ffmpeg pcm_s16be 3

ffmpeg -i input.mov -c:a pcm_s32be -i input.mov -vn output.aiff

ffprobe output:

ffprobe version N-65298-gde41798 Copyright (c) 2007-2014 the FFmpeg developers
  built on Aug  5 2014 01:59:43 with gcc 4.8.3 (GCC)
  configuration: --disable-static --enable-shared --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencor
e-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --ena
ble-decklink --enable-zlib
  libavutil      52. 97.100 / 52. 97.100
  libavcodec     55. 72.101 / 55. 72.101
  libavformat    55. 51.101 / 55. 51.101
  libavdevice    55. 13.102 / 55. 13.102
  libavfilter     4. 11.102 /  4. 11.102
  libswscale      2.  6.100 /  2.  6.100
  libswresample   0. 19.100 /  0. 19.100
  libpostproc    52.  3.100 / 52.  3.100
Input #0, aiff, from 'output.aiff':
  Duration: 00:00:03.24, start: 0.000000, bitrate: 1536 kb/s
    Stream #0:0: Audio: pcm_s16be, 48000 Hz, 2 channels, s16, 1536 kb/s