FFmpeg/libavcodec/opus_celt.c

/*
 * Copyright (c) 2012 Andrew D'Addesio
 * Copyright (c) 2013-2014 Mozilla Corporation
 * Copyright (c) 2016 Rostislav Pehlivanov <atomnuker@gmail.com>
 *
 * 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
 * Opus CELT decoder
 */

#include "opus_celt.h"
#include "opustab.h"
#include "opus_pvq.h"

static void celt_decode_coarse_energy(CeltFrame *f, OpusRangeCoder *rc)
{
    int i, j;
    float prev[2] = {0};
    float alpha, beta;
    const uint8_t *model;

    /* use the 2D z-transform to apply prediction in both */
    /* the time domain (alpha) and the frequency domain (beta) */

    if (opus_rc_tell(rc)+3 <= f->framebits && ff_opus_rc_dec_log(rc, 3)) {
        /* intra frame */
        alpha = 0;
        beta  = 1.0f - 4915.0f/32768.0f;
        model = ff_celt_coarse_energy_dist[f->size][1];
    } else {
        alpha = ff_celt_alpha_coef[f->size];
        beta  = 1.0f - ff_celt_beta_coef[f->size];
        model = ff_celt_coarse_energy_dist[f->size][0];
    }

    for (i = 0; i < CELT_MAX_BANDS; i++) {
        for (j = 0; j < f->channels; j++) {
            CeltBlock *block = &f->block[j];
            float value;
            int available;

            if (i < f->start_band || i >= f->end_band) {
                block->energy[i] = 0.0;
                continue;
            }

            available = f->framebits - opus_rc_tell(rc);
            if (available >= 15) {
                /* decode using a Laplace distribution */
                int k = FFMIN(i, 20) << 1;
                value = ff_opus_rc_dec_laplace(rc, model[k] << 7, model[k+1] << 6);
            } else if (available >= 2) {
                int x = ff_opus_rc_dec_cdf(rc, ff_celt_model_energy_small);
                value = (x>>1) ^ -(x&1);
            } else if (available >= 1) {
                value = -(float)ff_opus_rc_dec_log(rc, 1);
            } else value = -1;

            block->energy[i] = FFMAX(-9.0f, block->energy[i]) * alpha + prev[j] + value;
            prev[j] += beta * value;
        }
    }
}

static void celt_decode_fine_energy(CeltFrame *f, OpusRangeCoder *rc)
{
    int i;
    for (i = f->start_band; i < f->end_band; i++) {
        int j;
        if (!f->fine_bits[i])
            continue;

        for (j = 0; j < f->channels; j++) {
            CeltBlock *block = &f->block[j];
            int q2;
            float offset;
            q2 = ff_opus_rc_get_raw(rc, f->fine_bits[i]);
            offset = (q2 + 0.5f) * (1 << (14 - f->fine_bits[i])) / 16384.0f - 0.5f;
            block->energy[i] += offset;
        }
    }
}

static void celt_decode_final_energy(CeltFrame *f, OpusRangeCoder *rc)
{
    int priority, i, j;
    int bits_left = f->framebits - opus_rc_tell(rc);

    for (priority = 0; priority < 2; priority++) {
        for (i = f->start_band; i < f->end_band && bits_left >= f->channels; i++) {
            if (f->fine_priority[i] != priority || f->fine_bits[i] >= CELT_MAX_FINE_BITS)
                continue;

            for (j = 0; j < f->channels; j++) {
                int q2;
                float offset;
                q2 = ff_opus_rc_get_raw(rc, 1);
                offset = (q2 - 0.5f) * (1 << (14 - f->fine_bits[i] - 1)) / 16384.0f;
                f->block[j].energy[i] += offset;
                bits_left--;
            }
        }
    }
}

static void celt_decode_tf_changes(CeltFrame *f, OpusRangeCoder *rc)
{
    int i, diff = 0, tf_select = 0, tf_changed = 0, tf_select_bit;
    int consumed, bits = f->transient ? 2 : 4;

    consumed = opus_rc_tell(rc);
    tf_select_bit = (f->size != 0 && consumed+bits+1 <= f->framebits);

    for (i = f->start_band; i < f->end_band; i++) {
        if (consumed+bits+tf_select_bit <= f->framebits) {
            diff ^= ff_opus_rc_dec_log(rc, bits);
            consumed = opus_rc_tell(rc);
            tf_changed |= diff;
        }
        f->tf_change[i] = diff;
        bits = f->transient ? 4 : 5;
    }

    if (tf_select_bit && ff_celt_tf_select[f->size][f->transient][0][tf_changed] !=
                         ff_celt_tf_select[f->size][f->transient][1][tf_changed])
        tf_select = ff_opus_rc_dec_log(rc, 1);

    for (i = f->start_band; i < f->end_band; i++) {
        f->tf_change[i] = ff_celt_tf_select[f->size][f->transient][tf_select][f->tf_change[i]];
    }
}

static void celt_decode_allocation(CeltFrame *f, OpusRangeCoder *rc)
{
    // approx. maximum bit allocation for each band before boost/trim
    int cap[CELT_MAX_BANDS];
    int boost[CELT_MAX_BANDS];
    int threshold[CELT_MAX_BANDS];
    int bits1[CELT_MAX_BANDS];
    int bits2[CELT_MAX_BANDS];
    int trim_offset[CELT_MAX_BANDS];

    int skip_start_band = f->start_band;
    int dynalloc       = 6;
    int alloctrim      = 5;
    int extrabits      = 0;

    int skip_bit             = 0;
    int intensity_stereo_bit = 0;
    int dual_stereo_bit      = 0;

    int remaining, bandbits;
    int low, high, total, done;
    int totalbits;
    int consumed;
    int i, j;

    consumed = opus_rc_tell(rc);

    /* obtain spread flag */
    f->spread = CELT_SPREAD_NORMAL;
    if (consumed + 4 <= f->framebits)
        f->spread = ff_opus_rc_dec_cdf(rc, ff_celt_model_spread);

    /* generate static allocation caps */
    for (i = 0; i < CELT_MAX_BANDS; i++) {
        cap[i] = (ff_celt_static_caps[f->size][f->channels - 1][i] + 64)
                 * ff_celt_freq_range[i] << (f->channels - 1) << f->size >> 2;
    }

    /* obtain band boost */
    totalbits = f->framebits << 3; // convert to 1/8 bits
    consumed = opus_rc_tell_frac(rc);
    for (i = f->start_band; i < f->end_band; i++) {
        int quanta, band_dynalloc;

        boost[i] = 0;

        quanta = ff_celt_freq_range[i] << (f->channels - 1) << f->size;
        quanta = FFMIN(quanta << 3, FFMAX(6 << 3, quanta));
        band_dynalloc = dynalloc;
        while (consumed + (band_dynalloc<<3) < totalbits && boost[i] < cap[i]) {
            int add = ff_opus_rc_dec_log(rc, band_dynalloc);
            consumed = opus_rc_tell_frac(rc);
            if (!add)
                break;

            boost[i]     += quanta;
            totalbits    -= quanta;
            band_dynalloc = 1;
        }
        /* dynalloc is more likely to occur if it's already been used for earlier bands */
        if (boost[i])
            dynalloc = FFMAX(2, dynalloc - 1);
    }

    /* obtain allocation trim */
    if (consumed + (6 << 3) <= totalbits)
        alloctrim = ff_opus_rc_dec_cdf(rc, ff_celt_model_alloc_trim);

    /* anti-collapse bit reservation */
    totalbits = (f->framebits << 3) - opus_rc_tell_frac(rc) - 1;
    f->anticollapse_needed = 0;
    if (f->blocks > 1 && f->size >= 2 &&
        totalbits >= ((f->size + 2) << 3))
        f->anticollapse_needed = 1 << 3;
    totalbits -= f->anticollapse_needed;

    /* band skip bit reservation */
    if (totalbits >= 1 << 3)
        skip_bit = 1 << 3;
    totalbits -= skip_bit;

    /* intensity/dual stereo bit reservation */
    if (f->channels == 2) {
        intensity_stereo_bit = ff_celt_log2_frac[f->end_band - f->start_band];
        if (intensity_stereo_bit <= totalbits) {
            totalbits -= intensity_stereo_bit;
            if (totalbits >= 1 << 3) {
                dual_stereo_bit = 1 << 3;
                totalbits -= 1 << 3;
            }
        } else
            intensity_stereo_bit = 0;
    }

    for (i = f->start_band; i < f->end_band; i++) {
        int trim     = alloctrim - 5 - f->size;
        int band     = ff_celt_freq_range[i] * (f->end_band - i - 1);
        int duration = f->size + 3;
        int scale    = duration + f->channels - 1;

        /* PVQ minimum allocation threshold, below this value the band is
         * skipped */
        threshold[i] = FFMAX(3 * ff_celt_freq_range[i] << duration >> 4,
                             f->channels << 3);

        trim_offset[i] = trim * (band << scale) >> 6;

        if (ff_celt_freq_range[i] << f->size == 1)
            trim_offset[i] -= f->channels << 3;
    }

    /* bisection */
    low  = 1;
    high = CELT_VECTORS - 1;
    while (low <= high) {
        int center = (low + high) >> 1;
        done = total = 0;

        for (i = f->end_band - 1; i >= f->start_band; i--) {
            bandbits = ff_celt_freq_range[i] * ff_celt_static_alloc[center][i]
                       << (f->channels - 1) << f->size >> 2;

            if (bandbits)
                bandbits = FFMAX(0, bandbits + trim_offset[i]);
            bandbits += boost[i];

            if (bandbits >= threshold[i] || done) {
                done = 1;
                total += FFMIN(bandbits, cap[i]);
            } else if (bandbits >= f->channels << 3)
                total += f->channels << 3;
        }

        if (total > totalbits)
            high = center - 1;
        else
            low = center + 1;
    }
    high = low--;

    for (i = f->start_band; i < f->end_band; i++) {
        bits1[i] = ff_celt_freq_range[i] * ff_celt_static_alloc[low][i]
                   << (f->channels - 1) << f->size >> 2;
        bits2[i] = high >= CELT_VECTORS ? cap[i] :
                   ff_celt_freq_range[i] * ff_celt_static_alloc[high][i]
                   << (f->channels - 1) << f->size >> 2;

        if (bits1[i])
            bits1[i] = FFMAX(0, bits1[i] + trim_offset[i]);
        if (bits2[i])
            bits2[i] = FFMAX(0, bits2[i] + trim_offset[i]);
        if (low)
            bits1[i] += boost[i];
        bits2[i] += boost[i];

        if (boost[i])
            skip_start_band = i;
        bits2[i] = FFMAX(0, bits2[i] - bits1[i]);
    }

    /* bisection */
    low  = 0;
    high = 1 << CELT_ALLOC_STEPS;
    for (i = 0; i < CELT_ALLOC_STEPS; i++) {
        int center = (low + high) >> 1;
        done = total = 0;

        for (j = f->end_band - 1; j >= f->start_band; j--) {
            bandbits = bits1[j] + (center * bits2[j] >> CELT_ALLOC_STEPS);

            if (bandbits >= threshold[j] || done) {
                done = 1;
                total += FFMIN(bandbits, cap[j]);
            } else if (bandbits >= f->channels << 3)
                total += f->channels << 3;
        }
        if (total > totalbits)
            high = center;
        else
            low = center;
    }

    done = total = 0;
    for (i = f->end_band - 1; i >= f->start_band; i--) {
        bandbits = bits1[i] + (low * bits2[i] >> CELT_ALLOC_STEPS);

        if (bandbits >= threshold[i] || done)
            done = 1;
        else
            bandbits = (bandbits >= f->channels << 3) ?
                       f->channels << 3 : 0;

        bandbits     = FFMIN(bandbits, cap[i]);
        f->pulses[i] = bandbits;
        total      += bandbits;
    }

    /* band skipping */
    for (f->coded_bands = f->end_band; ; f->coded_bands--) {
        int allocation;
        j = f->coded_bands - 1;

        if (j == skip_start_band) {
            /* all remaining bands are not skipped */
            totalbits += skip_bit;
            break;
        }

        /* determine the number of bits available for coding "do not skip" markers */
        remaining   = totalbits - total;
        bandbits    = remaining / (ff_celt_freq_bands[j+1] - ff_celt_freq_bands[f->start_band]);
        remaining  -= bandbits  * (ff_celt_freq_bands[j+1] - ff_celt_freq_bands[f->start_band]);
        allocation  = f->pulses[j] + bandbits * ff_celt_freq_range[j]
                      + FFMAX(0, remaining - (ff_celt_freq_bands[j] - ff_celt_freq_bands[f->start_band]));

        /* a "do not skip" marker is only coded if the allocation is
           above the chosen threshold */
        if (allocation >= FFMAX(threshold[j], (f->channels + 1) <<3 )) {
            if (ff_opus_rc_dec_log(rc, 1))
                break;

            total      += 1 << 3;
            allocation -= 1 << 3;
        }

        /* the band is skipped, so reclaim its bits */
        total -= f->pulses[j];
        if (intensity_stereo_bit) {
            total -= intensity_stereo_bit;
            intensity_stereo_bit = ff_celt_log2_frac[j - f->start_band];
            total += intensity_stereo_bit;
        }

        total += f->pulses[j] = (allocation >= f->channels << 3) ?
                              f->channels << 3 : 0;
    }

    /* obtain stereo flags */
    f->intensity_stereo = 0;
    f->dual_stereo      = 0;
    if (intensity_stereo_bit)
        f->intensity_stereo = f->start_band +
                          ff_opus_rc_dec_uint(rc, f->coded_bands + 1 - f->start_band);
    if (f->intensity_stereo <= f->start_band)
        totalbits += dual_stereo_bit; /* no intensity stereo means no dual stereo */
    else if (dual_stereo_bit)
        f->dual_stereo = ff_opus_rc_dec_log(rc, 1);

    /* supply the remaining bits in this frame to lower bands */
    remaining = totalbits - total;
    bandbits  = remaining / (ff_celt_freq_bands[f->coded_bands] - ff_celt_freq_bands[f->start_band]);
    remaining -= bandbits * (ff_celt_freq_bands[f->coded_bands] - ff_celt_freq_bands[f->start_band]);
    for (i = f->start_band; i < f->coded_bands; i++) {
        int bits = FFMIN(remaining, ff_celt_freq_range[i]);

        f->pulses[i] += bits + bandbits * ff_celt_freq_range[i];
        remaining    -= bits;
    }

    for (i = f->start_band; i < f->coded_bands; i++) {
        int N = ff_celt_freq_range[i] << f->size;
        int prev_extra = extrabits;
        f->pulses[i] += extrabits;

        if (N > 1) {
            int dof;        // degrees of freedom
            int temp;       // dof * channels * log(dof)
            int offset;     // fine energy quantization offset, i.e.
                            // extra bits assigned over the standard
                            // totalbits/dof
            int fine_bits, max_bits;

            extrabits = FFMAX(0, f->pulses[i] - cap[i]);
            f->pulses[i] -= extrabits;

            /* intensity stereo makes use of an extra degree of freedom */
            dof = N * f->channels
                  + (f->channels == 2 && N > 2 && !f->dual_stereo && i < f->intensity_stereo);
            temp = dof * (ff_celt_log_freq_range[i] + (f->size<<3));
            offset = (temp >> 1) - dof * CELT_FINE_OFFSET;
            if (N == 2) /* dof=2 is the only case that doesn't fit the model */
                offset += dof<<1;

            /* grant an additional bias for the first and second pulses */
            if (f->pulses[i] + offset < 2 * (dof << 3))
                offset += temp >> 2;
            else if (f->pulses[i] + offset < 3 * (dof << 3))
                offset += temp >> 3;

            fine_bits = (f->pulses[i] + offset + (dof << 2)) / (dof << 3);
            max_bits  = FFMIN((f->pulses[i]>>3) >> (f->channels - 1),
                              CELT_MAX_FINE_BITS);

            max_bits  = FFMAX(max_bits, 0);

            f->fine_bits[i] = av_clip(fine_bits, 0, max_bits);

            /* if fine_bits was rounded down or capped,
               give priority for the final fine energy pass */
            f->fine_priority[i] = (f->fine_bits[i] * (dof<<3) >= f->pulses[i] + offset);

            /* the remaining bits are assigned to PVQ */
            f->pulses[i] -= f->fine_bits[i] << (f->channels - 1) << 3;
        } else {
            /* all bits go to fine energy except for the sign bit */
            extrabits = FFMAX(0, f->pulses[i] - (f->channels << 3));
            f->pulses[i] -= extrabits;
            f->fine_bits[i] = 0;
            f->fine_priority[i] = 1;
        }

        /* hand back a limited number of extra fine energy bits to this band */
        if (extrabits > 0) {
            int fineextra = FFMIN(extrabits >> (f->channels + 2),
                                  CELT_MAX_FINE_BITS - f->fine_bits[i]);
            f->fine_bits[i] += fineextra;

            fineextra <<= f->channels + 2;
            f->fine_priority[i] = (fineextra >= extrabits - prev_extra);
            extrabits -= fineextra;
        }
    }
    f->remaining = extrabits;

    /* skipped bands dedicate all of their bits for fine energy */
    for (; i < f->end_band; i++) {
        f->fine_bits[i]     = f->pulses[i] >> (f->channels - 1) >> 3;
        f->pulses[i]        = 0;
        f->fine_priority[i] = f->fine_bits[i] < 1;
    }
}

static void celt_denormalize(CeltFrame *f, CeltBlock *block, float *data)
{
    int i, j;

    for (i = f->start_band; i < f->end_band; i++) {
        float *dst = data + (ff_celt_freq_bands[i] << f->size);
        float norm = exp2(block->energy[i] + ff_celt_mean_energy[i]);

        for (j = 0; j < ff_celt_freq_range[i] << f->size; j++)
            dst[j] *= norm;
    }
}

static void celt_postfilter_apply_transition(CeltBlock *block, float *data)
{
    const int T0 = block->pf_period_old;
    const int T1 = block->pf_period;

    float g00, g01, g02;
    float g10, g11, g12;

    float x0, x1, x2, x3, x4;

    int i;

    if (block->pf_gains[0]     == 0.0 &&
        block->pf_gains_old[0] == 0.0)
        return;

    g00 = block->pf_gains_old[0];
    g01 = block->pf_gains_old[1];
    g02 = block->pf_gains_old[2];
    g10 = block->pf_gains[0];
    g11 = block->pf_gains[1];
    g12 = block->pf_gains[2];

    x1 = data[-T1 + 1];
    x2 = data[-T1];
    x3 = data[-T1 - 1];
    x4 = data[-T1 - 2];

    for (i = 0; i < CELT_OVERLAP; i++) {
        float w = ff_celt_window2[i];
        x0 = data[i - T1 + 2];

        data[i] +=  (1.0 - w) * g00 * data[i - T0]                          +
                    (1.0 - w) * g01 * (data[i - T0 - 1] + data[i - T0 + 1]) +
                    (1.0 - w) * g02 * (data[i - T0 - 2] + data[i - T0 + 2]) +
                    w         * g10 * x2                                    +
                    w         * g11 * (x1 + x3)                             +
                    w         * g12 * (x0 + x4);
        x4 = x3;
        x3 = x2;
        x2 = x1;
        x1 = x0;
    }
}

static void celt_postfilter_apply(CeltBlock *block, float *data, int len)
{
    const int T = block->pf_period;
    float g0, g1, g2;
    float x0, x1, x2, x3, x4;
    int i;

    if (block->pf_gains[0] == 0.0 || len <= 0)
        return;

    g0 = block->pf_gains[0];
    g1 = block->pf_gains[1];
    g2 = block->pf_gains[2];

    x4 = data[-T - 2];
    x3 = data[-T - 1];
    x2 = data[-T];
    x1 = data[-T + 1];

    for (i = 0; i < len; i++) {
        x0 = data[i - T + 2];
        data[i] += g0 * x2        +
                   g1 * (x1 + x3) +
                   g2 * (x0 + x4);
        x4 = x3;
        x3 = x2;
        x2 = x1;
        x1 = x0;
    }
}

static void celt_postfilter(CeltFrame *f, CeltBlock *block)
{
    int len = f->blocksize * f->blocks;

    celt_postfilter_apply_transition(block, block->buf + 1024);

    block->pf_period_old = block->pf_period;
    memcpy(block->pf_gains_old, block->pf_gains, sizeof(block->pf_gains));

    block->pf_period = block->pf_period_new;
    memcpy(block->pf_gains, block->pf_gains_new, sizeof(block->pf_gains));

    if (len > CELT_OVERLAP) {
        celt_postfilter_apply_transition(block, block->buf + 1024 + CELT_OVERLAP);
        celt_postfilter_apply(block, block->buf + 1024 + 2 * CELT_OVERLAP,
                              len - 2 * CELT_OVERLAP);

        block->pf_period_old = block->pf_period;
        memcpy(block->pf_gains_old, block->pf_gains, sizeof(block->pf_gains));
    }

    memmove(block->buf, block->buf + len, (1024 + CELT_OVERLAP / 2) * sizeof(float));
}

static int parse_postfilter(CeltFrame *f, OpusRangeCoder *rc, int consumed)
{
    static const float postfilter_taps[3][3] = {
        { 0.3066406250f, 0.2170410156f, 0.1296386719f },
        { 0.4638671875f, 0.2680664062f, 0.0           },
        { 0.7998046875f, 0.1000976562f, 0.0           }
    };
    int i;

    memset(f->block[0].pf_gains_new, 0, sizeof(f->block[0].pf_gains_new));
    memset(f->block[1].pf_gains_new, 0, sizeof(f->block[1].pf_gains_new));

    if (f->start_band == 0 && consumed + 16 <= f->framebits) {
        int has_postfilter = ff_opus_rc_dec_log(rc, 1);
        if (has_postfilter) {
            float gain;
            int tapset, octave, period;

            octave = ff_opus_rc_dec_uint(rc, 6);
            period = (16 << octave) + ff_opus_rc_get_raw(rc, 4 + octave) - 1;
            gain   = 0.09375f * (ff_opus_rc_get_raw(rc, 3) + 1);
            tapset = (opus_rc_tell(rc) + 2 <= f->framebits) ?
                     ff_opus_rc_dec_cdf(rc, ff_celt_model_tapset) : 0;

            for (i = 0; i < 2; i++) {
                CeltBlock *block = &f->block[i];

                block->pf_period_new = FFMAX(period, CELT_POSTFILTER_MINPERIOD);
                block->pf_gains_new[0] = gain * postfilter_taps[tapset][0];
                block->pf_gains_new[1] = gain * postfilter_taps[tapset][1];
                block->pf_gains_new[2] = gain * postfilter_taps[tapset][2];
            }
        }

        consumed = opus_rc_tell(rc);
    }

    return consumed;
}

static void process_anticollapse(CeltFrame *f, CeltBlock *block, float *X)
{
    int i, j, k;

    for (i = f->start_band; i < f->end_band; i++) {
        int renormalize = 0;
        float *xptr;
        float prev[2];
        float Ediff, r;
        float thresh, sqrt_1;
        int depth;

        /* depth in 1/8 bits */
        depth = (1 + f->pulses[i]) / (ff_celt_freq_range[i] << f->size);
        thresh = exp2f(-1.0 - 0.125f * depth);
        sqrt_1 = 1.0f / sqrtf(ff_celt_freq_range[i] << f->size);

        xptr = X + (ff_celt_freq_bands[i] << f->size);

        prev[0] = block->prev_energy[0][i];
        prev[1] = block->prev_energy[1][i];
        if (f->channels == 1) {
            CeltBlock *block1 = &f->block[1];

            prev[0] = FFMAX(prev[0], block1->prev_energy[0][i]);
            prev[1] = FFMAX(prev[1], block1->prev_energy[1][i]);
        }
        Ediff = block->energy[i] - FFMIN(prev[0], prev[1]);
        Ediff = FFMAX(0, Ediff);

        /* r needs to be multiplied by 2 or 2*sqrt(2) depending on LM because
        short blocks don't have the same energy as long */
        r = exp2(1 - Ediff);
        if (f->size == 3)
            r *= M_SQRT2;
        r = FFMIN(thresh, r) * sqrt_1;
        for (k = 0; k < 1 << f->size; k++) {
            /* Detect collapse */
            if (!(block->collapse_masks[i] & 1 << k)) {
                /* Fill with noise */
                for (j = 0; j < ff_celt_freq_range[i]; j++)
                    xptr[(j << f->size) + k] = (celt_rng(f) & 0x8000) ? r : -r;
                renormalize = 1;
            }
        }

        /* We just added some energy, so we need to renormalize */
        if (renormalize)
            celt_renormalize_vector(xptr, ff_celt_freq_range[i] << f->size, 1.0f);
    }
}

static void celt_decode_bands(CeltFrame *f, OpusRangeCoder *rc)
{
    float lowband_scratch[8 * 22];
    float norm[2 * 8 * 100];

    int totalbits = (f->framebits << 3) - f->anticollapse_needed;

    int update_lowband = 1;
    int lowband_offset = 0;

    int i, j;

    memset(f->block[0].coeffs, 0, sizeof(f->block[0].coeffs));
    memset(f->block[1].coeffs, 0, sizeof(f->block[0].coeffs));

    for (i = f->start_band; i < f->end_band; i++) {
        int band_offset = ff_celt_freq_bands[i] << f->size;
        int band_size   = ff_celt_freq_range[i] << f->size;
        float *X = f->block[0].coeffs + band_offset;
        float *Y = (f->channels == 2) ? f->block[1].coeffs + band_offset : NULL;

        int consumed = opus_rc_tell_frac(rc);
        float *norm2 = norm + 8 * 100;
        int effective_lowband = -1;
        unsigned int cm[2];
        int b;

        /* Compute how many bits we want to allocate to this band */
        if (i != f->start_band)
            f->remaining -= consumed;
        f->remaining2 = totalbits - consumed - 1;
        if (i <= f->coded_bands - 1) {
            int curr_balance = f->remaining / FFMIN(3, f->coded_bands-i);
            b = av_clip_uintp2(FFMIN(f->remaining2 + 1, f->pulses[i] + curr_balance), 14);
        } else
            b = 0;

        if (ff_celt_freq_bands[i] - ff_celt_freq_range[i] >= ff_celt_freq_bands[f->start_band] &&
            (update_lowband || lowband_offset == 0))
            lowband_offset = i;

        /* Get a conservative estimate of the collapse_mask's for the bands we're
        going to be folding from. */
        if (lowband_offset != 0 && (f->spread != CELT_SPREAD_AGGRESSIVE ||
                                    f->blocks > 1 || f->tf_change[i] < 0)) {
            int foldstart, foldend;

            /* This ensures we never repeat spectral content within one band */
            effective_lowband = FFMAX(ff_celt_freq_bands[f->start_band],
                                      ff_celt_freq_bands[lowband_offset] - ff_celt_freq_range[i]);
            foldstart = lowband_offset;
            while (ff_celt_freq_bands[--foldstart] > effective_lowband);
            foldend = lowband_offset - 1;
            while (ff_celt_freq_bands[++foldend] < effective_lowband + ff_celt_freq_range[i]);

            cm[0] = cm[1] = 0;
            for (j = foldstart; j < foldend; j++) {
                cm[0] |= f->block[0].collapse_masks[j];
                cm[1] |= f->block[f->channels - 1].collapse_masks[j];
            }
        } else
            /* Otherwise, we'll be using the LCG to fold, so all blocks will (almost
            always) be non-zero.*/
            cm[0] = cm[1] = (1 << f->blocks) - 1;

        if (f->dual_stereo && i == f->intensity_stereo) {
            /* Switch off dual stereo to do intensity */
            f->dual_stereo = 0;
            for (j = ff_celt_freq_bands[f->start_band] << f->size; j < band_offset; j++)
                norm[j] = (norm[j] + norm2[j]) / 2;
        }

        if (f->dual_stereo) {
            cm[0] = ff_celt_decode_band(f, rc, i, X, NULL, band_size, b / 2, f->blocks,
                                        effective_lowband != -1 ? norm + (effective_lowband << f->size) : NULL, f->size,
                                        norm + band_offset, 0, 1.0f, lowband_scratch, cm[0]);

            cm[1] = ff_celt_decode_band(f, rc, i, Y, NULL, band_size, b/2, f->blocks,
                                        effective_lowband != -1 ? norm2 + (effective_lowband << f->size) : NULL, f->size,
                                        norm2 + band_offset, 0, 1.0f, lowband_scratch, cm[1]);
        } else {
            cm[0] = ff_celt_decode_band(f, rc, i, X, Y, band_size, b, f->blocks,
                                        effective_lowband != -1 ? norm + (effective_lowband << f->size) : NULL, f->size,
                                        norm + band_offset, 0, 1.0f, lowband_scratch, cm[0]|cm[1]);
            cm[1] = cm[0];
        }

        f->block[0].collapse_masks[i]               = (uint8_t)cm[0];
        f->block[f->channels - 1].collapse_masks[i] = (uint8_t)cm[1];
        f->remaining += f->pulses[i] + consumed;

        /* Update the folding position only as long as we have 1 bit/sample depth */
        update_lowband = (b > band_size << 3);
    }
}

int ff_celt_decode_frame(CeltFrame *f, OpusRangeCoder *rc,
                         float **output, int channels, int frame_size,
                         int start_band,  int end_band)
{
    int i, j;
    int consumed;           // bits of entropy consumed thus far for this frame
    MDCT15Context *imdct;
    float imdct_scale = 1.0;

    if (channels != 1 && channels != 2) {
        av_log(f->avctx, AV_LOG_ERROR, "Invalid number of coded channels: %d\n",
               channels);
        return AVERROR_INVALIDDATA;
    }
    if (start_band < 0 || start_band > end_band || end_band > CELT_MAX_BANDS) {
        av_log(f->avctx, AV_LOG_ERROR, "Invalid start/end band: %d %d\n",
               start_band, end_band);
        return AVERROR_INVALIDDATA;
    }

    f->silence        = 0;
    f->transient      = 0;
    f->anticollapse   = 0;
    f->flushed        = 0;
    f->channels       = channels;
    f->start_band     = start_band;
    f->end_band       = end_band;
    f->framebits      = rc->rb.bytes * 8;

    f->size = av_log2(frame_size / CELT_SHORT_BLOCKSIZE);
    if (f->size > CELT_MAX_LOG_BLOCKS ||
        frame_size != CELT_SHORT_BLOCKSIZE * (1 << f->size)) {
        av_log(f->avctx, AV_LOG_ERROR, "Invalid CELT frame size: %d\n",
               frame_size);
        return AVERROR_INVALIDDATA;
    }

    if (!f->output_channels)
        f->output_channels = channels;

    memset(f->block[0].collapse_masks, 0, sizeof(f->block[0].collapse_masks));
    memset(f->block[1].collapse_masks, 0, sizeof(f->block[1].collapse_masks));

    consumed = opus_rc_tell(rc);

    /* obtain silence flag */
    if (consumed >= f->framebits)
        f->silence = 1;
    else if (consumed == 1)
        f->silence = ff_opus_rc_dec_log(rc, 15);


    if (f->silence) {
        consumed = f->framebits;
        rc->total_bits += f->framebits - opus_rc_tell(rc);
    }

    /* obtain post-filter options */
    consumed = parse_postfilter(f, rc, consumed);

    /* obtain transient flag */
    if (f->size != 0 && consumed+3 <= f->framebits)
        f->transient = ff_opus_rc_dec_log(rc, 3);

    f->blocks    = f->transient ? 1 << f->size : 1;
    f->blocksize = frame_size / f->blocks;

    imdct = f->imdct[f->transient ? 0 : f->size];

    if (channels == 1) {
        for (i = 0; i < CELT_MAX_BANDS; i++)
            f->block[0].energy[i] = FFMAX(f->block[0].energy[i], f->block[1].energy[i]);
    }

    celt_decode_coarse_energy(f, rc);
    celt_decode_tf_changes   (f, rc);
    celt_decode_allocation   (f, rc);
    celt_decode_fine_energy  (f, rc);
    celt_decode_bands        (f, rc);

    if (f->anticollapse_needed)
        f->anticollapse = ff_opus_rc_get_raw(rc, 1);

    celt_decode_final_energy(f, rc);

    /* apply anti-collapse processing and denormalization to
     * each coded channel */
    for (i = 0; i < f->channels; i++) {
        CeltBlock *block = &f->block[i];

        if (f->anticollapse)
            process_anticollapse(f, block, f->block[i].coeffs);

        celt_denormalize(f, block, f->block[i].coeffs);
    }

    /* stereo -> mono downmix */
    if (f->output_channels < f->channels) {
        f->dsp->vector_fmac_scalar(f->block[0].coeffs, f->block[1].coeffs, 1.0, FFALIGN(frame_size, 16));
        imdct_scale = 0.5;
    } else if (f->output_channels > f->channels)
        memcpy(f->block[1].coeffs, f->block[0].coeffs, frame_size * sizeof(float));

    if (f->silence) {
        for (i = 0; i < 2; i++) {
            CeltBlock *block = &f->block[i];

            for (j = 0; j < FF_ARRAY_ELEMS(block->energy); j++)
                block->energy[j] = CELT_ENERGY_SILENCE;
        }
        memset(f->block[0].coeffs, 0, sizeof(f->block[0].coeffs));
        memset(f->block[1].coeffs, 0, sizeof(f->block[1].coeffs));
    }

    /* transform and output for each output channel */
    for (i = 0; i < f->output_channels; i++) {
        CeltBlock *block = &f->block[i];
        float m = block->emph_coeff;

        /* iMDCT and overlap-add */
        for (j = 0; j < f->blocks; j++) {
            float *dst  = block->buf + 1024 + j * f->blocksize;

            imdct->imdct_half(imdct, dst + CELT_OVERLAP / 2, f->block[i].coeffs + j,
                              f->blocks, imdct_scale);
            f->dsp->vector_fmul_window(dst, dst, dst + CELT_OVERLAP / 2,
                                       ff_celt_window, CELT_OVERLAP / 2);
        }

        /* postfilter */
        celt_postfilter(f, block);

        /* deemphasis and output scaling */
        for (j = 0; j < frame_size; j++) {
            float tmp = block->buf[1024 - frame_size + j] + m;
            m = tmp * CELT_EMPH_COEFF;
            output[i][j] = tmp / 32768.;
        }
        block->emph_coeff = m;
    }

    if (channels == 1)
        memcpy(f->block[1].energy, f->block[0].energy, sizeof(f->block[0].energy));

    for (i = 0; i < 2; i++ ) {
        CeltBlock *block = &f->block[i];

        if (!f->transient) {
            memcpy(block->prev_energy[1], block->prev_energy[0], sizeof(block->prev_energy[0]));
            memcpy(block->prev_energy[0], block->energy,         sizeof(block->prev_energy[0]));
        } else {
            for (j = 0; j < CELT_MAX_BANDS; j++)
                block->prev_energy[0][j] = FFMIN(block->prev_energy[0][j], block->energy[j]);
        }

        for (j = 0; j < f->start_band; j++) {
            block->prev_energy[0][j] = CELT_ENERGY_SILENCE;
            block->energy[j]         = 0.0;
        }
        for (j = f->end_band; j < CELT_MAX_BANDS; j++) {
            block->prev_energy[0][j] = CELT_ENERGY_SILENCE;
            block->energy[j]         = 0.0;
        }
    }

    f->seed = rc->range;

    return 0;
}

void ff_celt_flush(CeltFrame *f)
{
    int i, j;

    if (f->flushed)
        return;

    for (i = 0; i < 2; i++) {
        CeltBlock *block = &f->block[i];

        for (j = 0; j < CELT_MAX_BANDS; j++)
            block->prev_energy[0][j] = block->prev_energy[1][j] = CELT_ENERGY_SILENCE;

        memset(block->energy, 0, sizeof(block->energy));
        memset(block->buf,    0, sizeof(block->buf));

        memset(block->pf_gains,     0, sizeof(block->pf_gains));
        memset(block->pf_gains_old, 0, sizeof(block->pf_gains_old));
        memset(block->pf_gains_new, 0, sizeof(block->pf_gains_new));

        block->emph_coeff = 0.0;
    }
    f->seed = 0;

    f->flushed = 1;
}

void ff_celt_free(CeltFrame **f)
{
    CeltFrame *frm = *f;
    int i;

    if (!frm)
        return;

    for (i = 0; i < FF_ARRAY_ELEMS(frm->imdct); i++)
        ff_mdct15_uninit(&frm->imdct[i]);

    av_freep(&frm->dsp);
    av_freep(f);
}

int ff_celt_init(AVCodecContext *avctx, CeltFrame **f, int output_channels)
{
    CeltFrame *frm;
    int i, ret;

    if (output_channels != 1 && output_channels != 2) {
        av_log(avctx, AV_LOG_ERROR, "Invalid number of output channels: %d\n",
               output_channels);
        return AVERROR(EINVAL);
    }

    frm = av_mallocz(sizeof(*frm));
    if (!frm)
        return AVERROR(ENOMEM);

    frm->avctx           = avctx;
    frm->output_channels = output_channels;

    for (i = 0; i < FF_ARRAY_ELEMS(frm->imdct); i++) {
        ret = ff_mdct15_init(&frm->imdct[i], 1, i + 3, -1.0f);
        if (ret < 0)
            goto fail;
    }

    frm->dsp = avpriv_float_dsp_alloc(avctx->flags & AV_CODEC_FLAG_BITEXACT);
    if (!frm->dsp) {
        ret = AVERROR(ENOMEM);
        goto fail;
    }

    ff_celt_flush(frm);

    *f = frm;

    return 0;
fail:
    ff_celt_free(&frm);
    return ret;
}