The research objective of this paper is to design H. The EXP-GOLOMB decoder in the 264 standard proposes an efficient and low-cost ASIC implementation based on the algorithm.
EXP-GOLOMB Code Principle and Decoding Algorithm Analysis
H. 264 Basic specifications, other syntax elements are used using Exp-golomb encoding in addition to the CAVLC encoding mode. Exp-Golomb coding is a rule-wide encoding method that is widely used in various video coding criteria. EXP-GOLOMB encodes the symbolic probability statistics to encode, indicating the probability of high probability, using a long code word to indicate a low probability, the code length corresponds to the encoded number index, so that the overall The average codeword is the shortest. Save a lot of storage space compared to the fixed length coding method.
H. The 264 is used in the 0th order EXP-GOLOMB code, and the coding rule is shown in Figure 1.
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The logical structure of Exp-golomb codewords is: [M Zeros] [1] [INFO]. Where the M 0 and the intermediate 1 is called a prefix, INFO is the information value of the M bit, so the length of each Exp-golomb codeword is 2m + 1. Each index word CodeNum can correspond to a codeword with the above structure, and the relationship between them is:
CODENUM = 2M + Info-1 (1)
As can be seen from the formula 1, the exp-golomb decoding can first detect the number of consecutive O, then remove the suffix, and the CODENUM value can be obtained by the formula. H. There are four Exp-golomb codes in 264: no symbolic UE (V), with symbolic SE (V), mapping ME (V), and truncated TE (V). Therefore, for the solution of the solution, there are four mapping methods depending on the type of syntax element, as shown in Table 2. After the mapping is completed according to the corresponding description, the output SYNTAX is the decoding value.
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EXP-GOLOMB decoder hardware structure design
The hardware structure of the EXP-GOLOMB decoder designed based on the above decoding algorithm is shown in Figure 1. The entire system is mainly composed of the following modules: an input code stream buffer shift module, a code length detection module, a CODENUM generating module, and a syntax element mapping module. After the system is powered on, the code stream buffer shift module is first supplied, and then the first detector in the code length detection module detects the number of consecutive 0, so that the current code length is sent to the accumulator. . At the same time, the results of the first test are sent together to the CODENUM computing module together to be decoded, and the CODENUM value is subtracted. Finally, the CODENUM is sent to four mapping unit processing, and the final decoding syntax element is output to the register by the selector. The entire decoding process is done with a clock cycle. The hardware structure of each function sub-module will be described in detail below.
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Input code stream buffer shift module
The input code stream buffer shift module is implemented H. 264 Key modules of real-time decoding. Since the code length cannot be determined in advance during each becoming long decoding process, the next codeword must be positioned while the code value is solved. This requires that the module has the characteristics of fast response and parallel output. Due to H. The maximum length of the EXP-GOLOMB code is defined in 264 does not exceed 32, and two 32-bit registers, a 32-bit barrel shifter, and a combination of accumulators are used to implement this feature, as shown on the left end of Figure 1. The register rn is responsible for reading data from the external module, and together with the register R1 as the input of the barrel shifter; in each decoded period, the barrel shifter is removed from the decoded stream, but also to load a new to-decode Flow; and the accumulator counts the processing of the code length, transmitting the barrel shift length, determines and controls the read and R1 update. This provides a continuous uninterrupted stream for subsequent processing units. Technology area
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