[asterisk-users] Change Asterisk MulticastRTP codec

Matthew Murphy mrmdev at outlook.com
Thu Oct 1 07:38:37 CDT 2015

Larry and Pete,
Thanks a bunch for jumping in and giving me some ideas! I am hoping to have something working soon with what you guys have given me. The end game for me is to be able to stream MP3s from a playlist. It appears like both solutions you guys have proposed may give me what I need. I will actually try both and let you know how it goes.

From: lmoore at omninet.net.au
To: asterisk-users at lists.digium.com
Date: Thu, 1 Oct 2015 06:15:17 +0800
Subject: Re: [asterisk-users] Change Asterisk MulticastRTP codec

    On my Asterisk 11 system I have the following in extensions.ael for


            8001    => {








    I believe in your case you need to set PJSIP_MEDIA_OFFER(ulaw) in a
    pre-dial handler prior to making the call.







    On 1/10/2015 1:51 AM, Matthew Murphy

      Greetings everyone,

        I was wondering if there was a way to change the codec that
          Asterisk uses when streaming via MulticastRTP. Or perhaps a
          way to transcode the multicast stream.

        In the CLI, when I have a multicast stream in progress, I
          am typing 'core show channel MulticastRTP/0x7f7........' to
          get lots of helpful information.

        I have noticed that when I do

          a MULTICAST page and send data from MP3Player, I get no
          sound on my speakers and get the following from 'core show
          channel PJSIP/xxx':

          NativeFormats: (slin)
          WriteFormat: slin
          ReadFormat: slin
          WriteTranscode: No 
          ReadTranscode: No 

        I have noticed that when I do a UNICAST page and send
            data from MP3Player, everything works flawlessly and I
          get the following from 'core show channel MulticastRTP':

          NativeFormats: (ulaw)
          WriteFormat: slin
          ReadFormat: slin
          WriteTranscode: Yes (slin at 8000)->(ulaw at 8000)
          ReadTranscode: Yes (ulaw at 8000)->(slin at 8000)


        The only thing that is changing is the following
          line in my extensions.conf file:

        ; For Multicast Paging
          same =>

          ; For Unicast Paging
          same =>


        Is there any way to get the MP3Player stream to transcode
          (as it does on the UNICAST stream) when I try to MULTICAST?

        Thanks for the help,





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