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Member "ffmpeg-4.0.1/libavcodec/aacenc_tns.c" (27 Feb 2018, 7755 Bytes) of package /linux/misc/ffmpeg-4.0.1.tar.xz:


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    1 /*
    2  * AAC encoder TNS
    3  * Copyright (C) 2015 Rostislav Pehlivanov
    4  *
    5  * This file is part of FFmpeg.
    6  *
    7  * FFmpeg is free software; you can redistribute it and/or
    8  * modify it under the terms of the GNU Lesser General Public
    9  * License as published by the Free Software Foundation; either
   10  * version 2.1 of the License, or (at your option) any later version.
   11  *
   12  * FFmpeg is distributed in the hope that it will be useful,
   13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
   14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   15  * Lesser General Public License for more details.
   16  *
   17  * You should have received a copy of the GNU Lesser General Public
   18  * License along with FFmpeg; if not, write to the Free Software
   19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
   20  */
   21 
   22 /**
   23  * @file
   24  * AAC encoder temporal noise shaping
   25  * @author Rostislav Pehlivanov ( atomnuker gmail com )
   26  */
   27 
   28 #include "libavutil/libm.h"
   29 #include "aacenc.h"
   30 #include "aacenc_tns.h"
   31 #include "aactab.h"
   32 #include "aacenc_utils.h"
   33 #include "aacenc_quantization.h"
   34 
   35 /* Could be set to 3 to save an additional bit at the cost of little quality */
   36 #define TNS_Q_BITS 4
   37 
   38 /* Coefficient resolution in short windows */
   39 #define TNS_Q_BITS_IS8 4
   40 
   41 /* We really need the bits we save here elsewhere */
   42 #define TNS_ENABLE_COEF_COMPRESSION
   43 
   44 /* TNS will only be used if the LPC gain is within these margins */
   45 #define TNS_GAIN_THRESHOLD_LOW      1.4f
   46 #define TNS_GAIN_THRESHOLD_HIGH     1.16f*TNS_GAIN_THRESHOLD_LOW
   47 
   48 static inline int compress_coeffs(int *coef, int order, int c_bits)
   49 {
   50     int i;
   51     const int low_idx   = c_bits ?  4 : 2;
   52     const int shift_val = c_bits ?  8 : 4;
   53     const int high_idx  = c_bits ? 11 : 5;
   54 #ifndef TNS_ENABLE_COEF_COMPRESSION
   55     return 0;
   56 #endif /* TNS_ENABLE_COEF_COMPRESSION */
   57     for (i = 0; i < order; i++)
   58         if (coef[i] >= low_idx && coef[i] <= high_idx)
   59             return 0;
   60     for (i = 0; i < order; i++)
   61         coef[i] -= (coef[i] > high_idx) ? shift_val : 0;
   62     return 1;
   63 }
   64 
   65 /**
   66  * Encode TNS data.
   67  * Coefficient compression is simply not lossless as it should be
   68  * on any decoder tested and as such is not active.
   69  */
   70 void ff_aac_encode_tns_info(AACEncContext *s, SingleChannelElement *sce)
   71 {
   72     TemporalNoiseShaping *tns = &sce->tns;
   73     int i, w, filt, coef_compress = 0, coef_len;
   74     const int is8 = sce->ics.window_sequence[0] == EIGHT_SHORT_SEQUENCE;
   75     const int c_bits = is8 ? TNS_Q_BITS_IS8 == 4 : TNS_Q_BITS == 4;
   76 
   77     if (!sce->tns.present)
   78         return;
   79 
   80     for (i = 0; i < sce->ics.num_windows; i++) {
   81         put_bits(&s->pb, 2 - is8, sce->tns.n_filt[i]);
   82         if (!tns->n_filt[i])
   83             continue;
   84         put_bits(&s->pb, 1, c_bits);
   85         for (filt = 0; filt < tns->n_filt[i]; filt++) {
   86             put_bits(&s->pb, 6 - 2 * is8, tns->length[i][filt]);
   87             put_bits(&s->pb, 5 - 2 * is8, tns->order[i][filt]);
   88             if (!tns->order[i][filt])
   89                 continue;
   90             put_bits(&s->pb, 1, tns->direction[i][filt]);
   91             coef_compress = compress_coeffs(tns->coef_idx[i][filt],
   92                                             tns->order[i][filt], c_bits);
   93             put_bits(&s->pb, 1, coef_compress);
   94             coef_len = c_bits + 3 - coef_compress;
   95             for (w = 0; w < tns->order[i][filt]; w++)
   96                 put_bits(&s->pb, coef_len, tns->coef_idx[i][filt][w]);
   97         }
   98     }
   99 }
  100 
  101 /* Apply TNS filter */
  102 void ff_aac_apply_tns(AACEncContext *s, SingleChannelElement *sce)
  103 {
  104     TemporalNoiseShaping *tns = &sce->tns;
  105     IndividualChannelStream *ics = &sce->ics;
  106     int w, filt, m, i, top, order, bottom, start, end, size, inc;
  107     const int mmm = FFMIN(ics->tns_max_bands, ics->max_sfb);
  108     float lpc[TNS_MAX_ORDER];
  109 
  110     for (w = 0; w < ics->num_windows; w++) {
  111         bottom = ics->num_swb;
  112         for (filt = 0; filt < tns->n_filt[w]; filt++) {
  113             top    = bottom;
  114             bottom = FFMAX(0, top - tns->length[w][filt]);
  115             order  = tns->order[w][filt];
  116             if (order == 0)
  117                 continue;
  118 
  119             // tns_decode_coef
  120             compute_lpc_coefs(tns->coef[w][filt], order, lpc, 0, 0, 0);
  121 
  122             start = ics->swb_offset[FFMIN(bottom, mmm)];
  123             end   = ics->swb_offset[FFMIN(   top, mmm)];
  124             if ((size = end - start) <= 0)
  125                 continue;
  126             if (tns->direction[w][filt]) {
  127                 inc = -1;
  128                 start = end - 1;
  129             } else {
  130                 inc = 1;
  131             }
  132             start += w * 128;
  133 
  134             /* AR filter */
  135             for (m = 0; m < size; m++, start += inc) {
  136                 for (i = 1; i <= FFMIN(m, order); i++) {
  137                     sce->coeffs[start] += lpc[i-1]*sce->pcoeffs[start - i*inc];
  138                 }
  139             }
  140         }
  141     }
  142 }
  143 
  144 /*
  145  * c_bits - 1 if 4 bit coefficients, 0 if 3 bit coefficients
  146  */
  147 static inline void quantize_coefs(double *coef, int *idx, float *lpc, int order,
  148                                   int c_bits)
  149 {
  150     int i;
  151     const float *quant_arr = tns_tmp2_map[c_bits];
  152     for (i = 0; i < order; i++) {
  153         idx[i] = quant_array_idx(coef[i], quant_arr, c_bits ? 16 : 8);
  154         lpc[i] = quant_arr[idx[i]];
  155     }
  156 }
  157 
  158 /*
  159  * 3 bits per coefficient with 8 short windows
  160  */
  161 void ff_aac_search_for_tns(AACEncContext *s, SingleChannelElement *sce)
  162 {
  163     TemporalNoiseShaping *tns = &sce->tns;
  164     int w, g, count = 0;
  165     double gain, coefs[MAX_LPC_ORDER];
  166     const int mmm = FFMIN(sce->ics.tns_max_bands, sce->ics.max_sfb);
  167     const int is8 = sce->ics.window_sequence[0] == EIGHT_SHORT_SEQUENCE;
  168     const int c_bits = is8 ? TNS_Q_BITS_IS8 == 4 : TNS_Q_BITS == 4;
  169     const int sfb_start = av_clip(tns_min_sfb[is8][s->samplerate_index], 0, mmm);
  170     const int sfb_end   = av_clip(sce->ics.num_swb, 0, mmm);
  171     const int order = is8 ? 7 : s->profile == FF_PROFILE_AAC_LOW ? 12 : TNS_MAX_ORDER;
  172     const int slant = sce->ics.window_sequence[0] == LONG_STOP_SEQUENCE  ? 1 :
  173                       sce->ics.window_sequence[0] == LONG_START_SEQUENCE ? 0 : 2;
  174     const int sfb_len = sfb_end - sfb_start;
  175     const int coef_len = sce->ics.swb_offset[sfb_end] - sce->ics.swb_offset[sfb_start];
  176 
  177     if (coef_len <= 0 || sfb_len <= 0) {
  178         sce->tns.present = 0;
  179         return;
  180     }
  181 
  182     for (w = 0; w < sce->ics.num_windows; w++) {
  183         float en[2] = {0.0f, 0.0f};
  184         int oc_start = 0, os_start = 0;
  185         int coef_start = sce->ics.swb_offset[sfb_start];
  186 
  187         for (g = sfb_start; g < sce->ics.num_swb && g <= sfb_end; g++) {
  188             FFPsyBand *band = &s->psy.ch[s->cur_channel].psy_bands[w*16+g];
  189             if (g > sfb_start + (sfb_len/2))
  190                 en[1] += band->energy;
  191             else
  192                 en[0] += band->energy;
  193         }
  194 
  195         /* LPC */
  196         gain = ff_lpc_calc_ref_coefs_f(&s->lpc, &sce->coeffs[w*128 + coef_start],
  197                                        coef_len, order, coefs);
  198 
  199         if (!order || !isfinite(gain) || gain < TNS_GAIN_THRESHOLD_LOW || gain > TNS_GAIN_THRESHOLD_HIGH)
  200             continue;
  201 
  202         tns->n_filt[w] = is8 ? 1 : order != TNS_MAX_ORDER ? 2 : 3;
  203         for (g = 0; g < tns->n_filt[w]; g++) {
  204             tns->direction[w][g] = slant != 2 ? slant : en[g] < en[!g];
  205             tns->order[w][g] = g < tns->n_filt[w] ? order/tns->n_filt[w] : order - oc_start;
  206             tns->length[w][g] = g < tns->n_filt[w] ? sfb_len/tns->n_filt[w] : sfb_len - os_start;
  207             quantize_coefs(&coefs[oc_start], tns->coef_idx[w][g], tns->coef[w][g],
  208                             tns->order[w][g], c_bits);
  209             oc_start += tns->order[w][g];
  210             os_start += tns->length[w][g];
  211         }
  212         count++;
  213     }
  214     sce->tns.present = !!count;
  215 }