Sometimes your browser saves a video you watched so it doesn't have to download it again, using a hash to track it.
If you try to open your d004...mp4 and get an error, the file might be incomplete. This happens often with interrupted downloads. You can try online repair tools or simply delete it if you don't recognize the origin. Final Thoughts d00439a7090a3c865f341c7d216450e7.mp4
Even an .mp4 can be a disguised threat. Use a tool like Windows Security or Malwarebytes to check the file first. Sometimes your browser saves a video you watched