either
find ./ -type f -regextype posix-egrep -regex '.*(flac)$' -exec flac2m3 {} \;
flac2mp3
being the following script:
#!/bin/bash
args=("$@")
avconv -i "$args" -qscale:a 0 "${args[@]/%flac/mp3}"
or everything at one line, i. e. (https://superuser.com/a/410323/432066):
find /run/user/1000/gvfs/smb-share\:server=sharedomain.local\,share=multimedia/Artist\ Name\ -\ The\ Album/ -type f -regextype posix-egrep -regex '.*(flac)$' -exec bash -c 'echo $(file="{}"; avconv -i "${file}" -qscale:a 0 "${file/%flac/mp3}")' \;