A fully offline, single-file HTML page for moving data between two devices via QR codes — intended for old phones whose radios (BLE, NFC, etc.) arevdead but whose cameras and browsers still work.
- Generate — encode text into a single QR code.
- Scan — decode a single QR via the camera.
- Send file — pick a file, choose chunk size / FPS / ECC, hit Start. Cycles through [header, chunk1…chunkN] forever at the chosen FPS. / Resume / Stop. - Start from — begin the loop at a chosen frame index; it then continues forward and wraps back to the header normally.
- Show frame + Show / − / + — display exactly one frame static, for resending a specific missing chunk. The number matches the chunk index shown in the receiver's missing-chunks grid (0 = header).
- Receive file — start the camera and point at the sender. Header autodetects, progress bar fills in, missing-chunks grid shows which ones haven't arrived yet. When complete, the file's CRC is verified and a Download button appears.
- Header:
QRX1|H|<total>|<filename>|<sizeBytes>|<crc32hex>
- Data:
QRX1|D|<idx>|<base64chunk>
(1-indexed) - Base64 alphabet has no
| , so parsing is justsplit('|') . - Receiver tracks chunks by index, ignores duplicates, dedupes header by CRC.
- Camera needs HTTPS or localhost — file:// won't grantgetUserMedia permission. Serve withpython3 -m http.server 8000 and visithttp://<your-laptop-ip>:8000/qrcode.html over the local network. iOS Safari additionally requires HTTPS for cross-device access — for a LAN setup,caddy or a self-signed cert helps. - If render fails on a frame ("code length overflow"), drop chunk size or drop ECC level.
- 500 chars × 3 fps ≈ 1.1 KB/s base64 ≈ 0.83 KB/s raw. A 100 KB file is roughly 2 minutes per loop; receiver typically needs 1-2 loops.
- If old devices struggle to decode: lower FPS, raise ECC to Q, shrink chunk to ~300 chars — produces smaller, less dense QRs.
source & further reading
github.com — original article