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104 lines
3.3 KiB
104 lines
3.3 KiB
/* |
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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 libavcodec/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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