aaccoder.c

/*
 * AAC coefficients encoder
 * Copyright (C) 2008-2009 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 coefficients encoder
 */

/***********************************
 *              TODOs:
 * speedup quantizer selection
 * add sane pulse detection
 ***********************************/

#include "libavutil/libm.h" // brought forward to work around cygwin header breakage

#include <float.h>
#include "libavutil/mathematics.h"
#include "avcodec.h"
#include "put_bits.h"
#include "aac.h"
#include "aacenc.h"
#include "aactab.h"
#include "aac_tablegen_decl.h"

/** Frequency in Hz for lower limit of noise substitution **/
#define NOISE_LOW_LIMIT 4500

/* Energy spread threshold value below which no PNS is used, this corresponds to
 * typically around 17Khz, after which PNS usage decays ending at 19Khz */
#define NOISE_SPREAD_THRESHOLD 0.5f

/* This constant gets divided by lambda to return ~1.65 which when multiplied
 * by the band->threshold and compared to band->energy is the boundary between
 * excessive PNS and little PNS usage. */
#define NOISE_LAMBDA_NUMERATOR 252.1f

/** Frequency in Hz for lower limit of intensity stereo   **/
#define INT_STEREO_LOW_LIMIT 6100

/** Total number of usable codebooks **/
#define CB_TOT 12

/** Total number of codebooks, including special ones **/
#define CB_TOT_ALL 15

/** bits needed to code codebook run value for long windows */
static const uint8_t run_value_bits_long[64] = {
     5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,
     5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5, 10,
    10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
    10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 15
};

/** bits needed to code codebook run value for short windows */
static const uint8_t run_value_bits_short[16] = {
    3, 3, 3, 3, 3, 3, 3, 6, 6, 6, 6, 6, 6, 6, 6, 9
};

static const uint8_t * const run_value_bits[2] = {
    run_value_bits_long, run_value_bits_short
};

#define ROUND_STANDARD 0.4054f
#define ROUND_TO_ZERO 0.1054f

/** Map to convert values from BandCodingPath index to a codebook index **/
static const uint8_t aac_cb_out_map[CB_TOT_ALL]  = {0,1,2,3,4,5,6,7,8,9,10,11,13,14,15};
/** Inverse map to convert from codebooks to BandCodingPath indices **/
static const uint8_t aac_cb_in_map[CB_TOT_ALL+1] = {0,1,2,3,4,5,6,7,8,9,10,11,0,12,13,14};

/**
 * Quantize one coefficient.
 * @return absolute value of the quantized coefficient
 * @see 3GPP TS26.403 5.6.2 "Scalefactor determination"
 */
static av_always_inline int quant(float coef, const float Q, const float rounding)
{
    float a = coef * Q;
    return sqrtf(a * sqrtf(a)) + rounding;
}

static void quantize_bands(int *out, const float *in, const float *scaled,
                           int size, float Q34, int is_signed, int maxval, const float rounding)
{
    int i;
    double qc;
    for (i = 0; i < size; i++) {
        qc = scaled[i] * Q34;
        out[i] = (int)FFMIN(qc + rounding, (double)maxval);
        if (is_signed && in[i] < 0.0f) {
            out[i] = -out[i];
        }
    }
}

static void abs_pow34_v(float *out, const float *in, const int size)
{
#ifndef USE_REALLY_FULL_SEARCH
    int i;
    for (i = 0; i < size; i++) {
        float a = fabsf(in[i]);
        out[i] = sqrtf(a * sqrtf(a));
    }
#endif /* USE_REALLY_FULL_SEARCH */
}

static const uint8_t aac_cb_range [12] = {0, 3, 3, 3, 3, 9, 9, 8, 8, 13, 13, 17};
static const uint8_t aac_cb_maxval[12] = {0, 1, 1, 2, 2, 4, 4, 7, 7, 12, 12, 16};

/**
 * Calculate rate distortion cost for quantizing with given codebook
 *
 * @return quantization distortion
 */
static av_always_inline float quantize_and_encode_band_cost_template(
                                struct AACEncContext *s,
                                PutBitContext *pb, const float *in,
                                const float *scaled, int size, int scale_idx,
                                int cb, const float lambda, const float uplim,
                                int *bits, int BT_ZERO, int BT_UNSIGNED,
                                int BT_PAIR, int BT_ESC, int BT_NOISE, int BT_STEREO,
                                const float ROUNDING)
{
    const int q_idx = POW_SF2_ZERO - scale_idx + SCALE_ONE_POS - SCALE_DIV_512;
    const float Q   = ff_aac_pow2sf_tab [q_idx];
    const float Q34 = ff_aac_pow34sf_tab[q_idx];
    const float IQ  = ff_aac_pow2sf_tab [POW_SF2_ZERO + scale_idx - SCALE_ONE_POS + SCALE_DIV_512];
    const float CLIPPED_ESCAPE = 165140.0f*IQ;
    int i, j;
    float cost = 0;
    const int dim = BT_PAIR ? 2 : 4;
    int resbits = 0;
    int off;

    if (BT_ZERO || BT_NOISE || BT_STEREO) {
        for (i = 0; i < size; i++)
            cost += in[i]*in[i];
        if (bits)
            *bits = 0;
        return cost * lambda;
    }
    if (!scaled) {
        abs_pow34_v(s->scoefs, in, size);
        scaled = s->scoefs;
    }
    quantize_bands(s->qcoefs, in, scaled, size, Q34, !BT_UNSIGNED, aac_cb_maxval[cb], ROUNDING);
    if (BT_UNSIGNED) {
        off = 0;
    } else {
        off = aac_cb_maxval[cb];
    }
    for (i = 0; i < size; i += dim) {
        const float *vec;
        int *quants = s->qcoefs + i;
        int curidx = 0;
        int curbits;
        float rd = 0.0f;
        for (j = 0; j < dim; j++) {
            curidx *= aac_cb_range[cb];
            curidx += quants[j] + off;
        }
        curbits =  ff_aac_spectral_bits[cb-1][curidx];
        vec     = &ff_aac_codebook_vectors[cb-1][curidx*dim];
        if (BT_UNSIGNED) {
            for (j = 0; j < dim; j++) {
                float t = fabsf(in[i+j]);
                float di;
                if (BT_ESC && vec[j] == 64.0f) { //FIXME: slow
                    if (t >= CLIPPED_ESCAPE) {
                        di = t - CLIPPED_ESCAPE;
                        curbits += 21;
                    } else {
                        int c = av_clip_uintp2(quant(t, Q, ROUNDING), 13);
                        di = t - c*cbrtf(c)*IQ;
                        curbits += av_log2(c)*2 - 4 + 1;
                    }
                } else {
                    di = t - vec[j]*IQ;
                }
                if (vec[j] != 0.0f)
                    curbits++;
                rd += di*di;
            }
        } else {
            for (j = 0; j < dim; j++) {
                float di = in[i+j] - vec[j]*IQ;
                rd += di*di;
            }
        }
        cost    += rd * lambda + curbits;
        resbits += curbits;
        if (cost >= uplim)
            return uplim;
        if (pb) {
            put_bits(pb, ff_aac_spectral_bits[cb-1][curidx], ff_aac_spectral_codes[cb-1][curidx]);
            if (BT_UNSIGNED)
                for (j = 0; j < dim; j++)
                    if (ff_aac_codebook_vectors[cb-1][curidx*dim+j] != 0.0f)
                        put_bits(pb, 1, in[i+j] < 0.0f);
            if (BT_ESC) {
                for (j = 0; j < 2; j++) {
                    if (ff_aac_codebook_vectors[cb-1][curidx*2+j] == 64.0f) {
                        int coef = av_clip_uintp2(quant(fabsf(in[i+j]), Q, ROUNDING), 13);
                        int len = av_log2(coef);

                        put_bits(pb, len - 4 + 1, (1 << (len - 4 + 1)) - 2);
                        put_sbits(pb, len, coef);
                    }
                }
            }
        }
    }

    if (bits)
        *bits = resbits;
    return cost;
}

static float quantize_and_encode_band_cost_NONE(struct AACEncContext *s, PutBitContext *pb,
                                                const float *in, const float *scaled,
                                                int size, int scale_idx, int cb,
                                                const float lambda, const float uplim,
                                                int *bits) {
    av_assert0(0);
    return 0.0f;
}

#define QUANTIZE_AND_ENCODE_BAND_COST_FUNC(NAME, BT_ZERO, BT_UNSIGNED, BT_PAIR, BT_ESC, BT_NOISE, BT_STEREO, ROUNDING) \
static float quantize_and_encode_band_cost_ ## NAME(                                         \
                                struct AACEncContext *s,                                     \
                                PutBitContext *pb, const float *in,                          \
                                const float *scaled, int size, int scale_idx,                \
                                int cb, const float lambda, const float uplim,               \
                                int *bits) {                                                 \
    return quantize_and_encode_band_cost_template(                                           \
                                s, pb, in, scaled, size, scale_idx,                          \
                                BT_ESC ? ESC_BT : cb, lambda, uplim, bits,                   \
                                BT_ZERO, BT_UNSIGNED, BT_PAIR, BT_ESC, BT_NOISE, BT_STEREO,  \
                                ROUNDING);                                                   \
}

QUANTIZE_AND_ENCODE_BAND_COST_FUNC(ZERO,  1, 0, 0, 0, 0, 0, ROUND_STANDARD)
QUANTIZE_AND_ENCODE_BAND_COST_FUNC(SQUAD, 0, 0, 0, 0, 0, 0, ROUND_STANDARD)
QUANTIZE_AND_ENCODE_BAND_COST_FUNC(UQUAD, 0, 1, 0, 0, 0, 0, ROUND_STANDARD)
QUANTIZE_AND_ENCODE_BAND_COST_FUNC(SPAIR, 0, 0, 1, 0, 0, 0, ROUND_STANDARD)
QUANTIZE_AND_ENCODE_BAND_COST_FUNC(UPAIR, 0, 1, 1, 0, 0, 0, ROUND_STANDARD)
QUANTIZE_AND_ENCODE_BAND_COST_FUNC(ESC,   0, 1, 1, 1, 0, 0, ROUND_STANDARD)
QUANTIZE_AND_ENCODE_BAND_COST_FUNC(ESC_RTZ, 0, 1, 1, 1, 0, 0, ROUND_TO_ZERO)
QUANTIZE_AND_ENCODE_BAND_COST_FUNC(NOISE, 0, 0, 0, 0, 1, 0, ROUND_STANDARD)
QUANTIZE_AND_ENCODE_BAND_COST_FUNC(STEREO,0, 0, 0, 0, 0, 1, ROUND_STANDARD)

static float (*const quantize_and_encode_band_cost_arr[])(
                                struct AACEncContext *s,
                                PutBitContext *pb, const float *in,
                                const float *scaled, int size, int scale_idx,
                                int cb, const float lambda, const float uplim,
                                int *bits) = {
    quantize_and_encode_band_cost_ZERO,
    quantize_and_encode_band_cost_SQUAD,
    quantize_and_encode_band_cost_SQUAD,
    quantize_and_encode_band_cost_UQUAD,
    quantize_and_encode_band_cost_UQUAD,
    quantize_and_encode_band_cost_SPAIR,
    quantize_and_encode_band_cost_SPAIR,
    quantize_and_encode_band_cost_UPAIR,
    quantize_and_encode_band_cost_UPAIR,
    quantize_and_encode_band_cost_UPAIR,
    quantize_and_encode_band_cost_UPAIR,
    quantize_and_encode_band_cost_ESC,
    quantize_and_encode_band_cost_NONE,     /* CB 12 doesn't exist */
    quantize_and_encode_band_cost_NOISE,
    quantize_and_encode_band_cost_STEREO,
    quantize_and_encode_band_cost_STEREO,
};

static float (*const quantize_and_encode_band_cost_rtz_arr[])(
                                struct AACEncContext *s,
                                PutBitContext *pb, const float *in,
                                const float *scaled, int size, int scale_idx,
                                int cb, const float lambda, const float uplim,
                                int *bits) = {
    quantize_and_encode_band_cost_ZERO,
    quantize_and_encode_band_cost_SQUAD,
    quantize_and_encode_band_cost_SQUAD,
    quantize_and_encode_band_cost_UQUAD,
    quantize_and_encode_band_cost_UQUAD,
    quantize_and_encode_band_cost_SPAIR,
    quantize_and_encode_band_cost_SPAIR,
    quantize_and_encode_band_cost_UPAIR,
    quantize_and_encode_band_cost_UPAIR,
    quantize_and_encode_band_cost_UPAIR,
    quantize_and_encode_band_cost_UPAIR,
    quantize_and_encode_band_cost_ESC_RTZ,
    quantize_and_encode_band_cost_NONE,     /* CB 12 doesn't exist */
    quantize_and_encode_band_cost_NOISE,
    quantize_and_encode_band_cost_STEREO,
    quantize_and_encode_band_cost_STEREO,
};

#define quantize_and_encode_band_cost(                                  \
                                s, pb, in, scaled, size, scale_idx, cb, \
                                lambda, uplim, bits, rtz)               \
    ((rtz) ? quantize_and_encode_band_cost_rtz_arr : quantize_and_encode_band_cost_arr)[cb]( \
                                s, pb, in, scaled, size, scale_idx, cb, \
                                lambda, uplim, bits)

static float quantize_band_cost(struct AACEncContext *s, const float *in,
                                const float *scaled, int size, int scale_idx,
                                int cb, const float lambda, const float uplim,
                                int *bits, int rtz)
{
    return quantize_and_encode_band_cost(s, NULL, in, scaled, size, scale_idx,
                                         cb, lambda, uplim, bits, rtz);
}

static void quantize_and_encode_band(struct AACEncContext *s, PutBitContext *pb,
                                     const float *in, int size, int scale_idx,
                                     int cb, const float lambda, int rtz)
{
    quantize_and_encode_band_cost(s, pb, in, NULL, size, scale_idx, cb, lambda,
                                  INFINITY, NULL, rtz);
}

static float find_max_val(int group_len, int swb_size, const float *scaled) {
    float maxval = 0.0f;
    int w2, i;
    for (w2 = 0; w2 < group_len; w2++) {
        for (i = 0; i < swb_size; i++) {
            maxval = FFMAX(maxval, scaled[w2*128+i]);
        }
    }
    return maxval;
}

static int find_min_book(float maxval, int sf) {
    float Q = ff_aac_pow2sf_tab[POW_SF2_ZERO - sf + SCALE_ONE_POS - SCALE_DIV_512];
    float Q34 = sqrtf(Q * sqrtf(Q));
    int qmaxval, cb;
    qmaxval = maxval * Q34 + 0.4054f;
    if      (qmaxval ==  0) cb = 0;
    else if (qmaxval ==  1) cb = 1;
    else if (qmaxval ==  2) cb = 3;
    else if (qmaxval <=  4) cb = 5;
    else if (qmaxval <=  7) cb = 7;
    else if (qmaxval <= 12) cb = 9;
    else                    cb = 11;
    return cb;
}

/**
 * structure used in optimal codebook search
 */
typedef struct BandCodingPath {
    int prev_idx; ///< pointer to the previous path point
    float cost;   ///< path cost
    int run;
} BandCodingPath;

/**
 * Encode band info for single window group bands.
 */
static void encode_window_bands_info(AACEncContext *s, SingleChannelElement *sce,
                                     int win, int group_len, const float lambda)
{
    BandCodingPath path[120][CB_TOT_ALL];
    int w, swb, cb, start, size;
    int i, j;
    const int max_sfb  = sce->ics.max_sfb;
    const int run_bits = sce->ics.num_windows == 1 ? 5 : 3;
    const int run_esc  = (1 << run_bits) - 1;
    int idx, ppos, count;
    int stackrun[120], stackcb[120], stack_len;
    float next_minrd = INFINITY;
    int next_mincb = 0;

    abs_pow34_v(s->scoefs, sce->coeffs, 1024);
    start = win*128;
    for (cb = 0; cb < CB_TOT_ALL; cb++) {
        path[0][cb].cost     = 0.0f;
        path[0][cb].prev_idx = -1;
        path[0][cb].run      = 0;
    }
    for (swb = 0; swb < max_sfb; swb++) {
        size = sce->ics.swb_sizes[swb];
        if (sce->zeroes[win*16 + swb]) {
            for (cb = 0; cb < CB_TOT_ALL; cb++) {
                path[swb+1][cb].prev_idx = cb;
                path[swb+1][cb].cost     = path[swb][cb].cost;
                path[swb+1][cb].run      = path[swb][cb].run + 1;
            }
        } else {
            float minrd = next_minrd;
            int mincb = next_mincb;
            next_minrd = INFINITY;
            next_mincb = 0;
            for (cb = 0; cb < CB_TOT_ALL; cb++) {
                float cost_stay_here, cost_get_here;
                float rd = 0.0f;
                if (cb >= 12 && sce->band_type[win*16+swb] < aac_cb_out_map[cb] ||
                    cb  < aac_cb_in_map[sce->band_type[win*16+swb]] && sce->band_type[win*16+swb] > aac_cb_out_map[cb]) {
                    path[swb+1][cb].prev_idx = -1;
                    path[swb+1][cb].cost     = INFINITY;
                    path[swb+1][cb].run      = path[swb][cb].run + 1;
                    continue;
                }
                for (w = 0; w < group_len; w++) {
                    FFPsyBand *band = &s->psy.ch[s->cur_channel].psy_bands[(win+w)*16+swb];
                    rd += quantize_band_cost(s, sce->coeffs + start + w*128,
                                             s->scoefs + start + w*128, size,
                                             sce->sf_idx[(win+w)*16+swb], aac_cb_out_map[cb],
                                             lambda / band->threshold, INFINITY, NULL, 0);
                }
                cost_stay_here = path[swb][cb].cost + rd;
                cost_get_here  = minrd              + rd + run_bits + 4;
                if (   run_value_bits[sce->ics.num_windows == 8][path[swb][cb].run]
                    != run_value_bits[sce->ics.num_windows == 8][path[swb][cb].run+1])
                    cost_stay_here += run_bits;
                if (cost_get_here < cost_stay_here) {
                    path[swb+1][cb].prev_idx = mincb;
                    path[swb+1][cb].cost     = cost_get_here;
                    path[swb+1][cb].run      = 1;
                } else {
                    path[swb+1][cb].prev_idx = cb;
                    path[swb+1][cb].cost     = cost_stay_here;
                    path[swb+1][cb].run      = path[swb][cb].run + 1;
                }
                if (path[swb+1][cb].cost < next_minrd) {
                    next_minrd = path[swb+1][cb].cost;
                    next_mincb = cb;
                }
            }
        }
        start += sce->ics.swb_sizes[swb];
    }

    //convert resulting path from backward-linked list
    stack_len = 0;
    idx       = 0;
    for (cb = 1; cb < CB_TOT_ALL; cb++)
        if (path[max_sfb][cb].cost < path[max_sfb][idx].cost)
            idx = cb;
    ppos = max_sfb;
    while (ppos > 0) {
        av_assert1(idx >= 0);
        cb = idx;
        stackrun[stack_len] = path[ppos][cb].run;
        stackcb [stack_len] = cb;
        idx = path[ppos-path[ppos][cb].run+1][cb].prev_idx;
        ppos -= path[ppos][cb].run;
        stack_len++;
    }
    //perform actual band info encoding
    start = 0;
    for (i = stack_len - 1; i >= 0; i--) {
        cb = aac_cb_out_map[stackcb[i]];
        put_bits(&s->pb, 4, cb);
        count = stackrun[i];
        memset(sce->zeroes + win*16 + start, !cb, count);
        //XXX: memset when band_type is also uint8_t
        for (j = 0; j < count; j++) {
            sce->band_type[win*16 + start] = cb;
            start++;
        }
        while (count >= run_esc) {
            put_bits(&s->pb, run_bits, run_esc);
            count -= run_esc;
        }
        put_bits(&s->pb, run_bits, count);
    }
}

static void codebook_trellis_rate(AACEncContext *s, SingleChannelElement *sce,
                                  int win, int group_len, const float lambda)
{
    BandCodingPath path[120][CB_TOT_ALL];
    int w, swb, cb, start, size;
    int i, j;
    const int max_sfb  = sce->ics.max_sfb;
    const int run_bits = sce->ics.num_windows == 1 ? 5 : 3;
    const int run_esc  = (1 << run_bits) - 1;
    int idx, ppos, count;
    int stackrun[120], stackcb[120], stack_len;
    float next_minbits = INFINITY;
    int next_mincb = 0;

    abs_pow34_v(s->scoefs, sce->coeffs, 1024);
    start = win*128;
    for (cb = 0; cb < CB_TOT_ALL; cb++) {
        path[0][cb].cost     = run_bits+4;
        path[0][cb].prev_idx = -1;
        path[0][cb].run      = 0;
    }
    for (swb = 0; swb < max_sfb; swb++) {
        size = sce->ics.swb_sizes[swb];
        if (sce->zeroes[win*16 + swb]) {
            float cost_stay_here = path[swb][0].cost;
            float cost_get_here  = next_minbits + run_bits + 4;
            if (   run_value_bits[sce->ics.num_windows == 8][path[swb][0].run]
                != run_value_bits[sce->ics.num_windows == 8][path[swb][0].run+1])
                cost_stay_here += run_bits;
            if (cost_get_here < cost_stay_here) {
                path[swb+1][0].prev_idx = next_mincb;
                path[swb+1][0].cost     = cost_get_here;
                path[swb+1][0].run      = 1;
            } else {
                path[swb+1][0].prev_idx = 0;
                path[swb+1][0].cost     = cost_stay_here;
                path[swb+1][0].run      = path[swb][0].run + 1;
            }
            next_minbits = path[swb+1][0].cost;
            next_mincb = 0;
            for (cb = 1; cb < CB_TOT_ALL; cb++) {
                path[swb+1][cb].cost = 61450;
                path[swb+1][cb].prev_idx = -1;
                path[swb+1][cb].run = 0;
            }
        } else {
            float minbits = next_minbits;
            int mincb = next_mincb;
            int startcb = sce->band_type[win*16+swb];
            startcb = aac_cb_in_map[startcb];
            next_minbits = INFINITY;
            next_mincb = 0;
            for (cb = 0; cb < startcb; cb++) {
                path[swb+1][cb].cost = 61450;
                path[swb+1][cb].prev_idx = -1;
                path[swb+1][cb].run = 0;
            }
            for (cb = startcb; cb < CB_TOT_ALL; cb++) {
                float cost_stay_here, cost_get_here;
                float bits = 0.0f;
                if (cb >= 12 && sce->band_type[win*16+swb] != aac_cb_out_map[cb]) {
                    path[swb+1][cb].cost = 61450;
                    path[swb+1][cb].prev_idx = -1;
                    path[swb+1][cb].run = 0;
                    continue;
                }
                for (w = 0; w < group_len; w++) {
                    bits += quantize_band_cost(s, sce->coeffs + start + w*128,
                                               s->scoefs + start + w*128, size,
                                               sce->sf_idx[win*16+swb],
                                               aac_cb_out_map[cb],
                                               0, INFINITY, NULL, 0);
                }
                cost_stay_here = path[swb][cb].cost + bits;
                cost_get_here  = minbits            + bits + run_bits + 4;
                if (   run_value_bits[sce->ics.num_windows == 8][path[swb][cb].run]
                    != run_value_bits[sce->ics.num_windows == 8][path[swb][cb].run+1])
                    cost_stay_here += run_bits;
                if (cost_get_here < cost_stay_here) {
                    path[swb+1][cb].prev_idx = mincb;
                    path[swb+1][cb].cost     = cost_get_here;
                    path[swb+1][cb].run      = 1;
                } else {
                    path[swb+1][cb].prev_idx = cb;
                    path[swb+1][cb].cost     = cost_stay_here;
                    path[swb+1][cb].run      = path[swb][cb].run + 1;
                }
                if (path[swb+1][cb].cost < next_minbits) {
                    next_minbits = path[swb+1][cb].cost;
                    next_mincb = cb;
                }
            }
        }
        start += sce->ics.swb_sizes[swb];
    }

    //convert resulting path from backward-linked list
    stack_len = 0;
    idx       = 0;
    for (cb = 1; cb < CB_TOT_ALL; cb++)
        if (path[max_sfb][cb].cost < path[max_sfb][idx].cost)
            idx = cb;
    ppos = max_sfb;
    while (ppos > 0) {
        av_assert1(idx >= 0);
        cb = idx;
        stackrun[stack_len] = path[ppos][cb].run;
        stackcb [stack_len] = cb;
        idx = path[ppos-path[ppos][cb].run+1][cb].prev_idx;
        ppos -= path[ppos][cb].run;
        stack_len++;
    }
    //perform actual band info encoding
    start = 0;
    for (i = stack_len - 1; i >= 0; i--) {
        cb = aac_cb_out_map[stackcb[i]];
        put_bits(&s->pb, 4, cb);
        count = stackrun[i];
        memset(sce->zeroes + win*16 + start, !cb, count);
        //XXX: memset when band_type is also uint8_t
        for (j = 0; j < count; j++) {
            sce->band_type[win*16 + start] = cb;
            start++;
        }
        while (count >= run_esc) {
            put_bits(&s->pb, run_bits, run_esc);
            count -= run_esc;
        }
        put_bits(&s->pb, run_bits, count);
    }
}

/** Return the minimum scalefactor where the quantized coef does not clip. */
static av_always_inline uint8_t coef2minsf(float coef) {
    return av_clip_uint8(log2f(coef)*4 - 69 + SCALE_ONE_POS - SCALE_DIV_512);
}

/** Return the maximum scalefactor where the quantized coef is not zero. */
static av_always_inline uint8_t coef2maxsf(float coef) {
    return av_clip_uint8(log2f(coef)*4 +  6 + SCALE_ONE_POS - SCALE_DIV_512);
}

typedef struct TrellisPath {
    float cost;
    int prev;
} TrellisPath;

#define TRELLIS_STAGES 121
#define TRELLIS_STATES (SCALE_MAX_DIFF+1)

static void set_special_band_scalefactors(AACEncContext *s, SingleChannelElement *sce)
{
    int w, g, start = 0;
    int minscaler_n = sce->sf_idx[0], minscaler_i = sce->sf_idx[0];
    int bands = 0;

    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
        start = 0;
        for (g = 0;  g < sce->ics.num_swb; g++) {
            if (sce->band_type[w*16+g] == INTENSITY_BT || sce->band_type[w*16+g] == INTENSITY_BT2) {
                sce->sf_idx[w*16+g] = av_clip(ceilf(log2f(sce->is_ener[w*16+g])*2), -155, 100);
                minscaler_i = FFMIN(minscaler_i, sce->sf_idx[w*16+g]);
                bands++;
            } else if (sce->band_type[w*16+g] == NOISE_BT) {
                sce->sf_idx[w*16+g] = av_clip(4+log2f(sce->pns_ener[w*16+g])*2, -100, 155);
                minscaler_n = FFMIN(minscaler_n, sce->sf_idx[w*16+g]);
                bands++;
            }
            start += sce->ics.swb_sizes[g];
        }
    }

    if (!bands)
        return;

    /* Clip the scalefactor indices */
    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
        for (g = 0;  g < sce->ics.num_swb; g++) {
            if (sce->band_type[w*16+g] == INTENSITY_BT || sce->band_type[w*16+g] == INTENSITY_BT2) {
                sce->sf_idx[w*16+g] = av_clip(sce->sf_idx[w*16+g], minscaler_i, minscaler_i + SCALE_MAX_DIFF);
            } else if (sce->band_type[w*16+g] == NOISE_BT) {
                sce->sf_idx[w*16+g] = av_clip(sce->sf_idx[w*16+g], minscaler_n, minscaler_n + SCALE_MAX_DIFF);
            }
        }
    }
}

static void search_for_quantizers_anmr(AVCodecContext *avctx, AACEncContext *s,
                                       SingleChannelElement *sce,
                                       const float lambda)
{
    int q, w, w2, g, start = 0;
    int i, j;
    int idx;
    TrellisPath paths[TRELLIS_STAGES][TRELLIS_STATES];
    int bandaddr[TRELLIS_STAGES];
    int minq;
    float mincost;
    float q0f = FLT_MAX, q1f = 0.0f, qnrgf = 0.0f;
    int q0, q1, qcnt = 0;

    for (i = 0; i < 1024; i++) {
        float t = fabsf(sce->coeffs[i]);
        if (t > 0.0f) {
            q0f = FFMIN(q0f, t);
            q1f = FFMAX(q1f, t);
            qnrgf += t*t;
            qcnt++;
        }
    }

    if (!qcnt) {
        memset(sce->sf_idx, 0, sizeof(sce->sf_idx));
        memset(sce->zeroes, 1, sizeof(sce->zeroes));
        return;
    }

    //minimum scalefactor index is when minimum nonzero coefficient after quantizing is not clipped
    q0 = coef2minsf(q0f);
    //maximum scalefactor index is when maximum coefficient after quantizing is still not zero
    q1 = coef2maxsf(q1f);
    if (q1 - q0 > 60) {
        int q0low  = q0;
        int q1high = q1;
        //minimum scalefactor index is when maximum nonzero coefficient after quantizing is not clipped
        int qnrg = av_clip_uint8(log2f(sqrtf(qnrgf/qcnt))*4 - 31 + SCALE_ONE_POS - SCALE_DIV_512);
        q1 = qnrg + 30;
        q0 = qnrg - 30;
        if (q0 < q0low) {
            q1 += q0low - q0;
            q0  = q0low;
        } else if (q1 > q1high) {
            q0 -= q1 - q1high;
            q1  = q1high;
        }
    }

    for (i = 0; i < TRELLIS_STATES; i++) {
        paths[0][i].cost    = 0.0f;
        paths[0][i].prev    = -1;
    }
    for (j = 1; j < TRELLIS_STAGES; j++) {
        for (i = 0; i < TRELLIS_STATES; i++) {
            paths[j][i].cost    = INFINITY;
            paths[j][i].prev    = -2;
        }
    }
    idx = 1;
    abs_pow34_v(s->scoefs, sce->coeffs, 1024);
    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
        start = w*128;
        for (g = 0; g < sce->ics.num_swb; g++) {
            const float *coefs = sce->coeffs + start;
            float qmin, qmax;
            int nz = 0;

            bandaddr[idx] = w * 16 + g;
            qmin = INT_MAX;
            qmax = 0.0f;
            for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                FFPsyBand *band = &s->psy.ch[s->cur_channel].psy_bands[(w+w2)*16+g];
                if (band->energy <= band->threshold || band->threshold == 0.0f) {
                    sce->zeroes[(w+w2)*16+g] = 1;
                    continue;
                }
                sce->zeroes[(w+w2)*16+g] = 0;
                nz = 1;
                for (i = 0; i < sce->ics.swb_sizes[g]; i++) {
                    float t = fabsf(coefs[w2*128+i]);
                    if (t > 0.0f)
                        qmin = FFMIN(qmin, t);
                    qmax = FFMAX(qmax, t);
                }
            }
            if (nz) {
                int minscale, maxscale;
                float minrd = INFINITY;
                float maxval;
                //minimum scalefactor index is when minimum nonzero coefficient after quantizing is not clipped
                minscale = coef2minsf(qmin);
                //maximum scalefactor index is when maximum coefficient after quantizing is still not zero
                maxscale = coef2maxsf(qmax);
                minscale = av_clip(minscale - q0, 0, TRELLIS_STATES - 1);
                maxscale = av_clip(maxscale - q0, 0, TRELLIS_STATES);
                maxval = find_max_val(sce->ics.group_len[w], sce->ics.swb_sizes[g], s->scoefs+start);
                for (q = minscale; q < maxscale; q++) {
                    float dist = 0;
                    int cb = find_min_book(maxval, sce->sf_idx[w*16+g]);
                    for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                        FFPsyBand *band = &s->psy.ch[s->cur_channel].psy_bands[(w+w2)*16+g];
                        dist += quantize_band_cost(s, coefs + w2*128, s->scoefs + start + w2*128, sce->ics.swb_sizes[g],
                                                   q + q0, cb, lambda / band->threshold, INFINITY, NULL, 0);
                    }
                    minrd = FFMIN(minrd, dist);

                    for (i = 0; i < q1 - q0; i++) {
                        float cost;
                        cost = paths[idx - 1][i].cost + dist
                               + ff_aac_scalefactor_bits[q - i + SCALE_DIFF_ZERO];
                        if (cost < paths[idx][q].cost) {
                            paths[idx][q].cost    = cost;
                            paths[idx][q].prev    = i;
                        }
                    }
                }
            } else {
                for (q = 0; q < q1 - q0; q++) {
                    paths[idx][q].cost = paths[idx - 1][q].cost + 1;
                    paths[idx][q].prev = q;
                }
            }
            sce->zeroes[w*16+g] = !nz;
            start += sce->ics.swb_sizes[g];
            idx++;
        }
    }
    idx--;
    mincost = paths[idx][0].cost;
    minq    = 0;
    for (i = 1; i < TRELLIS_STATES; i++) {
        if (paths[idx][i].cost < mincost) {
            mincost = paths[idx][i].cost;
            minq = i;
        }
    }
    while (idx) {
        sce->sf_idx[bandaddr[idx]] = minq + q0;
        minq = paths[idx][minq].prev;
        idx--;
    }
    //set the same quantizers inside window groups
    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w])
        for (g = 0;  g < sce->ics.num_swb; g++)
            for (w2 = 1; w2 < sce->ics.group_len[w]; w2++)
                sce->sf_idx[(w+w2)*16+g] = sce->sf_idx[w*16+g];
}

/**
 * two-loop quantizers search taken from ISO 13818-7 Appendix C
 */
static void search_for_quantizers_twoloop(AVCodecContext *avctx,
                                          AACEncContext *s,
                                          SingleChannelElement *sce,
                                          const float lambda)
{
    int start = 0, i, w, w2, g;
    int destbits = avctx->bit_rate * 1024.0 / avctx->sample_rate / avctx->channels * (lambda / 120.f);
    float dists[128] = { 0 }, uplims[128] = { 0 };
    float maxvals[128];
    int fflag, minscaler;
    int its  = 0;
    int allz = 0;
    float minthr = INFINITY;

    // for values above this the decoder might end up in an endless loop
    // due to always having more bits than what can be encoded.
    destbits = FFMIN(destbits, 5800);
    //XXX: some heuristic to determine initial quantizers will reduce search time
    //determine zero bands and upper limits
    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
        for (g = 0;  g < sce->ics.num_swb; g++) {
            int nz = 0;
            float uplim = 0.0f, energy = 0.0f;
            for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                FFPsyBand *band = &s->psy.ch[s->cur_channel].psy_bands[(w+w2)*16+g];
                uplim  += band->threshold;
                energy += band->energy;
                if (band->energy <= band->threshold || band->threshold == 0.0f) {
                    sce->zeroes[(w+w2)*16+g] = 1;
                    continue;
                }
                nz = 1;
            }
            uplims[w*16+g] = uplim *512;
            sce->zeroes[w*16+g] = !nz;
            if (nz)
                minthr = FFMIN(minthr, uplim);
            allz |= nz;
        }
    }
    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
        for (g = 0;  g < sce->ics.num_swb; g++) {
            if (sce->zeroes[w*16+g]) {
                sce->sf_idx[w*16+g] = SCALE_ONE_POS;
                continue;
            }
            sce->sf_idx[w*16+g] = SCALE_ONE_POS + FFMIN(log2f(uplims[w*16+g]/minthr)*4,59);
        }
    }

    if (!allz)
        return;
    abs_pow34_v(s->scoefs, sce->coeffs, 1024);

    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
        start = w*128;
        for (g = 0;  g < sce->ics.num_swb; g++) {
            const float *scaled = s->scoefs + start;
            maxvals[w*16+g] = find_max_val(sce->ics.group_len[w], sce->ics.swb_sizes[g], scaled);
            start += sce->ics.swb_sizes[g];
        }
    }

    //perform two-loop search
    //outer loop - improve quality
    do {
        int tbits, qstep;
        minscaler = sce->sf_idx[0];
        //inner loop - quantize spectrum to fit into given number of bits
        qstep = its ? 1 : 32;
        do {
            int prev = -1;
            tbits = 0;
            for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
                start = w*128;
                for (g = 0;  g < sce->ics.num_swb; g++) {
                    const float *coefs = sce->coeffs + start;
                    const float *scaled = s->scoefs + start;
                    int bits = 0;
                    int cb;
                    float dist = 0.0f;

                    if (sce->zeroes[w*16+g] || sce->sf_idx[w*16+g] >= 218) {
                        start += sce->ics.swb_sizes[g];
                        continue;
                    }
                    minscaler = FFMIN(minscaler, sce->sf_idx[w*16+g]);
                    cb = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]);
                    for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                        int b;
                        dist += quantize_band_cost(s, coefs + w2*128,
                                                   scaled + w2*128,
                                                   sce->ics.swb_sizes[g],
                                                   sce->sf_idx[w*16+g],
                                                   cb,
                                                   1.0f,
                                                   INFINITY,
                                                   &b,
                                                   0);
                        bits += b;
                    }
                    dists[w*16+g] = dist - bits;
                    if (prev != -1) {
                        bits += ff_aac_scalefactor_bits[sce->sf_idx[w*16+g] - prev + SCALE_DIFF_ZERO];
                    }
                    tbits += bits;
                    start += sce->ics.swb_sizes[g];
                    prev = sce->sf_idx[w*16+g];
                }
            }
            if (tbits > destbits) {
                for (i = 0; i < 128; i++)
                    if (sce->sf_idx[i] < 218 - qstep)
                        sce->sf_idx[i] += qstep;
            } else {
                for (i = 0; i < 128; i++)
                    if (sce->sf_idx[i] > 60 - qstep)
                        sce->sf_idx[i] -= qstep;
            }
            qstep >>= 1;
            if (!qstep && tbits > destbits*1.02 && sce->sf_idx[0] < 217)
                qstep = 1;
        } while (qstep);

        fflag = 0;
        minscaler = av_clip(minscaler, 60, 255 - SCALE_MAX_DIFF);

        for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
            for (g = 0; g < sce->ics.num_swb; g++) {
                int prevsc = sce->sf_idx[w*16+g];
                if (dists[w*16+g] > uplims[w*16+g] && sce->sf_idx[w*16+g] > 60) {
                    if (find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]-1))
                        sce->sf_idx[w*16+g]--;
                    else //Try to make sure there is some energy in every band
                        sce->sf_idx[w*16+g]-=2;
                }
                sce->sf_idx[w*16+g] = av_clip(sce->sf_idx[w*16+g], minscaler, minscaler + SCALE_MAX_DIFF);
                sce->sf_idx[w*16+g] = FFMIN(sce->sf_idx[w*16+g], 219);
                if (sce->sf_idx[w*16+g] != prevsc)
                    fflag = 1;
                sce->band_type[w*16+g] = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]);
            }
        }
        its++;
    } while (fflag && its < 10);
}

static void search_for_quantizers_faac(AVCodecContext *avctx, AACEncContext *s,
                                       SingleChannelElement *sce,
                                       const float lambda)
{
    int start = 0, i, w, w2, g;
    float uplim[128], maxq[128];
    int minq, maxsf;
    float distfact = ((sce->ics.num_windows > 1) ? 85.80 : 147.84) / lambda;
    int last = 0, lastband = 0, curband = 0;
    float avg_energy = 0.0;
    if (sce->ics.num_windows == 1) {
        start = 0;
        for (i = 0; i < 1024; i++) {
            if (i - start >= sce->ics.swb_sizes[curband]) {
                start += sce->ics.swb_sizes[curband];
                curband++;
            }
            if (sce->coeffs[i]) {
                avg_energy += sce->coeffs[i] * sce->coeffs[i];
                last = i;
                lastband = curband;
            }
        }