libavcodec/ac3.h

   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 AC3_H
  28 #define 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 typedef struct AC3BitAllocParameters {
  47     int fscod; /* frequency */
  48     int halfratecod;
  49     int sgain, sdecay, fdecay, dbknee, floor;
  50     int cplfleak, cplsleak;
  51 } AC3BitAllocParameters;
  52
  53 /**
  54  * @struct AC3HeaderInfo
  55  * Coded AC-3 header values up to the lfeon element, plus derived values.
  56  */
  57 typedef struct {
  58     /** @defgroup coded Coded elements
  59      * @{
  60      */
  61     uint16_t sync_word;
  62     uint16_t crc1;
  63     uint8_t fscod;
  64     uint8_t frmsizecod;
  65     uint8_t bsid;
  66     uint8_t bsmod;
  67     uint8_t acmod;
  68     uint8_t cmixlev;
  69     uint8_t surmixlev;
  70     uint8_t dsurmod;
  71     uint8_t lfeon;
  72     /** @} */
  73
  74     /** @defgroup derived Derived values
  75      * @{
  76      */
  77     uint8_t halfratecod;
  78     uint16_t sample_rate;
  79     uint32_t bit_rate;
  80     uint8_t channels;
  81     uint16_t frame_size;
  82     /** @} */
  83 } AC3HeaderInfo;
  84
  85
  86 void ac3_common_init(void);
  87
  88 /**
  89  * Calculates the log power-spectral density of the input signal.
  90  * This gives a rough estimate of signal power in the frequency domain by using
  91  * the spectral envelope (exponents).  The psd is also separately grouped
  92  * into critical bands for use in the calculating the masking curve.
  93  * 128 units in psd = -6 dB.  The dbknee parameter in AC3BitAllocParameters
  94  * determines the reference level.
  95  *
  96  * @param[in]  exp        frequency coefficient exponents
  97  * @param[in]  start      starting bin location
  98  * @param[in]  end        ending bin location
  99  * @param[out] psd        signal power for each frequency bin
 100  * @param[out] bndpsd     signal power for each critical band
 101  */
 102 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
 103                                int16_t *bndpsd);
 104
 105 /**
 106  * Calculates the masking curve.
 107  * First, the excitation is calculated using parameters in \p s and the signal
 108  * power in each critical band.  The excitation is compared with a predefined
 109  * hearing threshold table to produce the masking curve.  If delta bit
 110  * allocation information is provided, it is used for adjusting the masking
 111  * curve, usually to give a closer match to a better psychoacoustic model.
 112  *
 113  * @param[in]  s          adjustable bit allocation parameters
 114  * @param[in]  bndpsd     signal power for each critical band
 115  * @param[in]  start      starting bin location
 116  * @param[in]  end        ending bin location
 117  * @param[in]  fgain      fast gain (estimated signal-to-mask ratio)
 118  * @param[in]  is_lfe     whether or not the channel being processed is the LFE
 119  * @param[in]  deltbae    delta bit allocation exists (none, reuse, or new)
 120  * @param[in]  deltnseg   number of delta segments
 121  * @param[in]  deltoffst  location offsets for each segment
 122  * @param[in]  deltlen    length of each segment
 123  * @param[in]  deltba     delta bit allocation for each segment
 124  * @param[out] mask       calculated masking curve
 125  */
 126 void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *bndpsd,
 127                                 int start, int end, int fgain, int is_lfe,
 128                                 int deltbae, int deltnseg, uint8_t *deltoffst,
 129                                 uint8_t *deltlen, uint8_t *deltba,
 130                                 int16_t *mask);
 131
 132 /**
 133  * Calculates bit allocation pointers.
 134  * The SNR is the difference between the masking curve and the signal.  AC-3
 135  * uses this value for each frequency bin to allocate bits.  The \p snroffset
 136  * parameter is a global adjustment to the SNR for all bins.
 137  *
 138  * @param[in]  mask       masking curve
 139  * @param[in]  psd        signal power for each frequency bin
 140  * @param[in]  start      starting bin location
 141  * @param[in]  end        ending bin location
 142  * @param[in]  snroffset  SNR adjustment
 143  * @param[in]  floor      noise floor
 144  * @param[out] bap        bit allocation pointers
 145  */
 146 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
 147                                int snroffset, int floor, uint8_t *bap);
 148
 149 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
 150                                    int8_t *exp, int start, int end,
 151                                    int snroffset, int fgain, int is_lfe,
 152                                    int deltbae,int deltnseg,
 153                                    uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba);
 154
 155 #endif /* AC3_H */