A video mixer is a device used in video production to combine multiple video sources into a single output. It allows operators to switch between different video feeds, add effects, and control transitions in real-time. This is essential for live broadcasts, events, and video editing, ensuring a smooth viewing experience. Video mixers can be hardware-based or software-based, with many modern options available for computers. They often include features like audio mixing, video effects, and color correction, making them versatile tools for both amateur and professional videographers.