Send Files Through Light: Decimen Optical Transfer Streams QR Codes at 130 KB/s
Decimen Optical Transfer: fountain-coded QR file transfer
Decimen Optical Transfer is an open-source web app that transmits files between devices using only a screen and a camera. It encodes data as an endless stream of animated QR codes, which the receiving device captures and reconstructs. No network, app, or pairing required—just point your camera at the screen. The system uses fountain coding (Luby transform) to handle dropped frames gracefully, achieving speeds up to 130 KB/s phone-to-phone. Files up to 64 MB are supported, with SHA-256 verification and optional gzip compression. The project is MIT-licensed and available at decimen.app.
A screen-to-camera link has no back-channel, so the sender streams fountain-coded frames — the receiver collects any ~K·1.15 distinct frames in any order and peels the file out.
- smalltorch
Naturally the first thing to test should be how far of a link can you create with LOS.
Radio's get intercepted, this is a cheap laser link.
- legulere
The actual article explaining the use for fountain codes in this use case:
- elric
Neat, finally an easy way of transferring files between devices that doesn't rely on online services -- no clue why we didn't solve that ages ago.
Adding encryption shouldn't be hard, as long as you can communicate the keys out of band.
Could probably achieve the same result using audio instead of video, but maybe that would be too annoying?
- felooboolooomba
Is there a way to negotiate ongoing FPS? I was sending at 60 but only receiving at 40. When I changed TX to 30 the speed went though the roof! I better call a builder.
Otherwise ridiculously cool project. May author's pillow always be cool on both sides.
- thisisauserid
I visual reminder that perfect compression is indistinguishable from random noise.