Simplest way to proxy RSTP streams

Question

Suppose we have an RTSP stream, which is outside of a companies extranet. Due to certain events, a huge number of employees are likely to view the current live stream. Given the number of employees is > some hundred, the outbound internet connection might not be fast enough.

Since RTSP isn't stateless, do proxies even exist?

Please propose ways to proxy the RTSP stream, so that only low bandwidth of the internet-connection gets consumer by the proxy itself.

Do (open-source) products exist, which I may configure or adopt to form a RTSP proxy?

Any, finally, is my question too general? Is the payload data / encoding of the underlying live stream of importance regarding my proxy question?