QRL

Web Sender

The web sender encodes a file or folder into a sequence of QR codes and displays them in the browser at a configurable frame rate. No installation required.

Open at: https://minimike86.github.io/QRL/qrl_web/sender.html
Or locally: cd qrl_web && python -m http.server 8765 → http://localhost:8765/sender.html

Workflow

Select a file or folder using the file or folder picker buttons.
Adjust settings as needed (see below). The ETA estimate updates live.
Press Start Transfer. The manifest QR appears first and the sender auto-pauses.
Open the receiver on the destination device and start its camera.
Press Resume on the sender when the receiver is ready. QR codes begin cycling.
The receiver auto-downloads the file when the transfer completes.

In sequential mode, if the receiver reports missing chunks, enter them in the Replay missing chunks field and press Replay to re-transmit only those chunks.

Settings

Chunk size (bytes)

Payload bytes per QR frame. Default: 600 B.

Smaller values produce more reliable, lower-density QR codes that are easier to scan.
Larger values reduce the total number of frames (faster transfers in ideal conditions).
Recommended range: 400–800 B. Reduce if codes fail to scan consistently.

FPS

Target frames per second. Default: 3.

Higher FPS transfers faster but the receiver camera must keep up.
3–5 fps is reliable in most lighting; increase only in good conditions.
The sender displays actual FPS alongside the target.

Error correction

Reed-Solomon redundancy baked into each QR code. Default: L.

Level	Redundancy	Notes
L	7%	Maximum payload capacity. Use in clean, direct lighting.
M	15%	Light noise tolerance.
Q	25%	Good for compressed remote desktop streams.
H	30%	Maximum robustness. Use when scanning through heavy compression.

Higher levels recover from more scan noise but reduce usable payload per frame, increasing chunk count.

QR size (px)

Rendered canvas size in pixels. Default: 420 px.

Larger codes are easier to scan from a distance or through a low-resolution camera.
420–600 px suits most setups. Increase if the receiver struggles to focus.

Frames per chunk

How many consecutive frames each chunk is held before advancing. Default: 1 (sequential mode only).

Set to 2–3 if the receiver is missing many chunks at your configured FPS.
ETA scales proportionally with this setting.

Fountain mode

When enabled, the sender generates an infinite stream of XOR-coded packets (LT codes) instead of cycling through sequential chunks. Default: off.

Use fountain mode when:

Scanning is intermittent or unreliable.
You want hands-off operation with no replay step.
The receiver may join late.

Sequential mode is preferable when the transfer environment is stable and you want predictable chunk-by-chunk progress with a clear completion point.

See ARCHITECTURE.md for the technical details.

Display panel

The right-hand panel shows the current QR code alongside live statistics:

Stat	Description
FRAME	Current chunk number (sequential) or packet number (fountain)
TOTAL CHUNKS	Total source chunks N
CYCLES	Sequential: full loops completed. Fountain: equivalent packet-sets sent.
ACTUAL FPS	Measured frame rate
Progress bar	Sequential: position in current cycle. Fountain: position within current cycle (wraps).
Chunk label	`chunk N / total` (sequential) or `fountain pkt N` (fountain)

The manifest frame is labelled MANIFEST and appears first. The sender pauses here automatically.

Compression

Compression runs automatically before chunking:

Files ≥ 256 bytes are gzip-compressed at level 6.
If the result is ≥ 95% of the original size (e.g. already-compressed JPEG, ZIP, MP4), the original is sent uncompressed.
The manifest records whether compression was applied; the receiver decompresses transparently.

Folder transfers

Select a folder with Select Folder. The sender packs the entire directory into a .zip archive in memory before chunking. The web receiver downloads the .zip; the Python client unpacks it automatically.

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