Voicemails saving as sln16

We have seen voicemails saving as sln16 rather than wav (wav49) as of today; not all of them and not consistently. We’ve also seen out-of-order meta data played back when going through voicemails. We’re running FreePBX w/Voicemail module and Asterisk 16.17.0.

Voicemails will be saved in the ALL the formats you have defined as format= in your /etc/asterisk/voicemail.conf file.

http://www.asteriskdocs.org/en/3rd_Edition/asterisk-book-html-chunk/Voicemail_id263499.html In the gooey, voicemail -> settings -> general > format

There is no setting specifying sln:


I don’t know if there was a recent FreePBX update that caused this, but all of a sudden, voicemails are not always recorded in WAV.

wav in lower case is an RIFF (Microsoft .wav) wrapper around 8kHz, 16 bit, signed linear mono. If you want RIFF around GSM, you need to use upper case. sln16 is 16kHz, with no RIFF wrapper.

According to the documentation, sln should not even be a format option. I removed the “format” line altogether so that it will fallback on defaults, but even after that, we’re still seeing voicemails drop as sln intermittently – see below from today:

-rw-r–r-- 1 asterisk asterisk 331 Aug 11 09:06 msg0012.txt
-rw-r–r-- 1 asterisk asterisk 1100160 Aug 11 09:06 msg0012.sln16
-rw-r–r-- 1 asterisk asterisk 327 Aug 11 09:06 msg0013.txt
-rw-r–r-- 1 asterisk asterisk 812800 Aug 11 09:06 msg0013.sln16
-rw-r–r-- 1 asterisk asterisk 342 Aug 11 09:06 msg0014.txt
-rw-r–r-- 1 asterisk asterisk 1349760 Aug 11 09:06 msg0014.sln16
-rw-r–r-- 1 asterisk asterisk 362604 Aug 11 12:45 msg0015.wav
-rw-r–r-- 1 asterisk asterisk 327 Aug 11 12:45 msg0015.txt

When the dialplan asks for an audio file, only the base name is used , asterisk will translate from the cheapest format available to the media stream, comedian mail is legacy software and will save the voicemails in ALL of the formats listed with format= line, so for any msgnnnn.txt their would be one of each of those files possible if that lines is empty then a msgnnnn.wav files is the default however if you have g722 connections they might fallback to sln16,

Asterisk’s cost of translation is

rasterisk -x 'core show translation'

some background at


To check for out of order metadata of a suspected extension

ls -lsrt  /var/spool/asterisk/voicemail/default/<suspected>/INBOX/*.txt

I should point out that nothing changed on the system, so this may have been related to an automatic update that occurred over the weekend.

The system is configured only for ulaw/alaw – no other codecs are being used.

And for efficiency Asterisk will trans-code sln16 to your requirements mostly as needed, with that possible exception that email clients will need to pre-define their preferred codec(s) and you will need to honor and to be abreast of that choice if using externnotify That way iphones, androids and even windows clients will get what they need ( a long story here, just stroke all your clients as needed) you can override the system defaults individually per client with the options box . . .

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