[Linphone-users]TrueSpeech codec

[Robert W. Brewer]

I'm working on adding Yahoo voicechat capability
to one of the open source messaging clients.  What
is known so far is that Yahoo uses the proprietary
TrueSpeech codec under Windows and RTP as a
transport.  It also appears that Linphone has a
nice modular design which would make it easy to
use only the needed pieces to interoperate with
Yahoo.  Since the mplayer movie player can already 
play TrueSpeech files by loading the .dll using 
code from Wine, I have been able to use that code 
to decompress TrueSpeech files without the rest of 
mplayer, and very soon I will be able to create 
TrueSpeech files too.

There are a couple of possible design alternatives
I have thought of, and I'd like some feedback from 
other Linphone people about it.

1. Take the relevant code from Linphone and
incorporate it into the messaging client.  The
advantage of this is that the Linphone codebase is
not "polluted" with support for the TrueSpeech
codec or anything else. The disadvantage of this
scheme is the user now has two separate places to
configure soundcard settings, and there will be
sound device conflicts when a user has the
messenger running a voicechat and a Linphone call
comes in, etc.

2. Remote control of Linphone.  The messaging
client (Yahoo or in the future MSN messenger,
etc.) could command an already-running Linphone
process to initiate or answer a voice call on a
given port with a given codec, etc.  The messenger
client would handle all proprietary call setup and
signalling, and Linphone would just handle fairly
standard RTP streams carrying voice traffic (but 
maybe with a proprietary codec).  Linphone then 
becomes a central place for controlling volume 
levels, sound setup, etc.  It
also seems like a nice division of labor between
the two apps.  Of course Linphone would also need
to notify the requesting app when the call is
ended for whatever reason, etc.  For this to work
the TrueSpeech codec would need to be added into
Linphone as well as some form of IPC with other 
apps.  One can even envision the possibility of a 
3-way call with another Linphone user via SIP and 
a Yahoo user via its protocol.

Of course, starting off with option 1 and later
migrating to option 2 is a possibility as well.

Assuming I use code from Linphone to do this, with
either option I will most likely add support for
the TrueSpeech codec into my copy of Linphone to
test out the concept.  I would be happy to provide
this back to the Linphone developers if it is
wanted.  Having that infrastructure in the
codebase could also allow other proprietary codecs
to be used, but only on x86 boxes (since x86 
Windows .dlls would be used).

Comments and suggestions are appreciated.

-Rob

PS.  Yes, I wish all the messengers would get
together and standardize on SIP and allow various
codecs to be used.  Until then I'm willing to put 
some effort in to be able to talk to more people 
while running Linux.