The joke videos from the original game return in Metal Gear Solid Delta: Snake Eater, and can be comfortably enjoyed after completing the game for the first time. However, unlike the regular cutscenes, these must be actively collected in-game from NPCs in the form of film reels.
This guide is all about how to unlock the Secret Theater film reels in Metal Gear Solid Delta: Snake Eater.
Where To Collect Secret Theater Film Reels
The 8mm Film Reels you are seeking are plainly visible on any NPCs that are carrying them, affixed to their body.
In order to get the reels you will have to stalk the target and then hold them up, as any kind of physical takedowns are not an option.
Approach the target from outside of their line of sight, then enter stalk mode to deaden the sound of your footsteps. As soon as the prompt appears you can draw a weapon to hold them up. This will cause the target to disarm and allow you to maneuver around to where you can threaten them with your firearm, to the point where they will relinquish any loot, including the precious but fragile reels.
You must avoid any kind of physical contact with the target, as even a non-lethal attack will effectively destroy the reel for this run, unless you reload a save of course.
Below is a complete video guide that shows you locations of all the 15 reels.
That is how to get and watch all Secret Theater film reels in Metal Gear Solid Delta: Snake Eater.