# livekit-cameras

Publishes 20 Logitech C920 webcam streams (video + cleaned audio) to a
LiveKit room.

Each camera becomes one LiveKit participant (`cam-01` .. `cam-20`) that
publishes:
- a camera video track (1280x720 @ 30 fps by default, MJPG from V4L2)
- a microphone audio track (16 kHz mono, cleaned with speechbrain)

Identity is the USB serial, pinned by udev (`/dev/camNN` + `slots.json`).
`--cameras 1,5` means participants `cam-01` and `cam-05`, not discovery order.

## Layout

```
run.py              orchestrator: discovery + per-camera worker processes
run_worker.py       one camera: ffmpeg capture -> LiveKit track publish
discovery.py        serial-based camera <-> ALSA card discovery
audio_cleanup.py    speechbrain SpectralMaskEnhancement (16 kHz) + fallback
tokens.py           LiveKit JWT generation
config.py           .env / environment configuration
prefetch_model.py   one-time speechbrain model download
generate_udev_rules.py  (re)generate udev pinning + slots.json from live state
slots.json          stable slot map: cam-NN -> USB serial, /dev/camNN, ALSA card
smoke_test.py       one-camera LiveKit publish with enhancement ON
scripts/bench_enhance.py  RTF bench (1 s window / 200 ms hop)
deploy/livekit-cameras.service  optional systemd unit (do not enable blindly)
```

## Setup

```bash
uv venv --python 3.12
uv pip install -p .venv/bin/python -r pyproject.toml   # or: uv sync
cp .env.example .env    # then fill in LIVEKIT_URL / API_KEY / API_SECRET
.venv/bin/python prefetch_model.py     # download speechbrain model once
```

## Stable camera identity (cam-01 is always cam-01)

Each C920 has a unique built-in USB serial — that is the camera's UUID.
udev rules (`/etc/udev/rules.d/99-c920-pin.rules`, generated from the live
state) bind every slot to a serial, so identity survives reboots, hub
reordering, and any connect sequence:

- video:  `/dev/cam01` .. `/dev/cam20` (primary UVC node; `.meta` = metadata)
- audio:  fixed ALSA card per slot, `hw:2,0` .. `hw:21,0` (SOUND_CARD_INDEX)

`discovery.py` assigns identities from `slots.json` (serial lookup, with a
port-based fallback for cameras not yet in the map). To re-map slots (e.g.
after physically swapping cameras), regenerate:

```bash
.venv/bin/python generate_udev_rules.py --write
sudo udevadm control --reload-rules
sudo udevadm trigger --subsystem-match=video4linux --action=add
sudo udevadm trigger --subsystem-match=sound --action=add
```

The generator bakes the **current physical wiring** as canonical. Do not
re-run `--write` unless you intend to remap slots.

## Run

```bash
.venv/bin/python run.py                  # all 20 cameras
.venv/bin/python run.py --cameras 1,5    # subset
.venv/bin/python run.py --once           # status report after timeout
```

## Audio cleanup

C920 mics are 16 kHz **stereo**. Each hop (default 200 ms) is kept
stereo through a SpeechBrain preprocessor, then published as mono:

1. `AudioNormalizer(mix="keep")` at 16 kHz
2. Delay-and-Sum beamform (GCC-PHAT TDOA) — the live path from the
   SpeechBrain [multi-microphone beamforming tutorial](https://speechbrain.readthedocs.io/en/latest/tutorials/preprocessing/multi-microphone-beamforming.html)
   (`speechbrain.lobes.beamform_multimic.DelaySum_Beamformer`)
3. `speechbrain/metricgan-plus-voicebank` neural enhancement on a 1 s
   rolling window (`ENHANCE_CHUNK_S=1.0`, `ENHANCE_HOP_S=0.2`)

One worker process per camera loads the modules once and reuses them.
`enhance_batch` must be called with `lengths=torch.tensor([1.0])`
(relative, not sample count). `ENHANCE_MODE=off` (or a failed model
load with `auto`) skips MetricGAN; `BEAMFORM_MODE=off` averages L/R
instead of Delay-and-Sum. DSP high-pass + soft-clip is the last-resort
fallback so streams still work.

Until the 1 s window is full, hops use the DSP fallback so LiveKit is
not silent on startup.

## Appliance boot / power button

This box is meant to behave like an appliance:

- Power button while **off** → BIOS/OS boot → `livekit-cameras` waits for
  USB cameras + LiveKit, then publishes.
- Power button while **on** → full `poweroff` (not sleep). Suspend/hibernate
  targets are masked. Drop-in:
  `/etc/systemd/logind.conf.d/50-power-button.conf`

## systemd (enabled)

- `livekit-server.service` — **local TEST** LiveKit on :7880 (autostart for now)
- `livekit-cameras.service` — publishers. `Wants=` the test server, does not
  `Require` it. Destination is `LIVEKIT_URL` in `.env` (currently
  `ws://127.0.0.1:7880`).

When the real/remote LiveKit exists, change `.env` `LIVEKIT_URL` and:

```bash
systemctl disable --now livekit-server
systemctl restart livekit-cameras
```

```bash
systemctl status livekit-cameras livekit-server
journalctl -u livekit-cameras -f
systemctl restart livekit-cameras   # pick up newly plugged cameras
```

## Notes

- Video uses MJPG directly from the UVC interface (`ffmpeg -f v4l2
  -input_format mjpeg`) — cheap, and converts to BGRA for LiveKit.
- Audio: ALSA mics on these C920s deliver 16 kHz **stereo** only; the
  worker beamforms (Delay-and-Sum) then enhances, and publishes **mono**
  to LiveKit.
- Camera identity is USB serial via `slots.json` / udev; USB port is
  fallback only for cameras not yet in the map.
- Workers auto-restart (up to 10 times) if a camera drops.
- Local smoke: `.venv/bin/python smoke_test.py` (needs livekit-server on 7880).