JP2000091920A - Video and audio compression device - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To significantly reduce the bit allocation calculation processing by calculating the bit allocation processing that occupies about half of the compression processing of the image / audio compression apparatus based on the scale factor. I do. SOLUTION: A scaling section 102 normalizes the maximum amplitude of an output of a subband analysis section 101 to divide data sampled at regular intervals into 32 subbands and uses it as a scale factor. Scale factor selection information calculation unit 1
03, the bit allocation calculation unit 104 for each subband, the quantization unit 10 that quantizes the data processed by the subband analysis unit using the calculated bit allocation and the scale factor.
5, a bit stream generation unit 106 for generating an audio stream from a header, bit allocation, SCFSI (scale factor selection information), scale factor of each sub-band, and quantized data. Calculate the distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video / audio compression apparatus such as a video camera, an electronic still camera, and a telephone.

[0002]

2. Description of the Related Art As an audio compression device, for example, ISO / IEC 11
FIG. 5 shows a block diagram of an audio compression apparatus (LAYERII) described in 172-3: 1993 (E) (MPEG1 audio) (hereinafter, this is a known example).

In FIG. 5, reference numeral 501 denotes a sub-band analyzer which divides input audio data into 32 bands, 502
Is a scaling unit that calculates a scale factor that is the maximum amplitude for every 12 consecutive samples of each subband, 50
Reference numeral 3 denotes a scale factor selection information calculation unit for sharing when the change amount of the scale factor is small. Reference numeral 504 denotes a psychoacoustic processing unit for calculating the bit allocation of each subband using the psychoacoustic input sound data. A quantization unit that quantizes the data processed by the subband analysis unit 501 using the bit allocation calculated by the psychoacoustic processing unit 504 and the scale factor calculated by the scale factor selection information calculation unit 503; And a bit stream generating unit for generating the bit stream.

[0004]

In the above-mentioned known example, an enormous amount of calculation is required for a series of audio compression processing. Because of the enormous amount of computation, audio data cannot be compressed and processed in real time by software using a microcomputer, so a dedicated LSI for audio was required.

[0005] Here, the present inventor has previously proposed in Japanese Patent Application No. 9-360.
FIG. 6 shows an audio compression / decompression device filed in Japanese Patent Application No. 602.
This is because the sub-band analysis unit 601 and the scaling unit 60
2, a scale factor selection information calculation unit 603, a bit allocation selection unit 604, a bit allocation table unit 605, a quantization unit 606, and a bit stream generation unit 607. By setting 605, the amount of calculation for audio processing is reduced by eliminating the psychoacoustic processing unit 504 of the above-mentioned known example.

In this Japanese Patent Application No. 9-360602,
Bit rates commonly used (for example, 128 kb
(approximately ps), the number of bits per subband is increased, so that the compression process can be performed effectively. But,
In the case of a low bit rate where the number of bits per subband is small, or for voice biased to a specific band, the number of bits allocated to each subband is small, so dynamic and efficient bit allocation is required. Is done.

[0007]

In order to attain the above object, the present invention provides a method of calculating the bit allocation based on a scale factor, which occupies about half of the operation amount of the audio compression processing. The operation of the processing unit 504 can be reduced substantially, and high-quality and high-compression audio compression can be realized even for audio having a low bit rate or a bias in a specific band.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

First, the operation of the embodiment of the present invention will be described.

FIG. 4 is a system block diagram of one embodiment of the present invention. In the figure, 401 is a lens, 402
Denotes an image sensor, 403 denotes a camera signal processing unit which converts an image signal obtained from the image sensor 402 into a video signal for photographing on a television or the like, 404 denotes a microphone, and 405 converts audio collected by the microphone 404 to digital. A / D converter 406, a video processor for compressing the video signal of the camera signal processor 403 to generate a video stream, and 407 temporarily store the audio data converted to digital by the A / D converter 405. An audio buffer 408 is an MPEG CODEC unit composed of a video processing unit 406 and an audio buffer 407, and 409 is an MPEG Audio unit 41 for compressing audio data in the audio buffer 407 and generating an audio stream.
A multiplexing unit 0 synchronizes the video stream generated by the video processing unit 406 with the audio stream generated by the MPEG audio unit 409 to generate a system stream, and 411 denotes an MPEG audio unit 409.
And a multiplexing unit 410 and a microcomputer that writes the multiplexed system stream to the recording medium 413, an MPEG camera 412 that takes in video data and audio data and compresses it to generate a system stream, and 413, a system stream generated by the MPEG camera 412. This is a recording medium for recording.

An image is condensed by a lens 401 and the image pickup device 4
The video signal is converted into a video signal by a camera signal processing 403, and is compressed into a video stream compliant with MPEG by a video processing unit 406. On the other hand, audio
The sound is collected by the microphone 404, converted to digital by the A / D conversion unit 405, and converted to MPEG via the audio buffer 407.
The audio unit 409 compresses the audio stream into an audio stream compliant with MPEG Audio. The multiplexing unit 410 synchronizes the video stream and the audio stream and records them on the recording medium 413 in a format conforming to the MPEG system stream.

Next, the MPEG Audio unit 40 shown in FIG.
A first embodiment of the processing in step 9 will be described with reference to FIG.

Reference numeral 101 denotes a subband analysis unit that divides the audio data processed by the A / D conversion unit 405 into 32 bands, 102 denotes a scaling unit that uses the maximum amplitude of the data divided into 32 subbands as a scale factor, 10
Numeral 3 denotes a scale factor selection information calculation unit for sharing when the amount of change of the scale factor is small, 104 denotes a bit allocation calculation unit for calculating bit allocation of each subband based on the scale factor calculated by the scaling unit 102, and 105 denotes a bit allocation calculation unit. A quantum that quantizes the data processed in the subband analysis 101 using the scale factor calculated by the scaling unit 102 and the scale factor shared by the scale factor selection calculation unit 103 and the bit allocation calculated by the bit allocation calculation unit 104. , A header 106,
Bit allocation, SCFSI (SCALEFACTOR SELECTION IMF
ORMATION, scale factor selection information), a scale factor, and a bit stream generation unit that generates an audio stream from quantized data.

Next, a specific example of the bit allocation calculation unit 104 will be described with reference to FIGS. 7, 8, and 9. FIG.

In step 701, the maximum value of the scale factor of each subband calculated by the scaling unit 102 is obtained. In 702, the bit allocation of each subband is calculated from the maximum value of the scale factor. FIG. 8 shows a scale factor table described in the known example. There are 63 table numbers from 0 to 62, and the value of the scale factor increases as the table number decreases. The bit allocation is calculated according to the table number. As one specific example, calculation of bit allocation in the case of a sampling frequency of 32 kHz, a bit rate of 32 kbps, and LAYERII will be described with reference to FIG. FIG. 9 shows the bit allocation corresponding to the scale factor number. For example, when the maximum scale factor number calculated in 701 is 10, the bit allocation becomes 4 in subbands 0 to 5, and the subband 6
For １１11, the bit allocation is 3. Since human hearing is sensitive to low frequencies, sub-bands 0 to 5 are separated from sub-bands 6 to 11 in this way. Sampling frequency 3
In the case of 2 kHz, bit rate of 32 kbps and LAYERII, the subband used is MPEG Audio standard ISO / IE
C 11172-3: 12 subbands according to 1993 (E) (MPEG1 audio). Therefore, calculation is performed for each of the 12 subbands. In 703, 1 AAU (Audio Access Uni
(t, audio decoding unit), the number of bits that can be allocated to the sample excluding the header, bit allocation, SCFSI, and scale factor is calculated. 703 for 704
From the number of bits that can be allocated to the sample and the bit allocation of each subband in 702, it is checked whether the bit allocation allocated to each subband is within 1 AAU. When it is within the range, the process ends, but when the range is not within the range, at 705, the bit allocation is reduced based on psychoacoustics. The method of reducing the bit allocation focuses on the sub-bands where the bit allocation is large, and reduces the bit allocation one bit at a time. The order of reduction is in the order of the number of subbands, and is repeated until the number of subbands falls within the target 1 AAU.

Next, the MPEG Audio unit 40 shown in FIG.
A second embodiment of the processing in step 9 will be described with reference to FIG.

Reference numeral 201 denotes a subband analysis unit that divides the audio data processed by the A / D conversion unit 405 into 32 bands, 202 denotes a scaling unit that uses the maximum amplitude of the data divided into 32 subbands as a scale factor, 20
Reference numeral 3 denotes a scale factor selection information calculation unit that is used in common when the amount of change in the scale factor is small, 204 denotes several bit allocation tables, and 205 denotes the number of scale factors based on the SCFSI calculated by the scale factor selection information calculation unit 203. And a bit allocation table selecting unit for selecting an optimal bit allocation table from the bit allocation table unit 204 according to the number of the bit allocation tables, and a bit allocation table selecting unit 206 based on the scale factor calculated by the scaling unit 202. A bit allocation distribution unit 205 allocates the selected bit allocation table to each subband, and 207 denotes a scale factor selection calculation unit 20
3 and a quantization unit for quantizing the data processed by the sub-band analysis 201 using the scale factor shared by 3 and the bit allocation allocated by the bit allocation allocation unit 206. 208 denotes a header, bit allocation, SCFSI, scale A bit stream generation unit that generates an audio stream from the factor and the quantized data.

Next, a specific example of the bit allocation table unit 204 and the bit allocation distribution unit 206 when the sampling frequency is 32 kHz, the bit rate is 32 kbps, and the LAYER II uses 7 subbands will be described with reference to FIGS.

In FIG. 12, at 1201, the maximum scale factor is calculated every seven subbands. The maximum value of the scale factor of each subband calculated in 1202 is compared, and the subbands are ordered. In step 1203, the number of scale factors is calculated from the result of the scale factor selection information unit 203.

Here, the bit distribution tables (A), (B) and (C) used in the bit distribution table section 204 are shown in FIG. This is a bit allocation table when using 7 subbands out of 12 available subbands, and is selected from the bit allocation tables (A), (B), and (C) according to the number of scale factors of the scale factor selection information calculation unit 203. I do. When 7 sub-bands are used, the number of scale factors is 7 to 21. Bit distribution table selector 2
05, the bit allocation table (C) when the number of scale factors is 7 to 10, the bit allocation table (B) when the number of scale factors is 11 to 16, and the bit allocation table (A) when the number of scale factors is 17 to 21. select. In step 1204, the values in the bit allocation table are sorted in the order of the order in step 1202, that is, the bit allocation increases when the scale factor number is small. For example, if the bit allocation table (A) is selected in 205, the bit allocation 5 is allocated to the subband having the smallest scale factor number, the bit allocation 4 is allocated to the second smallest subband, and the third small subband is allocated. , The values of the selected bit distribution table are sequentially allocated.

Next, the MPEG Audio unit 40 shown in FIG.
A third embodiment of the processing in step 9 will be described with reference to FIG.

Reference numeral 301 denotes a sub-band analysis unit that divides the audio data processed by the A / D conversion unit 405 into 32 bands, 302 denotes a scaling unit that uses the maximum amplitude of the data divided into 32 sub-bands as a scale factor, 30
Numeral 3 denotes a scale factor selection information calculation unit for sharing when the amount of change in the scale factor is small, 304 denotes a bit allocation table unit in which bit allocations are stored in advance by the number of used subbands, and 305 denotes a scaling unit 30
2 is a bit allocation allocating unit that allocates the bit allocation of the bit allocation table unit 304 to each subband based on the scale factor calculated by
Quantization for quantizing the data processed by the sub-band analysis 301 using the scale factor shared by the scale factor selection calculation unit 303 and the bit allocation allocated by the bit allocation allocation unit 305. Unit, 307 is a header, bit allocation, SCFS
A stream generation unit that generates an audio stream from I, scale factor, and quantized data.

Next, a specific example of the bit allocation table section 304 and the bit allocation distribution section 305 when the sampling frequency is 32 kHz, the bit rate is 32 kbps, and the LAYER II uses 7 subbands will be described with reference to FIGS. I do.

In FIG. 12, at 1201, the maximum scale factor is calculated every seven subbands. The maximum value of the scale factor of each subband calculated in 1202 is compared, and the subbands are ordered. In step 1203, the number of scale factors is calculated from the result of the scale factor selection information unit 203.

Here, the bit distribution table section 304 is shown in FIG. This is a bit allocation table when using 7 sub-bands out of 12 available sub-bands, and is a table corresponding to a maximum of 21 scale factors. Compression processing is performed using this one table. In step 1204, the bit distribution tables are sorted in the order given in step 1202. Assign bit allocation 5 to the subband with the smallest scale factor number,
Allocate bit allocation 4 to the second smallest subband 3
Bit allocation 4 is allocated to the smallest sub-band in the order of the selected bit allocation table.

[0026]

According to the present invention, the bit allocation is calculated on the basis of the scale factor, thereby making it possible to perform complicated operations for low bit rates as well as for voices biased to a specific band as well as a normal bit rate. High-quality sound compression processing can be performed without using an operation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a video and audio compression apparatus according to the present invention.

FIG. 2 is a block diagram showing an embodiment of an image / audio compression apparatus according to the present invention.

FIG. 3 is a block diagram showing an embodiment of a video and audio compression apparatus according to the present invention.

FIG. 4 is a system block diagram showing an embodiment of an image / audio compression apparatus according to the present invention.

FIG. 5 is a conventional audio compression block diagram.

FIG. 6 is an audio compression block diagram.

FIG. 7 is a flowchart illustrating the present invention.

FIG. 8 is a scale factor table described in a known example.

FIG. 9 is a specific example of a table used for calculating bit allocation.

FIG. 10 is a specific example of a bit distribution table unit.

FIG. 11 is a specific example of a bit distribution table unit.

FIG. 12 is a flowchart illustrating the present invention.

[Explanation of symbols]

 101: Subband analysis unit 102: Scaling unit 103: Scale factor selection information calculation unit 104: Bit allocation calculation unit 105: Quantization unit 106: Bit stream generation unit 107・ MPEG Audio processing unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 7/24 H04N 7/13 Z (72) Inventor Tomomi Yazawa 1410 Inada, Hitachinaka-shi, Ibaraki Hitachi, Ltd. Within the Manufacturing Division

Claims (13)

[Claims] 1. A sub-band analyzer for processing data sampled at a fixed interval with a fixed number of samples and dividing the data into 32 sub-bands, and a scaling unit for normalizing the maximum amplitude of the output of the sub-band analyzer to use as a scale factor. A scale factor selection information calculation unit for sharing when the change amount of the scale factor is small, a bit allocation calculation unit for calculating the bit allocation of each subband, and the subband analysis unit using the calculated bit allocation and the scale factor. Quantizer that quantizes the data processed by, header, bit allocation, SCFSI (SCALEFACTOR SELECTION IMFOR
A video / audio compression apparatus comprising: a bit stream generation unit that generates an audio stream from MATION, scale factor selection information), a scale factor of each subband, and quantized data. 2. The bit allocation calculation unit according to claim 1,
A video and audio compression apparatus, wherein the calculation is performed based on the scale factor output by the scaling unit. 3. The video / audio compression apparatus according to claim 1, wherein the bit allocation calculation unit calculates the bit allocation based on a scale factor and a subband number output by the scaling unit. 4. A sub-band analyzer for processing data sampled at a fixed interval with a fixed number of samples and dividing the data into 32 sub-bands, and a scaling unit for normalizing the maximum amplitude of the output of the sub-band analyzer to use as a scale factor. When the change amount of the scale factor is small, a scale factor selection information calculation unit to be shared, a bit distribution table unit in which the number of quantization bits of each subband is previously stored as a plurality of tables, and an optimal table is selected from a plurality of bit distribution tables A bit allocation selection unit, a bit allocation allocation unit that allocates a bit allocation table selected by the bit allocation selection unit so that each subband is optimized, using the selected bit allocation table and a scale factor. Quantizes the data processed by the sub-band analyzer. Quantizer, header, bit allocation,
A video and audio compression apparatus comprising: a bit stream generation unit that generates an audio stream from SCFSI, a scale factor of each subband, and quantized data. 5. The video / audio compression apparatus according to claim 4, wherein the bit allocation table section is a plurality of tables in which bit allocation is allocated to all of the maximum usable subbands. 6. The video / audio compression apparatus according to claim 4, wherein the bit allocation table section is a plurality of tables in which bit allocation is assigned to several of the maximum usable subbands. 7. The video and audio compression apparatus according to claim 4, wherein the bit allocation table according to claim 4 comprises several tables corresponding to the number of scale factors. 8. The bit allocation selection unit according to claim 4, wherein the bit allocation selection unit outputs the S output from the scale factor selection information calculation unit.
An image / audio compression apparatus characterized in that the number of scale factors is calculated based on CFSI, and an optimum bit allocation table is selected according to the number of scale factors. 9. A sub-band analyzer for processing data sampled at a constant interval with a fixed number of samples and dividing the data into 32 sub-bands, and a scaling unit for normalizing the maximum amplitude of the output of the sub-band analyzer and using the scale as a scale factor. When the change amount of the scale factor is small, the scale factor selection information calculation unit to be commonized, the bit allocation table unit having the quantization bit number of each sub-band as a table in advance, and the sub-band to optimize the bit allocation of the bit allocation table unit A bit allocation allocating unit for allocating a bit allocation so that the data processed by the sub-band analysis unit is quantized using the selected bit allocation and the scale factor allocated to each sub-band by the bit allocation allocating unit. Quantization section, header, bit allocation, SCFSI, An image / audio compression apparatus, comprising: a bit stream generation unit that generates an audio stream from a sub-band scale factor and quantized data. 10. The video and audio compression apparatus according to claim 9, wherein the bit allocation table section is a single table in which bit allocation is allocated to all of the maximum usable subbands. 11. The video and audio compression apparatus according to claim 9, wherein the bit allocation table section is a single table in which bit allocation is allocated to several of the maximum usable subbands. 12. The video / audio compression apparatus according to claim 4, wherein the bit allocation distribution unit allocates the bit allocation table based on the scale factor output by the scaling unit. 13. The sub-band according to claim 4 or 10, wherein the table value of the scale factor is small (the actual scale factor is large) based on the scale factor output from said scaling unit. A video and audio compression apparatus characterized in that a large number of bits are allocated to a video signal.