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
48static 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 */
70void 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 */
102void 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 */
147static 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 */
161void 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}
216