How to solve such a problem of RTMP video broadcasting?

Question

Nginx

We have a server with Nginx-RTMP configured Ubuntu 14.04
The server catches the incoming stream at certain points, for example:
rtmp://localhost/cam1
rtmp://localhost/cam2
There is a mount point, for example /live where people connect and watch.
Tasks
1. Is it possible to somehow switch in real time with a command, what goes to the /live point?
That is, a command comes and the /live stream starts broadcasting, what comes from /cam1, another one comes and /cam2. Ie some kind of switching of cameras without any third-party software
2. Is it possible to permanently put a splash screen on the point /live (picture or video), if there are no /cam1 and /cam2 sources. Well, for example, both cameras collapse and people see: Technical problems have arisen.
If these tasks are not solved by NGINX, how can they be solved as part of linux
PS: do not offer OBS, you need a console solution.

Answer 1

1. You can. 2. You can.
nginx are not resolved, nginx-rtmp are resolved.
Are you familiar with Linux? Have you heard of symlinks?
A simple reliable solution is a simple script that creates/deletes symlinks.