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For a PC and a roku on the same network I would highly recommend Plex or Jellyfin. You store the video on your pc and stream it over to the tv over the network. They're both free, Plex is closed source and has some paid features if you want that, Jellyfin is totally open source.
I've been using Plex in this setup for a lot of years and its been rock solid.
Any legality concerns with Plex or jellyfin? (Have the VPN on during steam, or is it like a direct connection from comp to TV?)
Nah, you'll be fine.
Nope, both go directly from your PC to your tv. Plex does a log-in thing to their servers but that's just an account. Jellyfin is 100% local.
You sound like a beginner, which is totally fine.
If you're new to this and your files are on a laptop, just use VLC media player (it's free) and an HDMI cable to connect to your TV. Nothing more than that is needed.
Setting up a media library via Plex or Jellyfin, as others have suggested, is an excellent solution for basically having your own mini in-network Netflix, but it's not a simple solution for someone who's not used to doing some more in-depth technical things.
Do you have an HDMI cable? I have my laptop more or less permanently plugged into the TV for exactly the purpose of watching movies, whether pirated or otherwise.
I do - this might be the easiest option. Will that get sound over too? I don't have actual speakers on my comp, just headphones. Trying to get it set up so the wife and I can watch it on the TV as normal-a-viewing-experience as possible.
HDMI is intended to pass audio signal as well. You may have to make adjustments to the audio output settings on windows.
Plex is a thing that is fun
I run plex through a Chromecast into TV HDMI.
Wondering how others do it now....? Is it PCs plugged into TVs?
Or do modern TVs run Plex apps?
Roku, android TV, samsung, webOS, and a bunch of other random smart tv platforms all have plex apps. For direct hdmi I assume most people run a media center like kodi (xbmc).
Thanks!
Plex or jellyfin
You might aswell just go into the deep parts of the oceans and start with the are stack right now
If your TV has a USB port you can just plug in a USBstick or external drive.
Or connect a laptop or something via HDMI cable to the tv
Or you can go the full server route with jellyfin and stream to a pi connected to the tv
Check out 4kiptvprime.com they have a July sale on now. they will help you out.
to add to other answers about jellyfin, there's a roku app for it which is Quite Good in my experience https://channelstore.roku.com/details/cc5e559d08d9ec87c5f30dcebdeebc12/jellyfin