If your OS won't generate a preview, try opening it in a universal player like VLC Media Player . It can usually play files even if the header is slightly damaged.
If you have a specific video in mind (like a viral clip or a tutorial), let me know and I can tailor the content! The Mystery of 245.mp4: What’s Hiding in Your Downloads? 245.mp4
Before you double-click and hope for the best, here are three ways to figure out what’s inside: If your OS won't generate a preview, try