./ffmpeg -list_devices true
ffmpeg version N-65826-gc868b14 Copyright (c) 2000-2014 the FFmpeg developers
  built on Sep  8 2014 15:48:25 with Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
  configuration:
  libavutil      54.  6.100 / 54.  6.100
  libavcodec     56.  0.101 / 56.  0.101
  libavformat    56.  1.100 / 56.  1.100
  libavdevice    56.  0.100 / 56.  0.100
  libavfilter     5.  0.102 /  5.  0.102
  libswscale      3.  0.100 /  3.  0.100
  libswresample   1.  1.100 /  1.  1.100
Trailing options were found on the commandline.
Hyper fast Audio and Video encoder
usage: ffmpeg [options] [[infile options] -i infile]... {[outfile options] outfile}...

Use -h to get full help or, even better, run 'man ffmpeg'