A 2019 report warned that MP4 files downloaded from unknown sources can be used to deliver malware, specifically mentioning vulnerabilities patched in applications like WhatsApp.
did you get this file from (e.g., a specific app, website, or security camera)? What is the exact file name or extension? Are you getting a specific error when you try to open it? That MP4 file you downloaded might just be another malware Download VC77 mp4
It is possible "VC77" refers to a specific proprietary camera model or a niche software, and the file is a recording from that device. Recommendations: A 2019 report warned that MP4 files downloaded
EN 
EL