h1249862:/var/www/media/video# ffmpeg -i 20_orig.avi -s 128x96 -vcodec h263 -ar 8000 -ac 1 20.3gp
FFmpeg version SVN-r8743, Copyright (c) 2000-2007 Fabrice Bellard, et al.
  configuration: --enable-libmp3lame --enable-amr-nb --enable-amr-wb
  libavutil version: 49.4.0
  libavcodec version: 51.40.3
  libavformat version: 51.12.1
  built on Apr 16 2007 10:08:35, gcc: 3.3.5 (Debian 1:3.3.5-13)
Input #0, avi, from '20_orig.avi':
  Duration: 00:00:07.9, start: 0.000000, bitrate: 643 kb/s
  Stream #0.0: Video: IV50 / 0x30355649, 320x240, 15.02 fps(r)
  Stream #0.1: Audio: pcm_u8, 22050 Hz, mono, 176 kb/s
File '20.3gp' already exists. Overwrite ? [y/N] Y
PIX_FMT_YUV420P will be used as an intermediate format for rescaling
Output #0, 3gp, to '20.3gp':
  Stream #0.0: Video: h263, yuv420p, 128x96, q=2-31, 200 kb/s, 15.02 fps(c)
  Stream #0.1: Audio: amr_nb, 8000 Hz, mono, 64 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
[amr_nb @ 0x8489870]bitrate not supported: use one of 4.75k, 5.15k, 5.9k, 6.7k, 7.4k, 7.95k, 10.2k or 12.2k
Error while opening codec for output stream #0.1 - maybe incorrect parameters such as bit_rate, rate, width or height