Use Windows Media Player (Windows) or QuickTime (Mac).
MP4 is a universal container format supported by most modern players. VID-16997.mp4
If the file won't open, use VLC Media Player or Jellyfin , which support a wider range of internal codecs like H.264 or HEVC. 2. Repairing a Corrupt MP4 Forensic analysis of video file formats - ScienceDirect Use Windows Media Player (Windows) or QuickTime (Mac)