con:flvvideo doe$ ffmpeg -i input.flv
ffmpeg version 0.7.8, Copyright (c) 2000-2011 the FFmpeg developers
  built on Mar 23 2012 02:51:06 with gcc 4.2.1 (Apple Inc. build 5666) (dot 3)
  configuration: --prefix=/opt/local --enable-gpl --enable-postproc --enable-swscale --enable-avfilter --enable-libmp3lame --enable-libvorbis --enable-libtheora --enable-libdirac --enable-libschroedinger --enable-libopenjpeg --enable-libxvid --enable-libx264 --enable-libvpx --enable-libspeex --mandir=/opt/local/share/man --enable-shared --enable-pthreads --cc=/usr/bin/gcc-4.2 --arch=x86_64 --enable-yasm --enable-nonfree --enable-libfaac
  libavutil    50. 43. 0 / 50. 43. 0
  libavcodec   52.123. 0 / 52.123. 0
  libavformat  52.111. 0 / 52.111. 0
  libavdevice  52.  5. 0 / 52.  5. 0
  libavfilter   1. 80. 0 /  1. 80. 0
  libswscale    0. 14. 1 /  0. 14. 1
  libpostproc  51.  2. 0 / 51.  2. 0
[flv @ 0x102054400] Estimating duration from bitrate, this may be inaccurate

Seems stream 0 codec frame rate differs from container frame rate: 1000.00 (1000/1) -> 25.00 (25/1)
Input #0, flv, from 'input.flv':
  Metadata:
    duration        : 3058
    width           : 512
    height          : 288
    videodatarate   : 1074
    canSeekToEnd    : false
    videocodecid    : 2
    audiodatarate   : 128
    audiocodecid    : 2
    framerate       : 25
    creationdate    : Thu Mar 22 22:51:43 2012
  Duration: 00:50:57.80, start: 0.000000, bitrate: 1227 kb/s
    Stream #0.0: Video: flv, yuv420p, 512x288, 1099 kb/s, 25 tbr, 1k tbn, 1k tbc
    Stream #0.1: Audio: mp3, 44100 Hz, stereo, s16, 128 kb/s
At least one output file must be specified

--

con:flvvideo doe$ ffmpeg -i output.flv
ffmpeg version 0.7.8, Copyright (c) 2000-2011 the FFmpeg developers
  built on Mar 23 2012 02:51:06 with gcc 4.2.1 (Apple Inc. build 5666) (dot 3)
  configuration: --prefix=/opt/local --enable-gpl --enable-postproc --enable-swscale --enable-avfilter --enable-libmp3lame --enable-libvorbis --enable-libtheora --enable-libdirac --enable-libschroedinger --enable-libopenjpeg --enable-libxvid --enable-libx264 --enable-libvpx --enable-libspeex --mandir=/opt/local/share/man --enable-shared --enable-pthreads --cc=/usr/bin/gcc-4.2 --arch=x86_64 --enable-yasm --enable-nonfree --enable-libfaac
  libavutil    50. 43. 0 / 50. 43. 0
  libavcodec   52.123. 0 / 52.123. 0
  libavformat  52.111. 0 / 52.111. 0
  libavdevice  52.  5. 0 / 52.  5. 0
  libavfilter   1. 80. 0 /  1. 80. 0
  libswscale    0. 14. 1 /  0. 14. 1
  libpostproc  51.  2. 0 / 51.  2. 0
[flv @ 0x102054400] max_analyze_duration 5000000 reached at 5018000
[flv @ 0x102054400] Estimating duration from bitrate, this may be inaccurate
Input #0, flv, from 'output.flv':
  Metadata:
    audiodatarate   : 128
    duration        : 3058
    width           : 512
    height          : 288
    audiocodecid    : 2
    canSeekToEnd    : false
    videocodecid    : 2
    audiosamplerate : 44100
    audiosamplesize : 16
    stereo          : true
    videodatarate   : 1074
    framerate       : 25
    creationdate    : Thu Mar 22 22:51:43 2012
    encoder         : Lavf52.111.0
    filesize        : 78193287
  Duration: 00:08:33.00, start: 0.016000, bitrate: 1227 kb/s
    Stream #0.0: Video: [0][0][0][0] / 0x0000, 1099 kb/s, 1k tbr, 1k tbn, 1k tbc
    Stream #0.1: Audio: mp3, 44100 Hz, stereo, s16, 128 kb/s
At least one output file must be specified
con:flvvideo doe$

Command was: ffmpeg -v 10 -i input.flv -ss 1708 -t 513 -acodec copy -vcodec copy output.flv