[book club issue 13] packaging format of video files

FFmpeg Video packaging format

FFmpeg Supports many encapsulation formats , Include MP4、FL.V、 MKV、 TS And other video packaging formats 、MP3、 MC And other audio packaging formats RTMP、 RTSP、 HILS And so on network protocol encapsulation format .
And we focus on learning MP4 Video encapsulation format .

MP4 Package format

MP4 Basically, the encapsulation format can be considered as the most common video file format in daily life and work , Mainly because of its wide applicability , Not only in PC End (windows、 mac、 linux) Very good support , And on the mobile side (Android、 i0S) It can also be played smoothly .

MP4 Format standard

MP4 Format standard is ISO- 14496 Part 12 and ISO- 14496 Part 14, The specific features are as follows :

1. MP4 The document consists of many Box and FullBox.
2. FullBox yes Box An extension of , stay lleader Added in 8 position version Information and 24 Bit flags Information .
3. Every Box from Header and Data Two parts .
4. Header It contains the whole Box The length of the size of (size) And type (type) .
5. Data It contains actual data , It could be pure data , It can also be a son Box. When Box Medium Data Is a series of sub Box when , This Box Also known as Container ( Containers ).

MP4 ftyp Box

ftyp Box, - Generally located at the beginning of the file , Which includes MP4 Types of video files 、 edition 、 Compatibility agreement
Discussion and other information .

MP4 moov Containers

moov The container contains MP4 Media data information of video file , There are two sub containers inside : mvhd and
trak, The former defines the file header information , The latter defines... In the media file track Information .
Moov Containers are generally generated in by default MP4 End of file , When playing online, you need to load a complete file to open it normally , In order to quickly open the video , Need to put moov Put the container in MP4 In front of the file .

MP4 mdat Box

mdat Box, Used to store the actual data content of media files .

summary ：

The second day of study mainly explained the packaging format of video files , With the most common MP4 The format of video file describes the specific standard of format in detail , It can be said that I have re understood the most common format in life , Originally, it was packaged like this .