[Yunxiang book club issue 13] coding format of video files

Video coding formats generally include ：H263,H264,H265

H264 The rate control mode is : ABR

The frame types are ：I frame ,B frame ,P frame , The size relation is I>P>B

I The characteristics of the frame ： A full frame compression coding frame , Make a full frame image JPEG Compression and transmission , It is P The frame and B Frame reference frame , Its picture quality affects the following reference i The frame of p The frame and b The quality of the frame , By itself, it does not need to refer to other frames ,i Frame is the base frame , Each group contains only one I frame ,i The information data occupied by the frame is relatively large .

P frame ： Before decoding, the difference defined in this frame needs to be superimposed with the cached picture , Generate the final picture ,P Frames are I The frame is separated by 1-2 Frame encoding frame , You must decode I The whole image can be obtained only after the prediction value in the frame is superimposed with the prediction error , The compression of frames is very high .

B frame ：B The frame is from the front P Frame or I Frame with the following P Frame to predict , It has the highest compression ratio ,B Frame is not a reference frame , It doesn't cause the spread of decoding errors .