If this is a file on your device that you can't open, you can try using a universal player like VLC Media Player .
Right-click the file and select "Properties" (or "Get Info" on Mac) to see the date it was created, which might give you a hint. video (39).mp4
Is it a meme, a tutorial, or a news clip? If this is a file on your device
Where did you download it from (e.g., WhatsApp, Discord, or a specific website)? or a specific website)?