$ ./osdemo blah | ffmpeg -y -loop 1 -f image2pipe -vcodec ppm -i - -vcodec libxvid -t 30 test.avi
ffmpeg version 1.1.git-8aea2f0 Copyright (c) 2000-2013 the FFmpeg developers
  built on Jun 12 2013 13:52:05 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-libass --enable-libbluray --enable-gnutls --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      52. 35.101 / 52. 35.101
  libavcodec     55. 16.100 / 55. 16.100
  libavformat    55.  8.102 / 55.  8.102
  libavdevice    55.  2.100 / 55.  2.100
  libavfilter     3. 75.101 /  3. 75.101
  libswscale      2.  3.100 /  2.  3.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  3.100 / 52.  3.100
Input #0, image2pipe, from 'pipe:':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: ppm, rgb24, 400x400, 25 tbr, 25 tbn, 25 tbc
Output #0, avi, to 'test.avi':
  Metadata:
    ISFT            : Lavf55.8.102
    Stream #0:0: Video: mpeg4 (libxvid) (xvid / 0x64697678), yuv420p, 400x400, q=2-31, 200 kb/s, 25 tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (ppm -> libxvid)
pipe:: Input/output error
frame=    1 fps=0.0 q=8.0 Lsize=       8kB time=00:00:00.04 bitrate=1686.4kbits/s
video:3kB audio:0kB subtitle:0 global headers:0kB muxing overhead 209.431193%