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171 lines
6.4 KiB
171 lines
6.4 KiB
/* |
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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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/** |
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* Parses AC-3 frame header. |
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* Parses the header up to the lfeon element, which is the first 52 or 54 bits |
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* depending on the audio coding mode. |
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* @param buf[in] Array containing the first 7 bytes of the frame. |
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* @param hdr[out] Pointer to struct where header info is written. |
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* @return Returns 0 on success, -1 if there is a sync word mismatch, |
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* -2 if the bsid (version) element is invalid, -3 if the fscod (sample rate) |
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* element is invalid, or -4 if the frmsizecod (bit rate) element is invalid. |
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*/ |
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int ff_ac3_parse_header(const uint8_t buf[7], AC3HeaderInfo *hdr); |
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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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