aaccoder.c

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/*
 * 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 <math.h> // brought forward to work around cygwin header breakage
 
#include <float.h>
 
#include "libavutil/mathematics.h"
#include "mathops.h"
#include "avcodec.h"
#include "put_bits.h"
#include "aac.h"
#include "aacenc.h"
#include "aactab.h"
#include "aacenctab.h"
#include "aacenc_utils.h"
#include "aacenc_quantization.h"
 
#include "aacenc_is.h"
#include "aacenc_tns.h"
 
#include "libavcodec/aaccoder_twoloop.h"
 
/* Parameter of f(x) = a*(lambda/100), defines the maximum fourier spread
 * beyond which no PNS is used (since the SFBs contain tone rather than noise) */
#define NOISE_SPREAD_THRESHOLD 0.9f
 
/* Parameter of f(x) = a*(100/lambda), defines how much PNS is allowed to
 * replace low energy non zero bands */
#define NOISE_LAMBDA_REPLACE 1.948f
 
#include "libavcodec/aaccoder_trellis.h"
#include "libavcodec/aaccoder_nmr.h"
 
/* c * cbrtf(c), the reconstruction of every escape magnitude c */
static float esc_pow43[1 << 13];
 
av_cold void ff_aac_coder_init_tables(void)
{
    for (int c = 0; c < FF_ARRAY_ELEMS(esc_pow43); c++)
        esc_pow43[c] = c * cbrtf(c);
}
 
typedef float (*quantize_and_encode_band_func)(struct AACEncContext *s, PutBitContext *pb,
                                               const float *in, float *quant, const float *scaled,
                                               int size, int scale_idx, int cb,
                                               const float lambda, const float uplim,
                                               int *bits, float *energy);
 
/**
 * 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, float *out,
                                const float *scaled, int size, int scale_idx,
                                int cb, const float lambda, const float uplim,
                                int *bits, float *energy, 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;
    float cost = 0;
    float qenergy = 0;
    const int dim = BT_PAIR ? 2 : 4;
    int resbits = 0;
    int off;
 
    if (BT_ZERO || BT_NOISE || BT_STEREO) {
        for (int i = 0; i < size; i++)
            cost += in[i]*in[i];
        if (bits)
            *bits = 0;
        if (energy)
            *energy = qenergy;
        if (out) {
            for (int i = 0; i < size; i += dim)
                for (int j = 0; j < dim; j++)
                    out[i+j] = 0.0f;
        }
        return cost * lambda;
    }
    if (!scaled) {
        s->aacdsp.abs_pow34(s->scoefs, in, size);
        scaled = s->scoefs;
    }
    s->aacdsp.quant_bands(s->qcoefs, in, scaled, size, !BT_UNSIGNED, aac_cb_maxval[cb], Q34, ROUNDING);
    if (BT_UNSIGNED) {
        off = 0;
    } else {
        off = aac_cb_maxval[cb];
    }
    for (int i = 0; i < size; i += dim) {
        const float *vec;
        int *quants = s->qcoefs + i;
        int curidx = 0;
        int curbits;
        float quantized, rd = 0.0f;
        for (int 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 (int 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) {
                        quantized = CLIPPED_ESCAPE;
                        curbits += 21;
                    } else {
                        int c = av_clip_uintp2(quant(t, Q, ROUNDING), 13);
                        quantized = esc_pow43[c]*IQ;
                        curbits += av_log2(c)*2 - 4 + 1;
                    }
                } else {
                    quantized = vec[j]*IQ;
                }
                di = t - quantized;
                if (out)
                    out[i+j] = in[i+j] >= 0 ? quantized : -quantized;
                if (vec[j] != 0.0f)
                    curbits++;
                qenergy += quantized*quantized;
                rd += di*di;
            }
        } else {
            for (int j = 0; j < dim; j++) {
                quantized = vec[j]*IQ;
                qenergy += quantized*quantized;
                if (out)
                    out[i+j] = quantized;
                rd += (in[i+j] - quantized)*(in[i+j] - quantized);
            }
        }
        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 (int 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 (int j = 0; j < 2; j++) {
                    if (ff_aac_codebook_vectors[cb-1][curidx*2+j] == 64.0f) {
                        int coef = av_clip(quant(fabsf(in[i+j]), Q, ROUNDING), 16, (1 << 13) - 1);
                        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;
    if (energy)
        *energy = qenergy;
    return cost;
}
 
static inline float quantize_and_encode_band_cost_NONE(struct AACEncContext *s, PutBitContext *pb,
                                                const float *in, float *quant, const float *scaled,
                                                int size, int scale_idx, int cb,
                                                const float lambda, const float uplim,
                                                int *bits, float *energy) {
    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, float *quant,            \
                                const float *scaled, int size, int scale_idx,                \
                                int cb, const float lambda, const float uplim,               \
                                int *bits, float *energy) {                                  \
    return quantize_and_encode_band_cost_template(                                           \
                                s, pb, in, quant, scaled, size, scale_idx,                   \
                                BT_ESC ? ESC_BT : cb, lambda, uplim, bits, energy,           \
                                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 const quantize_and_encode_band_func quantize_and_encode_band_cost_arr[] =
{
    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 const quantize_and_encode_band_func quantize_and_encode_band_cost_rtz_arr[] =
{
    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,
};
 
float ff_quantize_and_encode_band_cost(struct AACEncContext *s, PutBitContext *pb,
                                       const float *in, float *quant, const float *scaled,
                                       int size, int scale_idx, int cb,
                                       const float lambda, const float uplim,
                                       int *bits, float *energy)
{
    return quantize_and_encode_band_cost_arr[cb](s, pb, in, quant, scaled, size,
                                                 scale_idx, cb, lambda, uplim,
                                                 bits, energy);
}
 
static inline void quantize_and_encode_band(struct AACEncContext *s, PutBitContext *pb,
                                            const float *in, float *out, int size, int scale_idx,
                                            int cb, const float lambda, int rtz)
{
    (rtz ? quantize_and_encode_band_cost_rtz_arr : quantize_and_encode_band_cost_arr)[cb](s, pb, in, out, NULL, size, scale_idx, cb,
                                     lambda, INFINITY, NULL, NULL);
}
 
/**
 * 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;
 
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;
    int prevscaler_n = -255, prevscaler_i = 0;
    int bands = 0;
 
    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])
                continue;
            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(roundf(log2f(sce->is_ener[w*16+g])*2), -155, 100);
                bands++;
            } else if (sce->band_type[w*16+g] == NOISE_BT) {
                sce->sf_idx[w*16+g] = av_clip(3+ceilf(log2f(sce->pns_ener[w*16+g])*2), -100, 155);
                if (prevscaler_n == -255)
                    prevscaler_n = sce->sf_idx[w*16+g];
                bands++;
            }
        }
    }
 
    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->zeroes[w*16+g])
                continue;
            if (sce->band_type[w*16+g] == INTENSITY_BT || sce->band_type[w*16+g] == INTENSITY_BT2) {
                sce->sf_idx[w*16+g] = prevscaler_i = av_clip(sce->sf_idx[w*16+g], prevscaler_i - SCALE_MAX_DIFF, prevscaler_i + SCALE_MAX_DIFF);
            } else if (sce->band_type[w*16+g] == NOISE_BT) {
                sce->sf_idx[w*16+g] = prevscaler_n = av_clip(sce->sf_idx[w*16+g], prevscaler_n - SCALE_MAX_DIFF, prevscaler_n + SCALE_MAX_DIFF);
            }
        }
    }
}
 
static void search_for_quantizers_fast(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->ch_layout.nb_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);
    //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]) {
        start = 0;
        for (g = 0; g < sce->ics.num_swb; g++) {
            int nz = 0;
            float uplim = 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;
                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->band_type[w*16+g] = 0;
            sce->zeroes[w*16+g] = !nz;
            if (nz)
                minthr = FFMIN(minthr, uplim);
            allz |= nz;
            start += sce->ics.swb_sizes[g];
        }
    }
    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;
    s->aacdsp.abs_pow34(s->scoefs, sce->coeffs, 1024);
    ff_quantize_band_cost_cache_init(s);
 
    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_cached(s, w + w2, g,
                                                          coefs + w2*128,
                                                          scaled + w2*128,
                                                          sce->ics.swb_sizes[g],
                                                          sce->sf_idx[w*16+g],
                                                          cb, 1.0f, INFINITY,
                                                          &b, NULL, 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_pns(AACEncContext *s, AVCodecContext *avctx, SingleChannelElement *sce)
{
    FFPsyBand *band;
    int w, g, w2, i;
    int wlen = 1024 / sce->ics.num_windows;
    int bandwidth, cutoff;
    float *PNS = &s->scoefs[0*128], *PNS34 = &s->scoefs[1*128];
    float *NOR34 = &s->scoefs[3*128];
    uint8_t nextband[128];
    const float lambda = s->lambda;
    const float freq_mult = avctx->sample_rate*0.5f/wlen;
    const float thr_mult = NOISE_LAMBDA_REPLACE*(100.0f/lambda);
    const float spread_threshold = FFMIN(0.75f, NOISE_SPREAD_THRESHOLD*FFMAX(0.5f, lambda/100.f));
    const float dist_bias = av_clipf(4.f * 120 / lambda, 0.25f, 4.0f);
    const float pns_transient_energy_r = FFMIN(0.7f, lambda / 140.f);
 
    int prev = -1000, prev_sf = -1;
 
    /* PNS candidacy must use the coder's actual coding bandwidth (s->bandwidth,
     * fixed at init), not a separate heuristic, or it evaluates a different band
     * range than the coder later codes. */
    bandwidth = s->bandwidth;
    cutoff = bandwidth * 2 * wlen / avctx->sample_rate;
 
    memcpy(sce->band_alt, sce->band_type, sizeof(sce->band_type));
    ff_init_nextband_map(sce, nextband);
    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
        int wstart = w*128;
        for (g = 0; g < sce->ics.num_swb; g++) {
            int noise_sfi;
            float dist1 = 0.0f, dist2 = 0.0f, noise_amp;
            float pns_energy = 0.0f, pns_tgt_energy, energy_ratio, dist_thresh;
            float sfb_energy = 0.0f, threshold = 0.0f, spread = 2.0f;
            float min_energy = -1.0f, max_energy = 0.0f;
            const int start = wstart+sce->ics.swb_offset[g];
            const float freq = (start-wstart)*freq_mult;
            const float freq_boost = FFMAX(0.88f*freq/NOISE_LOW_LIMIT, 1.0f);
            if (freq < NOISE_LOW_LIMIT || (start-wstart) >= cutoff) {
                if (!sce->zeroes[w*16+g])
                    prev_sf = sce->sf_idx[w*16+g];
                continue;
            }
            for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                band = &s->psy.ch[s->cur_channel].psy_bands[(w+w2)*16+g];
                sfb_energy += band->energy;
                spread     = FFMIN(spread, band->spread);
                threshold  += band->threshold;
                if (!w2) {
                    min_energy = max_energy = band->energy;
                } else {
                    min_energy = FFMIN(min_energy, band->energy);
                    max_energy = FFMAX(max_energy, band->energy);
                }
            }
 
            /* Ramps down at ~8000Hz and loosens the dist threshold */
            dist_thresh = av_clipf(2.5f*NOISE_LOW_LIMIT/freq, 0.5f, 2.5f) * dist_bias;
 
            /* PNS is acceptable when all of these are true:
             * 1. high spread energy (noise-like band)
             * 2. near-threshold energy (high PE means the random nature of PNS content will be noticed)
             * 3. on short window groups, all windows have similar energy (variations in energy would be destroyed by PNS)
             *
             * At this stage, point 2 is relaxed for zeroed bands near the noise threshold (hole avoidance is more important)
             */
            if ((!sce->zeroes[w*16+g] && !ff_sfdelta_can_remove_band(sce, nextband, prev_sf, w*16+g)) ||
                ((sce->zeroes[w*16+g] || !sce->band_alt[w*16+g]) && sfb_energy < threshold*sqrtf(1.0f/freq_boost)) || spread < spread_threshold ||
                (!sce->zeroes[w*16+g] && sce->band_alt[w*16+g] && sfb_energy > threshold*thr_mult*freq_boost) ||
                min_energy < pns_transient_energy_r * max_energy ) {
                sce->pns_ener[w*16+g] = sfb_energy;
                if (!sce->zeroes[w*16+g])
                    prev_sf = sce->sf_idx[w*16+g];
                continue;
            }
 
            pns_tgt_energy = sfb_energy*FFMIN(1.0f, spread*spread);
            noise_sfi = av_clip(roundf(log2f(pns_tgt_energy)*2), -100, 155); /* Quantize */
            noise_amp = -ff_aac_pow2sf_tab[noise_sfi + POW_SF2_ZERO];    /* Dequantize */
            if (prev != -1000) {
                int noise_sfdiff = noise_sfi - prev + SCALE_DIFF_ZERO;
                if (noise_sfdiff < 0 || noise_sfdiff > 2*SCALE_MAX_DIFF) {
                    if (!sce->zeroes[w*16+g])
                        prev_sf = sce->sf_idx[w*16+g];
                    continue;
                }
            }
            for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                float band_energy, scale, pns_senergy;
                const int start_c = (w+w2)*128+sce->ics.swb_offset[g];
                band = &s->psy.ch[s->cur_channel].psy_bands[(w+w2)*16+g];
                for (i = 0; i < sce->ics.swb_sizes[g]; i++) {
                    s->random_state  = lcg_random(s->random_state);
                    PNS[i] = s->random_state;
                }
                band_energy = s->fdsp->scalarproduct_float(PNS, PNS, sce->ics.swb_sizes[g]);
                scale = noise_amp/sqrtf(band_energy);
                s->fdsp->vector_fmul_scalar(PNS, PNS, scale, sce->ics.swb_sizes[g]);
                pns_senergy = s->fdsp->scalarproduct_float(PNS, PNS, sce->ics.swb_sizes[g]);
                pns_energy += pns_senergy;
                s->aacdsp.abs_pow34(NOR34, &sce->coeffs[start_c], sce->ics.swb_sizes[g]);
                s->aacdsp.abs_pow34(PNS34, PNS, sce->ics.swb_sizes[g]);
                dist1 += quantize_band_cost(s, &sce->coeffs[start_c],
                                            NOR34,
                                            sce->ics.swb_sizes[g],
                                            sce->sf_idx[(w+w2)*16+g],
                                            sce->band_alt[(w+w2)*16+g],
                                            lambda/band->threshold, INFINITY, NULL, NULL);
                /* Estimate rd on average as 5 bits for SF, 4 for the CB, plus spread energy * lambda/thr */
                dist2 += band->energy/(band->spread*band->spread)*lambda*dist_thresh/band->threshold;
            }
            if (g && sce->band_type[w*16+g-1] == NOISE_BT) {
                dist2 += 5;
            } else {
                dist2 += 9;
            }
            energy_ratio = pns_tgt_energy/pns_energy; /* Compensates for quantization error */
            sce->pns_ener[w*16+g] = energy_ratio*pns_tgt_energy;
            if (sce->zeroes[w*16+g] || !sce->band_alt[w*16+g] || (energy_ratio > 0.85f && energy_ratio < 1.25f && dist2 < dist1)) {
                sce->band_type[w*16+g] = NOISE_BT;
                sce->zeroes[w*16+g] = 0;
                prev = noise_sfi;
            } else {
                if (!sce->zeroes[w*16+g])
                    prev_sf = sce->sf_idx[w*16+g];
            }
        }
    }
}
 
static void mark_pns(AACEncContext *s, AVCodecContext *avctx, SingleChannelElement *sce)
{
    FFPsyBand *band;
    int w, g, w2;
    int wlen = 1024 / sce->ics.num_windows;
    int bandwidth, cutoff;
    const float lambda = s->lambda;
    const float freq_mult = avctx->sample_rate*0.5f/wlen;
    const float spread_threshold = FFMIN(0.75f, NOISE_SPREAD_THRESHOLD*FFMAX(0.5f, lambda/100.f));
    const float pns_transient_energy_r = FFMIN(0.7f, lambda / 140.f);
 
    /* PNS candidacy must use the coder's actual coding bandwidth (s->bandwidth,
     * fixed at init), not a separate heuristic, or it evaluates a different band
     * range than the coder later codes (NMR relies on this output directly). */
    bandwidth = s->bandwidth;
    cutoff = bandwidth * 2 * wlen / avctx->sample_rate;
 
    memcpy(sce->band_alt, sce->band_type, sizeof(sce->band_type));
    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
        for (g = 0; g < sce->ics.num_swb; g++) {
            float sfb_energy = 0.0f, threshold = 0.0f, spread = 2.0f;
            float min_energy = -1.0f, max_energy = 0.0f;
            const int start = sce->ics.swb_offset[g];
            const float freq = start*freq_mult;
            const float freq_boost = FFMAX(0.88f*freq/NOISE_LOW_LIMIT, 1.0f);
            if (freq < NOISE_LOW_LIMIT || start >= cutoff) {
                sce->can_pns[w*16+g] = 0;
                continue;
            }
            for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                band = &s->psy.ch[s->cur_channel].psy_bands[(w+w2)*16+g];
                sfb_energy += band->energy;
                spread     = FFMIN(spread, band->spread);
                threshold  += band->threshold;
                if (!w2) {
                    min_energy = max_energy = band->energy;
                } else {
                    min_energy = FFMIN(min_energy, band->energy);
                    max_energy = FFMAX(max_energy, band->energy);
                }
            }
 
            /* PNS is acceptable when all of these are true:
             * 1. high spread energy (noise-like band)
             * 2. near-threshold energy (high PE means the random nature of PNS content will be noticed)
             * 3. on short window groups, all windows have similar energy (variations in energy would be destroyed by PNS)
             */
            sce->pns_ener[w*16+g] = sfb_energy;
            {
                /* near-mask PNS class (E in [thr/4, 2*thr]): deletion
                 * candidates go to noise, not silence (AAC_PNSHOLE) */
                int near = sfb_energy < 2.0f * threshold &&
                           sfb_energy > threshold * 0.25f;
                if (near) {
                    /* deletion candidate: noise beats the ~silent rendition */
                    sce->can_pns[w*16+g] = spread >= spread_threshold &&
                                           min_energy >= 0.2f * max_energy;
                } else if (sfb_energy < threshold*sqrtf(1.5f/freq_boost) || spread < spread_threshold || min_energy < pns_transient_energy_r * max_energy) {
                    sce->can_pns[w*16+g] = 0;
                } else {
                    sce->can_pns[w*16+g] = 1;
                }
            }
        }
    }
}
 
static void search_for_ms(AACEncContext *s, ChannelElement *cpe)
{
    int start = 0, i, w, w2, g, sid_sf_boost, prev_mid, prev_side;
    uint8_t nextband0[128], nextband1[128];
    float *M   = s->scoefs + 128*0, *S   = s->scoefs + 128*1;
    float *L34 = s->scoefs + 128*2, *R34 = s->scoefs + 128*3;
    float *M34 = s->scoefs + 128*4, *S34 = s->scoefs + 128*5;
    const float lambda = s->lambda;
    const float mslambda = FFMIN(1.0f, lambda / 120.f);
    SingleChannelElement *sce0 = &cpe->ch[0];
    SingleChannelElement *sce1 = &cpe->ch[1];
    if (!cpe->common_window)
        return;
 
    /** Scout out next nonzero bands */
    ff_init_nextband_map(sce0, nextband0);
    ff_init_nextband_map(sce1, nextband1);
 
    prev_mid = sce0->sf_idx[0];
    prev_side = sce1->sf_idx[0];
    for (w = 0; w < sce0->ics.num_windows; w += sce0->ics.group_len[w]) {
        start = 0;
        for (g = 0; g < sce0->ics.num_swb; g++) {
            float bmax = bval2bmax(g * 17.0f / sce0->ics.num_swb) / 0.0045f;
            if (!cpe->is_mask[w*16+g])
                cpe->ms_mask[w*16+g] = 0;
            if (!sce0->zeroes[w*16+g] && !sce1->zeroes[w*16+g] && !cpe->is_mask[w*16+g]) {
                float Mmax = 0.0f, Smax = 0.0f;
 
                /* Must compute mid/side SF and book for the whole window group */
                for (w2 = 0; w2 < sce0->ics.group_len[w]; w2++) {
                    for (i = 0; i < sce0->ics.swb_sizes[g]; i++) {
                        M[i] = (sce0->coeffs[start+(w+w2)*128+i]
                              + sce1->coeffs[start+(w+w2)*128+i]) * 0.5;
                        S[i] =  M[i]
                              - sce1->coeffs[start+(w+w2)*128+i];
                    }
                    s->aacdsp.abs_pow34(M34, M, sce0->ics.swb_sizes[g]);
                    s->aacdsp.abs_pow34(S34, S, sce0->ics.swb_sizes[g]);
                    for (i = 0; i < sce0->ics.swb_sizes[g]; i++ ) {
                        Mmax = FFMAX(Mmax, M34[i]);
                        Smax = FFMAX(Smax, S34[i]);
                    }
                }
 
                for (sid_sf_boost = 0; sid_sf_boost < 4; sid_sf_boost++) {
                    float dist1 = 0.0f, dist2 = 0.0f;
                    int B0 = 0, B1 = 0;
                    int minidx;
                    int mididx, sididx;
                    int midcb, sidcb;
 
                    minidx = FFMIN(sce0->sf_idx[w*16+g], sce1->sf_idx[w*16+g]);
                    mididx = av_clip(minidx, 0, SCALE_MAX_POS - SCALE_DIV_512);
                    sididx = av_clip(minidx - sid_sf_boost * 3, 0, SCALE_MAX_POS - SCALE_DIV_512);
                    if (sce0->band_type[w*16+g] != NOISE_BT && sce1->band_type[w*16+g] != NOISE_BT
                        && (   !ff_sfdelta_can_replace(sce0, nextband0, prev_mid, mididx, w*16+g)
                            || !ff_sfdelta_can_replace(sce1, nextband1, prev_side, sididx, w*16+g))) {
                        /* scalefactor range violation, bad stuff, will decrease quality unacceptably */
                        continue;
                    }
 
                    midcb = find_min_book(Mmax, mididx);
                    sidcb = find_min_book(Smax, sididx);
 
                    /* No CB can be zero */
                    midcb = FFMAX(1,midcb);
                    sidcb = FFMAX(1,sidcb);
 
                    for (w2 = 0; w2 < sce0->ics.group_len[w]; w2++) {
                        FFPsyBand *band0 = &s->psy.ch[s->cur_channel+0].psy_bands[(w+w2)*16+g];
                        FFPsyBand *band1 = &s->psy.ch[s->cur_channel+1].psy_bands[(w+w2)*16+g];
                        float minthr = FFMIN(band0->threshold, band1->threshold);
                        int b1,b2,b3,b4;
                        for (i = 0; i < sce0->ics.swb_sizes[g]; i++) {
                            M[i] = (sce0->coeffs[start+(w+w2)*128+i]
                                  + sce1->coeffs[start+(w+w2)*128+i]) * 0.5;
                            S[i] =  M[i]
                                  - sce1->coeffs[start+(w+w2)*128+i];
                        }
 
                        s->aacdsp.abs_pow34(L34, sce0->coeffs+start+(w+w2)*128, sce0->ics.swb_sizes[g]);
                        s->aacdsp.abs_pow34(R34, sce1->coeffs+start+(w+w2)*128, sce0->ics.swb_sizes[g]);
                        s->aacdsp.abs_pow34(M34, M,                         sce0->ics.swb_sizes[g]);
                        s->aacdsp.abs_pow34(S34, S,                         sce0->ics.swb_sizes[g]);
                        dist1 += quantize_band_cost(s, &sce0->coeffs[start + (w+w2)*128],
                                                    L34,
                                                    sce0->ics.swb_sizes[g],
                                                    sce0->sf_idx[w*16+g],
                                                    sce0->band_type[w*16+g],
                                                    lambda / (band0->threshold + FLT_MIN), INFINITY, &b1, NULL);
                        dist1 += quantize_band_cost(s, &sce1->coeffs[start + (w+w2)*128],
                                                    R34,
                                                    sce1->ics.swb_sizes[g],
                                                    sce1->sf_idx[w*16+g],
                                                    sce1->band_type[w*16+g],
                                                    lambda / (band1->threshold + FLT_MIN), INFINITY, &b2, NULL);
                        dist2 += quantize_band_cost(s, M,
                                                    M34,
                                                    sce0->ics.swb_sizes[g],
                                                    mididx,
                                                    midcb,
                                                    lambda / (minthr + FLT_MIN), INFINITY, &b3, NULL);
                        dist2 += quantize_band_cost(s, S,
                                                    S34,
                                                    sce1->ics.swb_sizes[g],
                                                    sididx,
                                                    sidcb,
                                                    mslambda / (minthr * bmax + FLT_MIN), INFINITY, &b4, NULL);
                        B0 += b1+b2;
                        B1 += b3+b4;
                        dist1 -= b1+b2;
                        dist2 -= b3+b4;
                    }
                    cpe->ms_mask[w*16+g] = dist2 <= dist1 && B1 < B0;
                    if (cpe->ms_mask[w*16+g]) {
                        if (sce0->band_type[w*16+g] != NOISE_BT && sce1->band_type[w*16+g] != NOISE_BT) {
                            sce0->sf_idx[w*16+g] = mididx;
                            sce1->sf_idx[w*16+g] = sididx;
                            sce0->band_type[w*16+g] = midcb;
                            sce1->band_type[w*16+g] = sidcb;
                        } else if ((sce0->band_type[w*16+g] != NOISE_BT) ^ (sce1->band_type[w*16+g] != NOISE_BT)) {
                            /* ms_mask unneeded, and it confuses some decoders */
                            cpe->ms_mask[w*16+g] = 0;
                        }
                        break;
                    } else if (B1 > B0) {
                        /* More boost won't fix this */
                        break;
                    }
                }
            }
            if (!sce0->zeroes[w*16+g] && sce0->band_type[w*16+g] < RESERVED_BT)
                prev_mid = sce0->sf_idx[w*16+g];
            if (!sce1->zeroes[w*16+g] && !cpe->is_mask[w*16+g] && sce1->band_type[w*16+g] < RESERVED_BT)
                prev_side = sce1->sf_idx[w*16+g];
            start += sce0->ics.swb_sizes[g];
        }
    }
}
 
const AACCoefficientsEncoder ff_aac_coders[AAC_CODER_NB] = {
    [AAC_CODER_TWOLOOP] = {
        search_for_quantizers_twoloop,
        codebook_trellis_rate,
        quantize_and_encode_band,
        ff_aac_encode_tns_info,
        ff_aac_apply_tns,
        set_special_band_scalefactors,
        search_for_pns,
        mark_pns,
        ff_aac_search_for_tns,
        search_for_ms,
        ff_aac_search_for_is,
    },
    [AAC_CODER_FAST] = {
        search_for_quantizers_fast,
        codebook_trellis_rate,
        quantize_and_encode_band,
        ff_aac_encode_tns_info,
        ff_aac_apply_tns,
        set_special_band_scalefactors,
        search_for_pns,
        mark_pns,
        ff_aac_search_for_tns,
        search_for_ms,
        ff_aac_search_for_is,
    },
    [AAC_CODER_NMR] = {
        search_for_quantizers_nmr,
        codebook_trellis_rate,
        quantize_and_encode_band,
        ff_aac_encode_tns_info,
        ff_aac_apply_tns,
        set_special_band_scalefactors,
        NULL,                    /* PNS decided in the trellis (search_for_quantizers_nmr) */
        mark_pns,
        ff_aac_search_for_tns,
        NULL,
        NULL,
    },
};