My home computer network is connected to the ISP via Apple AirPort Time Capsule which has 2TB drive inside and so also serves as a home NAS. I also own an Apple TV device for entertainment: Netflix, Apple Movies, Hulu, Youtube, etc. Although, often I need to watch something that I downloaded from Youtube or Torrents. I used to use Plex for that purposes - it works pretty well, but has one major ‘issue’: it streams video from your computer to the Apple TV, so you need to keep the PC up and running during all the time you’re watching the video. So, the question appeared: is it possible to stream a video on Apple TV device from Apple AirPort Time Capsule?
The answer is: yes, it is possible. You should enable access to the Time Capsule’s disks, - use AirPort Utility for configuration: Disks tab -> Secure Shared Disks -> With Accounts. Kindly note, it should be exactly With Accounts, otherwise Apple TV won’t be able to connect to the Time Capsule’s disks. In the Accounts create a separate account (with login and password) for Apple TV and set it to Read Only access. Now, click Apply and AirPort will restart (so you’ll need to re-connect to the Wi-Fi if you’re using it).
Now, you should install on the Apple TV a video player application that supports connections via SMB. There are at least two not bad and free solutions: VLC and Elmedia Video Player - install both and see what works better for you. In the player, add a new video library shared folder via SMB: smb://x.x.x.x/ - where x.x.x.x is the IP address of your AirPort device (use the login and password you created above).
That’s it! Now you can copy your video files in the folder that is accessible from the Apple TV account you have just created, and play them back using the chosen video player application. No need to use Plex, no need to keep computer being up.