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Channel coupling is an optional AC-3 feature that increases quality by combining high frequency information from multiple channels into a single channel. The per-channel high frequency information is sent with less accuracy in both the frequency and time domains. This allows more bits to be used for lower frequencies while preserving enough information to reconstruct the high frequencies.
229 lines
12 KiB
C
229 lines
12 KiB
C
/*
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* Common code between the AC-3 and E-AC-3 decoders
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* Copyright (c) 2007 Bartlomiej Wolowiec <bartek.wolowiec@gmail.com>
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*
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* This file is part of Libav.
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*
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* Libav 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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* Libav 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 Libav; 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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* Common code between the AC-3 and E-AC-3 decoders.
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*
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* Summary of MDCT Coefficient Grouping:
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* The individual MDCT coefficient indices are often referred to in the
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* (E-)AC-3 specification as frequency bins. These bins are grouped together
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* into subbands of 12 coefficients each. The subbands are grouped together
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* into bands as defined in the bitstream by the band structures, which
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* determine the number of bands and the size of each band. The full spectrum
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* of 256 frequency bins is divided into 1 DC bin + 21 subbands = 253 bins.
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* This system of grouping coefficients is used for channel bandwidth, stereo
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* rematrixing, channel coupling, enhanced coupling, and spectral extension.
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*
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* +-+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+-+
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* |1| |12| | [12|12|12|12] | | | | | | | | | | | | |3|
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* +-+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+-+
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* ~~~ ~~~~ ~~~~~~~~~~~~~ ~~~
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* | | | |
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* | | | 3 unused frequency bins--+
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* | | |
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* | | +--1 band containing 4 subbands
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* | |
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* | +--1 subband of 12 frequency bins
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* |
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* +--DC frequency bin
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*/
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#ifndef AVCODEC_AC3DEC_H
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#define AVCODEC_AC3DEC_H
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#include "libavutil/lfg.h"
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#include "ac3.h"
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#include "ac3dsp.h"
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#include "get_bits.h"
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#include "dsputil.h"
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#include "fft.h"
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#include "fmtconvert.h"
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#define AC3_OUTPUT_LFEON 8
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#define SPX_MAX_BANDS 17
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typedef struct {
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AVCodecContext *avctx; ///< parent context
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GetBitContext gbc; ///< bitstream reader
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uint8_t *input_buffer; ///< temp buffer to prevent overread
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///@defgroup bsi bit stream information
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///@{
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int frame_type; ///< frame type (strmtyp)
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int substreamid; ///< substream identification
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int frame_size; ///< current frame size, in bytes
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int bit_rate; ///< stream bit rate, in bits-per-second
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int sample_rate; ///< sample frequency, in Hz
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int num_blocks; ///< number of audio blocks
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int bitstream_mode; ///< bitstream mode (bsmod)
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int channel_mode; ///< channel mode (acmod)
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int channel_layout; ///< channel layout
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int lfe_on; ///< lfe channel in use
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int channel_map; ///< custom channel map
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int center_mix_level; ///< Center mix level index
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int surround_mix_level; ///< Surround mix level index
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int eac3; ///< indicates if current frame is E-AC-3
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///@}
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///@defgroup audfrm frame syntax parameters
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int snr_offset_strategy; ///< SNR offset strategy (snroffststr)
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int block_switch_syntax; ///< block switch syntax enabled (blkswe)
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int dither_flag_syntax; ///< dither flag syntax enabled (dithflage)
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int bit_allocation_syntax; ///< bit allocation model syntax enabled (bamode)
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int fast_gain_syntax; ///< fast gain codes enabled (frmfgaincode)
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int dba_syntax; ///< delta bit allocation syntax enabled (dbaflde)
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int skip_syntax; ///< skip field syntax enabled (skipflde)
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///@}
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///@defgroup cpl standard coupling
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int cpl_in_use[AC3_MAX_BLOCKS]; ///< coupling in use (cplinu)
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int cpl_strategy_exists[AC3_MAX_BLOCKS];///< coupling strategy exists (cplstre)
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int channel_in_cpl[AC3_MAX_CHANNELS]; ///< channel in coupling (chincpl)
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int phase_flags_in_use; ///< phase flags in use (phsflginu)
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int phase_flags[AC3_MAX_CPL_BANDS]; ///< phase flags (phsflg)
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int num_cpl_bands; ///< number of coupling bands (ncplbnd)
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uint8_t cpl_band_sizes[AC3_MAX_CPL_BANDS]; ///< number of coeffs in each coupling band
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int firstchincpl; ///< first channel in coupling
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int first_cpl_coords[AC3_MAX_CHANNELS]; ///< first coupling coordinates states (firstcplcos)
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int cpl_coords[AC3_MAX_CHANNELS][AC3_MAX_CPL_BANDS]; ///< coupling coordinates (cplco)
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///@}
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///@defgroup spx spectral extension
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///@{
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int spx_in_use; ///< spectral extension in use (spxinu)
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uint8_t channel_uses_spx[AC3_MAX_CHANNELS]; ///< channel uses spectral extension (chinspx)
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int8_t spx_atten_code[AC3_MAX_CHANNELS]; ///< spx attenuation code (spxattencod)
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int spx_src_start_freq; ///< spx start frequency bin
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int spx_dst_end_freq; ///< spx end frequency bin
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int spx_dst_start_freq; ///< spx starting frequency bin for copying (copystartmant)
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///< the copy region ends at the start of the spx region.
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int num_spx_bands; ///< number of spx bands (nspxbnds)
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uint8_t spx_band_sizes[SPX_MAX_BANDS]; ///< number of bins in each spx band
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uint8_t first_spx_coords[AC3_MAX_CHANNELS]; ///< first spx coordinates states (firstspxcos)
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float spx_noise_blend[AC3_MAX_CHANNELS][SPX_MAX_BANDS]; ///< spx noise blending factor (nblendfact)
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float spx_signal_blend[AC3_MAX_CHANNELS][SPX_MAX_BANDS];///< spx signal blending factor (sblendfact)
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///@}
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///@defgroup aht adaptive hybrid transform
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int channel_uses_aht[AC3_MAX_CHANNELS]; ///< channel AHT in use (chahtinu)
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int pre_mantissa[AC3_MAX_CHANNELS][AC3_MAX_COEFS][AC3_MAX_BLOCKS]; ///< pre-IDCT mantissas
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///@}
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///@defgroup channel channel
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int fbw_channels; ///< number of full-bandwidth channels
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int channels; ///< number of total channels
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int lfe_ch; ///< index of LFE channel
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float downmix_coeffs[AC3_MAX_CHANNELS][2]; ///< stereo downmix coefficients
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int downmixed; ///< indicates if coeffs are currently downmixed
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int output_mode; ///< output channel configuration
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int out_channels; ///< number of output channels
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///@}
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///@defgroup dynrng dynamic range
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float dynamic_range[2]; ///< dynamic range
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///@}
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///@defgroup bandwidth bandwidth
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int start_freq[AC3_MAX_CHANNELS]; ///< start frequency bin (strtmant)
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int end_freq[AC3_MAX_CHANNELS]; ///< end frequency bin (endmant)
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///@}
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///@defgroup rematrixing rematrixing
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int num_rematrixing_bands; ///< number of rematrixing bands (nrematbnd)
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int rematrixing_flags[4]; ///< rematrixing flags (rematflg)
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///@}
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///@defgroup exponents exponents
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int num_exp_groups[AC3_MAX_CHANNELS]; ///< Number of exponent groups (nexpgrp)
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int8_t dexps[AC3_MAX_CHANNELS][AC3_MAX_COEFS]; ///< decoded exponents
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int exp_strategy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS]; ///< exponent strategies (expstr)
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///@}
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///@defgroup bitalloc bit allocation
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AC3BitAllocParameters bit_alloc_params; ///< bit allocation parameters
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int first_cpl_leak; ///< first coupling leak state (firstcplleak)
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int snr_offset[AC3_MAX_CHANNELS]; ///< signal-to-noise ratio offsets (snroffst)
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int fast_gain[AC3_MAX_CHANNELS]; ///< fast gain values/SMR's (fgain)
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uint8_t bap[AC3_MAX_CHANNELS][AC3_MAX_COEFS]; ///< bit allocation pointers
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int16_t psd[AC3_MAX_CHANNELS][AC3_MAX_COEFS]; ///< scaled exponents
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int16_t band_psd[AC3_MAX_CHANNELS][AC3_CRITICAL_BANDS]; ///< interpolated exponents
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int16_t mask[AC3_MAX_CHANNELS][AC3_CRITICAL_BANDS]; ///< masking curve values
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int dba_mode[AC3_MAX_CHANNELS]; ///< delta bit allocation mode
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int dba_nsegs[AC3_MAX_CHANNELS]; ///< number of delta segments
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uint8_t dba_offsets[AC3_MAX_CHANNELS][8]; ///< delta segment offsets
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uint8_t dba_lengths[AC3_MAX_CHANNELS][8]; ///< delta segment lengths
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uint8_t dba_values[AC3_MAX_CHANNELS][8]; ///< delta values for each segment
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///@}
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///@defgroup dithering zero-mantissa dithering
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int dither_flag[AC3_MAX_CHANNELS]; ///< dither flags (dithflg)
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AVLFG dith_state; ///< for dither generation
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///@}
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///@defgroup imdct IMDCT
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int block_switch[AC3_MAX_CHANNELS]; ///< block switch flags (blksw)
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FFTContext imdct_512; ///< for 512 sample IMDCT
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FFTContext imdct_256; ///< for 256 sample IMDCT
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///@}
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///@defgroup opt optimization
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DSPContext dsp; ///< for optimization
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AC3DSPContext ac3dsp;
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FmtConvertContext fmt_conv; ///< optimized conversion functions
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float mul_bias; ///< scaling for float_to_int16 conversion
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///@}
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///@defgroup arrays aligned arrays
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DECLARE_ALIGNED(16, int, fixed_coeffs)[AC3_MAX_CHANNELS][AC3_MAX_COEFS]; ///> fixed-point transform coefficients
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DECLARE_ALIGNED(32, float, transform_coeffs)[AC3_MAX_CHANNELS][AC3_MAX_COEFS]; ///< transform coefficients
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DECLARE_ALIGNED(32, float, delay)[AC3_MAX_CHANNELS][AC3_BLOCK_SIZE]; ///< delay - added to the next block
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DECLARE_ALIGNED(32, float, window)[AC3_BLOCK_SIZE]; ///< window coefficients
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DECLARE_ALIGNED(32, float, tmp_output)[AC3_BLOCK_SIZE]; ///< temporary storage for output before windowing
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DECLARE_ALIGNED(32, float, output)[AC3_MAX_CHANNELS][AC3_BLOCK_SIZE]; ///< output after imdct transform and windowing
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///@}
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} AC3DecodeContext;
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/**
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* Parse the E-AC-3 frame header.
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* This parses both the bit stream info and audio frame header.
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*/
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int ff_eac3_parse_header(AC3DecodeContext *s);
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/**
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* Decode mantissas in a single channel for the entire frame.
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* This is used when AHT mode is enabled.
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*/
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void ff_eac3_decode_transform_coeffs_aht_ch(AC3DecodeContext *s, int ch);
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void ff_ac3_downmix_c(float (*samples)[256], float (*matrix)[2],
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int out_ch, int in_ch, int len);
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/**
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* Apply spectral extension to each channel by copying lower frequency
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* coefficients to higher frequency bins and applying side information to
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* approximate the original high frequency signal.
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*/
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void ff_eac3_apply_spectral_extension(AC3DecodeContext *s);
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#endif /* AVCODEC_AC3DEC_H */
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