Tip: Setup voicemail to send email with mp3 attachment

PRINCIPLE

The main principles are :

• Asterisk voicemail is configured to generate some wav attachements (uncompressed, best quality available)
• Instead of sending the mail to sendmail, Asterisk is configured to send the mail to one specific script
• This script will do all the job, and finally give back the mail to sendmail

The script will do some ordered tasks :

1. catch the stream,
2. analyse the email content,
3. seperate each mime part,
4. pullout the audio attachment,
5. compress it to mp3,
6. regenerate the mail content,
7. send it to sendmail as expected

With this approach, you just need some specific configuration on Asterisk side.
From Asterisk side, the emails are just sent thru another emailer, that's it !

Unlike other methods, you don't need any patch for Asterisk.
You are still using a regular Asterisk, available from your distribution.
So, you can apply any standard update.

Any update to a new Asterisk version should remain fully compatible.

INSTALL THE PACKAGES

First thing to do is to install the packages needed by our script (unix2dos, dos2unix & lame).

aptitude install dos2unix lame

SETUP THE MAIN SCRIPT

Once these packages are installed, we can generate the script that will do all the job.

As Asterisk generates the mail content, including the wav attachment encoded in base64, the script main job will be to :

1. get the attachment from the email content
2. convert it to mp3
3. regenerate the mail content with new attachment
4. send the mail thru sendmail

This job will be done with some very basic linux tools like sed, awk, grep, base64, unix2dos, ...

One important thing is to respect the body structure of the mail content, including the LF and CRLF used to separate lines, depending on the different mime parts. In fact, in the mail body genarated by Asterisk, all the lines are separated with LF, with the exception of the base64 coded audio attachment where they are separated with CRLF.

For the mp3 conversion, 2 compression options are available :

• CBR - Constant Bit Rate compression will create mp3 streams compatible with any device, but the size/quality ratio is not optimised.
• VBR - Variable Bit Rate is much more efficient in term of file size, but playback has been tested very poor on some smartphones.

The script is providing both the compression parameters, you just need to adjust it to your need.

The detailed phases of the script are as follow :

1. Creation of a temporary directory, randomly generated, where we will generate all the temporary files
2. Dumping of the mail content sent by Asterisk in a file
3. Detection of the boundary pattern which separate the differents mime parts in the mail
4. With this pattern, cutting of the mail content into mime parts
5. Decoding of the WAV attachment which is base64 coded (you have to ignore parasite caracters in some configurations)
6. Compression into mp3 format
7.  Coding of the mp3 audio file back to base64
8. Re-assembly of the full mail content, using the new mp3 attachment
9. Sending of the mail thru sendmail
10. Deletion of the temporary directory
     

This sendmailmp3 script will be placed side to the sendmail command, under /usr/sbin.

/usr/sbin/sendmailmp3:

#! /bin/sh
# Asterisk voicemail attachment conversion script
# Revision history :
# 22/11/2010 - V1.0 - Creation by N. Bernaerts
# 07/02/2012 - V1.1 - Add handling of mails without attachment (thanks to Paul Thompson)
# 01/05/2012 - V1.2 - Use mktemp, pushd & popd
# 08/05/2012 - V1.3 - Change mp3 compression to CBR to solve some smartphone compatibility (thanks to Luca Mancino)
# 01/08/2012 - V1.4 - Add PATH definition to avoid any problem (thanks to Christopher Wolff)

# set PATH
PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

# save the current directory
pushd .
 
# create a temporary directory and cd to it
TMPDIR=$(mktemp -d)
cd $TMPDIR
 
# dump the stream to a temporary file
cat >> stream.org
 
# get the boundary
BOUNDARY=`grep "boundary=" stream.org | cut -d'"' -f 2`
 
# cut the file into parts
# stream.part - header before the boundary
# stream.part1 - header after the bounday
# stream.part2 - body of the message
# stream.part3 - attachment in base64 (WAV file)
# stream.part4 - footer of the message
awk '/'$BOUNDARY'/{i++}{print > "stream.part"i}' stream.org
 
# if mail is having no audio attachment (plain text)
PLAINTEXT=`cat stream.part1 | grep 'plain'`
if [ "$PLAINTEXT" != "" ]
then
 
  # prepare to send the original stream
  cat stream.org > stream.new
 
# else, if mail is having audio attachment
else
 
  # cut the attachment into parts
  # stream.part3.head - header of attachment
  # stream.part3.wav.base64 - wav file of attachment (encoded base64)
  sed '7,$d' stream.part3 > stream.part3.wav.head
  sed '1,6d' stream.part3 > stream.part3.wav.base64
 
  # convert the base64 file to a wav file
  dos2unix -o stream.part3.wav.base64
  base64 -di stream.part3.wav.base64 > stream.part3.wav
 
  # convert wav file to mp3 file
  # -b 24 is using CBR, giving better compatibility on smartphones (you can use -b 32 to increase quality)
  # -V 2 is using VBR, a good compromise between quality and size for voice audio files
  lame -m m -b 24 stream.part3.wav stream.part3.mp3
 
  # convert back mp3 to base64 file
  base64 stream.part3.mp3 > stream.part3.mp3.base64
 
  # generate the new mp3 attachment header
  # change Type: audio/x-wav to Type: audio/mpeg
  # change name="msg----.wav" to name="msg----.mp3"
  sed 's/x-wav/mpeg/g' stream.part3.wav.head | sed 's/.wav/.mp3/g' > stream.part3.mp3.head
 
  # generate first part of mail body, converting it to LF only
  mv stream.part stream.new
  cat stream.part1 >> stream.new
  cat stream.part2 >> stream.new
  cat stream.part3.mp3.head >> stream.new
  dos2unix -o stream.new
 
  # append base64 mp3 to mail body, keeping CRLF
  unix2dos -o stream.part3.mp3.base64
  cat stream.part3.mp3.base64 >> stream.new
 
  # append end of mail body, converting it to LF only
  echo "" >> stream.tmp
  echo "" >> stream.tmp
  cat stream.part4 >> stream.tmp
  dos2unix -o stream.tmp
  cat stream.tmp >> stream.new
 
fi
 
# send the mail thru sendmail
cat stream.new | sendmail -t
 
# go back to original directory
popd
 
# remove all temporary files and temporary directory
rm -Rf $TMPDIR

 Be sure to make it executable.

NOTE: If you are using some other distributions than debian or ubuntu or some self  compiled packages, you may have to specify the full path for the executable files (/usr/local/bin/lame for example).

VOICEMAIL CONFIGURATION

On the Asterisk server side, we just need to configure the voicemail extension to use or script to send the mails.

This is done thru the voicemail.conf file, where :

• In the [general] section, you need to setup some email specific parameters
• In the [default] section (I suppose you use the default context for your voicemail), you need to setup the email address to use for each voicemail box.
   

So, finally your voicemail.conf configuration file should include these parameters : 

 /etc/asterisk/voicemail.conf：

[general]
; Formats for writing voicemail. WAV is the best quality.
format=wav
; Who the e-mail notification should appear to come from
serveremail=yourpabxname@your.domain.com
; the email should contain the voicemail as an attachment
attach=yes
; You override the default program to send e-mail to use the script
mailcmd=/usr/sbin/sendmailmp3

[default]
; here you declare your voicemail, the email address which will receive the email & the automatic deletion of the message after mail is sent
yourvoicemailid => , yourname , your.email@address.com, , delete=yes

Once the file is saved, you just need to restart Asterisk for the configuration to be operational.

/etc/init.d/asterisk restart

That's it !

From now on, your Asterisk server is sendind all the voicemails by email using mp3 attachments.

Hope it helps.