Valid license keys were historically provided on physical stickers attached to CD sleeves, instruction manuals, or the hardware packaging itself.
If you purchased a video capture card, USB TV tuner, or camera, look for a CD-ROM jacket or a sticker on the device itself. The license key is usually a 24-character alphanumeric code.
Are you trying to (like a VHS player) or just edit existing files? What capture hardware model do you own, if any?