decimen-optical-transfer: File Transfer at 418KB/s via Screen and Camera Without Network

File transfer between two devices is possible without network connection, app installation, or pairing. One screen displays the file as an infinite QR code stream, while the camera on the other device recognizes it to reconstruct the file. The transmission medium is light, and no permissions beyond camera access are required.

Supports files up to 64MB and text snippets, preserving filenames and media types. Compression is applied only when gzip is beneficial, and integrity is verified via SHA-256 before reception. Measured sustained transfer speeds are 418.5 KB/s from desktop to phone, and 199.2 KB/s between phones. Transferring a 1MB file takes 2.5 seconds (desktop→phone).

The core is a protocol based on Fountain codes (Luby transform). Since the screen-camera link has no backchannel, the sender transmits a frame stream, and the receiver can restore the file by collecting approximately K·1.15 unique frames regardless of order. Frame drops cause only time delays and do not affect accuracy. Encryption is not applied; this is a characteristic provided by the absence of a network, not confidentiality.

Supports 12 languages, with machine translations explicitly marked as such until native review. Streams can be exported as APNG or PNG sequences, usable as loop animations for video editing. Distributed under the AGPL-3.0 license; releases prior to v0.3.0 are under the MIT license.