For a successful AMR encoding in MediaCoder, you have these steps to follow:

  1. Update MediaCoder to 0.6.0.3760 or later
  2. Download and install AMR Codec Pack for MediaCoder
  3. Start MediaCoder, switch to Audio tab and set Audio Encoder to AMR
  4. You can choose between AMR-NB or AMR-WB in the AMR tab on the right side
  5. Do click on either AMR-NB or AMR-WB radio box as this clicking will make the correct resample and channel options (8Khz/mono for AMR-NB and 16Khz/mono for AMR-WB)