Sebicam

Local-network baby monitor. Phone A broadcasts encrypted audio via WebRTC; Phone B listens in a browser. Signaling is done by scanning QR codes between the two phones — the server only serves static files. Media flows peer-to-peer.

Try It

The app is hosted at https://valekjo.github.io/sebicam — open it on both phones and follow the usage steps below.

To use it without internet: open the link once on each phone to cache it, then save it to your home screen. One phone can act as a Wi-Fi hotspot for the other — the entire setup works offline since signaling is done via QR codes and media flows directly between the phones.

Development

npm install
npm run generate-cert   # one-time: generates self-signed TLS cert in certs/
npm run dev             # starts HTTPS server on port 3000

Open the printed Network URL (e.g. https://192.168.1.x:3000) on both phones. Accept the certificate warning on each device.

Usage

Phone A — Broadcaster

1. Open the app and choose Broadcaster
2. Allow microphone access
3. Tap Start — a QR code appears
4. Have Phone B scan this QR code
5. Tap Scan Response to scan Phone B's answer QR code
6. Audio streaming begins once both QR codes are exchanged

Phone B — Viewer

1. Open the app and choose Viewer
2. Scan the QR code shown on Phone A
3. A response QR code appears — show it to Phone A to scan
4. Audio from Phone A starts playing, with a live spectrogram

Architecture

Phone A (Broadcaster) ----QR codes----> Phone B (Viewer)
         \                                    /
          ======= WebRTC P2P (encrypted) ====

• Server: HTTPS static file server only — no signaling logic
• Signaling: Two-way QR code exchange between phones (no server involvement)
• Transport: WebRTC peer-to-peer with DTLS-SRTP encryption
• Audio only: no video streaming

Two-phase connection

The connection uses a two-phase handshake:

1. QR-based bootstrap — Compact binary-encoded SDPs (SBC1: format) exchanged via QR codes establish a WebRTC data channel
2. Full SDP over data channel — Once the data channel opens, full browser-generated SDPs are exchanged over it to negotiate audio codecs properly

This design exists because QR-encoded SDPs are too compact to represent all codec/extension details browsers need. The QR exchange only bootstraps connectivity; real media negotiation happens over the data channel.

Features

• Dark theme — designed for nighttime use
• Audio spectrogram — real-time frequency visualization on the viewer
• Battery status — broadcaster's battery level shown on both phones
• Audio level meter — visual indicator of sound in the room
• Stream duration — elapsed time counter
• Keep-alive — Wake Lock + silent audio oscillator + Media Session API to prevent the broadcaster from sleeping
• Offline support — service worker caches all assets for PWA-like usage
• Secure by default — HTTPS required, WebRTC media encrypted via DTLS-SRTP

Requirements

• Node.js 24+ (see .nvmrc)
• Both phones on the same local network
• openssl (for certificate generation)

Limitations

• LAN only — no TURN server, so it won't work across different networks
• Single viewer per session
• Self-signed certificate requires manually accepting the browser warning on each device