Pasted

#!/bin/bash
command -v cjxl >/dev/null 2>&1 || { echo "cjxl not found"; exit 1; }
command -v parallel >/dev/null 2>&1 || { echo "parallel not found"; exit 1; }
find . -iname '*.jpg' -print0 | parallel -0 --jobs 4 './cjxl --lossless_jpeg=1 --num_threads=1 "{}" "{.}.jxl" && [ -s "{.}.jxl" ] && rm "{}"'