It's based on <a target="_blank" rel="noopener noreferrer" href="https://en.wikipedia.org/wiki/WebRTC">WebRTC</a>, a free and open-source project for web browsers.
It's the reason why we encourage developers to use the <a target="_blank" rel="noopener noreferrer" href="https://docs.joinpeertube.org/contribute/plugins">PeerTube plugin API</a> to create their own monetization system.