2 * Common code between AC3 encoder and decoder
3 * Copyright (c) 2000, 2001, 2002 Fabrice Bellard.
5 * This file is part of FFmpeg.
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8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
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15 * Lesser General Public License for more details.
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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_ACMOD_DUALMONO = 0,
66 typedef struct AC3BitAllocParameters {
67 int fscod; /* frequency */
69 int sgain, sdecay, fdecay, dbknee, floor;
70 int cplfleak, cplsleak;
71 } AC3BitAllocParameters;
74 * @struct AC3HeaderInfo
75 * Coded AC-3 header values up to the lfeon element, plus derived values.
78 /** @defgroup coded Coded elements
94 /** @defgroup derived Derived values
106 void ac3_common_init(void);
109 * Calculates the log power-spectral density of the input signal.
110 * This gives a rough estimate of signal power in the frequency domain by using
111 * the spectral envelope (exponents). The psd is also separately grouped
112 * into critical bands for use in the calculating the masking curve.
113 * 128 units in psd = -6 dB. The dbknee parameter in AC3BitAllocParameters
114 * determines the reference level.
116 * @param[in] exp frequency coefficient exponents
117 * @param[in] start starting bin location
118 * @param[in] end ending bin location
119 * @param[out] psd signal power for each frequency bin
120 * @param[out] bndpsd signal power for each critical band
122 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
126 * Calculates the masking curve.
127 * First, the excitation is calculated using parameters in \p s and the signal
128 * power in each critical band. The excitation is compared with a predefined
129 * hearing threshold table to produce the masking curve. If delta bit
130 * allocation information is provided, it is used for adjusting the masking
131 * curve, usually to give a closer match to a better psychoacoustic model.
133 * @param[in] s adjustable bit allocation parameters
134 * @param[in] bndpsd signal power for each critical band
135 * @param[in] start starting bin location
136 * @param[in] end ending bin location
137 * @param[in] fgain fast gain (estimated signal-to-mask ratio)
138 * @param[in] is_lfe whether or not the channel being processed is the LFE
139 * @param[in] deltbae delta bit allocation exists (none, reuse, or new)
140 * @param[in] deltnseg number of delta segments
141 * @param[in] deltoffst location offsets for each segment
142 * @param[in] deltlen length of each segment
143 * @param[in] deltba delta bit allocation for each segment
144 * @param[out] mask calculated masking curve
146 void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *bndpsd,
147 int start, int end, int fgain, int is_lfe,
148 int deltbae, int deltnseg, uint8_t *deltoffst,
149 uint8_t *deltlen, uint8_t *deltba,
153 * Calculates bit allocation pointers.
154 * The SNR is the difference between the masking curve and the signal. AC-3
155 * uses this value for each frequency bin to allocate bits. The \p snroffset
156 * parameter is a global adjustment to the SNR for all bins.
158 * @param[in] mask masking curve
159 * @param[in] psd signal power for each frequency bin
160 * @param[in] start starting bin location
161 * @param[in] end ending bin location
162 * @param[in] snroffset SNR adjustment
163 * @param[in] floor noise floor
164 * @param[out] bap bit allocation pointers
166 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
167 int snroffset, int floor, uint8_t *bap);
169 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
170 int8_t *exp, int start, int end,
171 int snroffset, int fgain, int is_lfe,
172 int deltbae,int deltnseg,
173 uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba);