ac3enc.c

/*
 * The simplest AC-3 encoder
 * Copyright (c) 2000 Fabrice Bellard
 * Copyright (c) 2006-2010 Justin Ruggles <justin.ruggles@gmail.com>
 * Copyright (c) 2006-2010 Prakash Punnoor <prakash@punnoor.de>
 *
 * 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
 * The simplest AC-3 encoder.
 */

//#define DEBUG
//#define ASSERT_LEVEL 2

#include <stdint.h>

#include "libavutil/audioconvert.h"
#include "libavutil/avassert.h"
#include "libavutil/avstring.h"
#include "libavutil/crc.h"
#include "libavutil/opt.h"
#include "avcodec.h"
#include "put_bits.h"
#include "dsputil.h"
#include "ac3dsp.h"
#include "ac3.h"
#include "audioconvert.h"
#include "fft.h"


#ifndef CONFIG_AC3ENC_FLOAT
#define CONFIG_AC3ENC_FLOAT 0
#endif


/** Maximum number of exponent groups. +1 for separate DC exponent. */
#define AC3_MAX_EXP_GROUPS 85

#if CONFIG_AC3ENC_FLOAT
#define MAC_COEF(d,a,b) ((d)+=(a)*(b))
typedef float SampleType;
typedef float CoefType;
typedef float CoefSumType;
#else
#define MAC_COEF(d,a,b) MAC64(d,a,b)
typedef int16_t SampleType;
typedef int32_t CoefType;
typedef int64_t CoefSumType;
#endif

typedef struct AC3MDCTContext {
    const SampleType *window;           ///< MDCT window function
    FFTContext fft;                     ///< FFT context for MDCT calculation
} AC3MDCTContext;

/**
 * Encoding Options used by AVOption.
 */
typedef struct AC3EncOptions {
    /* AC-3 metadata options*/
    int dialogue_level;
    int bitstream_mode;
    float center_mix_level;
    float surround_mix_level;
    int dolby_surround_mode;
    int audio_production_info;
    int mixing_level;
    int room_type;
    int copyright;
    int original;
    int extended_bsi_1;
    int preferred_stereo_downmix;
    float ltrt_center_mix_level;
    float ltrt_surround_mix_level;
    float loro_center_mix_level;
    float loro_surround_mix_level;
    int extended_bsi_2;
    int dolby_surround_ex_mode;
    int dolby_headphone_mode;
    int ad_converter_type;

    /* other encoding options */
    int allow_per_frame_metadata;
    int stereo_rematrixing;
    int channel_coupling;
    int cpl_start;
} AC3EncOptions;

/**
 * Data for a single audio block.
 */
typedef struct AC3Block {
    uint8_t  **bap;                             ///< bit allocation pointers (bap)
    CoefType **mdct_coef;                       ///< MDCT coefficients
    int32_t  **fixed_coef;                      ///< fixed-point MDCT coefficients
    uint8_t  **exp;                             ///< original exponents
    uint8_t  **grouped_exp;                     ///< grouped exponents
    int16_t  **psd;                             ///< psd per frequency bin
    int16_t  **band_psd;                        ///< psd per critical band
    int16_t  **mask;                            ///< masking curve
    uint16_t **qmant;                           ///< quantized mantissas
    uint8_t  **cpl_coord_exp;                   ///< coupling coord exponents           (cplcoexp)
    uint8_t  **cpl_coord_mant;                  ///< coupling coord mantissas           (cplcomant)
    uint8_t  coeff_shift[AC3_MAX_CHANNELS];     ///< fixed-point coefficient shift values
    uint8_t  new_rematrixing_strategy;          ///< send new rematrixing flags in this block
    int      num_rematrixing_bands;             ///< number of rematrixing bands
    uint8_t  rematrixing_flags[4];              ///< rematrixing flags
    struct AC3Block *exp_ref_block[AC3_MAX_CHANNELS]; ///< reference blocks for EXP_REUSE
    int      new_cpl_strategy;                  ///< send new coupling strategy
    int      cpl_in_use;                        ///< coupling in use for this block     (cplinu)
    uint8_t  channel_in_cpl[AC3_MAX_CHANNELS];  ///< channel in coupling                (chincpl)
    int      num_cpl_channels;                  ///< number of channels in coupling
    uint8_t  new_cpl_coords;                    ///< send new coupling coordinates      (cplcoe)
    uint8_t  cpl_master_exp[AC3_MAX_CHANNELS];  ///< coupling coord master exponents    (mstrcplco)
    int      new_snr_offsets;                   ///< send new SNR offsets
    int      new_cpl_leak;                      ///< send new coupling leak info
    int      end_freq[AC3_MAX_CHANNELS];        ///< end frequency bin                  (endmant)
} AC3Block;

/**
 * AC-3 encoder private context.
 */
typedef struct AC3EncodeContext {
    AVClass *av_class;                      ///< AVClass used for AVOption
    AC3EncOptions options;                  ///< encoding options
    PutBitContext pb;                       ///< bitstream writer context
    DSPContext dsp;
    AC3DSPContext ac3dsp;                   ///< AC-3 optimized functions
    AC3MDCTContext mdct;                    ///< MDCT context

    AC3Block blocks[AC3_MAX_BLOCKS];        ///< per-block info

    int eac3;                               ///< indicates if this is E-AC-3 vs. AC-3
    int bitstream_id;                       ///< bitstream id                           (bsid)
    int bitstream_mode;                     ///< bitstream mode                         (bsmod)

    int bit_rate;                           ///< target bit rate, in bits-per-second
    int sample_rate;                        ///< sampling frequency, in Hz

    int frame_size_min;                     ///< minimum frame size in case rounding is necessary
    int frame_size;                         ///< current frame size in bytes
    int frame_size_code;                    ///< frame size code                        (frmsizecod)
    uint16_t crc_inv[2];
    int64_t bits_written;                   ///< bit count    (used to avg. bitrate)
    int64_t samples_written;                ///< sample count (used to avg. bitrate)

    int fbw_channels;                       ///< number of full-bandwidth channels      (nfchans)
    int channels;                           ///< total number of channels               (nchans)
    int lfe_on;                             ///< indicates if there is an LFE channel   (lfeon)
    int lfe_channel;                        ///< channel index of the LFE channel
    int has_center;                         ///< indicates if there is a center channel
    int has_surround;                       ///< indicates if there are one or more surround channels
    int channel_mode;                       ///< channel mode                           (acmod)
    const uint8_t *channel_map;             ///< channel map used to reorder channels

    int center_mix_level;                   ///< center mix level code
    int surround_mix_level;                 ///< surround mix level code
    int ltrt_center_mix_level;              ///< Lt/Rt center mix level code
    int ltrt_surround_mix_level;            ///< Lt/Rt surround mix level code
    int loro_center_mix_level;              ///< Lo/Ro center mix level code
    int loro_surround_mix_level;            ///< Lo/Ro surround mix level code

    int cutoff;                             ///< user-specified cutoff frequency, in Hz
    int bandwidth_code;                     ///< bandwidth code (0 to 60)               (chbwcod)
    int start_freq[AC3_MAX_CHANNELS];       ///< start frequency bin                    (strtmant)
    int cpl_end_freq;                       ///< coupling channel end frequency bin

    int cpl_on;                             ///< coupling turned on for this frame
    int cpl_enabled;                        ///< coupling enabled for all frames
    int num_cpl_subbands;                   ///< number of coupling subbands            (ncplsubnd)
    int num_cpl_bands;                      ///< number of coupling bands               (ncplbnd)
    uint8_t cpl_band_sizes[AC3_MAX_CPL_BANDS];  ///< number of coeffs in each coupling band

    int rematrixing_enabled;                ///< stereo rematrixing enabled

    /* bitrate allocation control */
    int slow_gain_code;                     ///< slow gain code                         (sgaincod)
    int slow_decay_code;                    ///< slow decay code                        (sdcycod)
    int fast_decay_code;                    ///< fast decay code                        (fdcycod)
    int db_per_bit_code;                    ///< dB/bit code                            (dbpbcod)
    int floor_code;                         ///< floor code                             (floorcod)
    AC3BitAllocParameters bit_alloc;        ///< bit allocation parameters
    int coarse_snr_offset;                  ///< coarse SNR offsets                     (csnroffst)
    int fast_gain_code[AC3_MAX_CHANNELS];   ///< fast gain codes (signal-to-mask ratio) (fgaincod)
    int fine_snr_offset[AC3_MAX_CHANNELS];  ///< fine SNR offsets                       (fsnroffst)
    int frame_bits_fixed;                   ///< number of non-coefficient bits for fixed parameters
    int frame_bits;                         ///< all frame bits except exponents and mantissas
    int exponent_bits;                      ///< number of bits used for exponents

    SampleType **planar_samples;
    uint8_t *bap_buffer;
    uint8_t *bap1_buffer;
    CoefType *mdct_coef_buffer;
    int32_t *fixed_coef_buffer;
    uint8_t *exp_buffer;
    uint8_t *grouped_exp_buffer;
    int16_t *psd_buffer;
    int16_t *band_psd_buffer;
    int16_t *mask_buffer;
    uint16_t *qmant_buffer;
    uint8_t *cpl_coord_exp_buffer;
    uint8_t *cpl_coord_mant_buffer;

    uint8_t exp_strategy[AC3_MAX_CHANNELS][AC3_MAX_BLOCKS]; ///< exponent strategies

    DECLARE_ALIGNED(32, SampleType, windowed_samples)[AC3_WINDOW_SIZE];
} AC3EncodeContext;

typedef struct AC3Mant {
    uint16_t *qmant1_ptr, *qmant2_ptr, *qmant4_ptr; ///< mantissa pointers for bap=1,2,4
    int mant1_cnt, mant2_cnt, mant4_cnt;    ///< mantissa counts for bap=1,2,4
} AC3Mant;

#define CMIXLEV_NUM_OPTIONS 3
static const float cmixlev_options[CMIXLEV_NUM_OPTIONS] = {
    LEVEL_MINUS_3DB, LEVEL_MINUS_4POINT5DB, LEVEL_MINUS_6DB
};

#define SURMIXLEV_NUM_OPTIONS 3
static const float surmixlev_options[SURMIXLEV_NUM_OPTIONS] = {
    LEVEL_MINUS_3DB, LEVEL_MINUS_6DB, LEVEL_ZERO
};

#define EXTMIXLEV_NUM_OPTIONS 8
static const float extmixlev_options[EXTMIXLEV_NUM_OPTIONS] = {
    LEVEL_PLUS_3DB,  LEVEL_PLUS_1POINT5DB,  LEVEL_ONE,       LEVEL_MINUS_4POINT5DB,
    LEVEL_MINUS_3DB, LEVEL_MINUS_4POINT5DB, LEVEL_MINUS_6DB, LEVEL_ZERO
};


#define OFFSET(param) offsetof(AC3EncodeContext, options.param)
#define AC3ENC_PARAM (AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_ENCODING_PARAM)

#define AC3ENC_TYPE_AC3_FIXED   0
#define AC3ENC_TYPE_AC3         1
#define AC3ENC_TYPE_EAC3        2

#if CONFIG_AC3ENC_FLOAT
#define AC3ENC_TYPE AC3ENC_TYPE_AC3
#include "ac3enc_opts_template.c"
static AVClass ac3enc_class = { "AC-3 Encoder", av_default_item_name,
                                ac3_options, LIBAVUTIL_VERSION_INT };
#undef AC3ENC_TYPE
#define AC3ENC_TYPE AC3ENC_TYPE_EAC3
#include "ac3enc_opts_template.c"
static AVClass eac3enc_class = { "E-AC-3 Encoder", av_default_item_name,
                                 eac3_options, LIBAVUTIL_VERSION_INT };
#else
#define AC3ENC_TYPE AC3ENC_TYPE_AC3_FIXED
#include "ac3enc_opts_template.c"
static AVClass ac3enc_class = { "Fixed-Point AC-3 Encoder", av_default_item_name,
                                ac3fixed_options, LIBAVUTIL_VERSION_INT };
#endif


/* prototypes for functions in ac3enc_fixed.c and ac3enc_float.c */

static av_cold void mdct_end(AC3MDCTContext *mdct);

static av_cold int mdct_init(AVCodecContext *avctx, AC3MDCTContext *mdct,
                             int nbits);

static void apply_window(DSPContext *dsp, SampleType *output, const SampleType *input,
                         const SampleType *window, unsigned int len);

static int normalize_samples(AC3EncodeContext *s);

static void scale_coefficients(AC3EncodeContext *s);


/**
 * LUT for number of exponent groups.
 * exponent_group_tab[coupling][exponent strategy-1][number of coefficients]
 */
static uint8_t exponent_group_tab[2][3][256];


/**
 * List of supported channel layouts.
 */
static const int64_t ac3_channel_layouts[] = {
     AV_CH_LAYOUT_MONO,
     AV_CH_LAYOUT_STEREO,
     AV_CH_LAYOUT_2_1,
     AV_CH_LAYOUT_SURROUND,
     AV_CH_LAYOUT_2_2,
     AV_CH_LAYOUT_QUAD,
     AV_CH_LAYOUT_4POINT0,
     AV_CH_LAYOUT_5POINT0,
     AV_CH_LAYOUT_5POINT0_BACK,
    (AV_CH_LAYOUT_MONO     | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_STEREO   | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_2_1      | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_SURROUND | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_2_2      | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_QUAD     | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_4POINT0  | AV_CH_LOW_FREQUENCY),
     AV_CH_LAYOUT_5POINT1,
     AV_CH_LAYOUT_5POINT1_BACK,
     0
};


/**
 * LUT to select the bandwidth code based on the bit rate, sample rate, and
 * number of full-bandwidth channels.
 * bandwidth_tab[fbw_channels-1][sample rate code][bit rate code]
 */
static const uint8_t ac3_bandwidth_tab[5][3][19] = {
//      32  40  48  56  64  80  96 112 128 160 192 224 256 320 384 448 512 576 640

    { {  0,  0,  0, 12, 16, 32, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0, 16, 20, 36, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0, 32, 40, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0, 20, 24, 32, 48, 48, 48, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  4, 24, 28, 36, 56, 56, 56, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0, 20, 44, 52, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0,  0,  0, 16, 24, 32, 40, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  4, 20, 28, 36, 44, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0,  0,  0, 20, 40, 48, 60, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 12, 24, 32, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 16, 28, 36, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 32, 48, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  8, 20, 32, 40, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 12, 24, 36, 44, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 28, 44, 60, 60, 60, 60, 60, 60 } }
};


/**
 * LUT to select the coupling start band based on the bit rate, sample rate, and
 * number of full-bandwidth channels. -1 = coupling off
 * ac3_coupling_start_tab[channel_mode-2][sample rate code][bit rate code]
 *
 * TODO: more testing for optimal parameters.
 *       multi-channel tests at 44.1kHz and 32kHz.
 */
static const int8_t ac3_coupling_start_tab[6][3][19] = {
//      32  40  48  56  64  80  96 112 128 160 192 224 256 320 384 448 512 576 640

    // 2/0
    { {  0,  0,  0,  0,  0,  0,  0,  1,  1,  7,  8, 11, 12, -1, -1, -1, -1, -1, -1 },
      {  0,  0,  0,  0,  0,  0,  1,  3,  5,  7, 10, 12, 13, -1, -1, -1, -1, -1, -1 },
      {  0,  0,  0,  0,  1,  2,  2,  9, 13, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },

    // 3/0
    { {  0,  0,  0,  0,  0,  0,  0,  0,  2,  2,  6,  9, 11, 12, 13, -1, -1, -1, -1 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  2,  2,  6,  9, 11, 12, 13, -1, -1, -1, -1 },
      { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },

    // 2/1 - untested
    { {  0,  0,  0,  0,  0,  0,  0,  0,  2,  2,  6,  9, 11, 12, 13, -1, -1, -1, -1 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  2,  2,  6,  9, 11, 12, 13, -1, -1, -1, -1 },
      { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },

    // 3/1
    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  3,  2, 10, 11, 11, 12, 12, 14, -1 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  3,  2, 10, 11, 11, 12, 12, 14, -1 },
      { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },

    // 2/2 - untested
    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  3,  2, 10, 11, 11, 12, 12, 14, -1 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  3,  2, 10, 11, 11, 12, 12, 14, -1 },
      { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },

    // 3/2
    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  1,  6,  8, 11, 12, 12, -1, -1 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  1,  6,  8, 11, 12, 12, -1, -1 },
      { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },
};


/**
 * Adjust the frame size to make the average bit rate match the target bit rate.
 * This is only needed for 11025, 22050, and 44100 sample rates or any E-AC-3.
 */
static void adjust_frame_size(AC3EncodeContext *s)
{
    while (s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {
        s->bits_written    -= s->bit_rate;
        s->samples_written -= s->sample_rate;
    }
    s->frame_size = s->frame_size_min +
                    2 * (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);
    s->bits_written    += s->frame_size * 8;
    s->samples_written += AC3_FRAME_SIZE;
}


/**
 * Deinterleave input samples.
 * Channels are reordered from Libav's default order to AC-3 order.
 */
static void deinterleave_input_samples(AC3EncodeContext *s,
                                       const SampleType *samples)
{
    int ch, i;

    /* deinterleave and remap input samples */
    for (ch = 0; ch < s->channels; ch++) {
        const SampleType *sptr;
        int sinc;

        /* copy last 256 samples of previous frame to the start of the current frame */
        memcpy(&s->planar_samples[ch][0], &s->planar_samples[ch][AC3_FRAME_SIZE],
               AC3_BLOCK_SIZE * sizeof(s->planar_samples[0][0]));

        /* deinterleave */
        sinc = s->channels;
        sptr = samples + s->channel_map[ch];
        for (i = AC3_BLOCK_SIZE; i < AC3_FRAME_SIZE+AC3_BLOCK_SIZE; i++) {
            s->planar_samples[ch][i] = *sptr;
            sptr += sinc;
        }
    }
}


/**
 * Apply the MDCT to input samples to generate frequency coefficients.
 * This applies the KBD window and normalizes the input to reduce precision
 * loss due to fixed-point calculations.
 */
static void apply_mdct(AC3EncodeContext *s)
{
    int blk, ch;

    for (ch = 0; ch < s->channels; ch++) {
        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
            AC3Block *block = &s->blocks[blk];
            const SampleType *input_samples = &s->planar_samples[ch][blk * AC3_BLOCK_SIZE];

            apply_window(&s->dsp, s->windowed_samples, input_samples, s->mdct.window, AC3_WINDOW_SIZE);

            block->coeff_shift[ch+1] = normalize_samples(s);

            s->mdct.fft.mdct_calcw(&s->mdct.fft, block->mdct_coef[ch+1],
                                   s->windowed_samples);
        }
    }
}


static void compute_coupling_strategy(AC3EncodeContext *s)
{
    int blk, ch;
    int got_cpl_snr;

    /* set coupling use flags for each block/channel */
    /* TODO: turn coupling on/off and adjust start band based on bit usage */
    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
        AC3Block *block = &s->blocks[blk];
        for (ch = 1; ch <= s->fbw_channels; ch++)
            block->channel_in_cpl[ch] = s->cpl_on;
    }

    /* enable coupling for each block if at least 2 channels have coupling
       enabled for that block */
    got_cpl_snr = 0;
    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
        AC3Block *block = &s->blocks[blk];
        block->num_cpl_channels = 0;
        for (ch = 1; ch <= s->fbw_channels; ch++)
            block->num_cpl_channels += block->channel_in_cpl[ch];
        block->cpl_in_use = block->num_cpl_channels > 1;
        if (!block->cpl_in_use) {
            block->num_cpl_channels = 0;
            for (ch = 1; ch <= s->fbw_channels; ch++)
                block->channel_in_cpl[ch] = 0;
        }

        block->new_cpl_strategy = !blk;
        if (blk) {
            for (ch = 1; ch <= s->fbw_channels; ch++) {
                if (block->channel_in_cpl[ch] != s->blocks[blk-1].channel_in_cpl[ch]) {
                    block->new_cpl_strategy = 1;
                    break;
                }
            }
        }
        block->new_cpl_leak = block->new_cpl_strategy;

        if (!blk || (block->cpl_in_use && !got_cpl_snr)) {
            block->new_snr_offsets = 1;
            if (block->cpl_in_use)
                got_cpl_snr = 1;
        } else {
            block->new_snr_offsets = 0;
        }
    }

    /* set bandwidth for each channel */
    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
        AC3Block *block = &s->blocks[blk];
        for (ch = 1; ch <= s->fbw_channels; ch++) {
            if (block->channel_in_cpl[ch])
                block->end_freq[ch] = s->start_freq[CPL_CH];
            else
                block->end_freq[ch] = s->bandwidth_code * 3 + 73;
        }
    }
}


/**
 * Calculate a single coupling coordinate.
 */
static inline float calc_cpl_coord(float energy_ch, float energy_cpl)
{
    float coord = 0.125;
    if (energy_cpl > 0)
        coord *= sqrtf(energy_ch / energy_cpl);
    return coord;
}


/**
 * Calculate coupling channel and coupling coordinates.
 * TODO: Currently this is only used for the floating-point encoder. I was
 *       able to make it work for the fixed-point encoder, but quality was
 *       generally lower in most cases than not using coupling. If a more
 *       adaptive coupling strategy were to be implemented it might be useful
 *       at that time to use coupling for the fixed-point encoder as well.
 */
static void apply_channel_coupling(AC3EncodeContext *s)
{
#if CONFIG_AC3ENC_FLOAT
    DECLARE_ALIGNED(16, float,   cpl_coords)      [AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][16] = {{{0}}};
    DECLARE_ALIGNED(16, int32_t, fixed_cpl_coords)[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][16] = {{{0}}};
    int blk, ch, bnd, i, j;
    CoefSumType energy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][16] = {{{0}}};
    int num_cpl_coefs = s->num_cpl_subbands * 12;

    /* calculate coupling channel from fbw channels */
    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
        AC3Block *block = &s->blocks[blk];
        CoefType *cpl_coef = &block->mdct_coef[CPL_CH][s->start_freq[CPL_CH]];
        if (!block->cpl_in_use)
            continue;
        memset(cpl_coef-1, 0, (num_cpl_coefs+4) * sizeof(*cpl_coef));
        for (ch = 1; ch <= s->fbw_channels; ch++) {
            CoefType *ch_coef = &block->mdct_coef[ch][s->start_freq[CPL_CH]];
            if (!block->channel_in_cpl[ch])
                continue;
            for (i = 0; i < num_cpl_coefs; i++)
                cpl_coef[i] += ch_coef[i];
        }
        /* note: coupling start bin % 4 will always be 1 and num_cpl_coefs
                 will always be a multiple of 12, so we need to subtract 1 from
                 the start and add 4 to the length when using optimized
                 functions which require 16-byte alignment. */

        /* coefficients must be clipped to +/- 1.0 in order to be encoded */
        s->dsp.vector_clipf(cpl_coef-1, cpl_coef-1, -1.0f, 1.0f, num_cpl_coefs+4);

        /* scale coupling coefficients from float to 24-bit fixed-point */
        s->ac3dsp.float_to_fixed24(&block->fixed_coef[CPL_CH][s->start_freq[CPL_CH]-1],
                                   cpl_coef-1, num_cpl_coefs+4);
    }

    /* calculate energy in each band in coupling channel and each fbw channel */
    /* TODO: possibly use SIMD to speed up energy calculation */
    bnd = 0;
    i = s->start_freq[CPL_CH];
    while (i < s->cpl_end_freq) {
        int band_size = s->cpl_band_sizes[bnd];
        for (ch = CPL_CH; ch <= s->fbw_channels; ch++) {
            for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
                AC3Block *block = &s->blocks[blk];
                if (!block->cpl_in_use || (ch > CPL_CH && !block->channel_in_cpl[ch]))
                    continue;
                for (j = 0; j < band_size; j++) {
                    CoefType v = block->mdct_coef[ch][i+j];
                    MAC_COEF(energy[blk][ch][bnd], v, v);
                }
            }
        }
        i += band_size;
        bnd++;
    }

    /* determine which blocks to send new coupling coordinates for */
    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
        AC3Block *block  = &s->blocks[blk];
        AC3Block *block0 = blk ? &s->blocks[blk-1] : NULL;
        int new_coords = 0;
        CoefSumType coord_diff[AC3_MAX_CHANNELS] = {0,};

        if (block->cpl_in_use) {
            /* calculate coupling coordinates for all blocks and calculate the
               average difference between coordinates in successive blocks */
            for (ch = 1; ch <= s->fbw_channels; ch++) {
                if (!block->channel_in_cpl[ch])
                    continue;

                for (bnd = 0; bnd < s->num_cpl_bands; bnd++) {
                    cpl_coords[blk][ch][bnd] = calc_cpl_coord(energy[blk][ch][bnd],
                                                              energy[blk][CPL_CH][bnd]);
                    if (blk > 0 && block0->cpl_in_use &&
                        block0->channel_in_cpl[ch]) {
                        coord_diff[ch] += fabs(cpl_coords[blk-1][ch][bnd] -
                                               cpl_coords[blk  ][ch][bnd]);
                    }
                }
                coord_diff[ch] /= s->num_cpl_bands;
            }

            /* send new coordinates if this is the first block, if previous
             * block did not use coupling but this block does, the channels
             * using coupling has changed from the previous block, or the
             * coordinate difference from the last block for any channel is
             * greater than a threshold value. */
            if (blk == 0) {
                new_coords = 1;
            } else if (!block0->cpl_in_use) {
                new_coords = 1;
            } else {
                for (ch = 1; ch <= s->fbw_channels; ch++) {
                    if (block->channel_in_cpl[ch] && !block0->channel_in_cpl[ch]) {
                        new_coords = 1;
                        break;
                    }
                }
                if (!new_coords) {
                    for (ch = 1; ch <= s->fbw_channels; ch++) {
                        if (block->channel_in_cpl[ch] && coord_diff[ch] > 0.04) {
                            new_coords = 1;
                            break;
                        }
                    }
                }
            }
        }
        block->new_cpl_coords = new_coords;
    }

    /* calculate final coupling coordinates, taking into account reusing of
       coordinates in successive blocks */
    for (bnd = 0; bnd < s->num_cpl_bands; bnd++) {
        blk = 0;
        while (blk < AC3_MAX_BLOCKS) {
            int blk1;
            CoefSumType energy_cpl;
            AC3Block *block  = &s->blocks[blk];

            if (!block->cpl_in_use) {
                blk++;
                continue;
            }

            energy_cpl = energy[blk][CPL_CH][bnd];
            blk1 = blk+1;
            while (!s->blocks[blk1].new_cpl_coords && blk1 < AC3_MAX_BLOCKS) {
                if (s->blocks[blk1].cpl_in_use)
                    energy_cpl += energy[blk1][CPL_CH][bnd];
                blk1++;
            }

            for (ch = 1; ch <= s->fbw_channels; ch++) {
                CoefType energy_ch;
                if (!block->channel_in_cpl[ch])
                    continue;
                energy_ch = energy[blk][ch][bnd];
                blk1 = blk+1;
                while (!s->blocks[blk1].new_cpl_coords && blk1 < AC3_MAX_BLOCKS) {
                    if (s->blocks[blk1].cpl_in_use)
                        energy_ch += energy[blk1][ch][bnd];
                    blk1++;
                }
                cpl_coords[blk][ch][bnd] = calc_cpl_coord(energy_ch, energy_cpl);
            }
            blk = blk1;
        }
    }

    /* calculate exponents/mantissas for coupling coordinates */
    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
        AC3Block *block = &s->blocks[blk];
        if (!block->cpl_in_use || !block->new_cpl_coords)
            continue;

        s->ac3dsp.float_to_fixed24(fixed_cpl_coords[blk][1],
                                   cpl_coords[blk][1],
                                   s->fbw_channels * 16);
        s->ac3dsp.extract_exponents(block->cpl_coord_exp[1],
                                    fixed_cpl_coords[blk][1],
                                    s->fbw_channels * 16);

        for (ch = 1; ch <= s->fbw_channels; ch++) {
            int bnd, min_exp, max_exp, master_exp;

            /* determine master exponent */
            min_exp = max_exp = block->cpl_coord_exp[ch][0];
            for (bnd = 1; bnd < s->num_cpl_bands; bnd++) {
                int exp = block->cpl_coord_exp[ch][bnd];
                min_exp = FFMIN(exp, min_exp);
                max_exp = FFMAX(exp, max_exp);
            }
            master_exp = ((max_exp - 15) + 2) / 3;
            master_exp = FFMAX(master_exp, 0);
            while (min_exp < master_exp * 3)
                master_exp--;
            for (bnd = 0; bnd < s->num_cpl_bands; bnd++) {
                block->cpl_coord_exp[ch][bnd] = av_clip(block->cpl_coord_exp[ch][bnd] -
                                                        master_exp * 3, 0, 15);
            }
            block->cpl_master_exp[ch] = master_exp;

            /* quantize mantissas */
            for (bnd = 0; bnd < s->num_cpl_bands; bnd++) {
                int cpl_exp  = block->cpl_coord_exp[ch][bnd];
                int cpl_mant = (fixed_cpl_coords[blk][ch][bnd] << (5 + cpl_exp + master_exp * 3)) >> 24;
                if (cpl_exp == 15)
                    cpl_mant >>= 1;
                else
                    cpl_mant -= 16;

                block->cpl_coord_mant[ch][bnd] = cpl_mant;
            }
        }
    }

    if (s->eac3) {
        /* set first cpl coords */
        int first_cpl_coords[AC3_MAX_CHANNELS];
        for (ch = 1; ch <= s->fbw_channels; ch++)
            first_cpl_coords[ch] = 1;
        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
            AC3Block *block = &s->blocks[blk];
            for (ch = 1; ch <= s->fbw_channels; ch++) {
                if (block->channel_in_cpl[ch]) {
                    if (first_cpl_coords[ch]) {
                        block->new_cpl_coords = 2;
                        first_cpl_coords[ch]  = 0;
                    }
                } else {
                    first_cpl_coords[ch] = 1;
                }
            }
        }

        /* set first cpl leak */
        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
            AC3Block *block = &s->blocks[blk];
            if (block->cpl_in_use) {
                block->new_cpl_leak = 2;
                break;
            }
        }
    }
#endif /* CONFIG_AC3ENC_FLOAT */
}


/**
 * Determine rematrixing flags for each block and band.
 */
static void compute_rematrixing_strategy(AC3EncodeContext *s)
{
    int nb_coefs;
    int blk, bnd, i;
    AC3Block *block, *block0;

    if (s->channel_mode != AC3_CHMODE_STEREO)
        return;

    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
        block = &s->blocks[blk];
        block->new_rematrixing_strategy = !blk;

        if (!s->rematrixing_enabled) {
            block0 = block;
            continue;
        }

        block->num_rematrixing_bands = 4;
        if (block->cpl_in_use) {
            block->num_rematrixing_bands -= (s->start_freq[CPL_CH] <= 61);
            block->num_rematrixing_bands -= (s->start_freq[CPL_CH] == 37);
            if (blk && block->num_rematrixing_bands != block0->num_rematrixing_bands)
                block->new_rematrixing_strategy = 1;
        }
        nb_coefs = FFMIN(block->end_freq[1], block->end_freq[2]);

        for (bnd = 0; bnd < block->num_rematrixing_bands; bnd++) {
            /* calculate calculate sum of squared coeffs for one band in one block */
            int start = ff_ac3_rematrix_band_tab[bnd];
            int end   = FFMIN(nb_coefs, ff_ac3_rematrix_band_tab[bnd+1]);
            CoefSumType sum[4] = {0,};
            for (i = start; i < end; i++) {
                CoefType lt = block->mdct_coef[1][i];
                CoefType rt = block->mdct_coef[2][i];
                CoefType md = lt + rt;
                CoefType sd = lt - rt;
                MAC_COEF(sum[0], lt, lt);
                MAC_COEF(sum[1], rt, rt);
                MAC_COEF(sum[2], md, md);
                MAC_COEF(sum[3], sd, sd);
            }

            /* compare sums to determine if rematrixing will be used for this band */
            if (FFMIN(sum[2], sum[3]) < FFMIN(sum[0], sum[1]))
                block->rematrixing_flags[bnd] = 1;
            else
                block->rematrixing_flags[bnd] = 0;

            /* determine if new rematrixing flags will be sent */
            if (blk &&
                block->rematrixing_flags[bnd] != block0->rematrixing_flags[bnd]) {
                block->new_rematrixing_strategy = 1;
            }
        }
        block0 = block;
    }
}


/**
 * Apply stereo rematrixing to coefficients based on rematrixing flags.
 */
static void apply_rematrixing(AC3EncodeContext *s)
{
    int nb_coefs;
    int blk, bnd, i;
    int start, end;
    uint8_t *flags;

    if (!s->rematrixing_enabled)
        return;

    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
        AC3Block *block = &s->blocks[blk];
        if (block->new_rematrixing_strategy)
            flags = block->rematrixing_flags;
        nb_coefs = FFMIN(block->end_freq[1], block->end_freq[2]);
        for (bnd = 0; bnd < block->num_rematrixing_bands; bnd++) {
            if (flags[bnd]) {
                start = ff_ac3_rematrix_band_tab[bnd];
                end   = FFMIN(nb_coefs, ff_ac3_rematrix_band_tab[bnd+1]);
                for (i = start; i < end; i++) {
                    int32_t lt = block->fixed_coef[1][i];
                    int32_t rt = block->fixed_coef[2][i];
                    block->fixed_coef[1][i] = (lt + rt) >> 1;
                    block->fixed_coef[2][i] = (lt - rt) >> 1;
                }
            }
        }
    }
}


/**
 * Initialize exponent tables.
 */
static av_cold void exponent_init(AC3EncodeContext *s)
{
    int expstr, i, grpsize;

    for (expstr = EXP_D15-1; expstr <= EXP_D45-1; expstr++) {
        grpsize = 3 << expstr;
        for (i = 12; i < 256; i++) {
            exponent_group_tab[0][expstr][i] = (i + grpsize - 4) / grpsize;
            exponent_group_tab[1][expstr][i] = (i              ) / grpsize;
        }
    }
    /* LFE */
    exponent_group_tab[0][0][7] = 2;
}


/**
 * Extract exponents from the MDCT coefficients.
 * This takes into account the normalization that was done to the input samples
 * by adjusting the exponents by the exponent shift values.
 */
static void extract_exponents(AC3EncodeContext *s)
{
    int blk, ch;

    for (ch = !s->cpl_on; ch <= s->channels; ch++) {
        for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
            AC3Block *block = &s->blocks[blk];
            s->ac3dsp.extract_exponents(block->exp[ch], block->fixed_coef[ch],
                                        AC3_MAX_COEFS);
        }
    }
}


/**
 * Exponent Difference Threshold.
 * New exponents are sent if their SAD exceed this number.
 */
#define EXP_DIFF_THRESHOLD 500


/**
 * Calculate exponent strategies for all channels.
 * Array arrangement is reversed to simplify the per-channel calculation.
 */
static void compute_exp_strategy(AC3EncodeContext *s)
{
    int ch, blk, blk1;

    for (ch = !s->cpl_on; ch <= s->fbw_channels; ch++) {
        uint8_t *exp_strategy = s->exp_strategy[ch];
        uint8_t *exp          = s->blocks[0].exp[ch];
        int exp_diff;

        /* estimate if the exponent variation & decide if they should be
           reused in the next frame */
        exp_strategy[0] = EXP_NEW;
        exp += AC3_MAX_COEFS;
        for (blk = 1; blk < AC3_MAX_BLOCKS; blk++, exp += AC3_MAX_COEFS) {
            if ((ch == CPL_CH && (!s->blocks[blk].cpl_in_use || !s->blocks[blk-1].cpl_in_use)) ||
                (ch  > CPL_CH && (s->blocks[blk].channel_in_cpl[ch] != s->blocks[blk-1].channel_in_cpl[ch]))) {
                exp_strategy[blk] = EXP_NEW;
                continue;
            }
            exp_diff = s->dsp.sad[0](NULL, exp, exp - AC3_MAX_COEFS, 16, 16);
            exp_strategy[blk] = EXP_REUSE;
            if (ch == CPL_CH && exp_diff > (EXP_DIFF_THRESHOLD * (s->blocks[blk].end_freq[ch] - s->start_freq[ch]) / AC3_MAX_COEFS))
                exp_strategy[blk] = EXP_NEW;
            else if (ch > CPL_CH && exp_diff > EXP_DIFF_THRESHOLD)
                exp_strategy[blk] = EXP_NEW;
        }

        /* now select the encoding strategy type : if exponents are often
           recoded, we use a coarse encoding */
        blk = 0;
        while (blk < AC3_MAX_BLOCKS) {
            blk1 = blk + 1;
            while (blk1 < AC3_MAX_BLOCKS && exp_strategy[blk1] == EXP_REUSE)
                blk1++;
            switch (blk1 - blk) {
            case 1:  exp_strategy[blk] = EXP_D45; break;
            case 2:
            case 3:  exp_strategy[blk] = EXP_D25; break;
            default: exp_strategy[blk] = EXP_D15; break;
            }
            blk = blk1;
        }
    }
    if (s->lfe_on) {
        ch = s->lfe_channel;
        s->exp_strategy[ch][0] = EXP_D15;
        for (blk = 1; blk < AC3_MAX_BLOCKS; blk++)
            s->exp_strategy[ch][blk] = EXP_REUSE;
    }
}


/**
 * Update the exponents so that they are the ones the decoder will decode.
 */
static void encode_exponents_blk_ch(uint8_t *exp, int nb_exps, int exp_strategy,
                                    int cpl)
{
    int nb_groups, i, k;

    nb_groups = exponent_group_tab[cpl][exp_strategy-1][nb_exps] * 3;

    /* for each group, compute the minimum exponent */
    switch(exp_strategy) {
    case EXP_D25:
        for (i = 1, k = 1-cpl; i <= nb_groups; i++) {
            uint8_t exp_min = exp[k];
            if (exp[k+1] < exp_min)
                exp_min = exp[k+1];
            exp[i-cpl] = exp_min;
            k += 2;
        }
        break;
    case EXP_D45:
        for (i = 1, k = 1-cpl; i <= nb_groups; i++) {
            uint8_t exp_min = exp[k];
            if (exp[k+1] < exp_min)
                exp_min = exp[k+1];
            if (exp[k+2] < exp_min)