (control)
+    ],
+)
+def test_pushed_block_never_crashes_analyzer(reset_engine, raw_floats):
+    # Arrange
+    eng.configure(SAMPLE_RATE, CHANNELS, CHUNK)
+    pcm = np.random.default_rng(0).standard_normal(raw_floats).astype(np.float32)
+    analyzer = AudioAnalyzer(sample_rate=SAMPLE_RATE, chunk_size=CHUNK)
+    stream = eng.AndroidAudioEngine.create_stream(0, True, {})
+    stream.initialize()
+
+    # Act
+    eng.push_samples(pcm.tobytes())
+    chunk = stream.read_chunk()
+
+    # Assert — chunk is a safe shape and analyze() does not raise.
+    assert chunk is not None
+    assert len(chunk) % CHANNELS == 0
+    assert len(chunk) <= CHUNK * CHANNELS
+    analysis = analyzer.analyze(chunk, CHANNELS)
+    assert isinstance(analysis, AudioAnalysis)
+
+
+# ---------------------------------------------------------------------------
+# Registry integration
+# ---------------------------------------------------------------------------
+
+
+def test_best_available_engine_is_android_when_active(on_android):
+    # Arrange
+    eng.configure(SAMPLE_RATE, CHANNELS, CHUNK)
+
+    # Act
+    best = AudioEngineRegistry.get_best_available_engine()
+
+    # Assert — priority 100 beats every desktop engine; demo only wins in demo mode.
+    assert best == "android_playback"
+
+
+def test_stream_via_registry_yields_pushed_chunk(on_android):
+    # Arrange
+    eng.configure(SAMPLE_RATE, CHANNELS, CHUNK)
+    samples = np.linspace(-1.0, 1.0, CHUNK * CHANNELS, dtype=np.float32)
+
+    # Act
+    stream = AudioEngineRegistry.create_stream("android_playback", 0, True, {})
+    stream.initialize()
+    eng.push_samples(samples.tobytes())
+    got = stream.read_chunk()
+
+    # Assert
+    assert stream.channels == CHANNELS
+    assert stream.sample_rate == SAMPLE_RATE
+    assert stream.chunk_size == CHUNK
+    np.testing.assert_array_equal(got, samples)
+
+
+def test_device_surfaces_through_capture_manager(on_android):
+    # Arrange
+    eng.configure(SAMPLE_RATE, CHANNELS, CHUNK)
+
+    # Act
+    devices = AudioCaptureManager.enumerate_devices()
+
+    # Assert — the Android device is enumerated and tagged with its engine.
+    android = [d for d in devices if d["engine_type"] == "android_playback"]
+    assert len(android) == 1
+    assert android[0]["name"] == "Android playback (system audio)"
+    assert android[0]["is_loopback"] is True