What is MP4?
How does the Mp4 format work?
First, the package format is presented. Multimedia encapsulation format (also called container format) refers to placing video data, audio data, etc. in a file according to certain rules. Common MKV, AVI and MP4 presented in this article are all package formats.
MP4 is one of the most common package formats and is widely used due to its cross-platform nature. The suffix for MP4 files is .mp4 and basically all major players and browsers support the MP4 format.
MP4 file format is mainly defined by MPEG-4 Part 12 and MPEG-4 Part 14. Among them, MPEG-4 Part 12 defines the ISO basic media file format for storing time-based media content. MPEG-4 Part 14 actually defines the MP4 file format and expands on the basis of MPEG-4 Part 12.
For students involved in work related to live broadcasts, audio and video, an understanding of the MP4 format is necessary. Below is a brief introduction.
MP4 File Format Overview
MP4 files are made up of several frames, each frame stores different information, and there is a tree structure between the frames, as shown in the initial figure.
There are many types of boxes, the following are 3 most important top level boxes:
ftyp: file type box, which describes the MP4 specification and the version with which the file complies;
moov: Movie Box, the media metadata information, there is only one.
mdat: Media data box, which stores the actual media data, usually there are several;
Although there are many types of boxes, the basic structure is the same. The next section will first introduce the box structure and then explain common boxes in more detail.
About HCV/HCV1
When talking about the MP4 specification, AVC is mentioned, sometimes it refers to “AVC file format”, sometimes it refers to “AVC (H.264) compression standard”, here is a simple distinction.
AVC file format: It is derived from the basic ISO file format and uses the AVC compression standard, which can be considered as an extension format of MP4. The corresponding mark is usually avc1, which is defined in MPEG-4 PART 15.
AVC Compression Standard (H.264): Defined in MPEG-4 Part 10.
The ISO base file format (Base Media File Format) is defined in MPEG-4 Part 12.
