/*
  * AAC encoder psychoacoustic model
  * Copyright (C) 2008 Konstantin Shishkov
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg 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.
  *
  * FFmpeg 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 FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 /**

  * @file

  * AAC encoder psychoacoustic model
  */
 
 #include "avcodec.h"
 #include "aactab.h"

 #include "psymodel.h"

 
 /***********************************
  *              TODOs:
  * try other bitrate controlling mechanism (maybe use ratecontrol.c?)
  * control quality for quality-based output
  **********************************/
 
 /**
  * constants for 3GPP AAC psychoacoustic model
  * @{
  */

 #define PSY_3GPP_THR_SPREAD_HI   1.5f // spreading factor for low-to-hi threshold spreading  (15 dB/Bark)
 #define PSY_3GPP_THR_SPREAD_LOW  3.0f // spreading factor for hi-to-low threshold spreading  (30 dB/Bark)

 /* spreading factor for low-to-hi energy spreading, long block, > 22kbps/channel (20dB/Bark) */
 #define PSY_3GPP_EN_SPREAD_HI_L1 2.0f
 /* spreading factor for low-to-hi energy spreading, long block, <= 22kbps/channel (15dB/Bark) */
 #define PSY_3GPP_EN_SPREAD_HI_L2 1.5f
 /* spreading factor for low-to-hi energy spreading, short block (15 dB/Bark) */
 #define PSY_3GPP_EN_SPREAD_HI_S  1.5f
 /* spreading factor for hi-to-low energy spreading, long block (30dB/Bark) */
 #define PSY_3GPP_EN_SPREAD_LOW_L 3.0f
 /* spreading factor for hi-to-low energy spreading, short block (20dB/Bark) */
 #define PSY_3GPP_EN_SPREAD_LOW_S 2.0f

 
 #define PSY_3GPP_RPEMIN      0.01f
 #define PSY_3GPP_RPELEV      2.0f

 #define PSY_3GPP_C1          3.0f           /* log2(8) */
 #define PSY_3GPP_C2          1.3219281f     /* log2(2.5) */
 #define PSY_3GPP_C3          0.55935729f    /* 1 - C2 / C1 */
 
 #define PSY_SNR_1DB          7.9432821e-1f  /* -1dB */
 #define PSY_SNR_25DB         3.1622776e-3f  /* -25dB */
 
 #define PSY_3GPP_SAVE_SLOPE_L  -0.46666667f
 #define PSY_3GPP_SAVE_SLOPE_S  -0.36363637f
 #define PSY_3GPP_SAVE_ADD_L    -0.84285712f
 #define PSY_3GPP_SAVE_ADD_S    -0.75f
 #define PSY_3GPP_SPEND_SLOPE_L  0.66666669f
 #define PSY_3GPP_SPEND_SLOPE_S  0.81818181f
 #define PSY_3GPP_SPEND_ADD_L   -0.35f
 #define PSY_3GPP_SPEND_ADD_S   -0.26111111f
 #define PSY_3GPP_CLIP_LO_L      0.2f
 #define PSY_3GPP_CLIP_LO_S      0.2f
 #define PSY_3GPP_CLIP_HI_L      0.95f
 #define PSY_3GPP_CLIP_HI_S      0.75f
 
 #define PSY_3GPP_AH_THR_LONG    0.5f
 #define PSY_3GPP_AH_THR_SHORT   0.63f
 
 enum {
     PSY_3GPP_AH_NONE,
     PSY_3GPP_AH_INACTIVE,
     PSY_3GPP_AH_ACTIVE
 };
 
 #define PSY_3GPP_BITS_TO_PE(bits) ((bits) * 1.18f)
 

 /* LAME psy model constants */
 #define PSY_LAME_FIR_LEN 21         ///< LAME psy model FIR order
 #define AAC_BLOCK_SIZE_LONG 1024    ///< long block size
 #define AAC_BLOCK_SIZE_SHORT 128    ///< short block size
 #define AAC_NUM_BLOCKS_SHORT 8      ///< number of blocks in a short sequence
 #define PSY_LAME_NUM_SUBBLOCKS 3    ///< Number of sub-blocks in each short block
 

 /**
  * @}
  */
 
 /**
  * information for single band used by 3GPP TS26.403-inspired psychoacoustic model
  */

 typedef struct AacPsyBand{

     float energy;       ///< band energy
     float thr;          ///< energy threshold
     float thr_quiet;    ///< threshold in quiet

     float nz_lines;     ///< number of non-zero spectral lines
     float active_lines; ///< number of active spectral lines
     float pe;           ///< perceptual entropy
     float pe_const;     ///< constant part of the PE calculation
     float norm_fac;     ///< normalization factor for linearization
     int   avoid_holes;  ///< hole avoidance flag

 }AacPsyBand;

 
 /**

  * single/pair channel context for psychoacoustic model
  */

 typedef struct AacPsyChannel{
     AacPsyBand band[128];               ///< bands information
     AacPsyBand prev_band[128];          ///< bands information from the previous frame

 
     float       win_energy;              ///< sliding average of channel energy
     float       iir_state[2];            ///< hi-pass IIR filter state
     uint8_t     next_grouping;           ///< stored grouping scheme for the next frame (in case of 8 short window sequence)
     enum WindowSequence next_window_seq; ///< window sequence to be used in the next frame

     /* LAME psy model specific members */
     float attack_threshold;              ///< attack threshold for this channel
     float prev_energy_subshort[AAC_NUM_BLOCKS_SHORT * PSY_LAME_NUM_SUBBLOCKS];
     int   prev_attack;                   ///< attack value for the last short block in the previous sequence

 }AacPsyChannel;

 
 /**

  * psychoacoustic model frame type-dependent coefficients
  */

 typedef struct AacPsyCoeffs{

     float ath;           ///< absolute threshold of hearing per bands
     float barks;         ///< Bark value for each spectral band in long frame
     float spread_low[2]; ///< spreading factor for low-to-high threshold spreading in long frame
     float spread_hi [2]; ///< spreading factor for high-to-low threshold spreading in long frame
     float min_snr;       ///< minimal SNR

 }AacPsyCoeffs;

 
 /**

  * 3GPP TS26.403-inspired psychoacoustic model specific data
  */

 typedef struct AacPsyContext{

     int chan_bitrate;     ///< bitrate per channel
     int frame_bits;       ///< average bits per frame
     int fill_level;       ///< bit reservoir fill level
     struct {
         float min;        ///< minimum allowed PE for bit factor calculation
         float max;        ///< maximum allowed PE for bit factor calculation
         float previous;   ///< allowed PE of the previous frame
         float correction; ///< PE correction factor
     } pe;

     AacPsyCoeffs psy_coef[2][64];

     AacPsyChannel *ch;
 }AacPsyContext;

 
 /**

  * LAME psy model preset struct
  */
 typedef struct {
     int   quality;  ///< Quality to map the rest of the vaules to.
      /* This is overloaded to be both kbps per channel in ABR mode, and
       * requested quality in constant quality mode.
       */
     float st_lrm;   ///< short threshold for L, R, and M channels
 } PsyLamePreset;
 
 /**
  * LAME psy model preset table for ABR
  */
 static const PsyLamePreset psy_abr_map[] = {
 /* TODO: Tuning. These were taken from LAME. */
 /* kbps/ch st_lrm   */
     {  8,  6.60},
     { 16,  6.60},
     { 24,  6.60},
     { 32,  6.60},
     { 40,  6.60},
     { 48,  6.60},
     { 56,  6.60},
     { 64,  6.40},
     { 80,  6.00},
     { 96,  5.60},
     {112,  5.20},
     {128,  5.20},
     {160,  5.20}
 };
 
 /**
 * LAME psy model preset table for constant quality
 */
 static const PsyLamePreset psy_vbr_map[] = {
 /* vbr_q  st_lrm    */
     { 0,  4.20},
     { 1,  4.20},
     { 2,  4.20},
     { 3,  4.20},
     { 4,  4.20},
     { 5,  4.20},
     { 6,  4.20},
     { 7,  4.20},
     { 8,  4.20},
     { 9,  4.20},
     {10,  4.20}
 };
 
 /**
  * LAME psy model FIR coefficient table
  */
 static const float psy_fir_coeffs[] = {
     -8.65163e-18 * 2, -0.00851586 * 2, -6.74764e-18 * 2, 0.0209036 * 2,
     -3.36639e-17 * 2, -0.0438162 * 2,  -1.54175e-17 * 2, 0.0931738 * 2,
     -5.52212e-17 * 2, -0.313819 * 2
 };
 
 /**
  * calculates the attack threshold for ABR from the above table for the LAME psy model
  */
 static float lame_calc_attack_threshold(int bitrate)
 {
     /* Assume max bitrate to start with */
     int lower_range = 12, upper_range = 12;
     int lower_range_kbps = psy_abr_map[12].quality;
     int upper_range_kbps = psy_abr_map[12].quality;
     int i;
 
     /* Determine which bitrates the value specified falls between.
      * If the loop ends without breaking our above assumption of 320kbps was correct.
      */
     for (i = 1; i < 13; i++) {
         if (FFMAX(bitrate, psy_abr_map[i].quality) != bitrate) {
             upper_range = i;
             upper_range_kbps = psy_abr_map[i    ].quality;
             lower_range = i - 1;
             lower_range_kbps = psy_abr_map[i - 1].quality;
             break; /* Upper range found */
         }
     }
 
     /* Determine which range the value specified is closer to */
     if ((upper_range_kbps - bitrate) > (bitrate - lower_range_kbps))
         return psy_abr_map[lower_range].st_lrm;
     return psy_abr_map[upper_range].st_lrm;
 }
 
 /**
  * LAME psy model specific initialization
  */
 static void lame_window_init(AacPsyContext *ctx, AVCodecContext *avctx) {

     int i, j;

 
     for (i = 0; i < avctx->channels; i++) {
         AacPsyChannel *pch = &ctx->ch[i];
 
         if (avctx->flags & CODEC_FLAG_QSCALE)
             pch->attack_threshold = psy_vbr_map[avctx->global_quality / FF_QP2LAMBDA].st_lrm;
         else
             pch->attack_threshold = lame_calc_attack_threshold(avctx->bit_rate / avctx->channels / 1000);
 

         for (j = 0; j < AAC_NUM_BLOCKS_SHORT * PSY_LAME_NUM_SUBBLOCKS; j++)
             pch->prev_energy_subshort[j] = 10.0f;

     }
 }
 
 /**

  * Calculate Bark value for given line.
  */

 static av_cold float calc_bark(float f)

 {
     return 13.3f * atanf(0.00076f * f) + 3.5f * atanf((f / 7500.0f) * (f / 7500.0f));
 }

 
 #define ATH_ADD 4
 /**
  * Calculate ATH value for given frequency.
  * Borrowed from Lame.
  */
 static av_cold float ath(float f, float add)
 {
     f /= 1000.0f;

     return    3.64 * pow(f, -0.8)

             - 6.8  * exp(-0.6  * (f - 3.4) * (f - 3.4))
             + 6.0  * exp(-0.15 * (f - 8.7) * (f - 8.7))
             + (0.6 + 0.04 * add) * 0.001 * f * f * f * f;
 }
 

 static av_cold int psy_3gpp_init(FFPsyContext *ctx) {

     AacPsyContext *pctx;

     float bark;

     int i, j, g, start;

     float prev, minscale, minath, minsnr, pe_min;
     const int chan_bitrate = ctx->avctx->bit_rate / ctx->avctx->channels;
     const int bandwidth    = ctx->avctx->cutoff ? ctx->avctx->cutoff : ctx->avctx->sample_rate / 2;
     const float num_bark   = calc_bark((float)bandwidth);

     ctx->model_priv_data = av_mallocz(sizeof(AacPsyContext));
     pctx = (AacPsyContext*) ctx->model_priv_data;

     pctx->chan_bitrate = chan_bitrate;
     pctx->frame_bits   = chan_bitrate * AAC_BLOCK_SIZE_LONG / ctx->avctx->sample_rate;
     pctx->pe.min       =  8.0f * AAC_BLOCK_SIZE_LONG * bandwidth / (ctx->avctx->sample_rate * 2.0f);
     pctx->pe.max       = 12.0f * AAC_BLOCK_SIZE_LONG * bandwidth / (ctx->avctx->sample_rate * 2.0f);
     ctx->bitres.size   = 6144 - pctx->frame_bits;
     ctx->bitres.size  -= ctx->bitres.size % 8;
     pctx->fill_level   = ctx->bitres.size;

     minath = ath(3410, ATH_ADD);

     for (j = 0; j < 2; j++) {

         AacPsyCoeffs *coeffs = pctx->psy_coef[j];
         const uint8_t *band_sizes = ctx->bands[j];

         float line_to_frequency = ctx->avctx->sample_rate / (j ? 256.f : 2048.0f);

         float avg_chan_bits = chan_bitrate / ctx->avctx->sample_rate * (j ? 128.0f : 1024.0f);
         /* reference encoder uses 2.4% here instead of 60% like the spec says */
         float bark_pe = 0.024f * PSY_3GPP_BITS_TO_PE(avg_chan_bits) / num_bark;
         float en_spread_low = j ? PSY_3GPP_EN_SPREAD_LOW_S : PSY_3GPP_EN_SPREAD_LOW_L;
         /* High energy spreading for long blocks <= 22kbps/channel and short blocks are the same. */
         float en_spread_hi  = (j || (chan_bitrate <= 22.0f)) ? PSY_3GPP_EN_SPREAD_HI_S : PSY_3GPP_EN_SPREAD_HI_L1;
 

         i = 0;
         prev = 0.0;

         for (g = 0; g < ctx->num_bands[j]; g++) {

             i += band_sizes[g];

             bark = calc_bark((i-1) * line_to_frequency);

             coeffs[g].barks = (bark + prev) / 2.0;

             prev = bark;

         }

         for (g = 0; g < ctx->num_bands[j] - 1; g++) {

             AacPsyCoeffs *coeff = &coeffs[g];
             float bark_width = coeffs[g+1].barks - coeffs->barks;

             coeff->spread_low[0] = pow(10.0, -bark_width * PSY_3GPP_THR_SPREAD_LOW);
             coeff->spread_hi [0] = pow(10.0, -bark_width * PSY_3GPP_THR_SPREAD_HI);

             coeff->spread_low[1] = pow(10.0, -bark_width * en_spread_low);
             coeff->spread_hi [1] = pow(10.0, -bark_width * en_spread_hi);
             pe_min = bark_pe * bark_width;
             minsnr = pow(2.0f, pe_min / band_sizes[g]) - 1.5f;
             coeff->min_snr = av_clipf(1.0f / minsnr, PSY_SNR_25DB, PSY_SNR_1DB);

         }
         start = 0;

         for (g = 0; g < ctx->num_bands[j]; g++) {

             minscale = ath(start * line_to_frequency, ATH_ADD);

             for (i = 1; i < band_sizes[g]; i++)

                 minscale = FFMIN(minscale, ath((start + i) * line_to_frequency, ATH_ADD));

             coeffs[g].ath = minscale - minath;
             start += band_sizes[g];

         }
     }
 

     pctx->ch = av_mallocz(sizeof(AacPsyChannel) * ctx->avctx->channels);

 
     lame_window_init(pctx, ctx->avctx);
 

     return 0;
 }
 
 /**
  * IIR filter used in block switching decision
  */
 static float iir_filter(int in, float state[2])
 {
     float ret;
 
     ret = 0.7548f * (in - state[0]) + 0.5095f * state[1];
     state[0] = in;
     state[1] = ret;
     return ret;
 }
 
 /**
  * window grouping information stored as bits (0 - new group, 1 - group continues)
  */
 static const uint8_t window_grouping[9] = {
     0xB6, 0x6C, 0xD8, 0xB2, 0x66, 0xC6, 0x96, 0x36, 0x36
 };
 
 /**
  * Tell encoder which window types to use.
  * @see 3GPP TS26.403 5.4.1 "Blockswitching"
  */
 static FFPsyWindowInfo psy_3gpp_window(FFPsyContext *ctx,
                                        const int16_t *audio, const int16_t *la,
                                        int channel, int prev_type)
 {
     int i, j;

     int br               = ctx->avctx->bit_rate / ctx->avctx->channels;
     int attack_ratio     = br <= 16000 ? 18 : 10;

     AacPsyContext *pctx = (AacPsyContext*) ctx->model_priv_data;
     AacPsyChannel *pch  = &pctx->ch[channel];

     uint8_t grouping     = 0;

     int next_type        = pch->next_window_seq;

     FFPsyWindowInfo wi;
 
     memset(&wi, 0, sizeof(wi));

     if (la) {

         float s[8], v;
         int switch_to_eight = 0;
         float sum = 0.0, sum2 = 0.0;
         int attack_n = 0;

         int stay_short = 0;

         for (i = 0; i < 8; i++) {
             for (j = 0; j < 128; j++) {

                 v = iir_filter(la[(i*128+j)*ctx->avctx->channels], pch->iir_state);

                 sum += v*v;
             }

             s[i]  = sum;

             sum2 += sum;
         }

         for (i = 0; i < 8; i++) {
             if (s[i] > pch->win_energy * attack_ratio) {

                 attack_n        = i + 1;

                 switch_to_eight = 1;
                 break;
             }
         }
         pch->win_energy = pch->win_energy*7/8 + sum2/64;
 
         wi.window_type[1] = prev_type;

         switch (prev_type) {

         case ONLY_LONG_SEQUENCE:
             wi.window_type[0] = switch_to_eight ? LONG_START_SEQUENCE : ONLY_LONG_SEQUENCE;

             next_type = switch_to_eight ? EIGHT_SHORT_SEQUENCE : ONLY_LONG_SEQUENCE;

             break;
         case LONG_START_SEQUENCE:
             wi.window_type[0] = EIGHT_SHORT_SEQUENCE;
             grouping = pch->next_grouping;

             next_type = switch_to_eight ? EIGHT_SHORT_SEQUENCE : LONG_STOP_SEQUENCE;

             break;
         case LONG_STOP_SEQUENCE:

             wi.window_type[0] = switch_to_eight ? LONG_START_SEQUENCE : ONLY_LONG_SEQUENCE;
             next_type = switch_to_eight ? EIGHT_SHORT_SEQUENCE : ONLY_LONG_SEQUENCE;

             break;
         case EIGHT_SHORT_SEQUENCE:

             stay_short = next_type == EIGHT_SHORT_SEQUENCE || switch_to_eight;
             wi.window_type[0] = stay_short ? EIGHT_SHORT_SEQUENCE : LONG_STOP_SEQUENCE;
             grouping = next_type == EIGHT_SHORT_SEQUENCE ? pch->next_grouping : 0;
             next_type = switch_to_eight ? EIGHT_SHORT_SEQUENCE : LONG_STOP_SEQUENCE;

             break;
         }

         pch->next_grouping = window_grouping[attack_n];

         pch->next_window_seq = next_type;

     } else {
         for (i = 0; i < 3; i++)

             wi.window_type[i] = prev_type;
         grouping = (prev_type == EIGHT_SHORT_SEQUENCE) ? window_grouping[0] : 0;
     }
 
     wi.window_shape   = 1;

     if (wi.window_type[0] != EIGHT_SHORT_SEQUENCE) {

         wi.num_windows = 1;
         wi.grouping[0] = 1;

     } else {

         int lastgrp = 0;
         wi.num_windows = 8;

         for (i = 0; i < 8; i++) {
             if (!((grouping >> i) & 1))

                 lastgrp = i;
             wi.grouping[lastgrp]++;
         }
     }
 
     return wi;
 }
 

 /* 5.6.1.2 "Calculation of Bit Demand" */
 static int calc_bit_demand(AacPsyContext *ctx, float pe, int bits, int size,
                            int short_window)
 {
     const float bitsave_slope  = short_window ? PSY_3GPP_SAVE_SLOPE_S  : PSY_3GPP_SAVE_SLOPE_L;
     const float bitsave_add    = short_window ? PSY_3GPP_SAVE_ADD_S    : PSY_3GPP_SAVE_ADD_L;
     const float bitspend_slope = short_window ? PSY_3GPP_SPEND_SLOPE_S : PSY_3GPP_SPEND_SLOPE_L;
     const float bitspend_add   = short_window ? PSY_3GPP_SPEND_ADD_S   : PSY_3GPP_SPEND_ADD_L;
     const float clip_low       = short_window ? PSY_3GPP_CLIP_LO_S     : PSY_3GPP_CLIP_LO_L;
     const float clip_high      = short_window ? PSY_3GPP_CLIP_HI_S     : PSY_3GPP_CLIP_HI_L;
     float clipped_pe, bit_save, bit_spend, bit_factor, fill_level;
 
     ctx->fill_level += ctx->frame_bits - bits;
     ctx->fill_level  = av_clip(ctx->fill_level, 0, size);
     fill_level = av_clipf((float)ctx->fill_level / size, clip_low, clip_high);
     clipped_pe = av_clipf(pe, ctx->pe.min, ctx->pe.max);
     bit_save   = (fill_level + bitsave_add) * bitsave_slope;
     assert(bit_save <= 0.3f && bit_save >= -0.05000001f);
     bit_spend  = (fill_level + bitspend_add) * bitspend_slope;
     assert(bit_spend <= 0.5f && bit_spend >= -0.1f);
     /* The bit factor graph in the spec is obviously incorrect.
      *      bit_spend + ((bit_spend - bit_spend))...
      * The reference encoder subtracts everything from 1, but also seems incorrect.
      *      1 - bit_save + ((bit_spend + bit_save))...
      * Hopefully below is correct.
      */
     bit_factor = 1.0f - bit_save + ((bit_spend - bit_save) / (ctx->pe.max - ctx->pe.min)) * (clipped_pe - ctx->pe.min);
     /* NOTE: The reference encoder attempts to center pe max/min around the current pe. */
     ctx->pe.max = FFMAX(pe, ctx->pe.max);
     ctx->pe.min = FFMIN(pe, ctx->pe.min);
 
     return FFMIN(ctx->frame_bits * bit_factor, ctx->frame_bits + size - bits);
 }
 
 static float calc_pe_3gpp(AacPsyBand *band)
 {
     float pe, a;
 
     band->pe           = 0.0f;
     band->pe_const     = 0.0f;
     band->active_lines = 0.0f;
     if (band->energy > band->thr) {
         a  = log2f(band->energy);
         pe = a - log2f(band->thr);
         band->active_lines = band->nz_lines;
         if (pe < PSY_3GPP_C1) {
             pe = pe * PSY_3GPP_C3 + PSY_3GPP_C2;
             a  = a  * PSY_3GPP_C3 + PSY_3GPP_C2;
             band->active_lines *= PSY_3GPP_C3;
         }
         band->pe       = pe * band->nz_lines;
         band->pe_const = a  * band->nz_lines;
     }
 
     return band->pe;
 }
 
 static float calc_reduction_3gpp(float a, float desired_pe, float pe,
                                  float active_lines)
 {
     float thr_avg, reduction;
 
     thr_avg   = powf(2.0f, (a - pe) / (4.0f * active_lines));
     reduction = powf(2.0f, (a - desired_pe) / (4.0f * active_lines)) - thr_avg;
 
     return FFMAX(reduction, 0.0f);
 }
 
 static float calc_reduced_thr_3gpp(AacPsyBand *band, float min_snr,
                                    float reduction)
 {
     float thr = band->thr;
 
     if (band->energy > thr) {
         thr = powf(thr, 0.25f) + reduction;
         thr = powf(thr, 4.0f);
 
         /* This deviates from the 3GPP spec to match the reference encoder.
          * It performs min(thr_reduced, max(thr, energy/min_snr)) only for bands
          * that have hole avoidance on (active or inactive). It always reduces the
          * threshold of bands with hole avoidance off.
          */
         if (thr > band->energy * min_snr && band->avoid_holes != PSY_3GPP_AH_NONE) {
             thr = FFMAX(band->thr, band->energy * min_snr);
             band->avoid_holes = PSY_3GPP_AH_ACTIVE;
         }
     }
 
     return thr;
 }
 

 /**
  * Calculate band thresholds as suggested in 3GPP TS26.403
  */

 static void psy_3gpp_analyze(FFPsyContext *ctx, int channel,

                              const float *coefs, const FFPsyWindowInfo *wi)

 {

     AacPsyContext *pctx = (AacPsyContext*) ctx->model_priv_data;
     AacPsyChannel *pch  = &pctx->ch[channel];

     int start = 0;
     int i, w, g;

     float desired_bits, desired_pe, delta_pe, reduction, spread_en[128] = {0};
     float a = 0.0f, active_lines = 0.0f, norm_fac = 0.0f;
     float pe = pctx->chan_bitrate > 32000 ? 0.0f : FFMAX(50.0f, 100.0f - pctx->chan_bitrate * 100.0f / 32000.0f);

     const int      num_bands   = ctx->num_bands[wi->num_windows == 8];
     const uint8_t *band_sizes  = ctx->bands[wi->num_windows == 8];
     AacPsyCoeffs  *coeffs      = pctx->psy_coef[wi->num_windows == 8];

     const float avoid_hole_thr = wi->num_windows == 8 ? PSY_3GPP_AH_THR_SHORT : PSY_3GPP_AH_THR_LONG;

 
     //calculate energies, initial thresholds and related values - 5.4.2 "Threshold Calculation"

     for (w = 0; w < wi->num_windows*16; w += 16) {
         for (g = 0; g < num_bands; g++) {

             AacPsyBand *band = &pch->band[w+g];

             float form_factor = 0.0f;

             band->energy = 0.0f;

             for (i = 0; i < band_sizes[g]; i++) {

                 band->energy += coefs[start+i] * coefs[start+i];

                 form_factor  += sqrtf(fabs(coefs[start+i]));
             }

             band->thr      = band->energy * 0.001258925f;

             band->nz_lines = form_factor / powf(band->energy / band_sizes[g], 0.25f);
 

             start += band_sizes[g];

         }
     }

     //modify thresholds and energies - spread, threshold in quiet, pre-echo control

     for (w = 0; w < wi->num_windows*16; w += 16) {

         AacPsyBand *bands = &pch->band[w];

         //5.4.2.3 "Spreading" & 5.4.3 "Spreaded Energy Calculation"

         spread_en[0] = bands[0].energy;
         for (g = 1; g < num_bands; g++) {

             bands[g].thr   = FFMAX(bands[g].thr,    bands[g-1].thr * coeffs[g].spread_hi[0]);

             spread_en[w+g] = FFMAX(bands[g].energy, spread_en[w+g-1] * coeffs[g].spread_hi[1]);
         }
         for (g = num_bands - 2; g >= 0; g--) {

             bands[g].thr   = FFMAX(bands[g].thr,   bands[g+1].thr * coeffs[g].spread_low[0]);

             spread_en[w+g] = FFMAX(spread_en[w+g], spread_en[w+g+1] * coeffs[g].spread_low[1]);
         }

         //5.4.2.4 "Threshold in quiet"

         for (g = 0; g < num_bands; g++) {

             AacPsyBand *band = &bands[g];

             band->thr_quiet = band->thr = FFMAX(band->thr, coeffs[g].ath);

             //5.4.2.5 "Pre-echo control"

             if (!(wi->window_type[0] == LONG_STOP_SEQUENCE || (wi->window_type[1] == LONG_START_SEQUENCE && !w)))

                 band->thr = FFMAX(PSY_3GPP_RPEMIN*band->thr, FFMIN(band->thr,
                                   PSY_3GPP_RPELEV*pch->prev_band[w+g].thr_quiet));

 
             /* 5.6.1.3.1 "Prepatory steps of the perceptual entropy calculation" */
             pe += calc_pe_3gpp(band);
             a  += band->pe_const;
             active_lines += band->active_lines;
 
             /* 5.6.1.3.3 "Selection of the bands for avoidance of holes" */
             if (spread_en[w+g] * avoid_hole_thr > band->energy || coeffs[g].min_snr > 1.0f)
                 band->avoid_holes = PSY_3GPP_AH_NONE;
             else
                 band->avoid_holes = PSY_3GPP_AH_INACTIVE;
         }
     }
 
     /* 5.6.1.3.2 "Calculation of the desired perceptual entropy" */
     ctx->pe[channel] = pe;
     desired_bits = calc_bit_demand(pctx, pe, ctx->bitres.bits, ctx->bitres.size, wi->num_windows == 8);
     desired_pe = PSY_3GPP_BITS_TO_PE(desired_bits);
     /* NOTE: PE correction is kept simple. During initial testing it had very
      *       little effect on the final bitrate. Probably a good idea to come
      *       back and do more testing later.
      */
     if (ctx->bitres.bits > 0)
         desired_pe *= av_clipf(pctx->pe.previous / PSY_3GPP_BITS_TO_PE(ctx->bitres.bits),
                                0.85f, 1.15f);
     pctx->pe.previous = PSY_3GPP_BITS_TO_PE(desired_bits);
 
     if (desired_pe < pe) {
         /* 5.6.1.3.4 "First Estimation of the reduction value" */
         for (w = 0; w < wi->num_windows*16; w += 16) {
             reduction = calc_reduction_3gpp(a, desired_pe, pe, active_lines);
             pe = 0.0f;
             a  = 0.0f;
             active_lines = 0.0f;
             for (g = 0; g < num_bands; g++) {
                 AacPsyBand *band = &pch->band[w+g];
 
                 band->thr = calc_reduced_thr_3gpp(band, coeffs[g].min_snr, reduction);
                 /* recalculate PE */
                 pe += calc_pe_3gpp(band);
                 a  += band->pe_const;
                 active_lines += band->active_lines;
             }
         }
 
         /* 5.6.1.3.5 "Second Estimation of the reduction value" */
         for (i = 0; i < 2; i++) {
             float pe_no_ah = 0.0f, desired_pe_no_ah;
             active_lines = a = 0.0f;
             for (w = 0; w < wi->num_windows*16; w += 16) {
                 for (g = 0; g < num_bands; g++) {
                     AacPsyBand *band = &pch->band[w+g];
 
                     if (band->avoid_holes != PSY_3GPP_AH_ACTIVE) {
                         pe_no_ah += band->pe;
                         a        += band->pe_const;
                         active_lines += band->active_lines;
                     }
                 }
             }
             desired_pe_no_ah = FFMAX(desired_pe - (pe - pe_no_ah), 0.0f);
             if (active_lines > 0.0f)
                 reduction += calc_reduction_3gpp(a, desired_pe_no_ah, pe_no_ah, active_lines);
 
             pe = 0.0f;
             for (w = 0; w < wi->num_windows*16; w += 16) {
                 for (g = 0; g < num_bands; g++) {
                     AacPsyBand *band = &pch->band[w+g];
 
                     if (active_lines > 0.0f)
                         band->thr = calc_reduced_thr_3gpp(band, coeffs[g].min_snr, reduction);
                     pe += calc_pe_3gpp(band);
                     band->norm_fac = band->active_lines / band->thr;
                     norm_fac += band->norm_fac;
                 }
             }
             delta_pe = desired_pe - pe;
             if (fabs(delta_pe) > 0.05f * desired_pe)
                 break;
         }
 
         if (pe < 1.15f * desired_pe) {
             /* 6.6.1.3.6 "Final threshold modification by linearization" */
             norm_fac = 1.0f / norm_fac;
             for (w = 0; w < wi->num_windows*16; w += 16) {
                 for (g = 0; g < num_bands; g++) {
                     AacPsyBand *band = &pch->band[w+g];
 
                     if (band->active_lines > 0.5f) {
                         float delta_sfb_pe = band->norm_fac * norm_fac * delta_pe;
                         float thr = band->thr;
 
                         thr *= powf(2.0f, delta_sfb_pe / band->active_lines);
                         if (thr > coeffs[g].min_snr * band->energy && band->avoid_holes == PSY_3GPP_AH_INACTIVE)
                             thr = FFMAX(band->thr, coeffs[g].min_snr * band->energy);
                         band->thr = thr;
                     }
                 }
             }
         } else {
             /* 5.6.1.3.7 "Further perceptual entropy reduction" */
             g = num_bands;
             while (pe > desired_pe && g--) {
                 for (w = 0; w < wi->num_windows*16; w+= 16) {
                     AacPsyBand *band = &pch->band[w+g];
                     if (band->avoid_holes != PSY_3GPP_AH_NONE && coeffs[g].min_snr < PSY_SNR_1DB) {
                         coeffs[g].min_snr = PSY_SNR_1DB;
                         band->thr = band->energy * PSY_SNR_1DB;
                         pe += band->active_lines * 1.5f - band->pe;
                     }
                 }
             }
             /* TODO: allow more holes (unused without mid/side) */

         }
     }

     for (w = 0; w < wi->num_windows*16; w += 16) {
         for (g = 0; g < num_bands; g++) {
             AacPsyBand *band     = &pch->band[w+g];
             FFPsyBand  *psy_band = &ctx->psy_bands[channel*PSY_MAX_BANDS+w+g];
 
             psy_band->threshold = band->thr;
             psy_band->energy    = band->energy;

         }
     }

     memcpy(pch->prev_band, pch->band, sizeof(pch->band));
 }
 
 static av_cold void psy_3gpp_end(FFPsyContext *apc)
 {

     AacPsyContext *pctx = (AacPsyContext*) apc->model_priv_data;

     av_freep(&pctx->ch);
     av_freep(&apc->model_priv_data);
 }
 

 static void lame_apply_block_type(AacPsyChannel *ctx, FFPsyWindowInfo *wi, int uselongblock)
 {
     int blocktype = ONLY_LONG_SEQUENCE;
     if (uselongblock) {
         if (ctx->next_window_seq == EIGHT_SHORT_SEQUENCE)
             blocktype = LONG_STOP_SEQUENCE;
     } else {
         blocktype = EIGHT_SHORT_SEQUENCE;
         if (ctx->next_window_seq == ONLY_LONG_SEQUENCE)
             ctx->next_window_seq = LONG_START_SEQUENCE;
         if (ctx->next_window_seq == LONG_STOP_SEQUENCE)
             ctx->next_window_seq = EIGHT_SHORT_SEQUENCE;
     }
 
     wi->window_type[0] = ctx->next_window_seq;
     ctx->next_window_seq = blocktype;
 }
 
 static FFPsyWindowInfo psy_lame_window(FFPsyContext *ctx,
                                        const int16_t *audio, const int16_t *la,
                                        int channel, int prev_type)
 {
     AacPsyContext *pctx = (AacPsyContext*) ctx->model_priv_data;
     AacPsyChannel *pch  = &pctx->ch[channel];
     int grouping     = 0;
     int uselongblock = 1;
     int attacks[AAC_NUM_BLOCKS_SHORT + 1] = { 0 };
     int i;
     FFPsyWindowInfo wi;
 
     memset(&wi, 0, sizeof(wi));
     if (la) {
         float hpfsmpl[AAC_BLOCK_SIZE_LONG];
         float const *pf = hpfsmpl;
         float attack_intensity[(AAC_NUM_BLOCKS_SHORT + 1) * PSY_LAME_NUM_SUBBLOCKS];
         float energy_subshort[(AAC_NUM_BLOCKS_SHORT + 1) * PSY_LAME_NUM_SUBBLOCKS];
         float energy_short[AAC_NUM_BLOCKS_SHORT + 1] = { 0 };
         int chans = ctx->avctx->channels;
         const int16_t *firbuf = la + (AAC_BLOCK_SIZE_SHORT/4 - PSY_LAME_FIR_LEN) * chans;
         int j, att_sum = 0;
 
         /* LAME comment: apply high pass filter of fs/4 */
         for (i = 0; i < AAC_BLOCK_SIZE_LONG; i++) {
             float sum1, sum2;
             sum1 = firbuf[(i + ((PSY_LAME_FIR_LEN - 1) / 2)) * chans];
             sum2 = 0.0;
             for (j = 0; j < ((PSY_LAME_FIR_LEN - 1) / 2) - 1; j += 2) {
                 sum1 += psy_fir_coeffs[j] * (firbuf[(i + j) * chans] + firbuf[(i + PSY_LAME_FIR_LEN - j) * chans]);
                 sum2 += psy_fir_coeffs[j + 1] * (firbuf[(i + j + 1) * chans] + firbuf[(i + PSY_LAME_FIR_LEN - j - 1) * chans]);
             }
             hpfsmpl[i] = sum1 + sum2;
         }
 
         /* Calculate the energies of each sub-shortblock */
         for (i = 0; i < PSY_LAME_NUM_SUBBLOCKS; i++) {
             energy_subshort[i] = pch->prev_energy_subshort[i + ((AAC_NUM_BLOCKS_SHORT - 1) * PSY_LAME_NUM_SUBBLOCKS)];
             assert(pch->prev_energy_subshort[i + ((AAC_NUM_BLOCKS_SHORT - 2) * PSY_LAME_NUM_SUBBLOCKS + 1)] > 0);
             attack_intensity[i] = energy_subshort[i] / pch->prev_energy_subshort[i + ((AAC_NUM_BLOCKS_SHORT - 2) * PSY_LAME_NUM_SUBBLOCKS + 1)];
             energy_short[0] += energy_subshort[i];
         }
 
         for (i = 0; i < AAC_NUM_BLOCKS_SHORT * PSY_LAME_NUM_SUBBLOCKS; i++) {
             float const *const pfe = pf + AAC_BLOCK_SIZE_LONG / (AAC_NUM_BLOCKS_SHORT * PSY_LAME_NUM_SUBBLOCKS);
             float p = 1.0f;
             for (; pf < pfe; pf++)
                 if (p < fabsf(*pf))
                     p = fabsf(*pf);
             pch->prev_energy_subshort[i] = energy_subshort[i + PSY_LAME_NUM_SUBBLOCKS] = p;
             energy_short[1 + i / PSY_LAME_NUM_SUBBLOCKS] += p;
             /* FIXME: The indexes below are [i + 3 - 2] in the LAME source.
              *          Obviously the 3 and 2 have some significance, or this would be just [i + 1]
              *          (which is what we use here). What the 3 stands for is ambigious, as it is both
              *          number of short blocks, and the number of sub-short blocks.
              *          It seems that LAME is comparing each sub-block to sub-block + 1 in the
              *          previous block.
              */
             if (p > energy_subshort[i + 1])
                 p = p / energy_subshort[i + 1];
             else if (energy_subshort[i + 1] > p * 10.0f)
                 p = energy_subshort[i + 1] / (p * 10.0f);
             else
                 p = 0.0;
             attack_intensity[i + PSY_LAME_NUM_SUBBLOCKS] = p;
         }
 
         /* compare energy between sub-short blocks */
         for (i = 0; i < (AAC_NUM_BLOCKS_SHORT + 1) * PSY_LAME_NUM_SUBBLOCKS; i++)
             if (!attacks[i / PSY_LAME_NUM_SUBBLOCKS])
                 if (attack_intensity[i] > pch->attack_threshold)
                     attacks[i / PSY_LAME_NUM_SUBBLOCKS] = (i % PSY_LAME_NUM_SUBBLOCKS) + 1;
 
         /* should have energy change between short blocks, in order to avoid periodic signals */
         /* Good samples to show the effect are Trumpet test songs */
         /* GB: tuned (1) to avoid too many short blocks for test sample TRUMPET */
         /* RH: tuned (2) to let enough short blocks through for test sample FSOL and SNAPS */
         for (i = 1; i < AAC_NUM_BLOCKS_SHORT + 1; i++) {
             float const u = energy_short[i - 1];
             float const v = energy_short[i];
             float const m = FFMAX(u, v);
             if (m < 40000) {                          /* (2) */
                 if (u < 1.7f * v && v < 1.7f * u) {   /* (1) */
                     if (i == 1 && attacks[0] < attacks[i])
                         attacks[0] = 0;
                     attacks[i] = 0;
                 }
             }
             att_sum += attacks[i];
         }
 
         if (attacks[0] <= pch->prev_attack)
             attacks[0] = 0;
 
         att_sum += attacks[0];
         /* 3 below indicates the previous attack happened in the last sub-block of the previous sequence */
         if (pch->prev_attack == 3 || att_sum) {
             uselongblock = 0;
 

             for (i = 1; i < AAC_NUM_BLOCKS_SHORT + 1; i++)
                 if (attacks[i] && attacks[i-1])
                     attacks[i] = 0;

         }
     } else {
         /* We have no lookahead info, so just use same type as the previous sequence. */
         uselongblock = !(prev_type == EIGHT_SHORT_SEQUENCE);
     }
 
     lame_apply_block_type(pch, &wi, uselongblock);
 
     wi.window_type[1] = prev_type;
     if (wi.window_type[0] != EIGHT_SHORT_SEQUENCE) {
         wi.num_windows  = 1;
         wi.grouping[0]  = 1;
         if (wi.window_type[0] == LONG_START_SEQUENCE)
             wi.window_shape = 0;
         else
             wi.window_shape = 1;
     } else {
         int lastgrp = 0;
 
         wi.num_windows = 8;
         wi.window_shape = 0;
         for (i = 0; i < 8; i++) {
             if (!((pch->next_grouping >> i) & 1))
                 lastgrp = i;
             wi.grouping[lastgrp]++;
         }
     }
 
     /* Determine grouping, based on the location of the first attack, and save for
      * the next frame.
      * FIXME: Move this to analysis.
      * TODO: Tune groupings depending on attack location
      * TODO: Handle more than one attack in a group
      */
     for (i = 0; i < 9; i++) {
         if (attacks[i]) {
             grouping = i;
             break;
         }
     }
     pch->next_grouping = window_grouping[grouping];
 
     pch->prev_attack = attacks[8];
 
     return wi;
 }

 
 const FFPsyModel ff_aac_psy_model =
 {
     .name    = "3GPP TS 26.403-inspired model",
     .init    = psy_3gpp_init,

     .window  = psy_lame_window,

     .analyze = psy_3gpp_analyze,
     .end     = psy_3gpp_end,
 };