% ffmpeg -i file.mp4 -f mp3 -b 320k file.mp3
ffmpeg version 0.7.13, Copyright (c) 2000-2011 the FFmpeg developers
  built on Aug 20 2012 00:18:36 with gcc 4.2.1 20070719  [FreeBSD]
  configuration: --prefix=/usr/local --mandir=/usr/local/man --enable-shared --enable-gpl --enable-postproc --enable-avfilter --enable-pthreads --enable-memalign-hack --enable-runtime-cpudetect --cc=cc --extra-cflags='-I/usr/local/include/vorbis -I/usr/local/include' --extra-ldflags='-L/usr/local/lib ' --extra-libs=-pthread --disable-debug --disable-sse --disable-mmx --disable-libaacplus --disable-indev=alsa --disable-outdev=alsa --disable-libopencore-amrnb --disable-libopencore-amrwb --disable-libcelt --disable-libdirac --disable-libfaac --enable-libfreetype --enable-frei0r --disable-libgsm --enable-libmp3lame --enable-libopencv --disable-libopenjpeg --disable-librtmp --enable-libschroedinger --disable-ffplay --disable-libspeex --enable-libtheora --disable-vaapi --disable-vdpau --disable-libvo-aacenc --disable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid
  libavutil    50. 43. 0 / 50. 43. 0
  libavcodec   52.123. 0 / 52.123. 0
  libavformat  52.111. 0 / 52.111. 0
  libavdevice  52.  5. 0 / 52.  5. 0
  libavfilter   1. 80. 0 /  1. 80. 0
  libswscale    0. 14. 1 /  0. 14. 1
  libpostproc  51.  2. 0 / 51.  2. 0
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'file.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2012-06-22 22:56:32
  Duration: 00:08:29.52, start: 0.000000, bitrate: 529 kb/s
    Stream #0.0(und): Video: h264 (High), yuv420p, 1280x720, 375 kb/s, 25 fps, 25 tbr, 50 tbn, 50 tbc
    Metadata:
      creation_time   : 1970-01-01 00:00:00
    Stream #0.1(und): Audio: aac, 44100 Hz, stereo, s16, 151 kb/s
    Metadata:
      creation_time   : 2012-06-22 22:56:33
File 'file.mp3' already exists. Overwrite ? [y/N] y
Output #0, mp3, to 'file.mp3':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    TDEN            : 2012-06-22 22:56:32
    TSSE            : Lavf52.111.0
    Stream #0.0(und): Audio: libmp3lame, 44100 Hz, stereo, s16, 64 kb/s
    Metadata:
      creation_time   : 2012-06-22 22:56:33
Stream mapping:
  Stream #0.1 -> #0.0
Press [q] to stop, [?] for help
size=    3981kB time=00:08:29.54 bitrate=  64.0kbits/s
video:0kB audio:3981kB global headers:0kB muxing overhead 0.007703%