Multipart UR Examples

envelope emits UR strings. Multipart QR output is handled by the companion mur tool, which splits a UR into fountain-coded QR frames or an animated QR sequence.

Create a UR with envelope

Any envelope UR can be passed to mur. This example creates a small salted envelope:

ENVELOPE=$(envelope subject type string "paper backup example" | envelope salt)

For a larger backup, use the command that creates the document you want to put on paper, then pass that UR to mur.

Numbered QR Frames

Use mur frames to write one PNG per multipart frame:

mur frames --max-fragment-len 80 --output backup-frames "$ENVELOPE"

--max-fragment-len controls the maximum fragment length used for fountain coding. Smaller fragments create more QR frames, but each frame is easier for a scanner to read. Larger fragments create fewer frames, but each QR code is denser.

Useful frame options include:

mur frames \
    --max-fragment-len 80 \
    --size 768 \
    --correction high \
    --cycles 4 \
    --output backup-frames \
    "$ENVELOPE"

The output directory will contain numbered PNG files suitable for printing one frame per page.

Animated QR

Use mur animate to produce an animated QR sequence:

mur animate --max-fragment-len 80 --cycles 4 --output backup.gif "$ENVELOPE"

The default animation format is GIF. --fps controls playback speed, and --cycles controls how many complete passes through the frame set are emitted.

Read from Standard Input

Both mur frames and mur animate accept - to read the UR from standard input:

envelope subject type string "paper backup example" |
    envelope salt |
    mur frames --max-fragment-len 80 --output backup-frames -

This keeps the generated UR out of the shell history.