mirror of https://git.ffmpeg.org/ffmpeg.git
160 lines
5.9 KiB
C
160 lines
5.9 KiB
C
/*
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* Common code between AC3 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 ac3.h
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* Common code between AC3 encoder and decoder.
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*/
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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 NB_BLOCKS 6 /* number of PCM blocks inside an AC3 frame */
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#define AC3_FRAME_SIZE (NB_BLOCKS * 256)
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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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typedef struct AC3BitAllocParameters {
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int fscod; /* frequency */
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int halfratecod;
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int sgain, sdecay, fdecay, dbknee, floor;
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int cplfleak, cplsleak;
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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 fscod;
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uint8_t frmsizecod;
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uint8_t bsid;
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uint8_t bsmod;
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uint8_t acmod;
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uint8_t cmixlev;
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uint8_t surmixlev;
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uint8_t dsurmod;
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uint8_t lfeon;
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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 halfratecod;
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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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/** @} */
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} AC3HeaderInfo;
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extern const uint16_t ff_ac3_frame_sizes[38][3];
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extern const uint8_t ff_ac3_channels[8];
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extern const uint16_t ff_ac3_freqs[3];
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extern const uint16_t ff_ac3_bitratetab[19];
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extern const int16_t ff_ac3_window[256];
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extern const uint8_t ff_sdecaytab[4];
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extern const uint8_t ff_fdecaytab[4];
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extern const uint16_t ff_sgaintab[4];
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extern const uint16_t ff_dbkneetab[4];
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extern const int16_t ff_floortab[8];
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extern const uint16_t ff_fgaintab[8];
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void ac3_common_init(void);
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/**
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* Calculates 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] bndpsd 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 *bndpsd);
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/**
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* Calculates the masking curve.
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* First, the excitation is calculated using parameters in \p 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] bndpsd 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] fgain 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] deltbae delta bit allocation exists (none, reuse, or new)
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* @param[in] deltnseg number of delta segments
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* @param[in] deltoffst location offsets for each segment
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* @param[in] deltlen length of each segment
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* @param[in] deltba delta bit allocation for each segment
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* @param[out] mask calculated masking curve
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*/
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void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *bndpsd,
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int start, int end, int fgain, int is_lfe,
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int deltbae, int deltnseg, uint8_t *deltoffst,
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uint8_t *deltlen, uint8_t *deltba,
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int16_t *mask);
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/**
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* Calculates 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 \p 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] snroffset SNR adjustment
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* @param[in] floor noise floor
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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 snroffset, int floor, uint8_t *bap);
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void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
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int8_t *exp, int start, int end,
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int snroffset, int fgain, int is_lfe,
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int deltbae,int deltnseg,
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uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba);
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