How to convert mp4 to mp3 files in linux

#!/bin/sh
 
if [ ! -d mp3 ] ;
    mkdir mp3
fi
 
for item in *.mp4; 
do
	ffmpeg -i "${item}" -vn \
       -acodec libmp3lame -ac 2 -ab 160k -ar 48000 \
        "mp3/${item%mp4}mp3"
done