aboutsummaryrefslogtreecommitdiffstats
path: root/libavcodec/aaccoder_twoloop.h
blob: 8e1bc88a8538f41e71a1bd1e4168c78c04d27fa5 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
/*
 * AAC encoder twoloop coder
 * 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 encoder twoloop coder
 * @author Konstantin Shishkov, Claudio Freire
 */

/**
 * This file contains a template for the twoloop coder function.
 * It needs to be provided, externally, as an already included declaration,
 * the following functions from aacenc_quantization/util.h. They're not included
 * explicitly here to make it possible to provide alternative implementations:
 *  - quantize_band_cost
 *  - abs_pow34_v
 *  - find_max_val
 *  - find_min_book
 *  - find_form_factor
 */

#ifndef AVCODEC_AACCODER_TWOLOOP_H
#define AVCODEC_AACCODER_TWOLOOP_H

#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"

/** Frequency in Hz for lower limit of noise substitution **/
#define NOISE_LOW_LIMIT 4000

#define sclip(x) av_clip(x,60,218)

/* Reflects the cost to change codebooks */
static inline int ff_pns_bits(SingleChannelElement *sce, int w, int g)
{
    return (!g || !sce->zeroes[w*16+g-1] || !sce->can_pns[w*16+g-1]) ? 9 : 5;
}

/**
 * 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, recomprd;
    int destbits = avctx->bit_rate * 1024.0 / avctx->sample_rate
        / ((avctx->flags & AV_CODEC_FLAG_QSCALE) ? 2.0f : avctx->channels)
        * (lambda / 120.f);
    int refbits = destbits;
    int toomanybits, toofewbits;
    char nzs[128];
    uint8_t nextband[128];
    int maxsf[128], minsf[128];
    float dists[128] = { 0 }, qenergies[128] = { 0 }, uplims[128], euplims[128], energies[128];
    float maxvals[128], spread_thr_r[128];
    float min_spread_thr_r, max_spread_thr_r;

    /**
     * rdlambda controls the maximum tolerated distortion. Twoloop
     * will keep iterating until it fails to lower it or it reaches
     * ulimit * rdlambda. Keeping it low increases quality on difficult
     * signals, but lower it too much, and bits will be taken from weak
     * signals, creating "holes". A balance is necessary.
     * rdmax and rdmin specify the relative deviation from rdlambda
     * allowed for tonality compensation
     */
    float rdlambda = av_clipf(2.0f * 120.f / lambda, 0.0625f, 16.0f);
    const float nzslope = 1.5f;
    float rdmin = 0.03125f;
    float rdmax = 1.0f;

    /**
     * sfoffs controls an offset of optmium allocation that will be
     * applied based on lambda. Keep it real and modest, the loop
     * will take care of the rest, this just accelerates convergence
     */
    float sfoffs = av_clipf(log2f(120.0f / lambda) * 4.0f, -5, 10);

    int fflag, minscaler, maxscaler, nminscaler;
    int its  = 0;
    int maxits = 30;
    int allz = 0;
    int tbits;
    int cutoff = 1024;
    int pns_start_pos;
    int prev;

    /**
     * zeroscale controls a multiplier of the threshold, if band energy
     * is below this, a zero is forced. Keep it lower than 1, unless
     * low lambda is used, because energy < threshold doesn't mean there's
     * no audible signal outright, it's just energy. Also make it rise
     * slower than rdlambda, as rdscale has due compensation with
     * noisy band depriorization below, whereas zeroing logic is rather dumb
     */
    float zeroscale;
    if (lambda > 120.f) {
        zeroscale = av_clipf(powf(120.f / lambda, 0.25f), 0.0625f, 1.0f);
    } else {
        zeroscale = 1.f;
    }

    if (s->psy.bitres.alloc >= 0) {
        /**
         * Psy granted us extra bits to use, from the reservoire
         * adjust for lambda except what psy already did
         */
        destbits = s->psy.bitres.alloc
            * (lambda / (avctx->global_quality ? avctx->global_quality : 120));
    }

    if (avctx->flags & AV_CODEC_FLAG_QSCALE) {
        /**
         * Constant Q-scale doesn't compensate MS coding on its own
         * No need to be overly precise, this only controls RD
         * adjustment CB limits when going overboard
         */
        if (s->options.mid_side && s->cur_type == TYPE_CPE)
            destbits *= 2;

        /**
         * When using a constant Q-scale, don't adjust bits, just use RD
         * Don't let it go overboard, though... 8x psy target is enough
         */
        toomanybits = 5800;
        toofewbits = destbits / 16;

        /** Don't offset scalers, just RD */
        sfoffs = sce->ics.num_windows - 1;
        rdlambda = sqrtf(rdlambda);

        /** search further */
        maxits *= 2;
    } else {
        /* When using ABR, be strict, but a reasonable leeway is
         * critical to allow RC to smoothly track desired bitrate
         * without sudden quality drops that cause audible artifacts.
         * Symmetry is also desirable, to avoid systematic bias.
         */
        toomanybits = destbits + destbits/8;
        toofewbits = destbits - destbits/8;

        sfoffs = 0;
        rdlambda = sqrtf(rdlambda);
    }

    /** and zero out above cutoff frequency */
    {
        int wlen = 1024 / sce->ics.num_windows;
        int bandwidth;

        /**
         * Scale, psy gives us constant quality, this LP only scales
         * bitrate by lambda, so we save bits on subjectively unimportant HF
         * rather than increase quantization noise. Adjust nominal bitrate
         * to effective bitrate according to encoding parameters,
         * AAC_CUTOFF_FROM_BITRATE is calibrated for effective bitrate.
         */
        float rate_bandwidth_multiplier = 1.5f;
        int frame_bit_rate = (avctx->flags & AV_CODEC_FLAG_QSCALE)
            ? (refbits * rate_bandwidth_multiplier * avctx->sample_rate / 1024)
            : (avctx->bit_rate / avctx->channels);

        /** Compensate for extensions that increase efficiency */
        if (s->options.pns || s->options.intensity_stereo)
            frame_bit_rate *= 1.15f;

        if (avctx->cutoff > 0) {
            bandwidth = avctx->cutoff;
        } else {
            bandwidth = FFMAX(3000, AAC_CUTOFF_FROM_BITRATE(frame_bit_rate, 1, avctx->sample_rate));
            s->psy.cutoff = bandwidth;
        }

        cutoff = bandwidth * 2 * wlen / avctx->sample_rate;
        pns_start_pos = NOISE_LOW_LIMIT * 2 * wlen / avctx->sample_rate;
    }

    /**
     * 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);
    toomanybits = FFMIN(toomanybits, 5800);
    toofewbits = FFMIN(toofewbits, 5800);
    /**
     * XXX: some heuristic to determine initial quantizers will reduce search time
     * determine zero bands and upper distortion limits
     */
    min_spread_thr_r = -1;
    max_spread_thr_r = -1;
    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
        for (g = start = 0;  g < sce->ics.num_swb; start += sce->ics.swb_sizes[g++]) {
            int nz = 0;
            float uplim = 0.0f, energy = 0.0f, spread = 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 (start >= cutoff || band->energy <= (band->threshold * zeroscale) || band->threshold == 0.0f) {
                    sce->zeroes[(w+w2)*16+g] = 1;
                    continue;
                }
                nz = 1;
            }
            if (!nz) {
                uplim = 0.0f;
            } else {
                nz = 0;
                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 * zeroscale) || band->threshold == 0.0f)
                        continue;
                    uplim += band->threshold;
                    energy += band->energy;
                    spread += band->spread;
                    nz++;
                }
            }
            uplims[w*16+g] = uplim;
            energies[w*16+g] = energy;
            nzs[w*16+g] = nz;
            sce->zeroes[w*16+g] = !nz;
            allz |= nz;
            if (nz && sce->can_pns[w*16+g]) {
                spread_thr_r[w*16+g] = energy * nz / (uplim * spread);
                if (min_spread_thr_r < 0) {
                    min_spread_thr_r = max_spread_thr_r = spread_thr_r[w*16+g];
                } else {
                    min_spread_thr_r = FFMIN(min_spread_thr_r, spread_thr_r[w*16+g]);
                    max_spread_thr_r = FFMAX(max_spread_thr_r, spread_thr_r[w*16+g]);
                }
            }
        }
    }

    /** Compute initial scalers */
    minscaler = 65535;
    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;
            }
            /**
             * log2f-to-distortion ratio is, technically, 2 (1.5db = 4, but it's power vs level so it's 2).
             * But, as offsets are applied, low-frequency signals are too sensitive to the induced distortion,
             * so we make scaling more conservative by choosing a lower log2f-to-distortion ratio, and thus
             * more robust.
             */
            sce->sf_idx[w*16+g] = av_clip(
                SCALE_ONE_POS
                    + 1.75*log2f(FFMAX(0.00125f,uplims[w*16+g]) / sce->ics.swb_sizes[g])
                    + sfoffs,
                60, SCALE_MAX_POS);
            minscaler = FFMIN(minscaler, sce->sf_idx[w*16+g]);
        }
    }

    /** Clip */
    minscaler = av_clip(minscaler, SCALE_ONE_POS - SCALE_DIV_512, SCALE_MAX_POS - SCALE_DIV_512);
    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] = av_clip(sce->sf_idx[w*16+g], minscaler, minscaler + SCALE_MAX_DIFF - 1);

    if (!allz)
        return;
    s->abs_pow34(s->scoefs, sce->coeffs, 1024);
    ff_quantize_band_cost_cache_init(s);

    for (i = 0; i < sizeof(minsf) / sizeof(minsf[0]); ++i)
        minsf[i] = 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 *scaled = s->scoefs + start;
            int minsfidx;
            maxvals[w*16+g] = find_max_val(sce->ics.group_len[w], sce->ics.swb_sizes[g], scaled);
            if (maxvals[w*16+g] > 0) {
                minsfidx = coef2minsf(maxvals[w*16+g]);
                for (w2 = 0; w2 < sce->ics.group_len[w]; w2++)
                    minsf[(w+w2)*16+g] = minsfidx;
            }
            start += sce->ics.swb_sizes[g];
        }
    }

    /**
     * Scale uplims to match rate distortion to quality
     * bu applying noisy band depriorization and tonal band priorization.
     * Maxval-energy ratio gives us an idea of how noisy/tonal the band is.
     * If maxval^2 ~ energy, then that band is mostly noise, and we can relax
     * rate distortion requirements.
     */
    memcpy(euplims, uplims, sizeof(euplims));
    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
        /** psy already priorizes transients to some extent */
        float de_psy_factor = (sce->ics.num_windows > 1) ? 8.0f / sce->ics.group_len[w] : 1.0f;
        start = w*128;
        for (g = 0;  g < sce->ics.num_swb; g++) {
            if (nzs[g] > 0) {
                float cleanup_factor = ff_sqrf(av_clipf(start / (cutoff * 0.75f), 1.0f, 2.0f));
                float energy2uplim = find_form_factor(
                    sce->ics.group_len[w], sce->ics.swb_sizes[g],
                    uplims[w*16+g] / (nzs[g] * sce->ics.swb_sizes[w]),
                    sce->coeffs + start,
                    nzslope * cleanup_factor);
                energy2uplim *= de_psy_factor;
                if (!(avctx->flags & AV_CODEC_FLAG_QSCALE)) {
                    /** In ABR, we need to priorize less and let rate control do its thing */
                    energy2uplim = sqrtf(energy2uplim);
                }
                energy2uplim = FFMAX(0.015625f, FFMIN(1.0f, energy2uplim));
                uplims[w*16+g] *= av_clipf(rdlambda * energy2uplim, rdmin, rdmax)
                                  * sce->ics.group_len[w];

                energy2uplim = find_form_factor(
                    sce->ics.group_len[w], sce->ics.swb_sizes[g],
                    uplims[w*16+g] / (nzs[g] * sce->ics.swb_sizes[w]),
                    sce->coeffs + start,
                    2.0f);
                energy2uplim *= de_psy_factor;
                if (!(avctx->flags & AV_CODEC_FLAG_QSCALE)) {
                    /** In ABR, we need to priorize less and let rate control do its thing */
                    energy2uplim = sqrtf(energy2uplim);
                }
                energy2uplim = FFMAX(0.015625f, FFMIN(1.0f, energy2uplim));
                euplims[w*16+g] *= av_clipf(rdlambda * energy2uplim * sce->ics.group_len[w],
                    0.5f, 1.0f);
            }
            start += sce->ics.swb_sizes[g];
        }
    }

    for (i = 0; i < sizeof(maxsf) / sizeof(maxsf[0]); ++i)
        maxsf[i] = SCALE_MAX_POS;

    //perform two-loop search
    //outer loop - improve quality
    do {
        //inner loop - quantize spectrum to fit into given number of bits
        int overdist;
        int qstep = its ? 1 : 32;
        do {
            int changed = 0;
            prev = -1;
            recomprd = 0;
            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;
                    float qenergy = 0.0f;

                    if (sce->zeroes[w*16+g] || sce->sf_idx[w*16+g] >= 218) {
                        start += sce->ics.swb_sizes[g];
                        if (sce->can_pns[w*16+g]) {
                            /** PNS isn't free */
                            tbits += ff_pns_bits(sce, w, g);
                        }
                        continue;
                    }
                    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;
                        float sqenergy;
                        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, &sqenergy,
                                                   0);
                        bits += b;
                        qenergy += sqenergy;
                    }
                    dists[w*16+g] = dist - bits;
                    qenergies[w*16+g] = qenergy;
                    if (prev != -1) {
                        int sfdiff = av_clip(sce->sf_idx[w*16+g] - prev + SCALE_DIFF_ZERO, 0, 2*SCALE_MAX_DIFF);
                        bits += ff_aac_scalefactor_bits[sfdiff];
                    }
                    tbits += bits;
                    start += sce->ics.swb_sizes[g];
                    prev = sce->sf_idx[w*16+g];
                }
            }
            if (tbits > toomanybits) {
                recomprd = 1;
                for (i = 0; i < 128; i++) {
                    if (sce->sf_idx[i] < (SCALE_MAX_POS - SCALE_DIV_512)) {
                        int maxsf_i = (tbits > 5800) ? SCALE_MAX_POS : maxsf[i];
                        int new_sf = FFMIN(maxsf_i, sce->sf_idx[i] + qstep);
                        if (new_sf != sce->sf_idx[i]) {
                            sce->sf_idx[i] = new_sf;
                            changed = 1;
                        }
                    }
                }
            } else if (tbits < toofewbits) {
                recomprd = 1;
                for (i = 0; i < 128; i++) {
                    if (sce->sf_idx[i] > SCALE_ONE_POS) {
                        int new_sf = FFMAX3(minsf[i], SCALE_ONE_POS, sce->sf_idx[i] - qstep);
                        if (new_sf != sce->sf_idx[i]) {
                            sce->sf_idx[i] = new_sf;
                            changed = 1;
                        }
                    }
                }
            }
            qstep >>= 1;
            if (!qstep && tbits > toomanybits && sce->sf_idx[0] < 217 && changed)
                qstep = 1;
        } while (qstep);

        overdist = 1;
        fflag = tbits < toofewbits;
        for (i = 0; i < 2 && (overdist || recomprd); ++i) {
            if (recomprd) {
                /** Must recompute distortion */
                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;
                        float qenergy = 0.0f;

                        if (sce->zeroes[w*16+g] || sce->sf_idx[w*16+g] >= 218) {
                            start += sce->ics.swb_sizes[g];
                            if (sce->can_pns[w*16+g]) {
                                /** PNS isn't free */
                                tbits += ff_pns_bits(sce, w, g);
                            }
                            continue;
                        }
                        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;
                            float sqenergy;
                            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, &sqenergy,
                                                    0);
                            bits += b;
                            qenergy += sqenergy;
                        }
                        dists[w*16+g] = dist - bits;
                        qenergies[w*16+g] = qenergy;
                        if (prev != -1) {
                            int sfdiff = av_clip(sce->sf_idx[w*16+g] - prev + SCALE_DIFF_ZERO, 0, 2*SCALE_MAX_DIFF);
                            bits += ff_aac_scalefactor_bits[sfdiff];
                        }
                        tbits += bits;
                        start += sce->ics.swb_sizes[g];
                        prev = sce->sf_idx[w*16+g];
                    }
                }
            }
            if (!i && s->options.pns && its > maxits/2 && tbits > toofewbits) {
                float maxoverdist = 0.0f;
                float ovrfactor = 1.f+(maxits-its)*16.f/maxits;
                overdist = recomprd = 0;
                for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
                    for (g = start = 0;  g < sce->ics.num_swb; start += sce->ics.swb_sizes[g++]) {
                        if (!sce->zeroes[w*16+g] && sce->sf_idx[w*16+g] > SCALE_ONE_POS && dists[w*16+g] > uplims[w*16+g]*ovrfactor) {
                            float ovrdist = dists[w*16+g] / FFMAX(uplims[w*16+g],euplims[w*16+g]);
                            maxoverdist = FFMAX(maxoverdist, ovrdist);
                            overdist++;
                        }
                    }
                }
                if (overdist) {
                    /* We have overdistorted bands, trade for zeroes (that can be noise)
                     * Zero the bands in the lowest 1.25% spread-energy-threshold ranking
                     */
                    float minspread = max_spread_thr_r;
                    float maxspread = min_spread_thr_r;
                    float zspread;
                    int zeroable = 0;
                    int zeroed = 0;
                    int maxzeroed, zloop;
                    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
                        for (g = start = 0;  g < sce->ics.num_swb; start += sce->ics.swb_sizes[g++]) {
                            if (start >= pns_start_pos && !sce->zeroes[w*16+g] && sce->can_pns[w*16+g]) {
                                minspread = FFMIN(minspread, spread_thr_r[w*16+g]);
                                maxspread = FFMAX(maxspread, spread_thr_r[w*16+g]);
                                zeroable++;
                            }
                        }
                    }
                    zspread = (maxspread-minspread) * 0.0125f + minspread;
                    /* Don't PNS everything even if allowed. It suppresses bit starvation signals from RC,
                     * and forced the hand of the later search_for_pns step.
                     * Instead, PNS a fraction of the spread_thr_r range depending on how starved for bits we are,
                     * and leave further PNSing to search_for_pns if worthwhile.
                     */
                    zspread = FFMIN3(min_spread_thr_r * 8.f, zspread,
                        ((toomanybits - tbits) * min_spread_thr_r + (tbits - toofewbits) * max_spread_thr_r) / (toomanybits - toofewbits + 1));
                    maxzeroed = FFMIN(zeroable, FFMAX(1, (zeroable * its + maxits - 1) / (2 * maxits)));
                    for (zloop = 0; zloop < 2; zloop++) {
                        /* Two passes: first distorted stuff - two birds in one shot and all that,
                         * then anything viable. Viable means not zero, but either CB=zero-able
                         * (too high SF), not SF <= 1 (that means we'd be operating at very high
                         * quality, we don't want PNS when doing VHQ), PNS allowed, and within
                         * the lowest ranking percentile.
                         */
                        float loopovrfactor = (zloop) ? 1.0f : ovrfactor;
                        int loopminsf = (zloop) ? (SCALE_ONE_POS - SCALE_DIV_512) : SCALE_ONE_POS;
                        int mcb;
                        for (g = sce->ics.num_swb-1; g > 0 && zeroed < maxzeroed; g--) {
                            if (sce->ics.swb_offset[g] < pns_start_pos)
                                continue;
                            for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
                                if (!sce->zeroes[w*16+g] && sce->can_pns[w*16+g] && spread_thr_r[w*16+g] <= zspread
                                    && sce->sf_idx[w*16+g] > loopminsf
                                    && (dists[w*16+g] > loopovrfactor*uplims[w*16+g] || !(mcb = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]))
                                        || (mcb <= 1 && dists[w*16+g] > FFMIN(uplims[w*16+g], euplims[w*16+g]))) ) {
                                    sce->zeroes[w*16+g] = 1;
                                    sce->band_type[w*16+g] = 0;
                                    zeroed++;
                                }
                            }
                        }
                    }
                    if (zeroed)
                        recomprd = fflag = 1;
                } else {
                    overdist = 0;
                }
            }
        }

        minscaler = SCALE_MAX_POS;
        maxscaler = 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]) {
                    minscaler = FFMIN(minscaler, sce->sf_idx[w*16+g]);
                    maxscaler = FFMAX(maxscaler, sce->sf_idx[w*16+g]);
                }
            }
        }

        minscaler = nminscaler = av_clip(minscaler, SCALE_ONE_POS - SCALE_DIV_512, SCALE_MAX_POS - SCALE_DIV_512);
        prev = -1;
        for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
            /** Start with big steps, end up fine-tunning */
            int depth = (its > maxits/2) ? ((its > maxits*2/3) ? 1 : 3) : 10;
            int edepth = depth+2;
            float uplmax = its / (maxits*0.25f) + 1.0f;
            uplmax *= (tbits > destbits) ? FFMIN(2.0f, tbits / (float)FFMAX(1,destbits)) : 1.0f;
            start = w * 128;
            for (g = 0; g < sce->ics.num_swb; g++) {
                int prevsc = sce->sf_idx[w*16+g];
                if (prev < 0 && !sce->zeroes[w*16+g])
                    prev = sce->sf_idx[0];
                if (!sce->zeroes[w*16+g]) {
                    const float *coefs = sce->coeffs + start;
                    const float *scaled = s->scoefs + start;
                    int cmb = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]);
                    int mindeltasf = FFMAX(0, prev - SCALE_MAX_DIFF);
                    int maxdeltasf = FFMIN(SCALE_MAX_POS - SCALE_DIV_512, prev + SCALE_MAX_DIFF);
                    if ((!cmb || dists[w*16+g] > uplims[w*16+g]) && sce->sf_idx[w*16+g] > FFMAX(mindeltasf, minsf[w*16+g])) {
                        /* Try to make sure there is some energy in every nonzero band
                         * NOTE: This algorithm must be forcibly imbalanced, pushing harder
                         *  on holes or more distorted bands at first, otherwise there's
                         *  no net gain (since the next iteration will offset all bands
                         *  on the opposite direction to compensate for extra bits)
                         */
                        for (i = 0; i < edepth && sce->sf_idx[w*16+g] > mindeltasf; ++i) {
                            int cb, bits;
                            float dist, qenergy;
                            int mb = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]-1);
                            cb = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]);
                            dist = qenergy = 0.f;
                            bits = 0;
                            if (!cb) {
                                maxsf[w*16+g] = FFMIN(sce->sf_idx[w*16+g]-1, maxsf[w*16+g]);
                            } else if (i >= depth && dists[w*16+g] < euplims[w*16+g]) {
                                break;
                            }
                            /* !g is the DC band, it's important, since quantization error here
                             * applies to less than a cycle, it creates horrible intermodulation
                             * distortion if it doesn't stick to what psy requests
                             */
                            if (!g && sce->ics.num_windows > 1 && dists[w*16+g] >= euplims[w*16+g])
                                maxsf[w*16+g] = FFMIN(sce->sf_idx[w*16+g], maxsf[w*16+g]);
                            for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                                int b;
                                float sqenergy;
                                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]-1,
                                                        cb,
                                                        1.0f,
                                                        INFINITY,
                                                        &b, &sqenergy,
                                                        0);
                                bits += b;
                                qenergy += sqenergy;
                            }
                            sce->sf_idx[w*16+g]--;
                            dists[w*16+g] = dist - bits;
                            qenergies[w*16+g] = qenergy;
                            if (mb && (sce->sf_idx[w*16+g] < mindeltasf || (
                                    (dists[w*16+g] < FFMIN(uplmax*uplims[w*16+g], euplims[w*16+g]))
                                    && (fabsf(qenergies[w*16+g]-energies[w*16+g]) < euplims[w*16+g])
                                ) )) {
                                break;
                            }
                        }
                    } else if (tbits > toofewbits && sce->sf_idx[w*16+g] < FFMIN(maxdeltasf, maxsf[w*16+g])
                            && (dists[w*16+g] < FFMIN(euplims[w*16+g], uplims[w*16+g]))
                            && (fabsf(qenergies[w*16+g]-energies[w*16+g]) < euplims[w*16+g])
                        ) {
                        /** Um... over target. Save bits for more important stuff. */
                        for (i = 0; i < depth && sce->sf_idx[w*16+g] < maxdeltasf; ++i) {
                            int cb, bits;
                            float dist, qenergy;
                            cb = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]+1);
                            if (cb > 0) {
                                dist = qenergy = 0.f;
                                bits = 0;
                                for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                                    int b;
                                    float sqenergy;
                                    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]+1,
                                                            cb,
                                                            1.0f,
                                                            INFINITY,
                                                            &b, &sqenergy,
                                                            0);
                                    bits += b;
                                    qenergy += sqenergy;
                                }
                                dist -= bits;
                                if (dist < FFMIN(euplims[w*16+g], uplims[w*16+g])) {
                                    sce->sf_idx[w*16+g]++;
                                    dists[w*16+g] = dist;
                                    qenergies[w*16+g] = qenergy;
                                } else {
                                    break;
                                }
                            } else {
                                maxsf[w*16+g] = FFMIN(sce->sf_idx[w*16+g], maxsf[w*16+g]);
                                break;
                            }
                        }
                    }
                    prev = sce->sf_idx[w*16+g] = av_clip(sce->sf_idx[w*16+g], mindeltasf, maxdeltasf);
                    if (sce->sf_idx[w*16+g] != prevsc)
                        fflag = 1;
                    nminscaler = FFMIN(nminscaler, sce->sf_idx[w*16+g]);
                    sce->band_type[w*16+g] = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]);
                }
                start += sce->ics.swb_sizes[g];
            }
        }

        /** SF difference limit violation risk. Must re-clamp. */
        prev = -1;
        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]) {
                    int prevsf = sce->sf_idx[w*16+g];
                    if (prev < 0)
                        prev = prevsf;
                    sce->sf_idx[w*16+g] = av_clip(sce->sf_idx[w*16+g], prev - SCALE_MAX_DIFF, prev + SCALE_MAX_DIFF);
                    sce->band_type[w*16+g] = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]);
                    prev = sce->sf_idx[w*16+g];
                    if (!fflag && prevsf != sce->sf_idx[w*16+g])
                        fflag = 1;
                }
            }
        }

        its++;
    } while (fflag && its < maxits);

    /** Scout out next nonzero bands */
    ff_init_nextband_map(sce, nextband);

    prev = -1;
    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
        /** Make sure proper codebooks are set */
        for (g = 0; g < sce->ics.num_swb; g++) {
            if (!sce->zeroes[w*16+g]) {
                sce->band_type[w*16+g] = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]);
                if (sce->band_type[w*16+g] <= 0) {
                    if (!ff_sfdelta_can_remove_band(sce, nextband, prev, w*16+g)) {
                        /** Cannot zero out, make sure it's not attempted */
                        sce->band_type[w*16+g] = 1;
                    } else {
                        sce->zeroes[w*16+g] = 1;
                        sce->band_type[w*16+g] = 0;
                    }
                }
            } else {
                sce->band_type[w*16+g] = 0;
            }
            /** Check that there's no SF delta range violations */
            if (!sce->zeroes[w*16+g]) {
                if (prev != -1) {
                    av_unused int sfdiff = sce->sf_idx[w*16+g] - prev + SCALE_DIFF_ZERO;
                    av_assert1(sfdiff >= 0 && sfdiff <= 2*SCALE_MAX_DIFF);
                } else if (sce->zeroes[0]) {
                    /** Set global gain to something useful */
                    sce->sf_idx[0] = sce->sf_idx[w*16+g];
                }
                prev = sce->sf_idx[w*16+g];
            }
        }
    }
}

#endif /* AVCODEC_AACCODER_TWOLOOP_H */