/* * AAC encoder psychoacoustic model * Copyright (C) 2008 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 psychoacoustic model */ #include "avcodec.h" #include "aactab.h" #include "psymodel.h" /*********************************** * TODOs: * thresholds linearization after their modifications for attaining given bitrate * try other bitrate controlling mechanism (maybe use ratecontrol.c?) * control quality for quality-based output **********************************/ /** * constants for 3GPP AAC psychoacoustic model * @{ */ #define PSY_3GPP_THR_SPREAD_HI 1.5f // spreading factor for low-to-hi threshold spreading (15 dB/Bark) #define PSY_3GPP_THR_SPREAD_LOW 3.0f // spreading factor for hi-to-low threshold spreading (30 dB/Bark) #define PSY_3GPP_RPEMIN 0.01f #define PSY_3GPP_RPELEV 2.0f /* LAME psy model constants */ #define PSY_LAME_FIR_LEN 21 ///< LAME psy model FIR order #define AAC_BLOCK_SIZE_LONG 1024 ///< long block size #define AAC_BLOCK_SIZE_SHORT 128 ///< short block size #define AAC_NUM_BLOCKS_SHORT 8 ///< number of blocks in a short sequence #define PSY_LAME_NUM_SUBBLOCKS 3 ///< Number of sub-blocks in each short block /** * @} */ /** * information for single band used by 3GPP TS26.403-inspired psychoacoustic model */ typedef struct AacPsyBand{ float energy; ///< band energy float thr; ///< energy threshold float thr_quiet; ///< threshold in quiet }AacPsyBand; /** * single/pair channel context for psychoacoustic model */ typedef struct AacPsyChannel{ AacPsyBand band[128]; ///< bands information AacPsyBand prev_band[128]; ///< bands information from the previous frame float win_energy; ///< sliding average of channel energy float iir_state[2]; ///< hi-pass IIR filter state uint8_t next_grouping; ///< stored grouping scheme for the next frame (in case of 8 short window sequence) enum WindowSequence next_window_seq; ///< window sequence to be used in the next frame /* LAME psy model specific members */ float attack_threshold; ///< attack threshold for this channel float prev_energy_subshort[AAC_NUM_BLOCKS_SHORT * PSY_LAME_NUM_SUBBLOCKS]; int prev_attack; ///< attack value for the last short block in the previous sequence }AacPsyChannel; /** * psychoacoustic model frame type-dependent coefficients */ typedef struct AacPsyCoeffs{ float ath; ///< absolute threshold of hearing per bands float barks; ///< Bark value for each spectral band in long frame float spread_low[2]; ///< spreading factor for low-to-high threshold spreading in long frame float spread_hi [2]; ///< spreading factor for high-to-low threshold spreading in long frame float min_snr; ///< minimal SNR }AacPsyCoeffs; /** * 3GPP TS26.403-inspired psychoacoustic model specific data */ typedef struct AacPsyContext{ AacPsyCoeffs psy_coef[2][64]; AacPsyChannel *ch; }AacPsyContext; /** * LAME psy model preset struct */ typedef struct { int quality; ///< Quality to map the rest of the vaules to. /* This is overloaded to be both kbps per channel in ABR mode, and * requested quality in constant quality mode. */ float st_lrm; ///< short threshold for L, R, and M channels } PsyLamePreset; /** * LAME psy model preset table for ABR */ static const PsyLamePreset psy_abr_map[] = { /* TODO: Tuning. These were taken from LAME. */ /* kbps/ch st_lrm */ { 8, 6.60}, { 16, 6.60}, { 24, 6.60}, { 32, 6.60}, { 40, 6.60}, { 48, 6.60}, { 56, 6.60}, { 64, 6.40}, { 80, 6.00}, { 96, 5.60}, {112, 5.20}, {128, 5.20}, {160, 5.20} }; /** * LAME psy model preset table for constant quality */ static const PsyLamePreset psy_vbr_map[] = { /* vbr_q st_lrm */ { 0, 4.20}, { 1, 4.20}, { 2, 4.20}, { 3, 4.20}, { 4, 4.20}, { 5, 4.20}, { 6, 4.20}, { 7, 4.20}, { 8, 4.20}, { 9, 4.20}, {10, 4.20} }; /** * LAME psy model FIR coefficient table */ static const float psy_fir_coeffs[] = { -8.65163e-18 * 2, -0.00851586 * 2, -6.74764e-18 * 2, 0.0209036 * 2, -3.36639e-17 * 2, -0.0438162 * 2, -1.54175e-17 * 2, 0.0931738 * 2, -5.52212e-17 * 2, -0.313819 * 2 }; /** * calculates the attack threshold for ABR from the above table for the LAME psy model */ static float lame_calc_attack_threshold(int bitrate) { /* Assume max bitrate to start with */ int lower_range = 12, upper_range = 12; int lower_range_kbps = psy_abr_map[12].quality; int upper_range_kbps = psy_abr_map[12].quality; int i; /* Determine which bitrates the value specified falls between. * If the loop ends without breaking our above assumption of 320kbps was correct. */ for (i = 1; i < 13; i++) { if (FFMAX(bitrate, psy_abr_map[i].quality) != bitrate) { upper_range = i; upper_range_kbps = psy_abr_map[i ].quality; lower_range = i - 1; lower_range_kbps = psy_abr_map[i - 1].quality; break; /* Upper range found */ } } /* Determine which range the value specified is closer to */ if ((upper_range_kbps - bitrate) > (bitrate - lower_range_kbps)) return psy_abr_map[lower_range].st_lrm; return psy_abr_map[upper_range].st_lrm; } /** * LAME psy model specific initialization */ static void lame_window_init(AacPsyContext *ctx, AVCodecContext *avctx) { int i, j; for (i = 0; i < avctx->channels; i++) { AacPsyChannel *pch = &ctx->ch[i]; if (avctx->flags & CODEC_FLAG_QSCALE) pch->attack_threshold = psy_vbr_map[avctx->global_quality / FF_QP2LAMBDA].st_lrm; else pch->attack_threshold = lame_calc_attack_threshold(avctx->bit_rate / avctx->channels / 1000); for (j = 0; j < AAC_NUM_BLOCKS_SHORT * PSY_LAME_NUM_SUBBLOCKS; j++) pch->prev_energy_subshort[j] = 10.0f; } } /** * Calculate Bark value for given line. */ static av_cold float calc_bark(float f) { return 13.3f * atanf(0.00076f * f) + 3.5f * atanf((f / 7500.0f) * (f / 7500.0f)); } #define ATH_ADD 4 /** * Calculate ATH value for given frequency. * Borrowed from Lame. */ static av_cold float ath(float f, float add) { f /= 1000.0f; return 3.64 * pow(f, -0.8) - 6.8 * exp(-0.6 * (f - 3.4) * (f - 3.4)) + 6.0 * exp(-0.15 * (f - 8.7) * (f - 8.7)) + (0.6 + 0.04 * add) * 0.001 * f * f * f * f; } static av_cold int psy_3gpp_init(FFPsyContext *ctx) { AacPsyContext *pctx; float bark; int i, j, g, start; float prev, minscale, minath; ctx->model_priv_data = av_mallocz(sizeof(AacPsyContext)); pctx = (AacPsyContext*) ctx->model_priv_data; minath = ath(3410, ATH_ADD); for (j = 0; j < 2; j++) { AacPsyCoeffs *coeffs = pctx->psy_coef[j]; const uint8_t *band_sizes = ctx->bands[j]; float line_to_frequency = ctx->avctx->sample_rate / (j ? 256.f : 2048.0f); i = 0; prev = 0.0; for (g = 0; g < ctx->num_bands[j]; g++) { i += band_sizes[g]; bark = calc_bark((i-1) * line_to_frequency); coeffs[g].barks = (bark + prev) / 2.0; prev = bark; } for (g = 0; g < ctx->num_bands[j] - 1; g++) { AacPsyCoeffs *coeff = &coeffs[g]; float bark_width = coeffs[g+1].barks - coeffs->barks; coeff->spread_low[0] = pow(10.0, -bark_width * PSY_3GPP_THR_SPREAD_LOW); coeff->spread_hi [0] = pow(10.0, -bark_width * PSY_3GPP_THR_SPREAD_HI); } start = 0; for (g = 0; g < ctx->num_bands[j]; g++) { minscale = ath(start * line_to_frequency, ATH_ADD); for (i = 1; i < band_sizes[g]; i++) minscale = FFMIN(minscale, ath((start + i) * line_to_frequency, ATH_ADD)); coeffs[g].ath = minscale - minath; start += band_sizes[g]; } } pctx->ch = av_mallocz(sizeof(AacPsyChannel) * ctx->avctx->channels); lame_window_init(pctx, ctx->avctx); return 0; } /** * IIR filter used in block switching decision */ static float iir_filter(int in, float state[2]) { float ret; ret = 0.7548f * (in - state[0]) + 0.5095f * state[1]; state[0] = in; state[1] = ret; return ret; } /** * window grouping information stored as bits (0 - new group, 1 - group continues) */ static const uint8_t window_grouping[9] = { 0xB6, 0x6C, 0xD8, 0xB2, 0x66, 0xC6, 0x96, 0x36, 0x36 }; /** * Tell encoder which window types to use. * @see 3GPP TS26.403 5.4.1 "Blockswitching" */ static FFPsyWindowInfo psy_3gpp_window(FFPsyContext *ctx, const int16_t *audio, const int16_t *la, int channel, int prev_type) { int i, j; int br = ctx->avctx->bit_rate / ctx->avctx->channels; int attack_ratio = br <= 16000 ? 18 : 10; AacPsyContext *pctx = (AacPsyContext*) ctx->model_priv_data; AacPsyChannel *pch = &pctx->ch[channel]; uint8_t grouping = 0; int next_type = pch->next_window_seq; FFPsyWindowInfo wi; memset(&wi, 0, sizeof(wi)); if (la) { float s[8], v; int switch_to_eight = 0; float sum = 0.0, sum2 = 0.0; int attack_n = 0; int stay_short = 0; for (i = 0; i < 8; i++) { for (j = 0; j < 128; j++) { v = iir_filter(la[(i*128+j)*ctx->avctx->channels], pch->iir_state); sum += v*v; } s[i] = sum; sum2 += sum; } for (i = 0; i < 8; i++) { if (s[i] > pch->win_energy * attack_ratio) { attack_n = i + 1; switch_to_eight = 1; break; } } pch->win_energy = pch->win_energy*7/8 + sum2/64; wi.window_type[1] = prev_type; switch (prev_type) { case ONLY_LONG_SEQUENCE: wi.window_type[0] = switch_to_eight ? LONG_START_SEQUENCE : ONLY_LONG_SEQUENCE; next_type = switch_to_eight ? EIGHT_SHORT_SEQUENCE : ONLY_LONG_SEQUENCE; break; case LONG_START_SEQUENCE: wi.window_type[0] = EIGHT_SHORT_SEQUENCE; grouping = pch->next_grouping; next_type = switch_to_eight ? EIGHT_SHORT_SEQUENCE : LONG_STOP_SEQUENCE; break; case LONG_STOP_SEQUENCE: wi.window_type[0] = switch_to_eight ? LONG_START_SEQUENCE : ONLY_LONG_SEQUENCE; next_type = switch_to_eight ? EIGHT_SHORT_SEQUENCE : ONLY_LONG_SEQUENCE; break; case EIGHT_SHORT_SEQUENCE: stay_short = next_type == EIGHT_SHORT_SEQUENCE || switch_to_eight; wi.window_type[0] = stay_short ? EIGHT_SHORT_SEQUENCE : LONG_STOP_SEQUENCE; grouping = next_type == EIGHT_SHORT_SEQUENCE ? pch->next_grouping : 0; next_type = switch_to_eight ? EIGHT_SHORT_SEQUENCE : LONG_STOP_SEQUENCE; break; } pch->next_grouping = window_grouping[attack_n]; pch->next_window_seq = next_type; } else { for (i = 0; i < 3; i++) wi.window_type[i] = prev_type; grouping = (prev_type == EIGHT_SHORT_SEQUENCE) ? window_grouping[0] : 0; } wi.window_shape = 1; if (wi.window_type[0] != EIGHT_SHORT_SEQUENCE) { wi.num_windows = 1; wi.grouping[0] = 1; } else { int lastgrp = 0; wi.num_windows = 8; for (i = 0; i < 8; i++) { if (!((grouping >> i) & 1)) lastgrp = i; wi.grouping[lastgrp]++; } } return wi; } /** * Calculate band thresholds as suggested in 3GPP TS26.403 */ static void psy_3gpp_analyze(FFPsyContext *ctx, int channel, const float *coefs, const FFPsyWindowInfo *wi) { AacPsyContext *pctx = (AacPsyContext*) ctx->model_priv_data; AacPsyChannel *pch = &pctx->ch[channel]; int start = 0; int i, w, g; const int num_bands = ctx->num_bands[wi->num_windows == 8]; const uint8_t *band_sizes = ctx->bands[wi->num_windows == 8]; AacPsyCoeffs *coeffs = pctx->psy_coef[wi->num_windows == 8]; //calculate energies, initial thresholds and related values - 5.4.2 "Threshold Calculation" for (w = 0; w < wi->num_windows*16; w += 16) { for (g = 0; g < num_bands; g++) { AacPsyBand *band = &pch->band[w+g]; band->energy = 0.0f; for (i = 0; i < band_sizes[g]; i++) band->energy += coefs[start+i] * coefs[start+i]; band->thr = band->energy * 0.001258925f; start += band_sizes[g]; } } //modify thresholds and energies - spread, threshold in quiet, pre-echo control for (w = 0; w < wi->num_windows*16; w += 16) { AacPsyBand *bands = &pch->band[w]; //5.4.2.3 "Spreading" & 5.4.3 "Spreaded Energy Calculation" for (g = 1; g < num_bands; g++) bands[g].thr = FFMAX(bands[g].thr, bands[g-1].thr * coeffs[g].spread_hi[0]); for (g = num_bands - 2; g >= 0; g--) bands[g].thr = FFMAX(bands[g].thr, bands[g+1].thr * coeffs[g].spread_low[0]); //5.4.2.4 "Threshold in quiet" for (g = 0; g < num_bands; g++) { AacPsyBand *band = &bands[g]; band->thr_quiet = band->thr = FFMAX(band->thr, coeffs[g].ath); //5.4.2.5 "Pre-echo control" if (!(wi->window_type[0] == LONG_STOP_SEQUENCE || (wi->window_type[1] == LONG_START_SEQUENCE && !w))) band->thr = FFMAX(PSY_3GPP_RPEMIN*band->thr, FFMIN(band->thr, PSY_3GPP_RPELEV*pch->prev_band[w+g].thr_quiet)); } } for (w = 0; w < wi->num_windows*16; w += 16) { for (g = 0; g < num_bands; g++) { AacPsyBand *band = &pch->band[w+g]; FFPsyBand *psy_band = &ctx->psy_bands[channel*PSY_MAX_BANDS+w+g]; psy_band->threshold = band->thr; psy_band->energy = band->energy; } } memcpy(pch->prev_band, pch->band, sizeof(pch->band)); } static av_cold void psy_3gpp_end(FFPsyContext *apc) { AacPsyContext *pctx = (AacPsyContext*) apc->model_priv_data; av_freep(&pctx->ch); av_freep(&apc->model_priv_data); } static void lame_apply_block_type(AacPsyChannel *ctx, FFPsyWindowInfo *wi, int uselongblock) { int blocktype = ONLY_LONG_SEQUENCE; if (uselongblock) { if (ctx->next_window_seq == EIGHT_SHORT_SEQUENCE) blocktype = LONG_STOP_SEQUENCE; } else { blocktype = EIGHT_SHORT_SEQUENCE; if (ctx->next_window_seq == ONLY_LONG_SEQUENCE) ctx->next_window_seq = LONG_START_SEQUENCE; if (ctx->next_window_seq == LONG_STOP_SEQUENCE) ctx->next_window_seq = EIGHT_SHORT_SEQUENCE; } wi->window_type[0] = ctx->next_window_seq; ctx->next_window_seq = blocktype; } static FFPsyWindowInfo psy_lame_window(FFPsyContext *ctx, const int16_t *audio, const int16_t *la, int channel, int prev_type) { AacPsyContext *pctx = (AacPsyContext*) ctx->model_priv_data; AacPsyChannel *pch = &pctx->ch[channel]; int grouping = 0; int uselongblock = 1; int attacks[AAC_NUM_BLOCKS_SHORT + 1] = { 0 }; int i; FFPsyWindowInfo wi; memset(&wi, 0, sizeof(wi)); if (la) { float hpfsmpl[AAC_BLOCK_SIZE_LONG]; float const *pf = hpfsmpl; float attack_intensity[(AAC_NUM_BLOCKS_SHORT + 1) * PSY_LAME_NUM_SUBBLOCKS]; float energy_subshort[(AAC_NUM_BLOCKS_SHORT + 1) * PSY_LAME_NUM_SUBBLOCKS]; float energy_short[AAC_NUM_BLOCKS_SHORT + 1] = { 0 }; int chans = ctx->avctx->channels; const int16_t *firbuf = la + (AAC_BLOCK_SIZE_SHORT/4 - PSY_LAME_FIR_LEN) * chans; int j, att_sum = 0; /* LAME comment: apply high pass filter of fs/4 */ for (i = 0; i < AAC_BLOCK_SIZE_LONG; i++) { float sum1, sum2; sum1 = firbuf[(i + ((PSY_LAME_FIR_LEN - 1) / 2)) * chans]; sum2 = 0.0; for (j = 0; j < ((PSY_LAME_FIR_LEN - 1) / 2) - 1; j += 2) { sum1 += psy_fir_coeffs[j] * (firbuf[(i + j) * chans] + firbuf[(i + PSY_LAME_FIR_LEN - j) * chans]); sum2 += psy_fir_coeffs[j + 1] * (firbuf[(i + j + 1) * chans] + firbuf[(i + PSY_LAME_FIR_LEN - j - 1) * chans]); } hpfsmpl[i] = sum1 + sum2; } /* Calculate the energies of each sub-shortblock */ for (i = 0; i < PSY_LAME_NUM_SUBBLOCKS; i++) { energy_subshort[i] = pch->prev_energy_subshort[i + ((AAC_NUM_BLOCKS_SHORT - 1) * PSY_LAME_NUM_SUBBLOCKS)]; assert(pch->prev_energy_subshort[i + ((AAC_NUM_BLOCKS_SHORT - 2) * PSY_LAME_NUM_SUBBLOCKS + 1)] > 0); attack_intensity[i] = energy_subshort[i] / pch->prev_energy_subshort[i + ((AAC_NUM_BLOCKS_SHORT - 2) * PSY_LAME_NUM_SUBBLOCKS + 1)]; energy_short[0] += energy_subshort[i]; } for (i = 0; i < AAC_NUM_BLOCKS_SHORT * PSY_LAME_NUM_SUBBLOCKS; i++) { float const *const pfe = pf + AAC_BLOCK_SIZE_LONG / (AAC_NUM_BLOCKS_SHORT * PSY_LAME_NUM_SUBBLOCKS); float p = 1.0f; for (; pf < pfe; pf++) if (p < fabsf(*pf)) p = fabsf(*pf); pch->prev_energy_subshort[i] = energy_subshort[i + PSY_LAME_NUM_SUBBLOCKS] = p; energy_short[1 + i / PSY_LAME_NUM_SUBBLOCKS] += p; /* FIXME: The indexes below are [i + 3 - 2] in the LAME source. * Obviously the 3 and 2 have some significance, or this would be just [i + 1] * (which is what we use here). What the 3 stands for is ambigious, as it is both * number of short blocks, and the number of sub-short blocks. * It seems that LAME is comparing each sub-block to sub-block + 1 in the * previous block. */ if (p > energy_subshort[i + 1]) p = p / energy_subshort[i + 1]; else if (energy_subshort[i + 1] > p * 10.0f) p = energy_subshort[i + 1] / (p * 10.0f); else p = 0.0; attack_intensity[i + PSY_LAME_NUM_SUBBLOCKS] = p; } /* compare energy between sub-short blocks */ for (i = 0; i < (AAC_NUM_BLOCKS_SHORT + 1) * PSY_LAME_NUM_SUBBLOCKS; i++) if (!attacks[i / PSY_LAME_NUM_SUBBLOCKS]) if (attack_intensity[i] > pch->attack_threshold) attacks[i / PSY_LAME_NUM_SUBBLOCKS] = (i % PSY_LAME_NUM_SUBBLOCKS) + 1; /* should have energy change between short blocks, in order to avoid periodic signals */ /* Good samples to show the effect are Trumpet test songs */ /* GB: tuned (1) to avoid too many short blocks for test sample TRUMPET */ /* RH: tuned (2) to let enough short blocks through for test sample FSOL and SNAPS */ for (i = 1; i < AAC_NUM_BLOCKS_SHORT + 1; i++) { float const u = energy_short[i - 1]; float const v = energy_short[i]; float const m = FFMAX(u, v); if (m < 40000) { /* (2) */ if (u < 1.7f * v && v < 1.7f * u) { /* (1) */ if (i == 1 && attacks[0] < attacks[i]) attacks[0] = 0; attacks[i] = 0; } } att_sum += attacks[i]; } if (attacks[0] <= pch->prev_attack) attacks[0] = 0; att_sum += attacks[0]; /* 3 below indicates the previous attack happened in the last sub-block of the previous sequence */ if (pch->prev_attack == 3 || att_sum) { uselongblock = 0; for (i = 1; i < AAC_NUM_BLOCKS_SHORT + 1; i++) if (attacks[i] && attacks[i-1]) attacks[i] = 0; } } else { /* We have no lookahead info, so just use same type as the previous sequence. */ uselongblock = !(prev_type == EIGHT_SHORT_SEQUENCE); } lame_apply_block_type(pch, &wi, uselongblock); wi.window_type[1] = prev_type; if (wi.window_type[0] != EIGHT_SHORT_SEQUENCE) { wi.num_windows = 1; wi.grouping[0] = 1; if (wi.window_type[0] == LONG_START_SEQUENCE) wi.window_shape = 0; else wi.window_shape = 1; } else { int lastgrp = 0; wi.num_windows = 8; wi.window_shape = 0; for (i = 0; i < 8; i++) { if (!((pch->next_grouping >> i) & 1)) lastgrp = i; wi.grouping[lastgrp]++; } } /* Determine grouping, based on the location of the first attack, and save for * the next frame. * FIXME: Move this to analysis. * TODO: Tune groupings depending on attack location * TODO: Handle more than one attack in a group */ for (i = 0; i < 9; i++) { if (attacks[i]) { grouping = i; break; } } pch->next_grouping = window_grouping[grouping]; pch->prev_attack = attacks[8]; return wi; } const FFPsyModel ff_aac_psy_model = { .name = "3GPP TS 26.403-inspired model", .init = psy_3gpp_init, .window = psy_lame_window, .analyze = psy_3gpp_analyze, .end = psy_3gpp_end, };