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e3faad811e
This commit improves the TNS implementation to the point where it's actually usable and very rarely results in nastyness (in all bitrates except extremely low bitrates it's increasing the quality and prevents some distortions from the coder being audiable). Also adds a double filter support which is only used if the energy difference between the top and bottom of the SFBs is above the thresholds defined in the header file. Looking at the bitstream that fdk_aac generates it sometimes used a double filter despite the specs stating that a single filter should be enough for almost all cases and purposes. Unlike FAAC or fdk_aac we sometimes use a reverse filter in case the energy difference isn't enought to use a double filter. This actually works better. Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>
53 lines
1.8 KiB
C
53 lines
1.8 KiB
C
/*
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* AAC encoder TNS
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* Copyright (C) 2015 Rostislav Pehlivanov
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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
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* AAC encoder temporal noise shaping
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* @author Rostislav Pehlivanov ( atomnuker gmail com )
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*/
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#ifndef AVCODEC_AACENC_TNS_H
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#define AVCODEC_AACENC_TNS_H
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#include "aacenc.h"
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/* Could be set to 3 to save an additional bit at the cost of little quality */
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#define TNS_Q_BITS 4
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/* TNS will only be used if the LPC gain is within these margins */
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#define TNS_GAIN_THRESHOLD_LOW 1.395f
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#define TNS_GAIN_THRESHOLD_HIGH 11.19f
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/* If the energy ratio between the low SFBs vs the high SFBs is not between
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* those two values, use 2 filters instead */
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#define TNS_E_RATIO_LOW 0.77
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#define TNS_E_RATIO_HIGH 1.23
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/* Do not use TNS if the psy band spread is below this value */
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#define TNS_SPREAD_THRESHOLD 37.081512f
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void ff_aac_encode_tns_info(AACEncContext *s, SingleChannelElement *sce);
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void ff_aac_apply_tns(AACEncContext *s, SingleChannelElement *sce);
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void ff_aac_search_for_tns(AACEncContext *s, SingleChannelElement *sce);
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#endif /* AVCODEC_AACENC_TNS_H */
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