the script extracts mp4 files to compressed mp3 audio

mp4-to-mp3-extractor.sh

#!/bin/bash
# all mp4 files in this directory
for file in ./*.mp4; do
    # create new mp3 name
    audio="${file%.mp4}.mp3"
	# if .mp4 is file and .mp3 does not exists
    if [ -f $file ] && [ ! -e $audio ]; then
		# ffmpeg will convert mp4 to mp3 with the strongest compressing (-q:a 9)
		# will show only panic logs
        ffmpeg -hide_banner -loglevel panic -i $file -vn -codec:a libmp3lame -q:a 9 $audio
		# show done message
        echo "extract from $file to $audio is done"
    fi
done