CN101022554A - Variable-length code decoding method based on zero-prefix code - Google Patents
Variable-length code decoding method based on zero-prefix code Download PDFInfo
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Abstract
A method for decoding variable length code based on zero prefix code includes generating a numbers of multiple fork trees based on zero prefix code and then carrying out variable length code decoding on code stream according to generated multiple fork tree. The structure of said multiple fork tree is also disclosed.
Description
Technical field
The invention belongs to the digital video decoding technical field, specifically, is the method for decoding about the CAVLC form that H.264/AVC quick reference stipulates in the standard.
Background technology
H.264/AVC be digital video coding standard of new generation, the cooperative development group (JVT) that it organizes ISO to form by International Telecommunication Association (ITU) and mpeg standard is developed jointly.H.264/AVC as the video technique standard, can be adapted to the every field of Video Applications, comprise the wireless application of low code check, Internet video is used, and the TV broadcast applications of high definition and DVD use.
H.264/AVC with former coding standard H.263, MPEG-4 is similar, it all is the hybrid coding pattern that adopts based on predictive transformation, the advantage of the standard before having absorbed simultaneously, on coding efficiency more H.263, MPEG-4 is enhanced, and can save 40% code check under the situation of equal quality.H.264/AVC code stream is divided into two levels, the video coding layer (VideoCoding Layer, VLC) and network abstract layer (Network Abstract Layer, NAL).Core data after video coding layer essential record compressed video content, the network abstract layer essential record is described the information of particular network environment, divides by such level, helps the encapsulation and the transmission control of data in network of video data.
H.264/AVC cataloged procedure mainly is divided into following components:
(1) infra-frame prediction is to eliminate spatial redundancies;
(2) carry out inter prediction by motion search, to eliminate temporal redundancy;
(3) residual block that the difference between original picture block and the prediction piece is formed carries out transform and quantization;
(4) the coefficient residual error that obtains after quantizing is reset and entropy coding.
Decode procedure mainly is divided into following components:
(1) entropy decoding is reset decoded coefficient;
(2) coefficient after resetting is carried out inverse quantization and inverse transformation;
(3) obtain predicting piece by infra-frame prediction or inter prediction;
(4) obtain decoded picture by prediction piece and residual block.
In H.264/AVC encoding, entropy coding is divided into two kinds: the binary arithmetic coding (CABAC) of variable length code of context-adaptive (CAVLC is called for short variable length code) and context-adaptive.The CAVLC entropy coding is a kind of Variable Length Code, Variable Length Code is the probability that utilizes different syntactic elements to occur in code stream, utilize the code word of different bit lengths that syntactic element is encoded, the code word that the syntactic element that probability of occurrence is high is lacked corresponding to bit length, the code word that the syntactic element that probability is lower is grown corresponding to bit length.In the process of coding, the form by code table is writing down the pairing code word of different syntax element information.Because in different frame of video, the probability distribution of syntax element information is inequality, adopt unified code table can not reach very high compression efficiency, in CAVLC entropy coding process, the information of the syntactic element of the image block correspondence of the vicinity that employing has been encoded is adjusted the code table of coding institute reference dynamically, make the probability distribution of code word in the selected code table of coding more approaching, to reach higher compression efficiency with the probability distribution of actual syntax element information.Adopt the CAVLC coding that the coefficient residual error is H.264/AVC carried out entropy coding, need the syntactic element of coding that TotalCoeff (number of non-0 coefficient in the retracing sequence) is arranged, TrailingOnes (retracing sequence end 1 or-1 number), total_zeros (number of last non-0 coefficient preceding 0 in the retracing sequence), run_before (number of each non-0 coefficient preceding 0 in the retracing sequence).The syntactic element correspondence of each different code tables, but TotalCoeff and TrailingOnes are the modes that adopts assembly coding, by to the syntactic element combined coding of two couplings and be merged into a code word to improve compression efficiency, because be incorporated in the code word behind two kinds of syntax element information codings, corresponding code table length increases when just encoding than a syntactic element to some extent.
In decode procedure, obtain the value of concrete syntactic element for the code word from code stream, need from the code stream memory, read the code word of equal length according to the length of the code word that occurs in the code table, mate with the code word in the code table then, if coupling is unsuccessful, then switch to the next code word that occurs in the code table, carry out identical operations.Adopting decodes in such a way needs frequent visit code stream memory, and can find correct code word after needing under the poorest situation whole code table traveled through, and finishes decode procedure.This processing method inefficiency is unsuitable for being applied in the real-time coding/decoding system.
Summary of the invention
The objective of the invention is for overcoming the weak point of prior art, propose a kind of decoding length changeable code method based on zero prefix code, the present invention generates multiway tree according to the CAVLC code table.Be the form of conversion CAVLC code table, this method,, is decoded with reference to the CAVCL code table to residual block for the user provides in meeting the code stream of prescribed by standard H.264/AVC in the application of the system that real-time is had relatively high expectations towards H.264/AVC; This method has higher efficient, can satisfy the application in the real time codec system.
The decoding length changeable code method based on zero prefix code that the present invention proposes is characterized in that this method comprises: generate a plurality of multiway trees based on 0 prefix code, according to this multiway tree code stream is carried out decoding length changeable code;
The structure of described multiway tree based on 0 prefix code comprises: by the 0 prefix code word bit sequence that a root node and multistage node thereof constitute, downstream site is the child node of its superior node; Wherein, root node only writes down the number of its child node, other nodes at different levels are except that the number of its child node of record, also write down the bit of described codeword sequence, the bit of described child node record is the bit of its superior node record and follow-up bit, there are at most 4 child nodes in each node, and each child node writes down the bit of the 0-3 0 of follow-up non-zero bit position and preceding 0 respectively; If the child node number of this node is 0, this node is a leaf node, and leaf node writes down the syntax element value with the code word correspondence simultaneously.
Principle of the present invention:
The present invention is based on the principle of Variable Length Code.Because what coded system was carried out is Variable Length Code, not having a code word in same code table row is the prefix of another code word, the CAVLC code table is converted to tree represents.Because in the CAVLC code table, the code word intermediate value is that 0 bit occupies bigger ratio, adopts 0 prefix trees to come CAVLC is changed, and can improve whole decoding efficiency.
The present invention has following characteristics:
1. because code word is stored by tree structure, only need read bitstream data in order, reduce visit memory.
2. only need visit corresponding multiway tree when decoding, needn't search for, improve decoding efficiency code table.
3. can corresponding a plurality of bits based on node in the multiway tree of 0 prefix code, for most code word, can travel through less node, just find corresponding syntax element information.
The present invention is applied in the real-time system, can decoder simplification, improve processing speed.
Description of drawings
Fig. 1 is the node structure of the multiway tree based on 0 prefix code of the present invention.
Fig. 2 is the CAVLC code table of syntactic element total_zeros institute reference in the present embodiment decoding.
The multiway tree structure that Fig. 3 is generated according to the CAVLC code table for present embodiment based on 0 prefix code.
Embodiment
The present invention will be described in detail below in conjunction with drawings and Examples.
The decoding length changeable code method based on zero prefix code that the present invention proposes is characterized in that this method comprises: generate a plurality of multiway trees based on 0 prefix code, according to this multiway tree code stream is carried out decoding length changeable code; Wherein, the structure based on the multiway tree of 0 prefix code comprises: by the 0 prefix code word bit sequence that a root node and multistage node thereof constitute, downstream site is the child node of its superior node; Wherein, root node only writes down the number of its child node, other nodes at different levels are except that the number of its child node of record, also write down the bit of described codeword sequence, the bit of described child node record is the bit of its superior node record and follow-up bit, there are at most 4 child nodes in each node, and each child node writes down the bit of the 0-3 0 of follow-up non-zero bit position and preceding 0 respectively; If the child node number of this node is 0, this node is leaf node (representing that then code word finishes), and leaf node writes down the syntax element value with the code word correspondence simultaneously.
The content of a node in this multiway tree as shown in Figure 1, comprises its child node number, child node pointer or syntax element value (if leaf node does not then have the child node pointer, if not leaf node, then not having syntax element value);
Above-mentioned multiway tree based on 0 prefix code is to utilize the code table of defined in the standard H.264/AVC to generate, its concrete generation method comprises: at first multiway tree is carried out initialization (promptly be initialized as and only contain the tree that a child node number is 0 root node), and variable E is set, its value is 1 or 0; Utilize this tree to generate multiway tree again, specifically may further comprise the steps based on 0 prefix code:
1) root node of putting tree is a present node, reads a code word in the code table, and first bit that bit pointer P points to code word is set, and finishes then to forward 5 to as code table);
2) N bit of this code word read in the position of pointer P indication, up to the bit place value that reads be 1 or N=3 or code word finish, moving hand P to the next one will read bit, and judge whether pointer P has arrived the end of code word, if code word finishes, then variable E puts 1, otherwise puts 0; If have 1 in the bit bit string that reads, then forward 3 to); If do not have 1 in the bit bit string that reads, then forward 4 to);
3) whether N child node judging present node exists, and as not existing, then sets up corresponding child node, whether the byte point number of judging present node is less than N, as less than N, the child node number of then revising present node is N, and mobile present node is to its N child node.If E=1, it is leaf node that present node then is set, and will be stored in this node deserved video grammar element information, finishes the conversion of current code word, forwards 1 to); If E=0 then forwards 2 to);
4) whether N+1 child node of disconnected present node exists, and as not existing, then sets up mutually deserved child node, whether the child node number of judging present node is less than N+1, as less than N+1, the child node number of then revising present node is N+1, and mobile present node is to its N+1 child node.If then present node is set is leaf node, and will be stored in this node, finish the conversion of current code word, forward 1 to) deserved video grammar element information; If E=0 then forwards 2 to).
5) structure based on the multiway tree of 0 prefix code finishes.
After finishing based on the multiway tree of 0 prefix code structure, in the decode procedure afterwards, just do not need to decode with reference to the code table in the standard H.264/AVC, only needing with reference to the multiway tree based on 0 prefix code be decodable code, can avoid the matching process of complexity like this.
The multiway tree based on 0 prefix code according to above-mentioned generation carries out decoding length changeable code to code stream, specifically may further comprise the steps:
1) root node that described multiway tree is set is a present node, bit pointer P is set points to the next code stream bit that will read, if code stream finishes, then forwards 6 to);
2) get the son node number N of present node, make N=N-1, child node counting K is set, and K=0;
3) the fruit code stream finishes, and then represents the code stream mistake, forwards 6 to); Otherwise, read the code stream bit that this pointer P points to, make K=K+1, pointer P move on to the next one will read bit, if the code stream bit value that reads is 1, then forward 4 to); If value is 0, then forward 5 to);
4) K the child node that present node is set is present node, judges whether present node is leaf node, if then read the video grammar element information that is stored in this node, and forward 1 to); If not leaf node, then forward 2 to);
5) make N=N-1,, and forward 4 to) if N=0 then makes K=K+1; Otherwise forward 3 to);
6) decoding of the current code stream of end.
So just finished with reference to based on the decoding of the multiway tree of 0 prefix code H.264/AVC residual block code stream.
By the following examples a kind of multiway tree coding/decoding method based on 0 prefix code according to the CAVLC code table proposed by the invention is elaborated.
The multiway tree based on 0 prefix code that present embodiment adopts adopts the son node number that this node is stored in the territory in each node, the span of child node is 0-4, wherein 0 represents leaf node.
Fig. 2 is the CAVLC code table of syntactic element total_zeros (number of last non-0 coefficient preceding 0 in the retracing sequence) institute's reference in the present embodiment decoding, wherein the value of the syntactic element total_zeros that decoding obtains is shown in code table first tabulation, the code word that may exist in the code stream is shown in eight tabulations of the secondary series to the of code table, with the syntax element value correspondence in the code word in the delegation and this row first row, the different TotalCoeff that obtains according to decoding (number of non-0 coefficient in the retracing sequence) value is chosen code word and is decoded from different row.
Present embodiment is listed as the multiway tree based on 0 prefix code that is converted to first of CAVLC code table among Fig. 2, as shown in Figure 3.Comprise a root node and level Four node among the figure, wherein, the node of the superiors is represented root node, and wherein writing down its child node is 4.The child node of a node of every grade (if exist) is followed successively by first child node of this node, second child node, the 3rd child node and the 4th child node by order from left to right.The Bit String on each node next door is represented one section bit bit string in certain code word of this nodes records, and the Bit String on leaf node next door is corresponding to one of its record complete code word.Present embodiment is that 000011 code word is decoded to one section bit stream, be with reference among Fig. 3 based on appropriate section in the multiway tree of 0 prefix code, as shown in Figure 3.Its coding/decoding method comprises: read the child node number in the root node, value is 4, reads bit stream, because front three all void value is 1 bit, subtract a bit so read son node number, i.e. 3 bits, and present node is moved to the 4th child node of root node; Read the child node number in the present node, value is 4, reads bit stream, because second for value is 1 bit, thus read 2 bits, and the 2nd child node that present node is set is present node; Read the child node number in the present node, value is 4, reads bit stream, because first for value is 1 bit, thus only read 1 bit, and the 1st child node that present node is set is present node; Read the child node number in the present node, value is 0, so this codeword decoding finishes, obtaining the total_zeros value is 7.
This code word is with reference in the process of decoding based on the multiway tree of 0 prefix code, only traveled through the part that a brace in this multiway tree has 3 progression nodes.As seen, adopt method of the present invention can obtain code word faster to deserved syntax element information.
Claims (3)
1, a kind of decoding length changeable code method based on zero prefix code is characterized in that this method comprises: generate a plurality of multiway trees based on 0 prefix code, according to this multiway tree code stream is carried out decoding length changeable code;
The structure of described multiway tree based on 0 prefix code comprises: by the 0 prefix code word bit sequence that a root node and multistage node thereof constitute, downstream site is the child node of its superior node; Wherein, root node only writes down the number of its child node, other nodes at different levels are except that the number of its child node of record, also write down the bit of described codeword sequence, the bit of described child node record is the bit of its superior node record and follow-up bit, there are at most 4 child nodes in each node, and each child node writes down the bit of the 0-3 0 of follow-up non-zero bit position and preceding 0 respectively; If the child node number of this node is 0, this node is a leaf node, and leaf node writes down the syntax element value with the code word correspondence simultaneously.
2, the method for claim 1, it is characterized in that the generation method of described multiway tree based on 0 prefix code, this method at first are initialized as multiway tree and only contain the initialization tree that a child node number is 0 root node, and variable E is set, its value is 1 or 0; Utilize this initialization to set the multiway tree that generates based on 0 prefix code again, specifically may further comprise the steps:
1) root node that tree is set is a present node, reads a code word in the code table, and first bit that bit pointer P points to code word is set, and finishes then to forward 5 to as code table);
2) read N bit of this code word from the position of pointer P indication, up to the bit place value that reads be 1 or N=3 or code word finish, moving hand P to the next one will read bit, and judge whether pointer P has arrived the end of code word, if code word finishes, then variable E puts 1, otherwise puts 0; If have 1 in the bit bit string that reads, then forward 3 to); If do not have 1 in the bit bit string that reads, then forward 4 to);
3) whether N child node judging present node exists, and as not existing, then sets up corresponding child node, whether the byte point number of judging present node is less than N, as less than N, the child node number of then revising present node is N, and mobile present node is to its N child node.If E=1, it is leaf node that present node then is set, and will be stored in this node deserved video grammar element information, finishes the conversion of current code word, forwards 1 to); If E=0 then forwards 2 to);
4) whether N+1 child node judging present node exists, and as not existing, then sets up mutually deserved child node, whether the child node number of judging present node is less than N+1, as less than N+1, the child node number of then revising present node is N+1, and mobile present node is to its N+1 child node.If then present node is set is leaf node, and will be stored in this node, finish the conversion of current code word, forward 1 to) deserved video grammar element information; If E=0 then forwards 2 to);
5) structure based on the multiway tree of 0 prefix code finishes.
3, the method for claim 1 is characterized in that, the described multiway tree based on 0 prefix code according to generation carries out decoding length changeable code to code stream, specifically may further comprise the steps:
1) root node that described multiway tree is set is a present node, bit pointer P is set points to the next code stream bit that will read, if code stream finishes, then forwards 6 to);
2) read the son node number N of present node, make N=N-1, child node counting K is set, and K=0;
3) if code stream finishes, then represent the code stream mistake, forward 6 to); Otherwise, read the code stream bit that this pointer P points to, make K=K+1, pointer P move on to the next one will read bit, if the code stream bit value that reads is 1, then forward 4 to); If value is 0, then forward 5 to);
4) K the child node that present node is set is present node, judges whether present node is leaf node, if then read the video grammar element information that is stored in this node, and forward 1 to); If not leaf node, then forward 2 to);
5) make N=N-1,, and forward 4 to) if N=0 then makes K=K+1; Otherwise forward 3 to);
Finish the decoding of current code stream.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102473315A (en) * | 2009-08-20 | 2012-05-23 | 汤姆森特许公司 | Method and apparatus for reusing tree structures to encode and decode binary sets |
| CN104579567A (en) * | 2015-01-08 | 2015-04-29 | 无锡清华信息科学与技术国家实验室物联网技术中心 | Method and device for coding reverse path |
| CN104661038A (en) * | 2009-12-10 | 2015-05-27 | Sk电信有限公司 | Decoding apparatus using a tree structure |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN1463500A (en) * | 2001-05-22 | 2003-12-24 | 皇家菲利浦电子有限公司 | Method of decoding variable-length codeword sequence |
| CN1331360C (en) * | 2004-02-24 | 2007-08-08 | 上海交通大学 | Method for decoding codes in variable lengths |
| CN1780398A (en) * | 2004-11-18 | 2006-05-31 | 上海乐金广电电子有限公司 | CAVLC decoding method |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102473315A (en) * | 2009-08-20 | 2012-05-23 | 汤姆森特许公司 | Method and apparatus for reusing tree structures to encode and decode binary sets |
| CN104661038A (en) * | 2009-12-10 | 2015-05-27 | Sk电信有限公司 | Decoding apparatus using a tree structure |
| CN104661038B (en) * | 2009-12-10 | 2018-01-05 | Sk电信有限公司 | Use the decoding apparatus of tree structure |
| CN104579567A (en) * | 2015-01-08 | 2015-04-29 | 无锡清华信息科学与技术国家实验室物联网技术中心 | Method and device for coding reverse path |
| CN104579567B (en) * | 2015-01-08 | 2018-10-12 | 无锡清华信息科学与技术国家实验室物联网技术中心 | The coding method of inverse path and device |
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