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FR-AI / ANALYSISWhy it is worth attention
It demonstrates a practical air-gapped file transfer using fountain codes (Luby transform) that requires no network, app, or pairing, and includes hard-won details for browser compatibility and robust decoding.
Who it is for
- Developers exploring offline data transfer methods
- Researchers in optical communication and fountain coding
- Makers building air-gapped or security-conscious systems
- Privacy advocates seeking untrackable local transfers
Use cases
- Transfer files between two devices without any network connection
- Securely exchange data in air-gapped environments (e.g., sensitive documents)
- Prototype and test optical communication channels with fountain codes
- Educational demo of Luby transform coding and browser-based vision APIs
Strengths
- No network, app, or permissions beyond camera access required
- Fountain codes guarantee correctness despite dropped frames; receiver can join mid-stream
- Self-describing frames enable automatic session recovery and restart
- Open-source MIT license with detailed implementation notes
Considerations
- Proof-of-concept with limited throughput (targets 512 KB or 2 MB images only)
- Requires bright screen, steady camera, and HTTPS; iOS camera frame rate quirks
- QR error correction set to minimum (L) – relies on fountain layer for erasure recovery, not corruption
README quick start
Decimen Optical Transfer: fountain-coded QR file transfer
Send a file between two devices using nothing but a screen and a camera. One page displays the file as an endless stream of animated QR codes; another device points its camera at it and reconstructs the file. No network path between the devices, no app, no pairing, no permissions beyond the camera. The payload travels as light.
This is a minimal proof of concept extracted from a larger experiment that reached 128 KB/s phone-to-phone with denser frames, multi-code grids, and an error-corrected color channel. This PoC keeps only the essential trick and transmits a 512 KB image (or a 2 MB one, selectable in the sender's settings) at a comfortable rate.
Mid-transfer: a phone pulling a 2 MB image out of the air at 129 KB/s.
Try it
npm install
npm run dev
- On the sending device (a laptop is ideal): open
https://localhost:5173/send/and it starts streaming immediately. Max screen brightness helps. - On the receiving device (a phone): open the
NetworkURL Vite prints (https://:5173/receive/), accept the certificate warning once, tap Start camera, and point it at the code. - A few seconds later: Transfer Complete! and the received image, verified by hash.
Why the dev server is https-only: the receiver uses getUserMedia, and
browsers remove that API entirely on insecure origins: a phone reaching
your dev server over plain http has no camera, full stop (localhost is
exempt, but your phone isn't localhost). That's a web platform rule, not a
choice. The dev server therefore ships with a self-signed certificate
(@vitejs/plugin-basic-ssl); the browser will warn on first visit. Tap
"Show Details" then "visit this website" (iOS) or "Advanced" then "Proceed"
(Android/desktop), and the page is still a secure context, so the camera
works. The odd-looking lvh.me hosts Vite prints are a public convenience
domain that resolves to 127.0.0.1 (same machine, nothing extra running).
Hold the phone steady, or better, prop it against something. Camera autofocus hunting from hand tremor is the #1 throughput killer.
How it works
The one-way channel problem. A screen-to-camera link has no back-channel: the receiver can't ask for retransmission, and it will inevitably miss frames (blur, refresh straddling, autofocus). Looping the frames and h
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