I've been thrown this problem by my partner, who uses an iPhone and iPad.
My household "TV" is actually a 1920x1080 monitor and audio amplifier, connected by HDMI to a dedicated media PC. This lets the media PC play videos from local hard drives, USB, the file server, a browser (Netflix), Blu-Ray drive, IP TV/radio, etc, to the monitor. The software on the media PC is a browser, or VLC.
My partner now wants to be able to play videos on their iPad over wifi to some kind of stream/video/server software running on the media PC, which can then play it onward to VLC or to the display. I suspect they are indifferent whether it's a dumb system that they play/pause/control at the iPad end, or a system that is managed by the software at the Windows end. But I'm pretty sure they would want "free" or "free for personal use" software.
I'm happy to install suitable software on my media PC for the purpose but no idea what technologies I need it to have, to do this, much less any recommended software at the PC or iPad end. I have a suspicion that the term used is casting, streaming, or mirroring, but no idea which of these describes what I'm trying to do, as I don't use any of these myself right now.
The media PC runs windows 8.1 but realistically most windows 10 software will run fine on it as well. My only restriction is I don't want to use Google products, which might affect Chrome solutions, if that's relevant.
They mentioned Airplay, but I have a Bonjour/mDNS server already on the network, which lets their iPad find my non-Airprint/non-Airplay printers on the network, so if simple streaming works, the PC software just needs to be able to receive a video stream, I could also manually add the media PC's data to my Bonjour server separately so that the iPad can find it like any Airplay device.
Finally, I'm not sure if any kind of Apple DRM is a problem, or precludes any solutions.
What are my best software options to achieve this?