I,p,b frame and Pts,dts relationship

Source: Internet
Author: User

Basic Concepts:

I Frame: Intra-frame encoding frame also known as intra picture,i frame is usually the first frame of each GOP (a video compression technique used by MPEG), which is moderately compressed as a reference point for random access and can be used as an image. I-frames can be seen as a product of a compressed image.

P Frame: Forward prediction coding frame, also known aspredictive-frame, by sufficiently lower than the image sequence of the previously encoded frame of time redundancy information to compress the amount of transmitted data encoded image, called the prediction frame;

B frame: Bidirectional prediction interpolation coding frame also known as bi-directional interpolated prediction frame, both considering with the source image sequence before the encoded frame, It also takes into account the time redundancy information between the encoded frames behind the source image sequence to compress the encoded image of the transmitted data, also called the bidirectional prediction frame;

Pts:presentation time Stamp. PTS are primarily used to measure when a decoded video frame is displayed.

Dts:decode time Stamp. DTS primarily identifies when the bit stream in memory is read into the decoder to decode.

The order of DTS and the order of PTS should be the same without the existence of B-frames.

I, P, B frames are different:

I frame: itself can be extracted by the video decompression algorithm into a single complete picture.

P frame: You need to refer to an I frame or b frame in front of it to generate a complete picture.

B frame: Refer to its previous I or P frame and a P-frame behind it to generate a complete picture.

A GOP is formed between two I frames, and the size of the BF can be set by parameter in x264, i.e. the number of B between I and P or two p.

The above-mentioned basic can be explained that if a B frame exists, the last frame of a GOP must be p.

different for DTS and pts:

DTS is primarily used for decoding video, which is used in the decoding phase. PTS are primarily used for video synchronization and output. Used when display. In the absence of a B frame. The output order of DTS and PTS is the same.


Here is an example of a GOP of 15, with its decoded reference frame and its decoding sequence in it:

such as: I-frame decoding does not depend on any other frames. The decoding of P frame depends on the I frame or p frame in front of it. The decoding of frame B depends on the nearest I-frame or P-frame and the nearest P-frame in front of it.

I,p,b frame and Pts,dts relationship

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