Convert mp4 file/s to mp3 using avconv
Avconv is alternative to ffmpeg. Avconv is a very fast video and audio converter that can also grab from a live audio/video source. It can also convert between arbitrary sample rates and resize video on the fly with a high quality polyphase filter.
conversion of mp4 file/s to mp3 by using avconv
avconv -i input.mp4 -vn -f mp3 output.mp3
Enjoy conversion to mp3... :-)