~/ffmpeg-streaming-test$ ffmpeg -i udp://localhost:4444 -vcodec copy -acodec copy test-output.flv
FFmpeg version SVN-r20602, Copyright (c) 2000-2009 Fabrice Bellard, et al.
  built on Nov 25 2009 01:33:50 with gcc 4.3.2
  configuration: --enable-gpl --enable-version3 --enable-nonfree --enable-pthreads --enable-libfaac --enable-libfaad --enable-libmp3lame --enable-libtheora --enable-libx264 --enable-libxvid --enable-x11grab
  libavutil     50. 4. 0 / 50. 4. 0
  libavcodec    52.42. 0 / 52.42. 0
  libavformat   52.39. 2 / 52.39. 2
  libavdevice   52. 2. 0 / 52. 2. 0
  libswscale     0. 7. 1 /  0. 7. 1

^Z
[1]+  Stopped                 ffmpeg -i udp://localhost:4444 -vcodec copy -acodec copy test-output.flv
~/ffmpeg-streaming-test$ bg
[1]+ ffmpeg -i udp://localhost:4444 -vcodec copy -acodec copy test-output.flv &

~/ffmpeg-streaming-test$ ffmpeg -i test-input.flv -vcodec copy -acodec copy udp://localhost:4444
FFmpeg version SVN-r20602, Copyright (c) 2000-2009 Fabrice Bellard, et al.
  built on Nov 25 2009 01:33:50 with gcc 4.3.2
  configuration: --enable-gpl --enable-version3 --enable-nonfree --enable-pthreads --enable-libfaac --enable-libfaad --enable-libmp3lame --enable-libtheora --enable-libx264 --enable-libxvid --enable-x11grab
  libavutil     50. 4. 0 / 50. 4. 0
  libavcodec    52.42. 0 / 52.42. 0
  libavformat   52.39. 2 / 52.39. 2
  libavdevice   52. 2. 0 / 52. 2. 0
  libswscale     0. 7. 1 /  0. 7. 1

Seems stream 0 codec frame rate differs from container frame rate: 1000.00 (1000/1) -> 29.92 (359/12)
Input #0, flv, from 'test-input.flv':
  Duration: 00:02:59.27, start: 0.000000, bitrate: 128 kb/s
    Stream #0.0: Video: flv, yuv420p, 352x288, 29.92 tbr, 1k tbn, 1k tbc
    Stream #0.1: Audio: mp3, 44100 Hz, 2 channels, s16, 128 kb/s
  Metadata
    duration        : 179
    width           : 352
    height          : 288
    videodatarate   : 0
    framerate       : 30
    videocodecid    : 2
    audiosamplerate : 44100
    audiosamplesize : 16
    stereo          : true
    audiocodecid    : 2
    filesize        : 20327145
Unable to find a suitable output format for 'udp://localhost:4444'