Use a tool like MediaInfo to see the encoding library . For example, if it says "Handbrake," it was a converted file; if it says "Ambarella," it's likely from a dashcam or action cam.
Software like OBS Studio or Nvidia ShadowPlay frequently uses this naming convention for "Instant Replays." 3. Mobile Device Backups
If you received this file from an unknown source, run it through VirusTotal before opening, as .mp4 files can occasionally exploit media player vulnerabilities.