[Telepathy] telepathy: problem fro accessing stream-engine

[Matthieu LAURENT]

I have success in making the telepathy client "tp_caller" (from project
telepathy-sofiasip) working.

I can see that interface
org.freedesktop.Telepathy.ChannelHandler, methode HandleChannel
of the stream-engine is accessed by the function tp_ch_handle_channel()
of the libtelepathy library

I don't see any binding in libtelepathy in order to access interface
org.freedesktop.Telepathy.StreamEngine, method SetOutputVolume for example

Could you tell me how to add this functionality in libtelepathy, and how
to call it from the telepathy client tp_caller, in oder to access
directly to the whole interface of the stream-engine (or if there is a
simplest way to access this function SetOutputVolume)?

thanks for your help

Matthieu