PeerStreamer

/*

 * Common code between the AC-3 encoder and decoder

 * Copyright (c) 2000, 2001, 2002 Fabrice Bellard

 *

 * This file is part of Libav.

 *

 * Libav 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.

 *

 * Libav 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 Libav; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

/**

 * @file

 * Common code between the AC-3 encoder and decoder.

 */

#ifndef AVCODEC_AC3_H

#define AVCODEC_AC3_H

#define AC3_MAX_CODED_FRAME_SIZE 3840 /* in bytes */

#define AC3_MAX_CHANNELS 6 /* including LFE channel */

#define AC3_MAX_COEFS   256

#define AC3_BLOCK_SIZE  256

#define AC3_MAX_BLOCKS    6

#define AC3_FRAME_SIZE (AC3_MAX_BLOCKS * 256)

#define AC3_WINDOW_SIZE (AC3_BLOCK_SIZE * 2)

#define AC3_CRITICAL_BANDS 50

#define AC3_MAX_CPL_BANDS  18

#include "ac3tab.h"

/* 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 bitstream_mode;

    uint8_t channel_mode;

    uint8_t lfe_on;

    uint8_t frame_type;

    int substreamid;                        ///< substream identification

    int center_mix_level;                   ///< Center mix level index

    int surround_mix_level;                 ///< Surround mix level index

    uint16_t channel_map;

    int num_blocks;                         ///< number of audio blocks

    /** @} */

    /** @defgroup derived Derived values

     * @{

     */

    uint8_t sr_shift;

    uint16_t sample_rate;

    uint32_t bit_rate;

    uint8_t channels;

    uint16_t frame_size;

    int64_t channel_layout;

    /** @} */

} AC3HeaderInfo;

typedef enum {

    EAC3_FRAME_TYPE_INDEPENDENT = 0,

    EAC3_FRAME_TYPE_DEPENDENT,

    EAC3_FRAME_TYPE_AC3_CONVERT,

    EAC3_FRAME_TYPE_RESERVED

} EAC3FrameType;

void ff_ac3_common_init(void);

/**

 * Calculate 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);

/**

 * Calculate the masking curve.

 * First, the excitation is calculated using parameters in 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

 * @return returns 0 for success, non-zero for error

 */

int 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);

/**

 * Calculate 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 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[in]  bap_tab    look-up table for bit allocation pointers

 * @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,

                               const uint8_t *bap_tab, uint8_t *bap);

#endif /* AVCODEC_AC3_H */