24/7 updating video loop?

Hello. I have a rather specific question about how to set up my media server.

The basics of it is:
I work at a cinema theatre. We have a huge flatscreen at the enterance where we are supposed to show trailers for the 6-10 films we are screening at the moment.
I was against the purchase of this huge flatscreen but nevermind. Now that we have it:
I want to set up a raspberry pi (3 mod B) based media server connected through hdmi to the screen that ENDLESSLY loops the video files present on the storage media (that will be managed through remote wifi access).
Basically I want to loop all the video files present on the sd-card automatically at startup. I have googled my ass off and followed several guides to try to set it up but all appears to be out of date and no longer working. I am now irritated.
The ideal situation would be that the pi is running 24/7 and we’re still able to upload video files to the sd-card that automatically gets added to the playlist. WITHOUT having to make new playlists manually.

Any input on this would be very much appreciated!