Convert mp4 to mp3 in linux

Convert mp4 video file to wav audio
avconv -i input.mp4 output.wav

Encode wav to mp3
lame --preset standard input.wav output.mp3
For different mp3 quality use another preset mode. Display all preset modes with: lame --preset help

Update mp3 with ID3 tag
eyeD3 --encoding=utf8 -a "Author" -t "Title" -A "Album" --add-image image.jpg:FRONT_COVER input.mp3


Copy out audio from mp4 file as AAC
avconv -i input.mp4 -c:a copy output.aac