CN110611819B - Coding method for improving quality of B frame in H.264 - Google Patents

Coding method for improving quality of B frame in H.264 Download PDF

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CN110611819B
CN110611819B CN201910705407.7A CN201910705407A CN110611819B CN 110611819 B CN110611819 B CN 110611819B CN 201910705407 A CN201910705407 A CN 201910705407A CN 110611819 B CN110611819 B CN 110611819B
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mode
skip
rdcost
ssd
coding distortion
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CN110611819A (en
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廖义
万俊青
谢亚光
陈勇
李日
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Hangzhou Arcvideo Technology Co ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/103—Selection of coding mode or of prediction mode
    • H04N19/109—Selection of coding mode or of prediction mode among a plurality of temporal predictive coding modes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/146—Data rate or code amount at the encoder output
    • H04N19/147—Data rate or code amount at the encoder output according to rate distortion criteria
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
    • H04N19/176—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a block, e.g. a macroblock
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/577—Motion compensation with bidirectional frame interpolation, i.e. using B-pictures
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/85—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression
    • H04N19/86—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression involving reduction of coding artifacts, e.g. of blockiness

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Abstract

The invention discloses an encoding method for improving the quality of a B frame in H.264. The method specifically comprises the following steps: obtaining the RDcost of SKIP, DIRECT, INTER16x16 and INTRA16x 16; judging that the RDcost of the SKIP is minimum, the RDcost of the DIRECT is smaller than the RDcost of the INTER16x16, and meanwhile, the coding distortion of the SKIP and the coding distortion of the INTRA16x16 mode meet requirements, selecting the SKIP as the optimal mode of the current macroblock, otherwise, obtaining the RDcosts of the INTERSub16x16, the INTRA8x8 and the INTRA4x 4; and judging that the RDcost of the SKIP is minimum, and the coding distortion of the SKIP and the coding distortion of the optimal INTRA meet the requirements, selecting the SKIP as the optimal mode of the current macro block, otherwise, selecting the mode with the minimum RDcost except the SKIP as the optimal mode. The invention has the beneficial effects that: the result of macro block mode selection is reasonable, the blocking effect is reduced, and the video quality is improved under low code rate.

Description

Coding method for improving quality of B frame in H.264
Technical Field
The invention relates to the technical field related to video coding, in particular to a coding method for improving the quality of a B frame in H.264.
Background
H.264 is a highly compressed digital video coding and decoding standard commonly proposed by the international organization for standardization (ISO) and the International Telecommunication Union (ITU), and is characterized by high compression efficiency, strong fault-tolerant capability and low coding delay, and the coding standard is widely applied to video monitoring systems, network video live broadcast, multimedia information storage and other aspects at present.
The video image data has strong relativity, the data of a plurality of adjacent pixels in a frame of image are similar or identical, which is spatial redundancy, the data between adjacent frames in the video also have a plurality of similarities or repetitions, which is temporal redundancy, the coding compression removes the redundant information in the data, the intra-frame coding technology can remove the spatial redundancy, and the inter-frame coding technology can remove the temporal redundancy.
The inter-frame coding divides the current frame image into several macro blocks by using the correlation existing between adjacent frames, and tries to search out the corresponding matching block of each macro block in the adjacent frames to predict the pixel value of the macro block in the current frame. In order to improve the accuracy of current macroblock prediction and the coding compression rate, an h.264 encoder selects a mode by using a lagrangian rate-distortion optimization method, taking a B frame as an example, the h.264 encoder sequentially finds the rate-distortion cost RDcost of a SKIP mode, a DIRECT mode, INTER (INTER16x16, INTER16x8, INTER8x16, INTER8x8) mode, and INTRA (INTRA 16x16, INTRA8x8, and INTRA4x 4) mode, and selects the mode with the minimum RDcost as an optimal prediction mode, wherein the RDcost is calculated as:
RD cost＝λ·R+SSD
wherein λ is Lagrange factor, R represents coding rate, and SSD represents coding distortion. The mode selection method based on Lagrange rate distortion optimization can analyze the bit number and coding distortion generated by each mode, so that the optimal mode can be selected.
In each mode, the SKIP mode adopts a time domain/space domain predicted motion vector to obtain a matching block so as to obtain a pixel predicted value of a current macro block, and the SKIP mode does not encode a pixel residual error and a motion vector residual error and is mainly characterized in that the encoding code rate is small but the distortion is large; the DIRECT mode carries out pixel residual error coding on the basis of the SKIP mode, so compared with the SKIP mode, the DIRECT mode has small coding distortion and large coding code rate; in the INTER mode, a more accurate motion vector is searched out through motion estimation to obtain a matching block, and a pixel residual error and a motion vector residual error can be coded, wherein the coding distortion of the INTER mode is smaller than that of SKIP/DIRECT generally; the INTRA-frame prediction mode is used for predicting the pixel value of the current macroblock, and is characterized by consuming a large amount of code rate but having small coding distortion, and when a matching block cannot be found, the INTRA-frame prediction mode can be used for reconstructing the pixel value of the current macroblock better.
x264 is an open-source H.264 video encoder, which adopts the techniques of scene change detection, adaptive B frame selection, interframe parallel coding, instruction set optimization, macroblock mode fast decision and the like, so that the H.264 encoder can better meet the requirements of fast and real-time coding. When a fast macroblock mode decision is made for a B frame, firstly, the RDcost of three modes including SKIP, DIRECT and INTER16x16 is obtained, and if the RDcost of the SKIP mode is minimum and the RDcost of the DIRECT mode is smaller than the RDcost of the INTER16x16 mode, the SKIP mode is determined to be the final mode of the current macroblock in advance and other modes are not analyzed, otherwise, the INTER16x16 (INTER16x8, INTER8x16 and INTER8x8) mode and the INTER mode are continuously analyzed, and the mode with the minimum RDcost is selected as the final mode.
In a complex scene with low code rate, the conventional x264 mode selection method is easy to give up an INTER mode because a proper matching block cannot be found, and the SKIP mode is finally selected because the SKIP mode is smaller than the RDcost of the INTRA mode. The unreasonable SKIP mode can cause the macro block coding distortion to be overlarge or discontinuous with the texture of the surrounding macro blocks, thereby causing the block effect and reducing the subjective quality.
Disclosure of Invention
The invention provides an encoding method for improving the quality of B frames in H.264, which improves the subjective quality and overcomes the defects in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
an encoding method for improving the quality of a B frame in H.264 specifically comprises the following steps:
(1) sequentially obtaining RDcost of 4 modes including SKIP, DIRECT, INTER16x16 and INTRA16x 16;
(2) judging whether the RDcost of the SKIP mode is minimum, and the RDcost of the DIRECT mode is smaller than the RDcost of the INTER16x16 mode, and if the coding distortion SSD _ SKIP of the SKIP mode and the coding distortion SSD _ INTRA16x16 of the INTRA16x16 mode meet the requirements, selecting the SKIP mode as the optimal mode of the current macroblock, and if not, executing the step (3);
(3) sequentially obtaining the RDcost of INTERSub16x16, INTRA8x8 and INTRA4x4 modes;
(4) and judging whether the RDcost of the SKIP mode is minimum or not, if so, selecting the SKIP mode as the optimal mode of the current macro block, and if so, selecting the mode with the minimum RDcost except the SKIP as the optimal mode, and if not, selecting the coding distortion SSD _ SKIP of the SKIP mode and the coding distortion SSD _ INTRA of the optimal INTRA mode to meet the requirements.
The invention analyzes the INTRA16x16 mode in advance, judges whether the coding distortion of the current macro block is too large by comparing the SSD of the SKIP mode and the SSD of the INTRA16x16 mode, and if so, other modes need to be continuously analyzed, thereby reducing the blocking effect caused by that the SKIP mode is quickly selected because a reasonable matching block cannot be found; after analyzing INTRA8x8 and INTRA4x4, by comparing SSD of SKIP mode and INTRA optimum mode, judging whether coding distortion of current macro block is too large if SKIP mode is adopted, if so, abandoning SKIP mode, thereby reducing blocking effect caused by that coding distortion of SKIP mode is larger but RDcost is smaller. By optimizing the macroblock mode selection of x264, the method ensures that the result of the macroblock mode selection is more reasonable, reduces the block effect and greatly improves the video quality under low code rate.
Preferably, in step (2), the coding distortion SSD _ SKIP of the SKIP mode and the coding distortion SSD _ INTRA16x16 of the INTRA16x16 mode satisfy the following condition:
SSD_SKIP<a*SSD_INTRA16×16
wherein: a is a constant, and the value range of a is [1,10 ].
Preferably, in step (4), the coding distortion SSD _ SKIP of the SKIP mode and the coding distortion SSD _ INTRA of the optimal INTRA mode satisfy the following condition:
SSD_SKIP<b*SSD_INTRA
wherein: b is a constant, and the value range of b is [1,10 ].
The invention has the beneficial effects that: by optimizing the macroblock mode selection of x264, the result of macroblock mode selection is more reasonable, the blocking effect is reduced, and the video quality under low code rate is greatly improved.
Drawings
FIG. 1 is a flow chart of the method of the present invention.
Detailed Description
The invention is further described with reference to the following figures and detailed description.
In the embodiment shown in fig. 1, an encoding method for improving the quality of a B frame in h.264 specifically includes the following steps:
(1) sequentially obtaining RDcost of 4 modes including SKIP, DIRECT, INTER16x16 and INTRA16x 16;
(2) judging whether the RDcost of the SKIP mode is minimum, and the RDcost of the DIRECT mode is smaller than the RDcost of the INTER16x16 mode, and if the coding distortion SSD _ SKIP of the SKIP mode and the coding distortion SSD _ INTRA16x16 of the INTRA16x16 mode meet the requirements, selecting the SKIP mode as the optimal mode of the current macroblock, and if not, executing the step (3);
wherein: coding distortion SSD _ SKIP for SKIP mode and SSD _ INTRA16x16 for INTRA16x16 mode satisfy the following conditions:
SSD_SKIP<a*SSD_INTRA16×16
wherein: a is a constant, and the value range of a is [1,10 ];
(3) sequentially obtaining the RDcost of INTERSub16x16, INTRA8x8 and INTRA4x4 modes;
(4) judging whether the RDcost of the SKIP mode is minimum or not, if so, selecting the SKIP mode as the optimal mode of the current macro block, and if so, selecting the mode with the minimum RDcost except the SKIP as the optimal mode, and if not, selecting the coding distortion SSD _ SKIP of the SKIP mode and the coding distortion SSD _ INTRA of the optimal INTRA mode to meet the requirements;
wherein: the coding distortion SSD _ SKIP of the SKIP mode and the coding distortion SSD _ INTRA of the optimal INTRA mode meet the following conditions:
SSD_SKIP<b*SSD_INTRA
wherein: b is a constant, and the value range of b is [1,10 ].
The invention analyzes the INTRA16x16 mode in advance, judges whether the coding distortion of the current macro block is too large by comparing the SSD of the SKIP mode and the SSD of the INTRA16x16 mode, and if so, other modes need to be continuously analyzed, thereby reducing the blocking effect caused by that the SKIP mode is quickly selected because a reasonable matching block cannot be found; after analyzing INTRA8x8 and INTRA4x4, by comparing SSD of SKIP mode and INTRA optimum mode, judging whether coding distortion of current macro block is too large if SKIP mode is adopted, if so, abandoning SKIP mode, thereby reducing blocking effect caused by that coding distortion of SKIP mode is larger but RDcost is smaller.
The existing x264 mode selection method adopts a lagrangian rate-distortion optimization-based method to obtain a macro block mode with the minimum rate-distortion cost, but the selected mode can not necessarily lead the subjective perception quality to be optimal. In a complex scene with low code rate, an INTER mode is abandoned easily because a proper matching block cannot be found, and a SKIP mode is selected finally because the SKIP mode is smaller than the RDcost of the INTRA mode. The unreasonable SKIP mode can cause the macro block coding distortion to be overlarge or discontinuous with the texture of the surrounding macro blocks, thereby causing the block effect and reducing the subjective quality. By optimizing the macroblock mode selection of x264, the method ensures that the result of the macroblock mode selection is more reasonable, reduces the block effect and greatly improves the video quality under low code rate.
Wherein, the influence of a and b on the inventive result is as follows:
a b video subjective quality Coding performance
3 3 Good taste -1.5％
2 3 Is very good -1.7％
2 1.5 Is very good -3.2％
The final result shows that the blocking effect of the H.264 video encoder in a complex scene under a low code rate can be obviously reduced, the subjective quality is obviously improved, and the performance is reduced within 3.2%.

Claims (1)

1. A coding method for improving the quality of a B frame in H.264 is characterized by comprising the following steps:
(1) sequentially obtaining RDcost of 4 modes including SKIP, DIRECT, INTER16x16 and INTRA16x 16;
(2) judging whether the RDcost of the SKIP mode is minimum, and the RDcost of the DIRECT mode is smaller than the RDcost of the INTER16x16 mode, and if the coding distortion SSD _ SKIP of the SKIP mode and the coding distortion SSD _ INTRA16x16 of the INTRA16x16 mode meet the requirements, selecting the SKIP mode as the optimal mode of the current macroblock, and if not, executing the step (3); coding distortion SSD _ SKIP for SKIP mode and SSD _ INTRA16x16 for INTRA16x16 mode satisfy the following conditions:
SSD_SKIP＜a*SSD_INTRA16×16
wherein: a is a constant, and the value range of a is [1,10 ];
(3) sequentially obtaining the RDcost of INTERSub16x16, INTRA8x8 and INTRA4x4 modes;
(4) judging whether the RDcost of the SKIP mode is minimum or not, if so, selecting the SKIP mode as the optimal mode of the current macro block, and if so, selecting the mode with the minimum RDcost except the SKIP as the optimal mode, and if not, selecting the coding distortion SSD _ SKIP of the SKIP mode and the coding distortion SSD _ INTRA of the optimal INTRA mode to meet the requirements; the coding distortion SSD _ SKIP of the SKIP mode and the coding distortion SSD _ INTRA of the optimal INTRA mode meet the following conditions:
SSD_SKIP＜b*SSD_INTRA
wherein: b is a constant, and the value range of b is [1,10 ].
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CN101527851B (en) * 2009-04-10 2010-08-11 清华大学深圳研究生院 Fast selecting method of P frame pattern in H. 264
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