2 * Common code between AC3 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,
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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 AC3 encoder and decoder.
32 #define AC3_MAX_CODED_FRAME_SIZE 3840 /* in bytes */
33 #define AC3_MAX_CHANNELS 6 /* including LFE channel */
35 #define NB_BLOCKS 6 /* number of PCM blocks inside an AC3 frame */
36 #define AC3_FRAME_SIZE (NB_BLOCKS * 256)
38 /* exponent encoding strategy */
46 /** Delta bit allocation strategy */
54 /** Channel mode (audio coding mode) */
56 AC3_CHMODE_DUALMONO = 0,
66 typedef struct AC3BitAllocParameters {
69 int slow_gain, slow_decay, fast_decay, db_per_bit, floor;
70 int cpl_fast_leak, cpl_slow_leak;
71 } AC3BitAllocParameters;
74 * @struct AC3HeaderInfo
75 * Coded AC-3 header values up to the lfeon element, plus derived values.
78 /** @defgroup coded Coded elements
89 /** @defgroup derived Derived values
101 void ac3_common_init(void);
104 * Calculates the log power-spectral density of the input signal.
105 * This gives a rough estimate of signal power in the frequency domain by using
106 * the spectral envelope (exponents). The psd is also separately grouped
107 * into critical bands for use in the calculating the masking curve.
108 * 128 units in psd = -6 dB. The dbknee parameter in AC3BitAllocParameters
109 * determines the reference level.
111 * @param[in] exp frequency coefficient exponents
112 * @param[in] start starting bin location
113 * @param[in] end ending bin location
114 * @param[out] psd signal power for each frequency bin
115 * @param[out] band_psd signal power for each critical band
117 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
121 * Calculates the masking curve.
122 * First, the excitation is calculated using parameters in \p s and the signal
123 * power in each critical band. The excitation is compared with a predefined
124 * hearing threshold table to produce the masking curve. If delta bit
125 * allocation information is provided, it is used for adjusting the masking
126 * curve, usually to give a closer match to a better psychoacoustic model.
128 * @param[in] s adjustable bit allocation parameters
129 * @param[in] band_psd signal power for each critical band
130 * @param[in] start starting bin location
131 * @param[in] end ending bin location
132 * @param[in] fast_gain fast gain (estimated signal-to-mask ratio)
133 * @param[in] is_lfe whether or not the channel being processed is the LFE
134 * @param[in] dba_mode delta bit allocation mode (none, reuse, or new)
135 * @param[in] dba_nsegs number of delta segments
136 * @param[in] dba_offsets location offsets for each segment
137 * @param[in] dba_lengths length of each segment
138 * @param[in] dba_values delta bit allocation for each segment
139 * @param[out] mask calculated masking curve
141 void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,
142 int start, int end, int fast_gain, int is_lfe,
143 int dba_mode, int dba_nsegs, uint8_t *dba_offsets,
144 uint8_t *dba_lengths, uint8_t *dba_values,
148 * Calculates bit allocation pointers.
149 * The SNR is the difference between the masking curve and the signal. AC-3
150 * uses this value for each frequency bin to allocate bits. The \p snroffset
151 * parameter is a global adjustment to the SNR for all bins.
153 * @param[in] mask masking curve
154 * @param[in] psd signal power for each frequency bin
155 * @param[in] start starting bin location
156 * @param[in] end ending bin location
157 * @param[in] snr_offset SNR adjustment
158 * @param[in] floor noise floor
159 * @param[out] bap bit allocation pointers
161 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
162 int snr_offset, int floor, uint8_t *bap);
164 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
165 int8_t *exp, int start, int end,
166 int snr_offset, int fast_gain, int is_lfe,
167 int dba_mode, int dba_nsegs,
168 uint8_t *dba_offsets, uint8_t *dba_lengths,
169 uint8_t *dba_values);
171 #endif /* FFMPEG_AC3_H */