Run the file through VirusTotal . Even though it has a .mp4 extension, attackers sometimes hide scripts inside media containers.
Check the "Details" tab for "Date Created" or "Origin." k20h56k5hgk5gf .mp4
These platforms often rename files to long alphanumeric strings. If you found this in a chat, check the message history to see who sent it. Run the file through VirusTotal