1 /* 2 * Common code between AC3 encoder and decoder 3 * Copyright (c) 2000, 2001, 2002 Fabrice Bellard. 4 * 5 * This file is part of FFmpeg. 6 * 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. 11 * 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. 16 * 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 20 */ 21 22 /** 23 * @file ac3.h 24 * Common code between AC3 encoder and decoder. 25 */ 26 27 #ifndef FFMPEG_AC3_H 28 #define FFMPEG_AC3_H 29 30 #include "ac3tab.h" 31 32 #define AC3_MAX_CODED_FRAME_SIZE 3840 /* in bytes */ 33 #define AC3_MAX_CHANNELS 6 /* including LFE channel */ 34 35 #define NB_BLOCKS 6 /* number of PCM blocks inside an AC3 frame */ 36 #define AC3_FRAME_SIZE (NB_BLOCKS * 256) 37 38 /* exponent encoding strategy */ 39 #define EXP_REUSE 0 40 #define EXP_NEW 1 41 42 #define EXP_D15 1 43 #define EXP_D25 2 44 #define EXP_D45 3 45 46 /** Delta bit allocation strategy */ 47 typedef enum { 48 DBA_REUSE = 0, 49 DBA_NEW, 50 DBA_NONE, 51 DBA_RESERVED 52 } AC3DeltaStrategy; 53 54 /** Channel mode (audio coding mode) */ 55 typedef enum { 56 AC3_CHMODE_DUALMONO = 0, 57 AC3_CHMODE_MONO, 58 AC3_CHMODE_STEREO, 59 AC3_CHMODE_3F, 60 AC3_CHMODE_2F1R, 61 AC3_CHMODE_3F1R, 62 AC3_CHMODE_2F2R, 63 AC3_CHMODE_3F2R 64 } AC3ChannelMode; 65 66 typedef struct AC3BitAllocParameters { 67 int sr_code; 68 int sr_shift; 69 int slow_gain, slow_decay, fast_decay, db_per_bit, floor; 70 int cpl_fast_leak, cpl_slow_leak; 71 } AC3BitAllocParameters; 72 73 /** 74 * @struct AC3HeaderInfo 75 * Coded AC-3 header values up to the lfeon element, plus derived values. 76 */ 77 typedef struct { 78 /** @defgroup coded Coded elements 79 * @{ 80 */ 81 uint16_t sync_word; 82 uint16_t crc1; 83 uint8_t sr_code; 84 uint8_t bitstream_id; 85 uint8_t channel_mode; 86 uint8_t lfe_on; 87 uint8_t frame_type; 88 /** @} */ 89 90 /** @defgroup derived Derived values 91 * @{ 92 */ 93 uint8_t sr_shift; 94 uint16_t sample_rate; 95 uint32_t bit_rate; 96 uint8_t channels; 97 uint16_t frame_size; 98 int center_mix_level; ///< Center mix level index 99 int surround_mix_level; ///< Surround mix level index 100 uint16_t channel_map; 101 /** @} */ 102 } AC3HeaderInfo; 103 104 typedef enum { 105 EAC3_FRAME_TYPE_INDEPENDENT = 0, 106 EAC3_FRAME_TYPE_DEPENDENT, 107 EAC3_FRAME_TYPE_AC3_CONVERT, 108 EAC3_FRAME_TYPE_RESERVED 109 } EAC3FrameType; 110 111 void ac3_common_init(void); 112 113 /** 114 * Calculates the log power-spectral density of the input signal. 115 * This gives a rough estimate of signal power in the frequency domain by using 116 * the spectral envelope (exponents). The psd is also separately grouped 117 * into critical bands for use in the calculating the masking curve. 118 * 128 units in psd = -6 dB. The dbknee parameter in AC3BitAllocParameters 119 * determines the reference level. 120 * 121 * @param[in] exp frequency coefficient exponents 122 * @param[in] start starting bin location 123 * @param[in] end ending bin location 124 * @param[out] psd signal power for each frequency bin 125 * @param[out] band_psd signal power for each critical band 126 */ 127 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd, 128 int16_t *band_psd); 129 130 /** 131 * Calculates the masking curve. 132 * First, the excitation is calculated using parameters in \p s and the signal 133 * power in each critical band. The excitation is compared with a predefined 134 * hearing threshold table to produce the masking curve. If delta bit 135 * allocation information is provided, it is used for adjusting the masking 136 * curve, usually to give a closer match to a better psychoacoustic model. 137 * 138 * @param[in] s adjustable bit allocation parameters 139 * @param[in] band_psd signal power for each critical band 140 * @param[in] start starting bin location 141 * @param[in] end ending bin location 142 * @param[in] fast_gain fast gain (estimated signal-to-mask ratio) 143 * @param[in] is_lfe whether or not the channel being processed is the LFE 144 * @param[in] dba_mode delta bit allocation mode (none, reuse, or new) 145 * @param[in] dba_nsegs number of delta segments 146 * @param[in] dba_offsets location offsets for each segment 147 * @param[in] dba_lengths length of each segment 148 * @param[in] dba_values delta bit allocation for each segment 149 * @param[out] mask calculated masking curve 150 */ 151 void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd, 152 int start, int end, int fast_gain, int is_lfe, 153 int dba_mode, int dba_nsegs, uint8_t *dba_offsets, 154 uint8_t *dba_lengths, uint8_t *dba_values, 155 int16_t *mask); 156 157 /** 158 * Calculates bit allocation pointers. 159 * The SNR is the difference between the masking curve and the signal. AC-3 160 * uses this value for each frequency bin to allocate bits. The \p snroffset 161 * parameter is a global adjustment to the SNR for all bins. 162 * 163 * @param[in] mask masking curve 164 * @param[in] psd signal power for each frequency bin 165 * @param[in] start starting bin location 166 * @param[in] end ending bin location 167 * @param[in] snr_offset SNR adjustment 168 * @param[in] floor noise floor 169 * @param[out] bap bit allocation pointers 170 */ 171 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end, 172 int snr_offset, int floor, uint8_t *bap); 173 174 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap, 175 int8_t *exp, int start, int end, 176 int snr_offset, int fast_gain, int is_lfe, 177 int dba_mode, int dba_nsegs, 178 uint8_t *dba_offsets, uint8_t *dba_lengths, 179 uint8_t *dba_values); 180 181 #endif /* FFMPEG_AC3_H */ 182