I've been looking into getting a smart tv and was doing some research on screensavers when I stumbled upon this video on Youtube. Within the video I noticed an option under Settings -> Device Preferences -> Screen Saver -> Screen Saver -> Photo Gallery and Screensaver -> Photo Sources -> External Drives.
The video doesn't show what this does or tell me which version of Android TV this is. But I was curious if this option would allow me to insert a USB drive into the TV and then have it load a custom looping video screensaver from it.
Source Video: https://youtu.be/7sjdwL1tDzE?t=111
Try Aerial Views, it's open source and has the option to play videos from local storage
https://play.google.com/store/apps/details?id=com.neilturner.aerialviews&gl=US