How to broadcast the contents of a container over socket.io?

Question

Node.js

Good afternoon.
I am making an application for webinars (chat, video from the host's camera and a container into which he can display material: videos, pictures, draw something, etc.). The user must observe in real time what the presenter outputs, and he does not see the controls.
I figured out the chat and rooms, I think I can also handle broadcasting from the host’s camera, but I didn’t find answers and resources suggesting the right idea how to implement such an idea with broadcasting the contents of the container. I understand that in fact it will be the second stream, which I have to distribute to everyone through the server and the socket, but how can this be implemented. Submit an idea, please.
Ps I have not come across webTRC and socket.io technologies before.