copying audio track from mp4, flv, etc. to mp3 on ubuntu 12.04

Using command line

1. First install the tools
   

   sudo apt-get install ffmpeg libavcodec-extra-53 libav-tools
   

2. Use this simple command to extract the audio file
   

   avconv -i /input-file-name-with-path output-filename.mp3
   

   For example to convert the "How fast.ogg" video file into how-fast.mp3 use this command:
   

   avconv -i /usr/share/example-content/Ubuntu_Free_Culture_Showcase/How\ fast.ogg how-fast.mp3

   from: http://askubuntu.com/questions/80954/how-can-i-extract-audio-from-mp4-or-flv-video-files