title: How to convert MP3 to AMR using ffmpeg in windows commandline
body: <p>Using windows based ffmpeg to convert MP3 to AMR.
  For some reason it fails with error as given below.</p>
  
  <p>Don't know how to given the correct parameters for AMR.</p>
  
  <pre><code>C:\Program Files (x86)\AMR to MP3 Converter&gt;ffmpeg -i mfile.mp3 -ar 8000 -ab 12.2k audio.amr
  FFmpeg version SVN-r26400, Copyright (c) 2000-2011 the FFmpeg developers
    built on Jan 18 2011 04:07:05 with gcc 4.4.2
    configuration: --enable-gpl --enable-version3 --enable-libgsm --enable-libvorb
  is --enable-libtheora --enable-libspeex --enable-libmp3lame --enable-libopenjpeg
   --enable-libschroedinger --enable-libopencore_amrwb --enable-libopencore_amrnb
  --enable-libvpx --disable-decoder=libvpx --arch=x86 --enable-runtime-cpudetect -
  -enable-libxvid --enable-libx264 --enable-librtmp --extra-libs='-lrtmp -lpolarss
  l -lws2_32 -lwinmm' --target-os=mingw32 --enable-avisynth --enable-w32threads --
  cross-prefix=i686-mingw32- --cc='ccache i686-mingw32-gcc' --enable-memalign-hack
  
    libavutil     50.36. 0 / 50.36. 0
    libavcore      0.16. 1 /  0.16. 1
    libavcodec    52.108. 0 / 52.108. 0
    libavformat   52.93. 0 / 52.93. 0
    libavdevice   52. 2. 3 / 52. 2. 3
    libavfilter    1.74. 0 /  1.74. 0
    libswscale     0.12. 0 /  0.12. 0
  [mp3 @ 003abeb0] max_analyze_duration reached
  [mp3 @ 003abeb0] Estimating duration from bitrate, this may be inaccurate
  Input #0, mp3, from 'mfile.mp3':
    Metadata:
      title           : SPL_TRACK
      artist          : Krishnan
      album           : Lord
      genre           : Lord
      track           : 5
    Duration: 00:30:06.00, start: 0.000000, bitrate: 127 kb/s
      Stream #0.0: Audio: mp3, 44100 Hz, 2 channels, s16, 128 kb/s
  [libopencore_amrnb @ 017e0d20] Only mono supported
  Output #0, amr, to 'audio.amr':
      Stream #0.0: Audio: libopencore_amrnb, 8000 Hz, 2 channels, s16, 12 kb/s
  Stream mapping:
    Stream #0.0 -&gt; #0.0
  Error while opening encoder for output stream #0.0 - maybe incorrect parameters
  such as bit_rate, rate, width or height
  </code></pre>