If you believe the file is safe, you can try opening it with the VLC Media Player , which is known for playing almost any MP4 file even if the name or header is slightly corrupted.
On Windows, you can right-click the file and select Properties > Details to see the video's length and frame width, which might help you identify what the video actually is. Download 0f71f09a a2344e76(0) mp4
If it won't play, you can upload the file to a service like CheckFileType.com to confirm it is actually a video and not another file type disguised with an .mp4 extension. If you believe the file is safe, you