Audio and video column - summary of basic knowledge

After reading many tutorials about audio and video on the Internet, they are not well written. Many basic concepts are not explained clearly, so I started to talk about how to develop audio and video. Therefore, today I will sort out some basic knowledge about audio and video to help people who need to learn audio and video. The progress of friends, everyone can make progress together and communicate together. Knowledge can only make greater progress through communication. OK, let’s get to the topic

# Basic knowledge

## Why do you need to compress

● The data volume of uncompressed digital video is huge

● Difficult to store

● Difficulty transferring



## Why can it be compressed

● Remove redundant information

 	Spatial redundancy: there is a strong correlation between adjacent pixels in the image

 	Temporal redundancy: content similarity between adjacent images of a video sequence

​ Coding redundancy: the probability of occurrence of different pixel values ​​​​is different

​ Visual redundancy: the human visual system is insensitive to certain details

​ Knowledge redundancy: the regular structure can be obtained from prior knowledge and background knowledge



 Data Compression Classification

● Lossless compression (Winzip)

​ The image is exactly the same after decompression before compression

​ low compression ratio

● Lossy compression (H.264)

​ Inconsistent images after decompression before compression

​ High compression ratio

​ Take advantage of the characteristics of the human visual system (the animation frequency and image details visible to the human eye are limited)



## Video encoding format

| Name| Launching Organization|
| ----------- | -------------- | -------- | ------------ |
| HEVC(H.265) | MPEG/ITU-T | 2013 | Under development |
| H.264 | MPEG/ITU-T | 2003 | Various Fields |
| MPEG4 | MPEG | 2001 | Tepid |
| MPEG2 | MPEG | 1994 | Digital TV |
| VP9 | Google | 2013 | Under development |
| VP8 | Google | 2008 | Unpopular |
|