KR100903958B1 - Method and device for decoding digital audio data, and record medium for performing method of decoding digital audio data - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the decoding of digital audio data, in which a filter bank having the longest clock occupancy time and a Huffman decoder having a constant clock occupancy time (ie, clock requirement) are processed in parallel in one frame period for decoding. In addition, the present invention implements, in hardware, a computing device shared by a plurality of memories operating in parallel, a dequantizer, and a filter bank. The data processing time of the entire decoding apparatus is shortened, and the performance of the entire decoding system can be improved due to the efficient distribution and use of the clock and can be applied to the portable apparatus.

Description

TECHNICAL AND DEVICE FOR DECODING DIGITAL AUDIO DATA, AND RECORD MEDIUM FOR PERFORMING METHOD OF DECODING DIGITAL AUDIO DATA}

1 is a schematic block diagram of a conventional digital audio data decoding apparatus.

2 is an operation timing diagram of a conventional digital audio data decoding apparatus.

3 is a schematic block diagram of a digital audio data decoding apparatus according to an embodiment of the present invention.

4 is a flowchart illustrating a digital audio data decoding method according to an embodiment of the present invention.

5 is an operation timing diagram of a digital audio data decoding apparatus according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

110, 210: Input buffer 120, 220: Deformatter

130, 230: Huffman decoder 140, 240: dequantizer

150, 250: filter bank 260: control unit

270: storage unit 280: ALU

The present invention relates to a method for decoding digital audio data, an apparatus for decoding digital audio data, and a recording medium for performing digital audio data decoding method, and more particularly, to a method for decoding digital audio data applicable to a portable terminal. To the device.

Recently dedicated digital audio capable of playing digital audio such as MPEG1 Audio Layer-3 (MP3), Dolby AC-3 (Audio Coding-3), Ogg Vorvis, WMA (abbreviated as "WMA") Portable terminals equipped with devices or digital audio playback functions have been rapidly spread, allowing users to listen to music conveniently at any time and place.

Digital audio has the advantage of being able to reduce the file size to less than 1/10 while minimizing the degradation of audio quality by compressing using a perceptual coding method based on human cognitive ability.

Among digital audio, WMA is an audio compression format developed by Microsoft that can support streaming and reduce file size to half MP3 while maintaining audio quality equivalent to MP3.

In general, files in WMA format are decoded by a software method through a program called Windows Media Player, also produced by Microsoft Corporation, and output as sound.

1 is a schematic block diagram of a conventional digital audio data decoding apparatus. Referring to FIG. 1, a conventional digital audio data decoding apparatus 100 includes an input buffer 110, a de-formatter 120, a Huffman decoder 130, and an inverse quantizer 140. ), A filter bank (150), a control unit (160), and a storage unit (170) including an Inverse Modified Cosine Transform (IMDCT) 151 and a Window / Overlap-Add (155).

The storage unit 170 includes a ROM 1 171, a ROM 2 172, and a ROM 3 173. The conventional digital audio data decoding apparatus 100 receives an audio bit stream and temporarily stores the audio bit stream in the input buffer 110. The audio bitstream stored in the input buffer 110 is transmitted to the formatter 120. The deformatter 120 decodes and analyzes a header having information necessary for decoding the audio data received from the audio bitstream, and extracts the encoded data.

Meanwhile, the encoded data is transferred to the Huffman decoder 130 and decoded using the Huffman table, and then passed through a dequantizer 140, a filter bank 150, and a digital-to-analog converter (DAC, not shown). These are converted into audible audio signals and output.

Huffman ROM 1 171 stores a Huffman table, ROM 2 172 stores quantization coefficients, and ROM 3 173 stores window coefficients.

Conventionally, the input audio bit stream is decoded while sequentially passing through the Huffman decoder 130, the dequantizer 140, the IMDCT 151, and the window / overlap adder 155.

2 is a timing diagram of the conventional digital audio data decoding apparatus that performs the sequential processing.

In the example of FIG. 2, 'A' indicates a clock period occupied by the deformatter 120, and 'B' indicates a clock interval occupied by the Huffman decoder 130, and 'C' indicates inverse quantization. The instrument 140 represents a clock section occupied when the filter 140 operates, and 'D' represents a clock segment occupied by the filter bank 150.

Referring to FIG. 2, in the conventional digital audio data decoding apparatus, a clock included in one frame includes a deformatter A, a Huffman decoder B, an inverse quantizer C, and a filter bank D. Occupies sequentially. Each device occupies a clock, which means it wakes up at that time and performs the action. Therefore, referring to FIG. 2, it can be seen that the deformatter A, the Huffman decoder B, the dequantizer C, and the filter bank D included in the conventional digital audio data decoding apparatus operate sequentially. It is.

However, among the devices, the Huffman decoder 130 does not have a constant clock requirement. This is because, in the case of Huffman decoding, the time to find a symbol depends on the length of the codeword of the input bitstream, and the codeword used for Huffman decoding varies every frame.

As such, since the clock requirement of the Huffman decoder 130 is not constant, the conventional digital audio decoder has a problem that it is difficult to fix the entire clock speed.

Therefore, the conventional digital audio decoder has a disadvantage in that it is difficult to predict the total clock cycle of the system.

In addition, in the related art, the algorithm has a complicated problem by implementing the process of FIG. 1 and FIG. 2 in software. That is, in order to output sound after decoding a file in WMA format using software, the sound output device equipped with the software should have a large storage space and maintain the CPU performance of a home computer. Obviously, the size of the device for decoding the file in WMA format should be increased in order to satisfy the CPU performance and the storage space required to support the operation of the software.

Therefore, it is inappropriate to decrypt the WMA format file using the software on a portable device (for example, a mobile phone, etc.) in which miniaturization is in progress.

That is, decrypting a file in WMA format using conventional software has a problem that it is difficult to apply to a portable device despite the superior decoding performance.

Accordingly, a first object of the present invention is to provide an apparatus for decoding digital audio data, which makes it possible to apply an audio file of WMA format to a portable device.

It is also a second object of the present invention to provide a method for decoding digital audio data, which makes it possible to apply an audio file of WMA format to a portable device.

A third object of the present invention is to provide a recording medium on which the decoding method of the digital audio data is recorded.

According to an aspect of the present invention, there is provided a method of decoding digital audio data, wherein the first header information and the first encoded data are extracted from the digital audio data of the first frame. An initialization step of decoding the encoded data; An inverse quantization step of inversely quantizing the decoded data; And performing inverse discrete cosine transform and window / overlap-add on the dequantized data, and performing second inverse on digital audio data of a next frame in parallel while performing the inverse discrete cosine transform and window / overlap-add. And extracting header information and second coded data and decoding the second coded data. The inverse quantization step and the parallel processing step may be repeatedly performed until the decoding of the digital audio data ends. Decoding of the initialization and parallel processing steps may be Huffman decoding. The initialization may write the encoded data to a first memory. The dequantization step may read the encoded data from the first memory, perform inverse quantization on the encoded data, and then write the dequantized data to a second memory. The parallel processing may read inversely quantized data from the second memory and perform inverse discrete cosine transform on the inversely quantized data. In the parallel processing step, the decoded data of the second coded data may be recorded in the first memory. The digital audio data may be data encoded by window media audio. In the parallel processing step, the windowed data of the previous frame is written to a third memory when the window / overlap-add is performed, and the windowed data of the current frame is read by reading the windowed data of the previous frame from the third memory. -Added data can overlap.

In addition, the apparatus for decoding digital audio data according to an aspect of the present invention for achieving the second object of the present invention comprises a first and second memory; A deformatter for extracting first header information and first encoded data from the digital audio data; A decoder which decodes the first coded data and stores the first coded data in the first memory; An inverse quantizer configured to read and dequantize the decoded data from the first memory and to store dequantized data in the second memory; A filter bank that reads the dequantized data from the second memory, performs inverse discrete cosine transform, and then performs window / overlap-add; And extracting second header information and second coded data for digital audio data of a next frame and performing decoding on the second coded data during inverse discrete cosine transform and window / overlap-add operation of the filter bank. And a controller for controlling the filter bank. In this case, the apparatus for decoding digital audio data may further include an operation unit which performs a complex / multiply / add operation for the inverse quantization and inverse discrete cosine transform and is shared by the inverse quantizer and the filter bank. The apparatus may further include a third memory configured to store windowed data of a previous frame for window / overlap-add of the filter bank. The second memory may store windowed data of a previous frame for window overlap add of the filter bank. The decoder may be a Huffman decoder. In addition, the digital audio data may be data encoded by window media audio.

In addition, the recording medium on which the decoding method of the digital audio data according to an aspect of the present invention for achieving the third object of the present invention is extracted the first header information and the first encoded data from the digital audio data of the first frame An initialization step of decoding the first encoded data; An inverse quantization step of inversely quantizing the decoded data; And perform inverse discrete cosine transform and window / overlap-add on the dequantized data, and digital audio of the next frame of the decoded data in parallel while performing the inverse discrete cosine transform and window / overlap-add. And extracting second header information and second encoded data from the data, and performing a parallel processing step of decoding the second encoded data.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art, and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. Hereinafter, the same reference numerals are used for the same components in the drawings, and redundant description of the same components is omitted.

3 is a schematic block diagram of a digital audio data decoding apparatus according to an embodiment of the present invention. Referring to FIG. 3, the digital audio data decoding apparatus 200 according to an embodiment of the present invention includes an input buffer 210, a deformatter 220, a Huffman decoder 230, a dequantizer 240, and a filter bank. 250, a controller 260, and a storage 270.

The input buffer 210 temporarily receives the input decoded data. The data to be decoded may be, for example, digital audio data having a bit stream form.

The controller 260 allows the bit stream type data (hereinafter, referred to as 'bit stream data') stored in the input buffer 210 to be transmitted to the deformatter 220 and / or the Huffman decoder 230.

The deformatter 220 performs a deformatting operation. Here, the deformatting operation means parsing a header and coded data (eg, Huffman coded data) having information necessary for decoding from bit stream data transmitted through the input buffer 210. At this time, the deformatter 220 includes a first deformatter for processing an ASF (Advanced Stream Format) header, which holds information for decoding WMA data, and a second for processing a packet information header included in each packet. It may include a deformatter. In addition, the deformatter 220 extracts coding information (eg, lossy coding or lossless coding) and Huffman table number information of the bit stream data from the header and transfers the Huffman table number information to the Huffman decoder 230.

The Huffman decoder 230 RLC encodes coded data in the bit stream data transferred through the input buffer 210 based on the coding information transmitted from the deformatter 220 and the Huffman table number information, for example, Huffman data. (Run-Length decoding) or VLC (Variable-Length decoding) decoding. The memory ROM1 271 stores a plurality of Huffman tables, and the Huffman decoder 230 performs decoding by referring to the Huffman table corresponding to the Huffman table number information from ROM1 (Read Only Memory 1, 271). do. The Huffman decoder 230 stores the decoding result in random access memory 1 (274).

Inverse quantizer 240 dequantizes the data decoded by Huffman decoder 230. ROM2 272 stores exponential values used to perform inverse quantization. In particular, the inverse quantizer 240 reads the decoding result of the Huffman decoder 230 from the RAM1 274 under the control of the controller 260 and receives the number of entropy information and quantization coefficients provided from the deformatter 220. Inverse quantization using a and stores the result in the RAM2 (275).

In another embodiment of the present invention, the digital audio data decoding apparatus may further include an Arithmetic-Logic Unit (ALU) 280. The inverse quantizer 240 preferably receives the exponential calculation result necessary for performing the inverse quantization from the calculator 280. By separating the operation units ALU 280 into separate hardware blocks, the processing algorithm of the dequantizer 250 may be simplified and the processing speed may be increased.

Arithmetic-Logic Unit (ALU) 280 is shared by inverse quantizer 240 and IMDCT 251, and is an exponential operation of inverse quantizer 240 and a complex / multiply / add operation of IMDCT 251. And process the result to each of the inverse quantizer 240 and the IMDCT (251). The arithmetic unit ALU 280 is separated into a separate hardware block, and the arithmetic operation performed by the inverse quantizer 240 and the IMDCT 251 is performed by the arithmetic unit ALU 280.

Filter bank 250 includes inverse discrete cosine transform (IMDCT) 251 and window / overlap-add 255. The filter bank 250 performs inverse discrete cosine conversion and window / overlap-add by using the processing result of the inverse quantizer 240 stored in the RAM2275. The IMDCT 251 converts the dequantized data from the dequantizer 240 into a signal in the time domain. In detail, the signal output in the frequency domain is converted into the signal in the time domain by reading the data output through the inverse quantizer stored in the RAM 275 and performing inverse modified discrete cosine transformation. In this case, the IMDCT 251 receives the processing result of the inverse quantizer 240 from the RAM2 275, performs inverse discrete cosine transformation, and stores the result in the RAM2 275. In addition, the IMDCT 251 preferably receives a complex / multiply / add operation result required for inverse discrete cosine transform from the calculator 280. By separating the operation units ALU 280 into separate hardware blocks, the processing algorithm of the IMDCT 251 may be simplified and the processing speed may be increased.

Meanwhile, the window / overlap adder 255 is a window processing part for each subband in order to soften the output sound. In general, the windowed 2N data of the previous frame and the 2N data of the current frame are windowed. Add to overlap. For this purpose, the window / overlap-adder 255 reads the window coefficient for window processing from the ROM3 273, writes the windowed data of the previous frame into the ROM3 273, and the window / overlap from the RAM3 403. The windowed data of the previous frame for the overlap-add is read and the overlap-add operation is performed with the windowed data of the current frame.

3 illustrates a case in which the previous frame data is stored in RAM3403, which is a separate memory. However, the previous frame data may be stored in RAM2 402 instead of in RAM3403. In other words, the RAM2 402 and the RAM3 403 may be integrated and implemented.

4 is a flowchart illustrating a digital audio data decoding method according to an embodiment of the present invention. 5 is an operation timing diagram of a digital audio data decoding apparatus for performing parallel processing according to an embodiment of the present invention. Referring to FIG. 5, 'A' represents a clock period occupied by the deformatter 220, 'B' represents a clock interval occupied by the Huffman decoder 230, and 'C' is an inverse. The quantizer 240 indicates a clock period occupied during operation, and 'D' indicates a clock period occupied by the filter bank 250 in operation.

Hereinafter, a digital audio data decoding method according to an embodiment of the present invention will be described with reference to FIGS. 3 to 5. 3 to 5, first, to perform window / overlap-add after inverse discrete cosine conversion, the memories RAM3 and 276 storing the windowed data of the previous frame are initialized (steps S200 and 5). Of 500).

When digital audio data is input through the input buffer 210, the controller 260 controls the deformatter 220 to extract header information and encoded data from the digital audio data of the first frame (step S205, 501 of FIG. 5). The Huffman decoder 230 is controlled to decode the encoded data of the first frame (S210, 503 of FIG. 5). Here, the encoded data may be Huffman encoded data. As such, the header information and the coded data extraction and decoding process (steps S205 and S210) for one frame are performed only at the beginning of the digital audio data decoding process according to an embodiment of the present invention. Hereinafter, it is defined as an initialization process.

The controller 260 performing the initialization process as described above controls the inverse quantizer 240 to perform inverse quantization on the decoded data of the current frame (step S215, 503 of FIG. 5).

The controller 260 controls the filter bank 250 to perform inverse discrete cosine transform and window / overlap-add on the dequantized data of the current frame (step S220, 504 of FIG. 5).

In addition, the controller 260 controls the formatter 220 and the Huffman decoder 230 in parallel with the operation of the filter bank 250, that is, performing inverse discrete cosine transform and window overlap add, so that the digital frame of the next frame is controlled. Extracting the header information and the encoded data with respect to the audio data (step S225, 511 of FIG. 5) and decoding the encoded data of the first frame (step S230, 512 of FIG. 5) are performed.

That is, the controller 260 controls to simultaneously perform the deformatting operation and the decoding operation on the data of the next frame while the filter bank 250 performs the operation on the data of the current frame.

Table 1 is a table showing the amount of calculation for each module of the WMA decoding system of FIG.

Average amount of computation (clock cycles required) Deformatter 5% Huffman Decryption 25% Dequantization 10% Filter bank 60% Sum 100%

Referring to Table 1, since the operation of the filter bank occupies more than half (about 60%) of the decoding processing period of one frame, other devices (eg, deformatters) that do not share memory with the filter bank 250 during that time. By driving the 220 and the Huffman decoder 230 together, the decoding processing period of one frame can be shortened.

In addition, since the clock occupancy (about 60%) of the filter bank 250 is more than twice as large as the clock occupancy (about 25%) of the Huffman decoder 230, the system due to the variation of the clock occupancy of the Huffman decoder 230 is increased. Cycle changes can be minimized.

3 to 5 again, the controller 260 determines whether the decoding of the data of the next frame (512 of FIG. 5) is finished (step S235), and when it is finished, the controller 260 filters the data of the current frame. It is determined whether the processing of the bank 250 is terminated (step S240), and only the processing of the filter bank 250 for the data of the current frame is repeatedly performed until the processing of the filter bank 250 is terminated for the data of the current frame. (Step S220). This is because the clock occupancy rate for the operation of the filter bank 250 is generally larger than the sum of the clock occupancy rates of the deformatter 220 and the Huffman decoder 230.

As a result of the determination of step S240, when the processing of the filter bank 250 for the data of the current frame is finished, the controller 260 moves to the next frame (step S245) and then repeats from the dequantization process (step S215). At this time, the repetitive operation from the dequantization process (step S215) continues until the decoding operation ends (step S250).

On the other hand, the movement to the next frame in step S245 does not mean that the frame is physically moved, but means logical movement. Since the processing of the current frame is finished, the following frame is changed to the current frame in the description and the next frame is changed. Changes to the next frame.

In the description of FIG. 4, the decoding of steps S210 and S230 is preferably Huffman decoding. However, the decoding method is not limited to Huffman decoding, but also includes all other decoding methods having a constant clock occupancy rate.

As shown in FIG. 3, the memory (RAM 274) connected to the Huffman decoder 230 is separated from the memory (RAM 275) connected to the IMDCT 251 and the window / overlap-adder 255. Step S220 (504 of FIG. 5), step S225 (511 of FIG. 5), and step S230 (512 of FIG. 5) may be performed in parallel. .

Referring to FIG. 5, in the digital audio data decoding apparatus of the present invention, except for the first frame, the clock occupancy time A of the deformatter and the clock occupancy time region B of the Huffman decoder do not exist independently. In other words, the deformatter and the Huffman decoder occupy the clock only in the 't0' period, and after that, the clock is shared with the filter bank. In other words, it can be seen that the deformatter and the Huffman decoder perform the processing on the frame during the clock occupancy time t2 of the filter bank performing the processing on the previous frame.

Therefore, referring to Tables 1 and 5, in the present invention, in the first and subsequent frames, the time for processing data of one frame is occupied by the dequantizer (10%) and the time occupied by the filter bank (60%). The sum adds only 70% per frame. In the conventional digital audio data decoding apparatus of FIG. 1, this means that the time occupied by the deformatter (5%), the time occupied by the Huffman decoder (25%), the time occupied by the dequantizer (10%), and the filter bank Compared to 100% of each frame in which all of the time occupied at is 100%, the clock cycles per frame are reduced by 30%, which reduces the overall data processing time.

The present invention relates to a method and apparatus for decoding digital audio data, comprising: a parallel processing of a filter bank having the longest clock occupancy time and a Huffman decoder having a constant clock occupancy time (that is, a clock requirement) in one frame period for decoding. The data processing time of the entire decoding system is shortened, and the performance of the overall decoding system can be improved due to the efficient distribution and use of the clock.

In addition, the present invention can simplify the decoding processing algorithm and increase the processing speed by implementing in hardware a computing device shared by a plurality of memories operating in parallel, a dequantizer and a filter bank. As a result, there is an advantage that makes it possible to apply an audio file in WMA format to a portable device.

Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

Claims (17)

In the decoding method of digital audio data in a portable terminal, An initialization step of extracting first header information and first coded data from digital audio data of a first frame, decoding the first coded data, and writing the first coded data to a first memory; An inverse quantization step of reading the decoded data from the first memory to perform inverse quantization on the encoded data and then writing the dequantized data to a second memory; And Read inverse quantized data of Nth (N is a natural number of two or more) frames from the second memory, perform inverse discrete cosine transform, perform window / overlap-add, inverse discrete cosine transform of Nth frame, and A parallel processing step of extracting second header information and second coded data with respect to digital audio data of the N + 1th frame in parallel during window / overlap-add and decoding the second coded data And decoding the digital audio data. The method of claim 1, wherein the dequantization step and the parallel processing step And decoding the digital audio data repeatedly until the decoding of the digital audio data ends. The method of claim 1, wherein the decoding of the initialization step and the parallel processing step is performed. And Huffman decoding. delete delete delete The method of claim 1, wherein the parallel processing step And decoding the decoded data of the second coded data into the first memory. The method of claim 1, wherein the parallel processing step When performing the window / overlap-add, the windowed data of the previous frame is written to the third memory, and the windowed data of the previous frame is read from the third memory to overlap with the windowed data of the current frame. And decoding the digital audio data. The method of claim 1, wherein the digital audio data is A method of decoding digital audio data, characterized in that it is data encoded by Window Media Audio. An apparatus for decoding digital audio data in a portable terminal, First and second memories; A deformatter for extracting first header information and first encoded data from the digital audio data; A decoder which decodes the first coded data and stores the first coded data in the first memory; An inverse quantizer configured to read and dequantize the decoded data from the first memory and to store dequantized data in the second memory; A filter bank configured to read inverse quantized data of an N (N is a natural number of two or more) frames from the second memory, perform inverse discrete cosine transform, and perform window / overlap-add; And Extracting second header information and second encoded data for digital audio data of an N + 1th frame during inverse discrete cosine transformation and window / overlap-add operation of the Nth frame of the filter bank, and performing the second encoding And a controller for controlling the decoder and the filter bank to decode the data. The method of claim 10, And performing a complex number / multiplication / add operation for the inverse quantization and inverse discrete cosine transform and shared by the inverse quantizer and the filter bank. The method of claim 10, And a third memory for storing windowed data of a previous frame for window / overlap-add of the filter bank. The method of claim 10, wherein the second memory is And windowed data of a previous frame for window overlap add of the filter bank. The method of claim 10, wherein the decoder And a Huffman decoder. The method of claim 10, wherein the digital audio data is A device for decoding digital audio data, characterized in that it is data encoded by Window Media Audio. delete In the recording medium in which a program of instructions executable by a digital processing apparatus capable of parallel processing when performing digital audio data decoding in a portable terminal is tangibly implemented, and which records a program that can be read by the digital processing apparatus, An initialization step of extracting first header information and first coded data from digital audio data of a first frame, decoding the first coded data, and writing the first coded data to a first memory; An inverse quantization step of reading the decoded data from the first memory to perform inverse quantization on the encoded data and then writing the dequantized data to a second memory; And Inverse quantized data of N (N is a natural number of two or more) frames is read from the second memory, inverse discrete cosine transform is performed, and window / overlap-add is performed, and inverse discrete cosine transform of the Nth frame is performed. And a parallel processing step of extracting second header information and second encoded data with respect to digital audio data of the N + 1th frame in parallel while performing window / overlap-add, and decoding the second encoded data. Recording medium that records the program to run.

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