MP4
The most widely played video file, opened by phones, editors and social apps.
See it in Motion ASCII. Upload a short video, then press Download video.
In plain words
An MP4 file holds a video, and usually its sound, in one package. Inside, the frames are squeezed hard, keeping mostly what changes between them. That makes long clips small enough to share. Almost every phone, app and editor can play it. Some browsers record MP4 straight from a canvas, and others record WebM.