Convert flac to mp3 concurrent

SOURCE="/dev/shm/album"
find "$SOURCE" -type f -regex '\(.*flac\|.*FLAC\)' | while IFS= read -r a
do {
while [ "$(ps auxww | grep -c "[f]fmpeg")" -gt 3 ]; do sleep 1; done
BASE=$(basename "$a")
< /dev/null ffmpeg -i "$SOURCE/$BASE" -qscale:a 0 "/dev/shm/music/${BASE[@]/%flac/mp3}" &
} done