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-bash-4.0# ffmpeg -i numbcut.mp4 -vn -af fade=out:3776:30 -acodec libfaac -ac 2 numbfade.mp4
ffmpeg version N-48389-g341e40f Copyright (c) 2000-2013 the FFmpeg developers
  built on Jan  1 2013 20:34:19 with gcc 4.4.4 (GCC) 20100630 (Red Hat 4.4.4-10)
  configuration: --enable-gpl --enable-version3 --enable-nonfree --enable-postproc --enable-libfaac --enable-libmp3lame --enable-libvorbis --enable-libx264
  libavutil      52. 13.100 / 52. 13.100
  libavcodec     54. 85.100 / 54. 85.100
  libavformat    54. 59.100 / 54. 59.100
  libavdevice    54.  3.102 / 54.  3.102
  libavfilter     3. 30.102 /  3. 30.102
  libswscale      2.  1.103 /  2.  1.103
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  2.100 / 52.  2.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'numbcut.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf54.59.100
  Duration: 00:02:07.04, start: 0.023220, bitrate: 129 kb/s
    Stream #0:0(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 127 kb/s
    Metadata:
      handler_name    : SoundHandler
File 'numbfade.mp4' already exists. Overwrite ? [y/N] y
Unable to parse option value "0x0" as image size
Error opening filters!