MP4 files open in the operating system's default video player. Many consider MP4 to be one of the best video formats available today. It is also a popular video format for streaming over the Internet, such as on YouTube. It is compatible with a wide range of devices and operating systems, using a codec to compress file size, resulting in a file that is easy to manage and store. MPEG-4 (MP4) is a container video format that can store multimedia data, usually audio and video.