While .mp4 files are generally safe, always ensure your media player is up to date to prevent "buffer overflow" exploits occasionally found in malicious video files [9].
If the video is a clip from a movie or viral event, take a screenshot of a clear frame and use Google Lens or Yandex Images to find the original source [7]. Security Warning 5_6096120831543347546.mp4
You generally cannot find the origin of a file by searching this number on Google because the ID is specific to the private or public channel where it was hosted [3]. How to Identify the Video Content While .mp4 files are generally safe