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VMD stands for "Voice Mail Detection" and mod_vmd is designed to detect the beep sound at the end of voicemail or answering machine greetings. This is useful in cases where you wish to leave a recorded message on the recipient's message system but don't want to have the pregnant pause that is common when using wait_for_silence.

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From mod_event_socket

To start the mod:

To stop the mod:

To get mod_vmd events:

Lua Example

This is an example of a callback in Lua:

Javascript example

This is an example of a callback in Javascript:

From Dialplan


To compile it simply add this to 'modules.conf':

And do not forget to rebuild and install:

To have FreeSWITCH load it on startup simply add this to '/usr/local/freeswitch/conf/autoload_configs/modules.conf.xml':


No voicemail detection can claim to be 100% accurate. The industry standard is 80% detection. This module if used properly should exceed the standard by a very wide margin.

If the signal quality is very poor the module may detect a single beep as many beeps and in very rare cases generate false positives. This is not usually an issue in detecting voicemail but keep it in mind when using the mod.

Related conversations

The following conversations took place shortly after the initial release of mod_vmd. They are not documentation per se but they do give some insight as to what the author (Eric Des Courtis) was thinking when he wrote the module as well as some thoughts from the FreeSWITCH developers.



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