/* * Common code between AC3 encoder and decoder * Copyright (c) 2000, 2001, 2002 Fabrice Bellard. * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA *//** * @file ac3.h * Common code between AC3 encoder and decoder. */#ifndef FFMPEG_AC3_H#define FFMPEG_AC3_H#include "ac3tab.h"#define AC3_MAX_CODED_FRAME_SIZE 3840 /* in bytes */#define AC3_MAX_CHANNELS 6 /* including LFE channel */#define NB_BLOCKS 6 /* number of PCM blocks inside an AC3 frame */#define AC3_FRAME_SIZE (NB_BLOCKS * 256)/* exponent encoding strategy */#define EXP_REUSE 0#define EXP_NEW   1#define EXP_D15   1#define EXP_D25   2#define EXP_D45   3/** Delta bit allocation strategy */typedef enum {    DBA_REUSE = 0,    DBA_NEW,    DBA_NONE,    DBA_RESERVED} AC3DeltaStrategy;/** Channel mode (audio coding mode) */typedef enum {    AC3_CHMODE_DUALMONO = 0,    AC3_CHMODE_MONO,    AC3_CHMODE_STEREO,    AC3_CHMODE_3F,    AC3_CHMODE_2F1R,    AC3_CHMODE_3F1R,    AC3_CHMODE_2F2R,    AC3_CHMODE_3F2R} AC3ChannelMode;typedef struct AC3BitAllocParameters {    int sr_code;    int sr_shift;    int slow_gain, slow_decay, fast_decay, db_per_bit, floor;    int cpl_fast_leak, cpl_slow_leak;} AC3BitAllocParameters;/** * @struct AC3HeaderInfo * Coded AC-3 header values up to the lfeon element, plus derived values. */typedef struct {    /** @defgroup coded Coded elements     * @{     */    uint16_t sync_word;    uint16_t crc1;    uint8_t sr_code;    uint8_t bitstream_id;    uint8_t channel_mode;    uint8_t lfe_on;    /** @} */    /** @defgroup derived Derived values     * @{     */    uint8_t sr_shift;    uint16_t sample_rate;    uint32_t bit_rate;    uint8_t channels;    uint16_t frame_size;    /** @} */} AC3HeaderInfo;void ac3_common_init(void);/** * Calculates the log power-spectral density of the input signal. * This gives a rough estimate of signal power in the frequency domain by using * the spectral envelope (exponents).  The psd is also separately grouped * into critical bands for use in the calculating the masking curve. * 128 units in psd = -6 dB.  The dbknee parameter in AC3BitAllocParameters * determines the reference level. * * @param[in]  exp        frequency coefficient exponents * @param[in]  start      starting bin location * @param[in]  end        ending bin location * @param[out] psd        signal power for each frequency bin * @param[out] band_psd   signal power for each critical band */void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,                               int16_t *band_psd);/** * Calculates the masking curve. * First, the excitation is calculated using parameters in \p s and the signal * power in each critical band.  The excitation is compared with a predefined * hearing threshold table to produce the masking curve.  If delta bit * allocation information is provided, it is used for adjusting the masking * curve, usually to give a closer match to a better psychoacoustic model. * * @param[in]  s            adjustable bit allocation parameters * @param[in]  band_psd     signal power for each critical band * @param[in]  start        starting bin location * @param[in]  end          ending bin location * @param[in]  fast_gain    fast gain (estimated signal-to-mask ratio) * @param[in]  is_lfe       whether or not the channel being processed is the LFE * @param[in]  dba_mode     delta bit allocation mode (none, reuse, or new) * @param[in]  dba_nsegs    number of delta segments * @param[in]  dba_offsets  location offsets for each segment * @param[in]  dba_lengths  length of each segment * @param[in]  dba_values   delta bit allocation for each segment * @param[out] mask         calculated masking curve */void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,                                int start, int end, int fast_gain, int is_lfe,                                int dba_mode, int dba_nsegs, uint8_t *dba_offsets,                                uint8_t *dba_lengths, uint8_t *dba_values,                                int16_t *mask);/** * Calculates bit allocation pointers. * The SNR is the difference between the masking curve and the signal.  AC-3 * uses this value for each frequency bin to allocate bits.  The \p snroffset * parameter is a global adjustment to the SNR for all bins. * * @param[in]  mask       masking curve * @param[in]  psd        signal power for each frequency bin * @param[in]  start      starting bin location * @param[in]  end        ending bin location * @param[in]  snr_offset SNR adjustment * @param[in]  floor      noise floor * @param[out] bap        bit allocation pointers */void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,                               int snr_offset, int floor, uint8_t *bap);void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,                                   int8_t *exp, int start, int end,                                   int snr_offset, int fast_gain, int is_lfe,                                   int dba_mode, int dba_nsegs,                                   uint8_t *dba_offsets, uint8_t *dba_lengths,                                   uint8_t *dba_values);#endif /* FFMPEG_AC3_H */