RTSP backchannel for two way audio

[jtzemp]

Hi, y'all!

I'm doing some preliminary research into building out a CCTV system for my home using ONVIF capable cameras. I'm looking at adding a few cameras that support 2-way audio, like an intercom.

I'm new to this, but it seems that the cameras that support ONVIF and two way audio (like an intercom) do so using a RTSP backchannel.

It's my understanding correct?

Is this possible with the current library? If not, is it something you'd be interested in seeing in a PR?