What is MP4 file?
MP4 is based on ISO/IEC 14496-12:2004 (MPEG-4 Part 12: ISO base media file format) which is directly based upon Apple’s QuickTime container format. It is essentially identical to the MOV format, but formally specifies support for Initial Object Descriptors (IOD) and other MPEG features.
MP4 file format is most commonly used to store digital video and digital audio streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images. Like most modern container formats, MP4 allows streaming over the Internet. A separate hint track is used to include streaming information in the file. The official filename extension for MPEG-4 Part 14 files is .mp4, thus the container format is often referred to simply as MP4.