Just got the Tab S 10.5 (laptop died last week - trying to survive on a tablet alone!). This video is in the videos folder by default. I disabled my ScreenSaver app and it disappeared - maybe this is the why you are not seeing it? Could've been accidentally disabled.
I like the display on this thing a lot! I have a few questions/concerns I'd like to bring up to the more experienced owners..
1.) What's you preferred way of sending local videos to TV? HDMI Cable? I have ChromeCast, but the new screenCast feature is not supported for the Tab S 10.5 yet 
2.) I just ordered a bluetooth mouse and keyboard - I was assuming a majority of BT devices will work? Is there a maximum # of BT devices?
3.) I don't game a ton, so I don't see performance issues, but it'd be nice to know that these 8 cores actually work properly. I do have an N64 emulator and Mario Kart 64 (I'm planning to use a USB hub into the OTG connector so I can connect my old school game pads). I wanted to ScreenCast to the TV as well; maybe I'm hoping for too much!
I'd love to hear about cool features, accessories, mods, etc.