What is a .mp4 file?

You downloaded a video, recorded your screen, or saved something from the internet. It's almost certainly an MP4. The format is behind YouTube, TikTok, Netflix streams, Zoom recordings, and the video your cousin posted of their cat. It plays on every browser, every phone, every smart TV, every operating system.

MP4 isn't actually a video format — it's a container. Think of it as a box that holds a video track (usually H.264 or H.265), an audio track (usually AAC), and optionally subtitles and metadata. The container doesn't determine quality; the codec inside does. This distinction matters when someone tells you their MP4 "looks bad" — the container is fine, their encoding settings aren't. A well-encoded MP4 at the right bitrate is indistinguishable from the source.

VLC plays everything. Your browser plays MP4 natively. When in doubt about what format to export, record, or convert to, the answer is MP4. It won the format wars by being good enough at everything and perfect for compatibility.