a bash script to convert the all m4a files to the mp3 by ffmpeg

convert_m4a_to_mp4.bash

# Regular Colors
Black='\033[0;30m'        # Black
Red='\033[0;31m'          # Red
Green='\033[0;32m'        # Green
Yellow='\033[0;33m'       # Yellow
Blue='\033[0;34m'         # Blue
Purple='\033[0;35m'       # Purple
Cyan='\033[0;36m'         # Cyan
White='\033[0;37m'        # White
NC='\033[0m' # No Color]'


# Create the converted directory
DIR="Converted"
if ! test -d "$DIR"; then
    echo "$DIR"
    mkdir "$DIR"
fi

# convert the files
for f in *.m4a; do
    new=$DIR/${f%.m4a}.mp3
    # check the target file is exists
    if test -f "$new"; then
        echo -e "${Blue}$new${Green} File is exists !$NC"
        continue
    fi
    # convert with ffmpeg   
    ffmpeg -i "$f" -codec:v copy -codec:a libmp3lame -q:a 0 "$new" ; 
done