What is MP4?
Definition
MP4 is a file format that holds video, audio and timing information in one file; it is the standard format for sharing video.
An MP4 is a container: the video inside is compressed with a codec, most often H.264. MP4 files play in browsers, on phones, in chat apps and on every video site.
MP4 is the safe answer to "what format should I send?". Other containers exist, such as MOV, MKV and WebM, and each has its uses, but none is accepted in as many places.