In our example we take "sound.mp3" and convert it to .wav.
Generally Asterisk for its wave needs one audio channel (-ac 1) / mono and 8000hz (-ar 8000) instead of the standard CD/MP3 of 44100hz.
Here is the command to convert into Asterisk .wav format:
ffmpeg -i sound.mp3 -ac 1 -ar 8000 sound.wav
Errors Asterisk may give you if the format is wrong:
-- Executing [91781891@cme:3] Playback("SIP/234-000........