Use video editing software to look for single-frame images or hidden text that isn't visible at normal playback speeds.
If you are viewing the file as part of an online puzzle or investigation:
Before interacting with an unfamiliar .mp4 file, determine where it originated:
Open the file in a Hex Editor to see if there are text strings or hidden "magic bytes" at the end of the file code. 4. Community Collaboration
If you found this on a public hosting site, exercise extreme caution.
Run the file through a service like VirusTotal to ensure it isn't a disguised executable.
These files often circulate in "creepypasta" or alternate reality game (ARG) communities.