# commonroom-recorder

Record a [commonroom](https://github.com/concept-collection/commonroom) call
from the command line, for transcribing the meeting afterwards.

The recorder joins a room as an ordinary, **visible** participant (default
name "Recorder") that stays muted the whole time. It receives every other
participant's audio and writes one WAV file per participant — so a transcript
with speaker attribution needs no diarization — plus the room chat and a
machine-readable event log. By default it also posts a one-line chat notice to
each participant so everyone knows the meeting is being recorded.

## Usage

```
npm install
npm run build
node dist/cli.js <room> [options]
```

Options:

```
--name <name>      Display name in the room (default: Recorder)
--out <dir>        Output directory (default: ./recordings/<room>-<timestamp>)
--duration <sec>   Stop automatically after this many seconds
--notice <text>    Chat line sent to each participant on connect
                   (default: "🔴 This meeting is being recorded.")
--no-notice        Don't send any recording notice
```

Stop with Ctrl-C. Requires Node >= 22 (built-in WebSocket). The WebRTC stack
is [`@roamhq/wrtc`](https://github.com/WonderInventions/node-webrtc), which
ships prebuilt binaries for Linux and macOS.

## Output

```
<out>/
  audio/<name>-<peer8>-segN.wav   one file per participant per connection
                                  (48 kHz mono s16 PCM, typically)
  chat.txt                        human-readable chat + join/left log
  events.jsonl                    every event with ISO timestamps: join, left,
                                  chat, mute/unmute, segment start/end
  manifest.json                   session summary: room, participants,
                                  segments with start/end times and durations
```

Everything is written incrementally (`tail -f chat.txt` works live; the
manifest is rewritten at every segment boundary and every 30 s), so a crash
loses at most about a second of audio. A file only starts when a participant's
first real audio arrives — someone who never unmutes produces no file. If a
participant disconnects and returns, they get a new numbered segment; the
manifest's per-segment start times let a transcript interleave speakers on one
timeline. During a segment, silence is padded by wall clock, so a sample's
position in the file always tracks elapsed time.

To transcribe: run each `audio/*.wav` through your transcriber of choice
(e.g. whisper), offset each result by its segment's `startedAt` from
`manifest.json`, and merge.

## How it works

The p2p layer is commonroom's, ported to Node: the same nostr
presence/signaling topics (knowing the room name IS the key), the same
schnorr-signed events (with a fresh ephemeral keypair per run), the same
deterministic-initiator WebRTC mesh and control data channel (hello, mute
notices, chat, bye). To the browsers in the room the recorder is
indistinguishable from a participant whose mic and camera are muted — it
counts toward the room cap of 8 and appears in the participant list.

Two deliberate deviations from the browser client:

- **Receive-only media.** The video m-line is negotiated `sendonly` from the
  recorder's side (a placeholder track that never produces a frame), so no
  video is ever sent to the recorder — with up to 7 participants that saves
  several Mbit/s and all the decode CPU. Audio is symmetric (a silent
  placeholder goes out, like any muted mic).
- **Files instead of tiles.** Each remote audio track feeds an `RTCAudioSink`
  whose PCM goes straight to an incrementally-written WAV.

## Testing

`npm run test:loopback` runs an end-to-end test with no browser: it starts the
recorder and a synthetic participant that "speaks" a 440 Hz sine and sends a
chat message, then verifies the WAV really contains the tone and the chat made
it to disk. It uses the real public nostr relays, so it needs network access.
For a real-world test, run the recorder and join the same room at
https://concept-collection.github.io/commonroom/ from a browser.