Windows offers a built in DLNA server within the Windows Media Player. If you're using Media Center, you must still be using Windows 7, as it was removed from Windows 10. Open Roku Media Player, and your Windows computer should show up as a media source. Assuming Windows transcodes the video correctly, you will be able to play them in RMP.
That said, Windows Media Player is a terrible media server. It's ability to transcode is hit or miss at best. WMC records in the WTV format. It's not a supported format by Roku, so it needs to be transcoded. If your recordings are from OTA broadcasts, then the video is MPEG-2 and the audio is AC3, both of which are supported by Roku. So all your media server needs to do is what's called transmux the file into a supported container.
There are several other media server choices that are far better than using Windows Media Player as your source, and they are all free to use. The first two have their own channel for Roku devices, and are likely the simplest for someone to use. That would be either Plex or Emby. If you want a DLNA server that provides more control over how your media is handled, I recommend Serviio. Disclosure, I am the author of the Roku profiles that are included with Serviio. You can install any or all of them on your Windows computer without interfering with Windows Media Center or each other, so you can play around and see what you like best. Will say that if you want caption support for ripped DVDs or Blu Rays, then Plex or Emby are the better choices. Serviio has the ability to display them, but you can't toggle them on/off from your player. They are burned into the video stream.
How to connect your Roku to the same TV that you're using as a computer monitor? Simply connect it to a different HDMI input. I am doing the same with a Samsung TV that acts as my work from home monitor, as well as a Roku Premiere connected to it.
Dan
Roku Community Streaming Expert
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