QRFerry

QRFerry moves a file from one device to another as a live animated QR stream. The sender and receiver run entirely in the browser; the file is never uploaded to an application server.

1. Open the root page on the sending screen and choose a file.
2. Open /scan on the receiving phone and allow rear-camera access.
3. Start the QR stream and keep the complete code inside the phone's guide.
4. Save the file when RaptorQ recovery and the whole-file checksum reach 100%.

Robust through Turbo 30 use one stable QR target. Turbo 60 uses two V30-L lanes, updating them alternately at 30 fps each so one remains stable during every display transition. The opt-in 1 Mbps laboratory profile uses the same dual-lane design with V40-L for a nominal 1.40 Mbps optical payload channel before camera loss. Dual modes require fullscreen sender playback, the receiver's Dual lane option, and a landscape phone held close and steady.

This inline preview is generated from the final privacy-redacted demo. The full-resolution recording remains local at videos/qrferrydemo_timed_redacted.mov and is intentionally excluded from Git.

• Brotli quality 11 and gzip level 9 are both attempted; only the smallest representation is retained, and only when it saves optical bytes.
• QR frames use raw byte mode, avoiding the Base45 expansion of the previous protocol.
• Every frame carries a compact binary header, a RaptorQ symbol, and CRC-32.
• File metadata is inside the protected RaptorQ object instead of repeating in descriptor beacons.
• Source and repair symbols are interleaved. The receiver can join mid-cycle, discard blur, accept frames out of order, and reconstruct after receiving enough unique symbols.
• Turbo 15 uses one V30-L code held for four refreshes on a 60 Hz screen. Turbo 30 holds one code for two refreshes. Turbo 60 alternates updates across two V30-L lanes, so each lane remains stable for two refreshes while their combined stream carries 60 symbols per second. The 1 Mbps laboratory profile applies the same scheme to two denser V40-L lanes.
• Playback is synchronized to browser display refreshes. The sender reports its measured render rate; the receiver reports negotiated and delivered camera fps, completed scans per second, and decoder p50/p95 latency.
• Dual scanning acquires at most two codes per exposure and accepts either stable lane; it avoids the density and acquisition cost of a four-code grid.
• Rendering uses fast_qr compiled to WebAssembly. Scanning uses ZXing-C++ compiled to WebAssembly. Fountain encoding and decoding use the RFC 6330 RaptorQ implementation compiled to WebAssembly.
• The receiver verifies the per-frame CRC, the complete RaptorQ object CRC, the transmitted compressed payload CRC, and the original file CRC before saving.

Requires Node.js >=22.13.0.

npm install
npm run dev

The project does not require a Python environment. If Python tooling is added, use uv for its environment and dependencies.

npm test

The harness checks:

• metadata, compression, and end-to-end checksum round trips;
• per-frame corruption rejection;
• RaptorQ reconstruction after unordered simulated camera-frame erasures;
• the actual V30-L WebAssembly renderer passed through the actual ZXing-C++ WebAssembly scanner with exposure noise;
• exact QR capacity for every profile;
• production builds and server rendering for both / and /scan.

Run npm run lint and npx tsc --noEmit for the additional source checks.