[root@ruibra audioTest]# ffmpeg -i ClickTest.wav -c:a libfdk_aac -vbr 3 ClickTest.m4a
ffmpeg version 1.2 Copyright (c) 2000-2013 the FFmpeg developers
  built on Apr 15 2013 19:57:05 with gcc 4.1.2 (GCC) 20080704 (Red Hat 4.1.2-51)
  configuration: --enable-gpl --enable-libmp3lame --enable-libvorbis
  libavutil      52. 18.100 / 52. 18.100
  libavcodec     54. 92.100 / 54. 92.100
  libavformat    54. 63.104 / 54. 63.104
  libavdevice    54.  3.103 / 54.  3.103
  libavfilter     3. 42.103 /  3. 42.103
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  2.100 / 52.  2.100
Unrecognized option 'vbr'.
Error splitting the argument list: Option not found