libavcodec/ac3.h

   1 /*
   2  * Common code between the AC-3 encoder and decoder
   3  * Copyright (c) 2000, 2001, 2002 Fabrice Bellard
   4  *
   5  * This file is part of Libav.
   6  *
   7  * Libav 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  * Libav 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 Libav; 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
  24  * Common code between the AC-3 encoder and decoder.
  25  */
  26
  27 #ifndef AVCODEC_AC3_H
  28 #define AVCODEC_AC3_H
  29
  30 #define AC3_MAX_CODED_FRAME_SIZE 3840 /* in bytes */
  31 #define AC3_MAX_CHANNELS 7            /**< maximum number of channels, including coupling channel */
  32 #define CPL_CH 0                      /**< coupling channel index */
  33
  34 #define AC3_MAX_COEFS   256
  35 #define AC3_BLOCK_SIZE  256
  36 #define AC3_MAX_BLOCKS    6
  37 #define AC3_FRAME_SIZE (AC3_MAX_BLOCKS * 256)
  38 #define AC3_WINDOW_SIZE (AC3_BLOCK_SIZE * 2)
  39 #define AC3_CRITICAL_BANDS 50
  40 #define AC3_MAX_CPL_BANDS  18
  41
  42 #include "ac3tab.h"
  43
  44 /* exponent encoding strategy */
  45 #define EXP_REUSE 0
  46 #define EXP_NEW   1
  47
  48 #define EXP_D15   1
  49 #define EXP_D25   2
  50 #define EXP_D45   3
  51
  52 /* pre-defined gain values */
  53 #define LEVEL_PLUS_3DB          1.4142135623730950
  54 #define LEVEL_PLUS_1POINT5DB    1.1892071150027209
  55 #define LEVEL_MINUS_1POINT5DB   0.8408964152537145
  56 #define LEVEL_MINUS_3DB         0.7071067811865476
  57 #define LEVEL_MINUS_4POINT5DB   0.5946035575013605
  58 #define LEVEL_MINUS_6DB         0.5000000000000000
  59 #define LEVEL_MINUS_9DB         0.3535533905932738
  60 #define LEVEL_ZERO              0.0000000000000000
  61 #define LEVEL_ONE               1.0000000000000000
  62
  63 /** Delta bit allocation strategy */
  64 typedef enum {
  65     DBA_REUSE = 0,
  66     DBA_NEW,
  67     DBA_NONE,
  68     DBA_RESERVED
  69 } AC3DeltaStrategy;
  70
  71 /** Channel mode (audio coding mode) */
  72 typedef enum {
  73     AC3_CHMODE_DUALMONO = 0,
  74     AC3_CHMODE_MONO,
  75     AC3_CHMODE_STEREO,
  76     AC3_CHMODE_3F,
  77     AC3_CHMODE_2F1R,
  78     AC3_CHMODE_3F1R,
  79     AC3_CHMODE_2F2R,
  80     AC3_CHMODE_3F2R
  81 } AC3ChannelMode;
  82
  83 typedef struct AC3BitAllocParameters {
  84     int sr_code;
  85     int sr_shift;
  86     int slow_gain, slow_decay, fast_decay, db_per_bit, floor;
  87     int cpl_fast_leak, cpl_slow_leak;
  88 } AC3BitAllocParameters;
  89
  90 /**
  91  * @struct AC3HeaderInfo
  92  * Coded AC-3 header values up to the lfeon element, plus derived values.
  93  */
  94 typedef struct AC3HeaderInfo {
  95     /** @name Coded elements
  96      * @{
  97      */
  98     uint16_t sync_word;
  99     uint16_t crc1;
 100     uint8_t sr_code;
 101     uint8_t bitstream_id;
 102     uint8_t bitstream_mode;
 103     uint8_t channel_mode;
 104     uint8_t lfe_on;
 105     uint8_t frame_type;
 106     int substreamid;                        ///< substream identification
 107     int center_mix_level;                   ///< Center mix level index
 108     int surround_mix_level;                 ///< Surround mix level index
 109     uint16_t channel_map;
 110     int num_blocks;                         ///< number of audio blocks
 111     /** @} */
 112
 113     /** @name Derived values
 114      * @{
 115      */
 116     uint8_t sr_shift;
 117     uint16_t sample_rate;
 118     uint32_t bit_rate;
 119     uint8_t channels;
 120     uint16_t frame_size;
 121     uint64_t channel_layout;
 122     /** @} */
 123 } AC3HeaderInfo;
 124
 125 typedef enum {
 126     EAC3_FRAME_TYPE_INDEPENDENT = 0,
 127     EAC3_FRAME_TYPE_DEPENDENT,
 128     EAC3_FRAME_TYPE_AC3_CONVERT,
 129     EAC3_FRAME_TYPE_RESERVED
 130 } EAC3FrameType;
 131
 132 void ff_ac3_common_init(void);
 133
 134 /**
 135  * Calculate the log power-spectral density of the input signal.
 136  * This gives a rough estimate of signal power in the frequency domain by using
 137  * the spectral envelope (exponents).  The psd is also separately grouped
 138  * into critical bands for use in the calculating the masking curve.
 139  * 128 units in psd = -6 dB.  The dbknee parameter in AC3BitAllocParameters
 140  * determines the reference level.
 141  *
 142  * @param[in]  exp        frequency coefficient exponents
 143  * @param[in]  start      starting bin location
 144  * @param[in]  end        ending bin location
 145  * @param[out] psd        signal power for each frequency bin
 146  * @param[out] band_psd   signal power for each critical band
 147  */
 148 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
 149                                int16_t *band_psd);
 150
 151 /**
 152  * Calculate the masking curve.
 153  * First, the excitation is calculated using parameters in s and the signal
 154  * power in each critical band.  The excitation is compared with a predefined
 155  * hearing threshold table to produce the masking curve.  If delta bit
 156  * allocation information is provided, it is used for adjusting the masking
 157  * curve, usually to give a closer match to a better psychoacoustic model.
 158  *
 159  * @param[in]  s            adjustable bit allocation parameters
 160  * @param[in]  band_psd     signal power for each critical band
 161  * @param[in]  start        starting bin location
 162  * @param[in]  end          ending bin location
 163  * @param[in]  fast_gain    fast gain (estimated signal-to-mask ratio)
 164  * @param[in]  is_lfe       whether or not the channel being processed is the LFE
 165  * @param[in]  dba_mode     delta bit allocation mode (none, reuse, or new)
 166  * @param[in]  dba_nsegs    number of delta segments
 167  * @param[in]  dba_offsets  location offsets for each segment
 168  * @param[in]  dba_lengths  length of each segment
 169  * @param[in]  dba_values   delta bit allocation for each segment
 170  * @param[out] mask         calculated masking curve
 171  * @return returns 0 for success, non-zero for error
 172  */
 173 int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,
 174                                int start, int end, int fast_gain, int is_lfe,
 175                                int dba_mode, int dba_nsegs, uint8_t *dba_offsets,
 176                                uint8_t *dba_lengths, uint8_t *dba_values,
 177                                int16_t *mask);
 178
 179 #endif /* AVCODEC_AC3_H */