Android: automatic brightness from local mic (LiteRT beat tracking)

[SlyWombat]

Feature

Android-app automatic master-brightness driven by the phone's local microphone, using LiteRT (TensorFlow Lite Runtime) on devices that support it to do real-time audio analysis. Map the dominant bass-beat envelope to visible brightness changes so the rig pulses with the music in the room without any external audio routing or DAW.

Behaviour

• Operator opens Stage tab. The current brightness slider is replaced with a modal button that toggles "Auto Brightness" on/off (and shows current state — idle / listening / clipping / no-mic).
• When enabled:
  • Mic stream is captured at the lowest viable sample rate for beat detection (e.g. 8 kHz mono, AGC off).
  • On supported hardware: an embedded LiteRT model (small CNN / spectral-flux beat tracker) runs on-device and emits a smoothed envelope every ~50 ms.
  • On unsupported hardware: fall back to a pure-DSP envelope follower (RMS + onset peak-pick on a band-passed low-frequency signal — kicks/bass).
  • Output is mapped to master brightness 0–255 with operator-tunable floor / ceiling / attack / release.
• When disabled: brightness reverts to whatever the manual slider last commanded; the modal button still shows current value.

Settings page

New section Auto Brightness:

• Enable/disable toggle (mirrors the Stage button).
• Mode: LiteRT (auto-detect, greyed out if unsupported) / DSP fallback.
• Mic source picker (built-in / Bluetooth / USB-C audio).
• Sensitivity (gain compensation).
• Floor / Ceiling brightness clamps.
• Attack / Release smoothing (ms).
• Test meter (live envelope bar + headroom indicator) so operator can dial it in before showtime.
• Permission gate: requests RECORD_AUDIO runtime permission; if denied the feature is hard-disabled and the modal button shows a "tap to grant mic" state.

Stage page

• Remove the master-brightness slider from the Stage tab.
• In its place: modal button Auto Brightness showing icon + state + current envelope value as a thin progress bar fill.
• Tapping opens a small modal (not the full Settings tab) with: Enable toggle, Sensitivity slider, Floor/Ceiling sliders, live meter. Done collapses it.
• Manual brightness is moved to the Settings tab (or to the modal as a fallback when feature is off) — Stage stays focused on live show controls.

Constraints

• Pure on-device — no audio leaves the phone.
• Must coexist with Pointer / Controller orient streams (mic + sensors at the same time).
• LiteRT model has to ship in the APK (size budget < 10 MB).
• Latency target: < 80 ms mic-to-DMX.
• No regressions when the feature is off — the rest of the Stage UI must behave identically to today.

Out of scope

• Spectral / colour mapping (just brightness for v1).
• Multi-band or tempo-locked sequencing — that's a separate effects-engine feature, not the master-brightness control.
• Non-Android platforms (Windows SPA brightness slider stays as-is).