You can't turn it off. It is a feature designed to protect the display, not unlike a screensaver from back in the day. Maybe if you used a different movie player it would help.
The TabPro S uses an OLED panel rather than LCD for the screen. LCD is the technology traditionally used in just about every laptop, tablet and flatscreen monitor these days. (replacing CRT's)
OLED/AMOLED rose to prominence in phones several years ago where its pixels can be individually lit up, making for darker blacks, a display that saves power displaying black and a display with more "pop." The downside is that it's more susceptible to burn-in and the auto-dimming is a feature designed to reduce risk.