[asterisk-dev] [Code Review] Incorrect Voicemail duration reported in messages containing silence

[mjordan]

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Review request for Asterisk Developers and russelb.


Summary
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The patch for ASTERISK-2234 is viewed as a regression in ASTERISK-16981.  ASTERISK-2234 changed the way voicemail duration is calculated in the presence of silence.  Instead of the duration being the length of the voicemail minus whatever silence accumulates at the end of a call (when that call ends in silence), the duration calculation was changed to include only the time in the audio stream that was not considered to be silence.  Consider a voicemail system set up to ensure a message has a minimum duration of 4 seconds, and a silence cutoff of 6 seconds.  This patch solved the following situation:
1. A person begins recording with 4 seconds of silence
2. Person says "hello?", taking 1 second
3. Person waits for 6 seconds and is hung up on

Prior to this patch, the voicemail's duration would be calculated at 5 seconds and would be allowed through; post-patch the duration would be calculated at 1 second and would be discarded.

Unfortunately, this has had the following side effects:
1. Voicemails that do contain some silence but are still valid are being dropped, particularly if the minsecs parameter is sufficiently large
2. Voicemail duration (reported through the email user option) is substantially off.

Both of these are significant issues - one, that we could be disposing of potentially important voicemails when the system administrator and its users would not expect us to (minsecs does not imply that it is the minimum amount of audio needed, but the minimum length of the entire message); two that we obviously report a duration that does not match the length of the attached sound file to the user.

Rolling back this patch resolves these issues - voicemail duration is calculated correctly (within +/- 1 second) and voicemail duration is calculated only minus the trailing silence.

However, since this removes a feature implemented in a prior patch, I expect there to be significant discussion with this proposed change.


This addresses bugs ASTERISK-16981 and ASTERISK-2234.
    https://issues.asterisk.org/jira/browse/ASTERISK-16981
    https://issues.asterisk.org/jira/browse/ASTERISK-2234


Diffs
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  /branches/1.8/main/app.c 333944 

Diff: https://reviewboard.asterisk.org/r/1403/diff


Testing
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Tested using 1.8 and the following:

minsecs = 4
silencethreshold = 128
maxsilence = 10

* Leaving voicemails with silence in the beginning, punctuated by audio, followed by 10 seconds of silence (message kept with correct duration)
* Leaving voicmeails that consisted of all silence (message dropped)
* Leaving voicemails of silence ended by '#' (message dropped)
* Leaving voicemail with silence, audio, silence, audio, silence, followed by '#' (message kept with correct duration)


Thanks,

mjordan

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