ffmpeg -i sample.3gp -b 400k -ar 44100 sample.flv
FFmpeg version SVN-r8404, Copyright (c) 2000-2007 Fabrice Bellard, et al.
  configuration: --enable-shared --enable-libmp3lame --enable-libfaad --enable-gpl --enable-amr_wb
  libavutil version: 49.3.0
  libavcodec version: 51.38.0
  libavformat version: 51.10.0
  built on Mar 28 2007 15:50:26, gcc: 4.1.1 20060525 (Red Hat 4.1.1-1)

Seems stream 1 codec frame rate differs from container frame rate: 1000.00 (1000/1) -> 15.00 (15/1)
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'sample.3gp':
  Duration: 00:00:05.0, start: 0.000000, bitrate: 45 kb/s
  Stream #0.0(eng): Audio: samr / 0x726D6173, 8000 Hz, mono
  Stream #0.1(eng): Video: mpeg4, yuv420p, 176x144, 15.00 fps(r)
Output #0, flv, to 'sample.flv':
  Stream #0.0: Video: flv, yuv420p, 176x144, q=2-31, 400 kb/s, 15.00 fps(c)
  Stream #0.1: Audio: mp3, 44100 Hz, mono, 64 kb/s
Stream mapping:
  Stream #0.1 -> #0.0
  Stream #0.0 -> #0.1
Unsupported codec (id=73728) for input stream #0.0