Concatenating MP3 files

some references:
http://www.howtogeek.com/howto/2719/how-to-convert-video-files-formats-to-mp3-with-vlc/

Convert mp4 and flv video to mp3 with VLC

http://schindlerweb.net/index.php/2012/04/16/merging-audio-files-with-vlc/
http://stackoverflow.com/questions/62618/what-is-the-best-way-to-merge-mp3-files