About the file format .MP4:

MP4 is a file format created by the Moving Picture Experts Group (MPEG) as a multimedia container format designed to store audiovisual data but can also be used to store other data such as subtitles and still images. Like most modern container formats, it allows streaming over the Internet. The MP4 is largely replacing earlier multimedia file formats, and creating some changes in the way that vendors sell audiovisual files to the public.