Self authenticating tamper resistant first meetings
I wouldn't consider voice or video to remain a secure means of identification for much longer.  Advances in real-time video stream editing are near enough to reality that I wouldn't build a new security system on it.

In the olden times in millennia past, you could have the computers on either end display a short MAC for both parties to alternate reading aloud one letter at a time to each other (quickly), and the lack of delay plus the sound of your partner's voice was a pretty good assurance that you weren't being MITM'ed.  But today, the technology available to a sophisticated attacker could render even that approach untrustworthy.  

If you are really that paranoid, you need to physically and privately exchange some other kind of okay/duress signal, such as a specific word or phrase; right leg crossed over left; carnation or rose on the table facing right or left; cigarette or other object in the left or right hand; book face down or face up, or any of a thousand other cheesy spy tradecraft signals.  But sometimes the old standbys can't be beat.