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.
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.
27 #define AC3_MAX_CODED_FRAME_SIZE 3840 /* in bytes */
28 #define AC3_MAX_CHANNELS 6 /* including LFE channel */
30 #define NB_BLOCKS 6 /* number of PCM blocks inside an AC3 frame */
31 #define AC3_FRAME_SIZE (NB_BLOCKS * 256)
33 /* exponent encoding strategy */
41 typedef struct AC3BitAllocParameters {
42 int fscod; /* frequency */
44 int sgain, sdecay, fdecay, dbknee, floor;
45 int cplfleak, cplsleak;
46 } AC3BitAllocParameters;
49 * @struct AC3HeaderInfo
50 * Coded AC-3 header values up to the lfeon element, plus derived values.
53 /** @defgroup coded Coded elements
69 /** @defgroup derived Derived values
80 extern const uint16_t ff_ac3_frame_sizes[38][3];
81 extern const uint8_t ff_ac3_channels[8];
82 extern const uint16_t ff_ac3_freqs[3];
83 extern const uint16_t ff_ac3_bitratetab[19];
84 extern const int16_t ff_ac3_window[256];
85 extern const uint8_t ff_sdecaytab[4];
86 extern const uint8_t ff_fdecaytab[4];
87 extern const uint16_t ff_sgaintab[4];
88 extern const uint16_t ff_dbkneetab[4];
89 extern const int16_t ff_floortab[8];
90 extern const uint16_t ff_fgaintab[8];
92 void ac3_common_init(void);
95 * Calculates the log power-spectral density of the input signal.
96 * This gives a rough estimate of signal power in the frequency domain by using
97 * the spectral envelope (exponents). The psd is also separately grouped
98 * into critical bands for use in the calculating the masking curve.
99 * 128 units in psd = -6 dB. The dbknee parameter in AC3BitAllocParameters
100 * determines the reference level.
102 * @param[in] exp frequency coefficient exponents
103 * @param[in] start starting bin location
104 * @param[in] end ending bin location
105 * @param[out] psd signal power for each frequency bin
106 * @param[out] bndpsd signal power for each critical band
108 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
112 * Calculates the masking curve.
113 * First, the excitation is calculated using parameters in \p s and the signal
114 * power in each critical band. The excitation is compared with a predefined
115 * hearing threshold table to produce the masking curve. If delta bit
116 * allocation information is provided, it is used for adjusting the masking
117 * curve, usually to give a closer match to a better psychoacoustic model.
119 * @param[in] s adjustable bit allocation parameters
120 * @param[in] bndpsd signal power for each critical band
121 * @param[in] start starting bin location
122 * @param[in] end ending bin location
123 * @param[in] fgain fast gain (estimated signal-to-mask ratio)
124 * @param[in] is_lfe whether or not the channel being processed is the LFE
125 * @param[in] deltbae delta bit allocation exists (none, reuse, or new)
126 * @param[in] deltnseg number of delta segments
127 * @param[in] deltoffst location offsets for each segment
128 * @param[in] deltlen length of each segment
129 * @param[in] deltba delta bit allocation for each segment
130 * @param[out] mask calculated masking curve
132 void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *bndpsd,
133 int start, int end, int fgain, int is_lfe,
134 int deltbae, int deltnseg, uint8_t *deltoffst,
135 uint8_t *deltlen, uint8_t *deltba,
139 * Calculates bit allocation pointers.
140 * The SNR is the difference between the masking curve and the signal. AC-3
141 * uses this value for each frequency bin to allocate bits. The \p snroffset
142 * parameter is a global adjustment to the SNR for all bins.
144 * @param[in] mask masking curve
145 * @param[in] psd signal power for each frequency bin
146 * @param[in] start starting bin location
147 * @param[in] end ending bin location
148 * @param[in] snroffset SNR adjustment
149 * @param[in] floor noise floor
150 * @param[out] bap bit allocation pointers
152 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
153 int snroffset, int floor, uint8_t *bap);
155 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
156 int8_t *exp, int start, int end,
157 int snroffset, int fgain, int is_lfe,
158 int deltbae,int deltnseg,
159 uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba);