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Long Term Prediction allows for prediction of spectral coefficients via the previously decoded time-dependent samples. This feature works well with harmonic content 2 or more frames long, like speech, human or non-human, piano music or any constant tones at very low bitrates. It should be noted that the current coder is highly efficient and the rate control system is unable to encode files at extremely low bitrates (less than 14kbps seems to be impossible) so this extension isn't capable of optimum operation. Dramatic difference is observable with some types of audio and speech but for the most part the audiable differences are subtle. The spectrum looks better however so the encoder is able to harvest the additional bits that this feature provies, should the user choose to enable it. So it's best to enable this feature only if encoding at the absolutely lowest bitrate that the encoder is capable of.
42 lines
1.5 KiB
C
42 lines
1.5 KiB
C
/*
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* AAC encoder long term prediction extension
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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 long term prediction extension
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* @author Rostislav Pehlivanov ( atomnuker gmail com )
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*/
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#ifndef AVCODEC_AACENC_LTP_H
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#define AVCODEC_AACENC_LTP_H
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#include "aacenc.h"
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void ff_aac_encode_ltp_info(AACEncContext *s, SingleChannelElement *sce,
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int common_window);
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void ff_aac_update_ltp(AACEncContext *s, SingleChannelElement *sce);
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void ff_aac_adjust_common_ltp(AACEncContext *s, ChannelElement *cpe);
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void ff_aac_ltp_insert_new_frame(AACEncContext *s);
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void ff_aac_search_for_ltp(AACEncContext *s, SingleChannelElement *sce,
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int common_window);
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#endif /* AVCODEC_AACENC_LTP_H */
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