[asterisk-users] meetme conference using g729?

[Tony Mountifield]

In article <6b542ec90710030216o797dbbc2o9942ab929b7f5dc9 at mail.gmail.com>,
Mark Quitoriano <markquitoriano at gmail.com> wrote:
> 
> yeah i still don't understand.  this is what i want to do. I want asterisk
> not to compress and decompress codecs. so either i can use SLIN as my codec
> for my SIP or IAX. or i can remove SLIN codec in meetme and change it to
> g729a so there's is no compression and decompression.
> 
> do you get what i want to do? Thanks!

Yes, but it can't be done. In order to allow each conference participant
to hear all the others at once, it is necessary to mix the audio by adding
the contents of each channel. It is impossible to mix G.729 compressed
because there is not a simple mathematical relationship between the output
data and multiple input data.

The mathematical way to do it would be what you are trying to avoid:
convert each incoming stream to signed linear samples, then perform the
mixing by adding those samples together, and then convert the outgoing
mixed stream back to G.729 or whatever.

This is what Asterisk does with any kind of codec that talks to Meetme,
whether it be uLaw, ALaw, GSM, G.729, ILBC, and it doesn't need all
participants to be using the same codec.

Why were you so set on mixing G.729 without decoding/encoding?

Cheers
Tony
-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org