#!/bin/bash

shopt -s globstar

if (($# < 1)); then
	echo "usage: ${0##*/} <directory>"
	exit
fi

if [[ ! -d $1 ]]; then
	echo "argument must be a directory"
	exit 1
fi

dir=${1%/}
copydir_suffix="_mp3"

find "$dir" -type d -exec mkdir -p ${dir}${copydir_suffix}/{} +
find "$dir" -type f -name '*.flac' -print0 | parallel -0 ffmpeg -i {} -qscale:a 0 '{=s#^([^/])(.*)\.flac$#\1'"${copydir_suffix}"'\2.mp3#=}'