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/234-00000008", "/var/lib/asterisk/sounds/sound") in new stack
[Sep 26 15:45:32] WARNING[4400][C-00000009]: format_wav.c:111 check_header_fmt: Unexpected frequency mismatch 44100 (expecting 8000)
[Sep 26 15:45:32] WARNING[4400][C-00000009]: file.c:510 fn_wrapper: Unable to open format wav
[Sep 26 15:45:32] WARNING[4400][C-00000009]: file.c:1303 ast_streamfile: Unable to open /var/lib/asterisk/sounds/sound (format (ulaw)): No such file or directory
[Sep 26 15:45:32] WARNING[4400][C-00000009]: app_playback.c:513 playback_exec: Playback failed on SIP/234-00000008 for /var/lib/asterisk/sounds/sound
 

    -- Executing [9132131@cme:3] Playback("SIP/234-00000006", "/var/lib/asterisk/sounds/sound") in new stack
[Sep 26 15:44:18] WARNING[4384][C-00000007]: format_wav.c:102 check_header_fmt: Not in mono 2
[Sep 26 15:44:18] WARNING[4384][C-00000007]: file.c:510 fn_wrapper: Unable to open format wav
[Sep 26 15:44:18] WARNING[4384][C-00000007]: file.c:1303 ast_streamfile: Unable to open /var/lib/asterisk/sounds/sound (format (ulaw)): No such file or directory
[Sep 26 15:44:18] WARNING[4384][C-00000007]: app_playback.c:513 playback_exec: Playback failed on SIP/234-00000006 for /var/lib/asterisk/sounds/sound
 

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