Unlike simple video files, MP4 is a "multimedia container." It can store video, audio, subtitles, and still images all in one file.
Разница между MPEG-4, AVC/H.264 и MP4 - Elecard 19448mp4
It is designed to provide high-quality video at relatively small file sizes, making it the "gold standard" for internet streaming and YouTube. Unlike simple video files, MP4 is a "multimedia container