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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9 * License as published by the Free Software Foundation; either
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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
81 * Parses AC-3 frame header.
82 * Parses the header up to the lfeon element, which is the first 52 or 54 bits
83 * depending on the audio coding mode.
84 * @param buf[in] Array containing the first 7 bytes of the frame.
85 * @param hdr[out] Pointer to struct where header info is written.
86 * @return Returns 0 on success, -1 if there is a sync word mismatch,
87 * -2 if the bsid (version) element is invalid, -3 if the fscod (sample rate)
88 * element is invalid, or -4 if the frmsizecod (bit rate) element is invalid.
90 int ff_ac3_parse_header(const uint8_t buf[7], AC3HeaderInfo *hdr);
92 extern const uint16_t ff_ac3_frame_sizes[38][3];
93 extern const uint8_t ff_ac3_channels[8];
94 extern const uint16_t ff_ac3_freqs[3];
95 extern const uint16_t ff_ac3_bitratetab[19];
96 extern const int16_t ff_ac3_window[256];
97 extern const uint8_t ff_sdecaytab[4];
98 extern const uint8_t ff_fdecaytab[4];
99 extern const uint16_t ff_sgaintab[4];
100 extern const uint16_t ff_dbkneetab[4];
101 extern const int16_t ff_floortab[8];
102 extern const uint16_t ff_fgaintab[8];
104 void ac3_common_init(void);
107 * Calculates the log power-spectral density of the input signal.
108 * This gives a rough estimate of signal power in the frequency domain by using
109 * the spectral envelope (exponents). The psd is also separately grouped
110 * into critical bands for use in the calculating the masking curve.
111 * 128 units in psd = -6 dB. The dbknee parameter in AC3BitAllocParameters
112 * determines the reference level.
114 * @param[in] exp frequency coefficient exponents
115 * @param[in] start starting bin location
116 * @param[in] end ending bin location
117 * @param[out] psd signal power for each frequency bin
118 * @param[out] bndpsd signal power for each critical band
120 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
124 * Calculates the masking curve.
125 * First, the excitation is calculated using parameters in \p s and the signal
126 * power in each critical band. The excitation is compared with a predefined
127 * hearing threshold table to produce the masking curve. If delta bit
128 * allocation information is provided, it is used for adjusting the masking
129 * curve, usually to give a closer match to a better psychoacoustic model.
131 * @param[in] s adjustable bit allocation parameters
132 * @param[in] bndpsd signal power for each critical band
133 * @param[in] start starting bin location
134 * @param[in] end ending bin location
135 * @param[in] fgain fast gain (estimated signal-to-mask ratio)
136 * @param[in] is_lfe whether or not the channel being processed is the LFE
137 * @param[in] deltbae delta bit allocation exists (none, reuse, or new)
138 * @param[in] deltnseg number of delta segments
139 * @param[in] deltoffst location offsets for each segment
140 * @param[in] deltlen length of each segment
141 * @param[in] deltba delta bit allocation for each segment
142 * @param[out] mask calculated masking curve
144 void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *bndpsd,
145 int start, int end, int fgain, int is_lfe,
146 int deltbae, int deltnseg, uint8_t *deltoffst,
147 uint8_t *deltlen, uint8_t *deltba,
151 * Calculates bit allocation pointers.
152 * The SNR is the difference between the masking curve and the signal. AC-3
153 * uses this value for each frequency bin to allocate bits. The \p snroffset
154 * parameter is a global adjustment to the SNR for all bins.
156 * @param[in] mask masking curve
157 * @param[in] psd signal power for each frequency bin
158 * @param[in] start starting bin location
159 * @param[in] end ending bin location
160 * @param[in] snroffset SNR adjustment
161 * @param[in] floor noise floor
162 * @param[out] bap bit allocation pointers
164 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
165 int snroffset, int floor, uint8_t *bap);
167 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
168 int8_t *exp, int start, int end,
169 int snroffset, int fgain, int is_lfe,
170 int deltbae,int deltnseg,
171 uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba);