[Freeswitch-users] Patch: VMD Configurable MIN_TIME

[Andrew Fritz]

I've created a patch to override the value of MIN_TIME in the vmd 
modules using a channel variable. In this way, it can be configured on a 
call by call basis. The channel variable is name "vmd_min_time".  I 
didn't add the other detection parameters, but doing so would be 
straight forward. So, in our app, we can catch T-Mobile and the other 
problematic cell carriers beeps.

I did this because in our app, we would rather have false positives than 
miss the start of recording on a voice mail system. This way, anyone 
using the VMD module can configure the vmd module to be as touchy or 
hard to trigger as they would like.

I not sure how to implement it (at least in the vmd module code), but a 
way to make mod_vmd more robust to false positives, especially with 
short beeps would be to have it look for short silence immediately 
proceeding and/or following the beep. I've noticed that it tends to 
trigger on noise if there is tone in the noise, if for example I extend 
a syllable in a word or I have music on in the background.

However on a voice mail system there will likely be a short near silence 
before the tone and an indefinite silence after it. In fact, background 
noise should be non-existent, except for line noise which should be 
Gaussian and not look like a structured tone. Looking for a beep + near 
silence after it for some period should eliminate many false positive 
where tones are embedded in other sounds (e.g. music or someone holding 
a vowel for longer than normal).

Andrew
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