Without plugins like ten years ago the only way to view a RTSP stream if browser does not direcly support it is to proxy/re-stream it in any other format that is supported. Different options are in this How to stream RTSP live video in Firefox and Chrome now that the VLC plugin is not supported anymore?

There are things like websockets and so that js can use to connect to a server and stream on but they all need to proxify as well (js cannot access a raw tcp or udp ports/connectors directly).

And as long it is and "old" protocol don't expect to be reimplemented.