Xia CaoJun ffmpeg 4.3 audio and video foundation to engineering application

One . Color mode

RGB
RGB The main purpose of color model is to detect in electronic system , Represent and display images , Such as TV and computer , But it is also used in traditional photography .

The basic part is not enough to describe , For more information, click on the title in Wikipedia .

YUV
Y'UV The invention of color TV is due to the transition period between color TV and black-and-white TV . Black and white video only Y（Luma,Luminance） video , That's the gray scale value . It's time for color TV specifications , In order to YUV/YIQ To process color TV images , hold UV As of color C（Chrominance or Chroma）, If you ignore C The signal , So the rest Y（Luma） The signal is the same as the previous black and white TV frequency , In this way, we can solve the problem of compatibility between color TV and black-and-white TV .Y'UV The biggest advantage is that it takes up very little bandwidth , Because the human eye is sensitive to brightness , Not sensitive to color , So reduce some of it UV The amount of data , But the human eye doesn't feel .

YUV Also known as YCbCr, For each component, the following is true ：

Y：Luminance, brightness , That is, gray value . In addition to the brightness signal , It also contains more green channels .
U：Cb, The difference between the blue channel and the brightness .
V：Cr, The difference between the red channel and the brightness .
Here's the picture , You can see 3 The effect difference of components .

Two . Basic video concepts

frame (Frame)
A simple understanding of frames is for every picture in a video or animation , Video and animation effects are made up of countless images , Every picture is a frame .

 

frames (Frames)
The number of frames is actually the abbreviation of the number of frames generated , It can be explained as the number of still pictures

Frame rate (Frame Rate)
Frame rate (Frame rate) = frames (Frames)/ Time (Time), In frames per second (f/s, frames per second, fps).

The refresh rate
The number of times the screen is refreshed per second , It is divided into vertical refresh rate and horizontal refresh rate , Generally speaking, we refer to the vertical refresh rate , In Hertz (Hz) In units of , The higher the refresh rate , The more stable the image , The more natural and clear the image is .

at present , Most monitors press... According to their settings 30Hz、 60Hz、 120Hz perhaps 144Hz Refresh at the same frequency . The most common refresh rate is 60 Hz. This is to inherit the previous TV refresh rate of 60Hz Set up .

Key value of frame rate
10~12 FPS： Because of the special physiological structure of human eyes , If the frame rate of the viewed picture is higher than about 10 to 12 At the frame , It would be considered coherent , This phenomenon is called visual persistence .
24 FPS： Generally, the number of frames for shooting and playing movies is per second 24 frame .
60 FPS： This frame rate has a high smoothness for human eye recognition .
85 FPS： The limits of human brain processing video , The human eye cannot distinguish higher frequency differences .
60FPS
When doing page performance optimization , Commonly used 60FPS As a benchmark , Therefore, we need to try to control the rendering of each frame in 16ms Inside , Only in this way can one second be achieved 60 The fluency of the frame .

The resolution of the
video 、 The size or size of a picture .