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A clever demo of light-based file transfer that is easy to admire and hard to turn into a business.

AI roast score: 52/100 (D)

The idea

Cool trick: send files by blinking QR codes from one screen to another. Bad business: you are betting people will choose a slower, fussier path over AirDrop, Bluetooth, and “just send it.”

In the founder's own words

bashalarmistalt/decimen-optical-transfer

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 Network URL Vite prints
( https://<lan-ip>: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 hoping is
miserable: miss one frame and you wait a full cycle for it to come around.

Fountain codes fix this completely. The sender never sends the file's
blocks directly. Each frame is the XOR of a pseudorandom subset of blocks;
the subset is derived deterministically from the frame's sequence number,
with subset sizes drawn from a robust-soliton distribution ( Luby transform
coding ). The receiver
collec

The roast

This is a neat engineering stunt, not yet a company. You say it is a way to send a file using “nothing but a screen and a camera,” but your own setup already asks for a laptop, a phone, HTTPS warnings, a bright screen, and steady hands. That is a lot of friction for a problem people already solve in one tap with built-in tools. The real pain here is not the codec. It is distribution and habit. Your profile says you are a solo founder, you are building software, you have no funding, and you are aiming at consumers with a free product. That means you do not get to win by being technically impressive. You win only if this becomes the default way people share files in a moment where existing options fail. Right now that case is not proven. The biggest issue is that your own writeup is obsessed with throughput, hashes, and fountain codes, while normal users care about “does it work fast, on my phone, without drama.” A product that needs a dev-server certificate warning and a camera pointed at a screen is fighting the platform, the user, and every native sharing feature at once. That is a hard three-way losing battle unless you find a very specific niche.

Red flags

Verdict

Keep it as a sharp demo or niche utility, but do not pretend this is a broad consumer startup until you prove a painful use case that native sharing cannot touch.

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