> audio and video capture has to start going before call is actually established at signaling level, in order to minimize call establishment delay. Audio maybe going through Bluetooth, for example, and waking up Handsfree mode of BT may take 1-2 sec

As a user, while I can accept capture starting before I answer, I cannot accept sending. I understand how it helps the speed of establishing calls.

But it means the only thing needed to spy on me from that is a software change ON THE OTHER SIDE. No way to know from my side if I'm good or not.