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ac3.h
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1 /*
2  * Common code between the AC-3 encoder and decoder
3  * Copyright (c) 2000, 2001, 2002 Fabrice Bellard
4  *
5  * This file is part of FFmpeg.
6  *
7  * FFmpeg is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * FFmpeg is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with FFmpeg; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
22 /**
23  * @file
24  * Common code between the AC-3 encoder and decoder.
25  */
26 
27 #ifndef AVCODEC_AC3_H
28 #define AVCODEC_AC3_H
29 
30 #define AC3_MAX_CODED_FRAME_SIZE 3840 /* in bytes */
31 #define AC3_MAX_CHANNELS 7 /**< maximum number of channels, including coupling channel */
32 #define CPL_CH 0 /**< coupling channel index */
33 
34 #define AC3_MAX_COEFS 256
35 #define AC3_BLOCK_SIZE 256
36 #define AC3_MAX_BLOCKS 6
37 #define AC3_FRAME_SIZE (AC3_MAX_BLOCKS * 256)
38 #define AC3_WINDOW_SIZE (AC3_BLOCK_SIZE * 2)
39 #define AC3_CRITICAL_BANDS 50
40 #define AC3_MAX_CPL_BANDS 18
41 
42 #include "libavutil/opt.h"
43 #include "avcodec.h"
44 #include "ac3tab.h"
45 
46 /* exponent encoding strategy */
47 #define EXP_REUSE 0
48 #define EXP_NEW 1
49 
50 #define EXP_D15 1
51 #define EXP_D25 2
52 #define EXP_D45 3
53 
54 /* pre-defined gain values */
55 #define LEVEL_PLUS_3DB 1.4142135623730950
56 #define LEVEL_PLUS_1POINT5DB 1.1892071150027209
57 #define LEVEL_MINUS_1POINT5DB 0.8408964152537145
58 #define LEVEL_MINUS_3DB 0.7071067811865476
59 #define LEVEL_MINUS_4POINT5DB 0.5946035575013605
60 #define LEVEL_MINUS_6DB 0.5000000000000000
61 #define LEVEL_MINUS_9DB 0.3535533905932738
62 #define LEVEL_ZERO 0.0000000000000000
63 #define LEVEL_ONE 1.0000000000000000
64 
65 /** Delta bit allocation strategy */
66 typedef enum {
67  DBA_REUSE = 0,
72 
73 /** Channel mode (audio coding mode) */
74 typedef enum {
84 
85 typedef struct AC3BitAllocParameters {
86  int sr_code;
87  int sr_shift;
91 
92 /**
93  * @struct AC3HeaderInfo
94  * Coded AC-3 header values up to the lfeon element, plus derived values.
95  */
96 typedef struct AC3HeaderInfo {
97  /** @name Coded elements
98  * @{
99  */
100  uint16_t sync_word;
101  uint16_t crc1;
108  int substreamid; ///< substream identification
109  int center_mix_level; ///< Center mix level index
110  int surround_mix_level; ///< Surround mix level index
111  uint16_t channel_map;
112  int num_blocks; ///< number of audio blocks
113  /** @} */
114 
115  /** @name Derived values
116  * @{
117  */
119  uint16_t sample_rate;
120  uint32_t bit_rate;
122  uint16_t frame_size;
123  uint64_t channel_layout;
124  /** @} */
125 } AC3HeaderInfo;
126 
127 typedef enum {
132 } EAC3FrameType;
133 
134 void ff_ac3_common_init(void);
135 
136 /**
137  * Calculate the log power-spectral density of the input signal.
138  * This gives a rough estimate of signal power in the frequency domain by using
139  * the spectral envelope (exponents). The psd is also separately grouped
140  * into critical bands for use in the calculating the masking curve.
141  * 128 units in psd = -6 dB. The dbknee parameter in AC3BitAllocParameters
142  * determines the reference level.
143  *
144  * @param[in] exp frequency coefficient exponents
145  * @param[in] start starting bin location
146  * @param[in] end ending bin location
147  * @param[out] psd signal power for each frequency bin
148  * @param[out] band_psd signal power for each critical band
149  */
150 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
151  int16_t *band_psd);
152 
153 /**
154  * Calculate the masking curve.
155  * First, the excitation is calculated using parameters in s and the signal
156  * power in each critical band. The excitation is compared with a predefined
157  * hearing threshold table to produce the masking curve. If delta bit
158  * allocation information is provided, it is used for adjusting the masking
159  * curve, usually to give a closer match to a better psychoacoustic model.
160  *
161  * @param[in] s adjustable bit allocation parameters
162  * @param[in] band_psd signal power for each critical band
163  * @param[in] start starting bin location
164  * @param[in] end ending bin location
165  * @param[in] fast_gain fast gain (estimated signal-to-mask ratio)
166  * @param[in] is_lfe whether or not the channel being processed is the LFE
167  * @param[in] dba_mode delta bit allocation mode (none, reuse, or new)
168  * @param[in] dba_nsegs number of delta segments
169  * @param[in] dba_offsets location offsets for each segment
170  * @param[in] dba_lengths length of each segment
171  * @param[in] dba_values delta bit allocation for each segment
172  * @param[out] mask calculated masking curve
173  * @return returns 0 for success, non-zero for error
174  */
175 int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,
176  int start, int end, int fast_gain, int is_lfe,
177  int dba_mode, int dba_nsegs, uint8_t *dba_offsets,
178  uint8_t *dba_lengths, uint8_t *dba_values,
179  int16_t *mask);
180 
181 #endif /* AVCODEC_AC3_H */