Move data between two devices via QR codes. Works on old phones with dead radios but working camera + browser.
Protocol: QRX1|H|total|flags|filename|sizeBytes|crc32hex (header) and QRX1|D|idx|base64chunk (data). CRC32 over original bytes. Gzip compression optional.
Tips for old phones: Use lower FPS (1-2), smaller chunk size (200-400), good lighting. Keep phone steady. Use ECC H for noisy environments.