The format is a multimedia container used to store video, audio, subtitles, and images.

These files can store descriptive data (metadata) such as title, author, and date, which help media players organize content. How to Identify or Open the File

If you have a file named 21578e10.mp4 and are unsure of its contents: Video Metadata Starter Kit: What You Need to Know - JWX

It is widely used for streaming and is compatible with almost all modern devices, from smartphones to gaming consoles.