Video is the heaviest thing most of us ever attach: screen recordings, camera clips, whole talks. It was born in wherever your camera, screen recorder or download came from, and its real weak spot is nothing inherently; every container brings its own quirks.
MP3 is the format that taught music to travel: small, scrappy, and welcome absolutely everywhere. MPEG-1 Audio Layer III. Perceptual coding: it throws away the parts of the signal your ear is least likely to miss. That makes it the right destination when what you need is playing on anything with a speaker, from new phones to twenty-year-old car stereos.