#!/bin/zsh
directory=~/Music
extension=m4a
codec=aac

find $directory -type f -name "*.$extension" -print0 | while read -d $'' file
do
    file_codec="$(ffprobe -v quiet -show_streams -print_format json $file | jq '.streams[0].codec_name')"
    [[ "${file_codec//"}" != $codec ]] && echo $file
done