ubuntu@omap:~$ ffmpeg -f v4l2 -s 640x360 -r 15 -vcodec mjpeg  -i /dev/video0 -f flv -b 20000k rtmp://server/live/livestream

ffmpeg version git-2012-08-08-b615dbb Copyright (c) 2000-2012 the FFmpeg developers
  built on Aug  8 2012 18:08:47 with gcc 4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5)
  configuration: --enable-gpl --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-librtmp --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-nonfree --enable-version3 --enable-x11grab
  libavutil      51. 67.100 / 51. 67.100
  libavcodec     54. 51.100 / 54. 51.100
  libavformat    54. 22.101 / 54. 22.101
  libavdevice    54.  2.100 / 54.  2.100
  libavfilter     3.  6.100 /  3.  6.100
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
[video4linux2,v4l2 @ 0x110f6b0] The v4l2 frame is 51325 bytes, but 230400 bytes are expected
[video4linux2,v4l2 @ 0x110f6b0] Could not find codec parameters for stream 0 (Video: mjpeg, 640x360, 27648 kb/s): unspecified pixel format
Consider increasing the value for the 'analyzeduration' and 'probesize' options
[video4linux2,v4l2 @ 0x110f6b0] Estimating duration from bitrate, this may be inaccurate
/dev/video0: could not find codec parameters