The .mp4 suffix is a common trope in Analog Horror or ARGs (Alternate Reality Games) to make fictional scary stories feel like "lost footage" found on a hard drive. Stories often involve "extra" roommates who aren't human or roommates who have undergone a personality change.
Videos detailing a roommate returning from a trip (like an Ayahuasca retreat) with a completely altered, frightening personality. Less-roomate.mp4
Stories about roommates who never leave their rooms, leading to disturbing discoveries. leading to disturbing discoveries.