Make a lossy copy of your music library. https://elfakyn.com/knowledge/organize-your-music

convert_library.sh

#!/usr/bin/env bash
HELP_STRING=\
"Make a lossy copy of your music library. https://elfakyn.com/knowledge/organize-your-music

Prerequisites: parallel, opus-tools

Usage:
  $(basename $0) SOURCE_DIR DEST_DIR"

if [ "$1" = "--help" ] || [ "$1" = "-h" ]; then
	echo "$HELP_STRING"
	exit 0
fi

if [ $# -ne 2 ]; then
	echo "Error: Expected 2 parameters, got $#. Usage: $(basename $0) SOURCE_DIR DEST_DIR"
	exit 2
fi

if [[ $(realpath "$2") = $(realpath "$1")/* || $(realpath "$1") = $(realpath "$2")/* ]]; then
	echo "Error: SOURCE_DIR and DEST_DIR overlap. Please specify non-overlapping source and destination directories."
	exit 1
fi

if ! command -v opusenc >/dev/null 2>&1; then
	echo "Error: opusenc not found. Install opus-tools."
	exit 1
fi

if ! command -v parallel >/dev/null 2>&1; then
	echo "Error: parallel not found. Install parallel."
	exit 1
fi

convert_library_process_file() { # source dir, dest dir, file
    source="$3"
    dest="$2/$(realpath -s --relative-to="$1" "$source")"
    mkdir -p "$(dirname "$dest")"

    if [ "${source##*.}" == "flac" ]; then
        dest="${dest%.flac}.opus"
    fi

    if [ "$dest" -nt "$source" ]; then
        return
    fi

    if [ "${source##*.}" == "flac" ]; then
        # FLAC
        opusenc --quiet --vbr --bitrate 256 "$source" "$dest"
    elif [ "${source##*.}" == "m3u" ] || [ "${source##*.}" == "m3u8" ]; then
        # Playlist
        sed 's/\.flac\b/\.opus/g' "$source" > "$dest"
    else
        # Everything else
        cp "$source" "$dest"
    fi
}

export -f convert_library_process_file

find "$1" -type f | parallel --progress --jobs 14 --eta --bar convert_library_process_file ${1@Q} ${2@Q} {} \;