seablade@Architeuthis:/media/thomas.vecchione$ ffmpeg -f concat -i temp.txt msg.mp4
ffmpeg version 0.8.5-4:0.8.5-0ubuntu0.12.04.2+codecs1, Copyright (c) 2000-2012 the Libav developers
  built on Feb  5 2013 14:34:24 with gcc 4.6.3
*** THIS PROGRAM IS DEPRECATED ***
This program is only provided for compatibility and will be removed in a future
release. Please use avconv instead.
Unknown input format: 'concat'