2 * Common code between the AC-3 encoder and decoder
3 * Copyright (c) 2000, 2001, 2002 Fabrice Bellard
5 * This file is part of FFmpeg.
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.
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.
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
24 * Common code between the AC-3 encoder and decoder.
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 */
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
42 #include "libavutil/opt.h"
46 /* exponent encoding strategy */
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
65 /** Delta bit allocation strategy */
73 /** Channel mode (audio coding mode) */
75 AC3_CHMODE_DUALMONO = 0,
85 typedef struct AC3BitAllocParameters {
88 int slow_gain, slow_decay, fast_decay, db_per_bit, floor;
89 int cpl_fast_leak, cpl_slow_leak;
90 } AC3BitAllocParameters;
93 * @struct AC3HeaderInfo
94 * Coded AC-3 header values up to the lfeon element, plus derived values.
96 typedef struct AC3HeaderInfo {
97 /** @name Coded elements
103 uint8_t bitstream_id;
104 uint8_t bitstream_mode;
105 uint8_t channel_mode;
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
115 /** @name Derived values
119 uint16_t sample_rate;
123 uint64_t channel_layout;
128 EAC3_FRAME_TYPE_INDEPENDENT = 0,
129 EAC3_FRAME_TYPE_DEPENDENT,
130 EAC3_FRAME_TYPE_AC3_CONVERT,
131 EAC3_FRAME_TYPE_RESERVED
134 void ff_ac3_common_init(void);
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.
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
150 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
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.
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
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,
181 #endif /* AVCODEC_AC3_H */