screen goes blank after X minutes
 

Not really sure how many exactly, but after maybe 10 minutes of watching a video the screen goes blank. It's quite annoying, and I have no idea what file or command to stop this behavior.

I assume it's some sort of screen saver or battery saver type program/setting. This is not my laptop, and I use xscreensaver manually when I'm going to be AFK.

So, what file/command do I need to edit to stop the screen from going blank?

try running this
it will disable x11 automatic screen saving.
If you use some fancy desktop like xfce or kde, they will do this for you when you are watching a video or doing something

You might need 'xset s off' as well. Oddly enough, gamepad input from RPC3S isn't considered "input" for the sake of screen blanking. If I forget to turn it off, I'll be in a game, usually in an action spot, and the screen will turn off until I reach for the mouse and move it.

You do not describe your setup. Some monitors will go dark to save power without what the consider "real activity". Maybe it is your monitor ? If so there may be a setup button you can mess with.

If you use a media player there might be a "Disable screensaver" option.
In vlc:
Tools > Preferences
choose "show settings: all" (bottom left corner)
choose Video in left hand column
tick the box "Disable screensaver"

In SMPlayer:
Options > Preferences
General (in left hand column), choose Video tab
tick the box "Disable screensaver"

On my display I can use this to start the screensaver and dpms:
To stop the screeensaver and dpms:
I use xsceensaver-settings to configure the screensaver and dpms behavior.

caffeine-ng-3.4.2-x86_64-2_SBo
caffeine-ng (Status bar application to stop the screensaver)
Caffeine is a little daemon that sits in your systray, and prevents the screensaver from showing up, or the system from going to sleep. It does so when an application is fullscreened (eg: youtube), or when you click on the systray icon (which you can do, when, eg: reading).