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ffmpeg / libavcodec / ac3.h @ 12dffc45

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/*
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 * Common code between the AC-3 encoder and decoder
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 * Copyright (c) 2000, 2001, 2002 Fabrice Bellard
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 *
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 * This file is part of FFmpeg.
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 *
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 * FFmpeg is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * FFmpeg is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with FFmpeg; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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/**
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 * @file
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 * Common code between the AC-3 encoder and decoder.
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 */
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#ifndef AVCODEC_AC3_H
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#define AVCODEC_AC3_H
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#define AC3_MAX_CODED_FRAME_SIZE 3840 /* in bytes */
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#define AC3_MAX_CHANNELS 6 /* including LFE channel */
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#define AC3_MAX_COEFS   256
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#define AC3_BLOCK_SIZE  256
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#define AC3_MAX_BLOCKS    6
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#define AC3_FRAME_SIZE (AC3_MAX_BLOCKS * 256)
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#define AC3_WINDOW_SIZE (AC3_BLOCK_SIZE * 2)
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#define AC3_CRITICAL_BANDS 50
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#define AC3_MAX_CPL_BANDS  18
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#include "ac3tab.h"
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/* exponent encoding strategy */
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#define EXP_REUSE 0
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#define EXP_NEW   1
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#define EXP_D15   1
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#define EXP_D25   2
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#define EXP_D45   3
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/** Delta bit allocation strategy */
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typedef enum {
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    DBA_REUSE = 0,
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    DBA_NEW,
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    DBA_NONE,
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    DBA_RESERVED
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} AC3DeltaStrategy;
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/** Channel mode (audio coding mode) */
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typedef enum {
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    AC3_CHMODE_DUALMONO = 0,
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    AC3_CHMODE_MONO,
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    AC3_CHMODE_STEREO,
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    AC3_CHMODE_3F,
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    AC3_CHMODE_2F1R,
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    AC3_CHMODE_3F1R,
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    AC3_CHMODE_2F2R,
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    AC3_CHMODE_3F2R
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} AC3ChannelMode;
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typedef struct AC3BitAllocParameters {
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    int sr_code;
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    int sr_shift;
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    int slow_gain, slow_decay, fast_decay, db_per_bit, floor;
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    int cpl_fast_leak, cpl_slow_leak;
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} AC3BitAllocParameters;
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/**
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 * @struct AC3HeaderInfo
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 * Coded AC-3 header values up to the lfeon element, plus derived values.
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 */
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typedef struct {
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    /** @defgroup coded Coded elements
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     * @{
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     */
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    uint16_t sync_word;
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    uint16_t crc1;
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    uint8_t sr_code;
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    uint8_t bitstream_id;
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    uint8_t channel_mode;
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    uint8_t lfe_on;
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    uint8_t frame_type;
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    int substreamid;                        ///< substream identification
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    int center_mix_level;                   ///< Center mix level index
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    int surround_mix_level;                 ///< Surround mix level index
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    uint16_t channel_map;
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    int num_blocks;                         ///< number of audio blocks
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    /** @} */
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    /** @defgroup derived Derived values
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     * @{
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     */
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    uint8_t sr_shift;
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    uint16_t sample_rate;
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    uint32_t bit_rate;
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    uint8_t channels;
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    uint16_t frame_size;
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    int64_t channel_layout;
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    /** @} */
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} AC3HeaderInfo;
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typedef enum {
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    EAC3_FRAME_TYPE_INDEPENDENT = 0,
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    EAC3_FRAME_TYPE_DEPENDENT,
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    EAC3_FRAME_TYPE_AC3_CONVERT,
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    EAC3_FRAME_TYPE_RESERVED
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} EAC3FrameType;
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void ff_ac3_common_init(void);
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/**
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 * Calculate the log power-spectral density of the input signal.
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 * This gives a rough estimate of signal power in the frequency domain by using
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 * the spectral envelope (exponents).  The psd is also separately grouped
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 * into critical bands for use in the calculating the masking curve.
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 * 128 units in psd = -6 dB.  The dbknee parameter in AC3BitAllocParameters
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 * determines the reference level.
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 *
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 * @param[in]  exp        frequency coefficient exponents
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 * @param[in]  start      starting bin location
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 * @param[in]  end        ending bin location
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 * @param[out] psd        signal power for each frequency bin
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 * @param[out] band_psd   signal power for each critical band
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 */
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void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
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                               int16_t *band_psd);
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/**
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 * Calculate the masking curve.
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 * First, the excitation is calculated using parameters in s and the signal
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 * power in each critical band.  The excitation is compared with a predefined
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 * hearing threshold table to produce the masking curve.  If delta bit
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 * allocation information is provided, it is used for adjusting the masking
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 * curve, usually to give a closer match to a better psychoacoustic model.
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 *
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 * @param[in]  s            adjustable bit allocation parameters
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 * @param[in]  band_psd     signal power for each critical band
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 * @param[in]  start        starting bin location
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 * @param[in]  end          ending bin location
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 * @param[in]  fast_gain    fast gain (estimated signal-to-mask ratio)
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 * @param[in]  is_lfe       whether or not the channel being processed is the LFE
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 * @param[in]  dba_mode     delta bit allocation mode (none, reuse, or new)
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 * @param[in]  dba_nsegs    number of delta segments
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 * @param[in]  dba_offsets  location offsets for each segment
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 * @param[in]  dba_lengths  length of each segment
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 * @param[in]  dba_values   delta bit allocation for each segment
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 * @param[out] mask         calculated masking curve
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 * @return returns 0 for success, non-zero for error
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 */
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int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,
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                               int start, int end, int fast_gain, int is_lfe,
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                               int dba_mode, int dba_nsegs, uint8_t *dba_offsets,
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                               uint8_t *dba_lengths, uint8_t *dba_values,
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                               int16_t *mask);
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/**
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 * Calculate bit allocation pointers.
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 * The SNR is the difference between the masking curve and the signal.  AC-3
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 * uses this value for each frequency bin to allocate bits.  The snroffset
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 * parameter is a global adjustment to the SNR for all bins.
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 *
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 * @param[in]  mask       masking curve
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 * @param[in]  psd        signal power for each frequency bin
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 * @param[in]  start      starting bin location
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 * @param[in]  end        ending bin location
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 * @param[in]  snr_offset SNR adjustment
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 * @param[in]  floor      noise floor
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 * @param[in]  bap_tab    look-up table for bit allocation pointers
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 * @param[out] bap        bit allocation pointers
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 */
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void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
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                               int snr_offset, int floor,
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                               const uint8_t *bap_tab, uint8_t *bap);
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#endif /* AVCODEC_AC3_H */