host-001:Downloads luca$ ffmpeg -i big_buck_bunny_1080p_h264.mov -vn -c:a copy somefile.aac
ffmpeg version 1.0.1 Copyright (c) 2000-2012 the FFmpeg developers
  built on Dec  5 2012 21:12:10 with Apple clang version 4.1 (tags/Apple/clang-421.11.66) (based on LLVM 3.1svn)
  configuration: --prefix=/opt/local --enable-swscale --enable-avfilter --enable-libmp3lame --enable-libvorbis --enable-libopus --enable-libtheora --enable-libschroedinger --enable-libopenjpeg --enable-libmodplug --enable-libvpx --enable-libspeex --enable-libfreetype --mandir=/opt/local/share/man --enable-shared --enable-pthreads --cc=/usr/bin/clang --arch=x86_64 --enable-yasm --enable-gpl --enable-postproc --enable-libx264 --enable-libxvid
  libavutil      51. 73.101 / 51. 73.101
  libavcodec     54. 59.100 / 54. 59.100
  libavformat    54. 29.104 / 54. 29.104
  libavdevice    54.  2.101 / 54.  2.101
  libavfilter     3. 17.100 /  3. 17.100
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'big_buck_bunny_1080p_h264.mov':
  Metadata:
    major_brand     : qt
    minor_version   : 537199360
    compatible_brands: qt
    creation_time   : 2008-05-27 18:40:35
    timecode        : 00:00:00:00
  Duration: 00:09:56.46, start: 0.000000, bitrate: 9725 kb/s
    Stream #0:0(eng): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 1920x1080, 9282 kb/s, 24 fps, 24 tbr, 2400 tbn, 4800 tbc
    Metadata:
      creation_time   : 2008-05-27 18:40:35
      handler_name    : Apple Alias Data Handler
    Stream #0:1(eng): Data: none (tmcd / 0x64636D74)
    Metadata:
      creation_time   : 2008-05-27 18:40:35
      handler_name    : Apple Alias Data Handler
      timecode        : 00:00:00:00
    Stream #0:2(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, 5.1, s16, 437 kb/s
    Metadata:
      creation_time   : 2008-05-27 18:40:35
      handler_name    : Apple Alias Data Handler
Output #0, adts, to 'somefile.aac':
  Metadata:
    major_brand     : qt
    minor_version   : 537199360
    compatible_brands: qt
    timecode        : 00:00:00:00
    encoder         : Lavf54.29.104
    Stream #0:0(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, 5.1, 437 kb/s
    Metadata:
      creation_time   : 2008-05-27 18:40:35
      handler_name    : Apple Alias Data Handler
Stream mapping:
  Stream #0:2 -> #0:0 (copy)
Press [q] to stop, [?] for help
size=   32054kB time=00:09:56.48 bitrate= 440.2kbits/s
video:0kB audio:31863kB subtitle:0 global headers:0kB muxing overhead 0.599855%