Two separate things to note, I believe @Uvita666 is running into the first.
- Not all routers support “U-turn Routing”
So you need some way to give VRChat a URL that will resolve to PUBLICIP for other people, and LOCALIP for you. Personally I use a dynamic DNS, and in my Windows PC hosts file I have an entry for that host that points the hostname to the computers LAN ip. But maybe 127.0.0.1 would work. (Crossed out as I think you’re using a different PC to stream than play VRC) Make sure you’re pointing at the correct PC 
C:\Windows\System32\drivers\etc\hosts is the file, personally I open up notepad as administrator, and then edit the hosts file. I actually close all notepad windows before doing that, just so I make sure I don’t leave any notepads running as admin.
Some routers also support custom DNS, but that gets complicated, as you have to be sure that your PC actually talks to the router for DNS, and set it up there. But that would be useful if you’re using Quest Standalone
- Protocol conflict between Windows and Android with RTSP
Summary: RTSP works so weird I’d say it almost works on Quest
- UDP RTSP doesn’t work through most NAT firewalls
- ExoPlayer (Quest/Android) doesn’t support rtspt:// protocol, and with rtsp:// protocol it requires to be offered UDP, when told an invalid transport, that counts as an error in the version that VRChat/AVPro is running
- ExoPlayer will try and play a UDP stream for about 8 seconds, and then try TCP
- rtspt:// protocol is used for PC clients to have the media engine require a TCP connection
My workaround is a small adjustment to MediaMTX
But then i ran into another problem: Most video players have a timeout of 10 seconds. Getting a Quest 2 user to connect to RTSP takes almost 10 seconds, so with someone fairly close to me, the connection takes a few tries to get going.
So after you raise the general timeout from 10 seconds to 15 seconds for your world, things work. But if a Quest user needs to resync the video, they need to be told to give it 10 seconds
Here is a link to a Canny where someone is asking for RTSP to just be forced to use TCP
Please give it an upvote.
In the mean time you could try a world called Black Gold, it has a video player where you can give Quest users a separate link from the PC users. Other worlds have features like that, but I know that black gold works.