Asterisk MixMonitor() save or convert .gsm/.wav call file to .mp3


I want to convert my .gsm/.wav files to .mp3 files because ever since Adobe Flash has been wiped out, the recordings need to be downloaded and then played instead of seamlessly being played on the portal.

.wav files are really voluminous (90Kb for a 5-second call) so I would want to convert my .gsm/.wav files into .mp3.

p.s. I make use of mixmonitor as well and NOT monitor.

Let me know if there’s a need for more information from my side.

Thanks and looking forward to receiving a reply from all the experts.


What you probably want to do is to use .WAV, aka .wav49, in Asterisk, as these put a .wav wrapper on GSM data, and GSM is a low bit rate codec that is better suited to telephone quality speech. Asterisk treats .wav as signed linear, and .WAV as GSM.

Generally, though, you can post-process with sox to convert to most formats.

Just my personal opinion, but you should be aware that GSM is heavily compressed and sounds pretty awful. If you want good quality call recordings, it’d be recommended to keep them as G711 WAV or perhaps FLAC, which uses lossless compression. Not sure if sox does flac though…
Many browsers can also play wav files.

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