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105 lines
3.3 KiB
C
105 lines
3.3 KiB
C
/*
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* AAC encoder psychoacoustic model
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* Copyright (C) 2008 Konstantin Shishkov
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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* @file aacpsy.c
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* AAC encoder psychoacoustic model
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*/
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#include "avcodec.h"
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#include "aacpsy.h"
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#include "aactab.h"
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/***********************************
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* TODOs:
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* General:
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* better audio preprocessing (add DC highpass filter?)
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* more psy models
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* maybe improve coefficient quantization function in some way
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*
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* 3GPP-based psy model:
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* thresholds linearization after their modifications for attaining given bitrate
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* try other bitrate controlling mechanism (maybe use ratecontrol.c?)
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* control quality for quality-based output
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**********************************/
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/**
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* Quantize one coefficient.
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* @return absolute value of the quantized coefficient
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* @see 3GPP TS26.403 5.6.2 "Scalefactor determination"
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*/
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static av_always_inline int quant(float coef, const float Q)
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{
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return av_clip((int)(pow(fabsf(coef) * Q, 0.75) + 0.4054), 0, 8191);
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}
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static inline float get_approximate_quant_error(float *c, int size, int scale_idx)
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{
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int i;
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int q;
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float coef, unquant, sum = 0.0f;
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const float Q = ff_aac_pow2sf_tab[200 - scale_idx + SCALE_ONE_POS - SCALE_DIV_512];
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const float IQ = ff_aac_pow2sf_tab[200 + scale_idx - SCALE_ONE_POS + SCALE_DIV_512];
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for(i = 0; i < size; i++){
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coef = fabs(c[i]);
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q = quant(c[i], Q);
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unquant = (q * cbrt(q)) * IQ;
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sum += (coef - unquant) * (coef - unquant);
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}
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return sum;
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}
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/**
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* constants for 3GPP AAC psychoacoustic model
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* @{
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*/
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#define PSY_3GPP_SPREAD_LOW 1.5f // spreading factor for ascending threshold spreading (15 dB/Bark)
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#define PSY_3GPP_SPREAD_HI 3.0f // spreading factor for descending threshold spreading (30 dB/Bark)
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/**
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* @}
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*/
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/**
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* information for single band used by 3GPP TS26.403-inspired psychoacoustic model
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*/
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typedef struct Psy3gppBand{
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float energy; ///< band energy
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float ffac; ///< form factor
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}Psy3gppBand;
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/**
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* psychoacoustic model frame type-dependent coefficients
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*/
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typedef struct Psy3gppCoeffs{
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float ath [64]; ///< absolute threshold of hearing per bands
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float barks [64]; ///< Bark value for each spectral band in long frame
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float spread_low[64]; ///< spreading factor for low-to-high threshold spreading in long frame
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float spread_hi [64]; ///< spreading factor for high-to-low threshold spreading in long frame
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}Psy3gppCoeffs;
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/**
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* Calculate Bark value for given line.
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*/
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static inline float calc_bark(float f)
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{
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return 13.3f * atanf(0.00076f * f) + 3.5f * atanf((f / 7500.0f) * (f / 7500.0f));
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}
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