avplay -f alsa -i hw:0 -f video4linux2 -i /dev/video0
avplay version 0.8.1-4:0.8.1-0ubuntu1, Copyright (c) 2003-2011 the Libav developers
  built on Mar 22 2012 05:09:06 with gcc 4.6.3
Argument '/dev/video0' provided as input filename, but 'hw:0' was already specified.