How to make a cross-browser live stream from an RTSP stream?

Question

fmpeg

There is a camera that broadcasts in RTSP, a server that converts the video and uploads it to the site, a zoo from IE9 - EDGE, Firefox, Chrome and others like them. Perhaps even Safari, but we do not take into account poppy drivers, they asked for it themselves, let them put chrome with a fox.
The task is to make the video play correctly on all the above listed browsers.
flash & html5:
Flash is dead. Yes, and I want to use html5, here you can even turn away from users with ie 9 https://caniuse.com/#search=video or use something like "Video for Everybody", "" for (html5 + flash) but the problem with formats are not going anywhere.
Formats:
mp4 - a good option in terms of cross-browser compatibility, but as far as I understand, it's better to discard it right away, since mp4 cannot be streamed.
m3u8 is an option for mac and android browsers. HLS out of the box only works on safari
ogg - doesn't work in ie and safari without plugins (so far I've settled on this option)
webm - doesn't seem to work in ie and safari without plugins either.
dash and webm failed to start with rtsp input stream.
Used ffmpeg, MP4Box, vlc, a few other broadcast oriented programs, nothing comes out. Either a file is needed for input and not an rtsp stream, or broadcasting is not supported by the codec (as is the case with mp4)
At the moment I am still considering the option with mjpeg