root@debian:/etc# ffmpeg -i /var/www/webcam_yesterday.flv -vf "fieldorder=bff"
FFmpeg version SVN-r0.5.6-4:0.5.6-3, Copyright (c) 2000-2009 Fabrice Bellard, et al.
  configuration: --extra-version=4:0.5.6-3 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libdirac --enable-libgsm --enable-libopenjpeg --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --disable-stripping --disable-vhook --enable-runtime-cpudetect --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libfaad --enable-libdc1394 --enable-shared --disable-static
  libavutil     49.15. 0 / 49.15. 0
  libavcodec    52.20. 1 / 52.20. 1
  libavformat   52.31. 0 / 52.31. 0
  libavdevice   52. 1. 0 / 52. 1. 0
  libavfilter    0. 4. 0 /  0. 4. 0
  libswscale     0. 7. 1 /  0. 7. 1
  libpostproc   51. 2. 0 / 51. 2. 0
  built on Dec 31 2011 15:16:11, gcc: 4.4.5

Seems stream 0 codec frame rate differs from container frame rate: 1000.00 (1000/1) -> 1.00 (1/1)
Input #0, flv, from '/var/www/webcam_yesterday.flv':
  Duration: 01:17:00.00, start: 0.000000, bitrate: 53 kb/s
    Stream #0.0: Video: flv, yuv420p, 640x480, 53 kb/s, 1 tbr, 1k tbn, 1k tbc
ffmpeg: unrecognized option '-vf'