What exactly is a billed minute in Zoom’s fully customizable SDK

I currently use WebRTC (Vonage) to stream audio/video for my web product. Pricing is billed per subscriber minute. For example, if I have 2 people on the conference for 30 minutes this means person A is viewing person B and person B is viewing person A. This comes to a total of 60 subscriber minutes. If the conference was only 1 way, for example A views B only, then it would come to 30 subscriber minutes. If I had 3 people on the conference with everyone viewing everyone else, the subscriber minutes total for only 1 person will be 60 minutes. Then to get the total for the entire 30 minute session I need to multiply by the total number of participants, 3 in this case, to get 180 minutes.

What is zooms pricing plan in this regard? Do you have a concept of subscriber minutes? Or are the minutes flat. By flat I mean it doesn’t matter how many subscribers are viewing each other, it’s just the total time of the session that counts.