Webinar and several cameras at the presenter. What platform and software can do this?

Question

Software and Internet Services

We want to organize an online broadcast of lectures. One of the requirements is multiple video sources (i.e. desktop video, lecturer camera, and whiteboard camera). It is assumed that the listener will see one of the video sources large and thumbnails of the others with the ability to switch between them on click. What platform or software can do this? Free of charge, of course.
Maybe for a purely webinar, the requirement is a little strange, but we want to broadcast a lecture at which people are present. As an extreme option (we think it is not very convenient for listeners) - make a video switcher through manycam, and have the assistant switch video streams. Still, I want the student to choose which picture to watch.

Answer 1

In bigbluebutton, this can be organized, in general (if the cameras are hooked up to different computers).
But it's selfhosted.