1135 lines
37 KiB
C
1135 lines
37 KiB
C
/*
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* AC-3 Audio Decoder
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* This code is developed as part of Google Summer of Code 2006 Program.
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*
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* Copyright (c) 2006 Kartikey Mahendra BHATT (bhattkm at gmail dot com).
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* Copyright (c) 2007 Justin Ruggles
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*
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* Portions of this code are derived from liba52
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* http://liba52.sourceforge.net
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* Copyright (C) 2000-2003 Michel Lespinasse <walken@zoy.org>
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* Copyright (C) 1999-2000 Aaron Holtzman <aholtzma@ess.engr.uvic.ca>
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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 General Public
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* License as published by the Free Software Foundation; either
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* version 2 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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* General Public License for more details.
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*
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* You should have received a copy of the GNU 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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#include <stdio.h>
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#include <stddef.h>
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#include <math.h>
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#include <string.h>
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#include "avcodec.h"
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#include "ac3_parser.h"
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#include "bitstream.h"
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#include "dsputil.h"
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#include "random.h"
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/**
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* Table of bin locations for rematrixing bands
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* reference: Section 7.5.2 Rematrixing : Frequency Band Definitions
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*/
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static const uint8_t rematrix_band_tbl[5] = { 13, 25, 37, 61, 253 };
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/* table for exponent to scale_factor mapping
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* scale_factor[i] = 2 ^ -(i + 15)
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*/
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static float scale_factors[25];
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/** table for grouping exponents */
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static uint8_t exp_ungroup_tbl[128][3];
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/** tables for ungrouping mantissas */
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static float b1_mantissas[32][3];
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static float b2_mantissas[128][3];
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static float b3_mantissas[8];
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static float b4_mantissas[128][2];
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static float b5_mantissas[16];
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/**
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* Quantization table: levels for symmetric. bits for asymmetric.
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* reference: Table 7.18 Mapping of bap to Quantizer
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*/
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static const uint8_t qntztab[16] = {
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0, 3, 5, 7, 11, 15,
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5, 6, 7, 8, 9, 10, 11, 12, 14, 16
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};
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/** dynamic range table. converts codes to scale factors. */
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static float dynrng_tbl[256];
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/** dialogue normalization table */
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static float dialnorm_tbl[32];
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/* Adjustmens in dB gain */
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#define LEVEL_MINUS_3DB 0.7071067811865476
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#define LEVEL_MINUS_4POINT5DB 0.5946035575013605
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#define LEVEL_MINUS_6DB 0.5000000000000000
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#define LEVEL_MINUS_9DB 0.3535533905932738
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#define LEVEL_ZERO 0.0000000000000000
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#define LEVEL_ONE 1.0000000000000000
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static const float gain_levels[6] = {
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LEVEL_ZERO,
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LEVEL_ONE,
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LEVEL_MINUS_3DB,
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LEVEL_MINUS_4POINT5DB,
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LEVEL_MINUS_6DB,
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LEVEL_MINUS_9DB
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};
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/**
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* Table for center mix levels
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* reference: Section 5.4.2.4 cmixlev
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*/
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static const uint8_t clevs[4] = { 2, 3, 4, 3 };
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/**
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* Table for surround mix levels
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* reference: Section 5.4.2.5 surmixlev
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*/
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static const uint8_t slevs[4] = { 2, 4, 0, 4 };
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/**
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* Table for default stereo downmixing coefficients
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* reference: Section 7.8.2 Downmixing Into Two Channels
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*/
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static const uint8_t ac3_default_coeffs[8][5][2] = {
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{ { 1, 0 }, { 0, 1 }, },
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{ { 2, 2 }, },
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{ { 1, 0 }, { 0, 1 }, },
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{ { 1, 0 }, { 3, 3 }, { 0, 1 }, },
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{ { 1, 0 }, { 0, 1 }, { 4, 4 }, },
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{ { 1, 0 }, { 3, 3 }, { 0, 1 }, { 5, 5 }, },
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{ { 1, 0 }, { 0, 1 }, { 4, 0 }, { 0, 4 }, },
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{ { 1, 0 }, { 3, 3 }, { 0, 1 }, { 4, 0 }, { 0, 4 }, },
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};
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/* override ac3.h to include coupling channel */
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#undef AC3_MAX_CHANNELS
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#define AC3_MAX_CHANNELS 7
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#define CPL_CH 0
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#define AC3_OUTPUT_LFEON 8
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typedef struct {
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int acmod;
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int dsurmod;
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int blksw[AC3_MAX_CHANNELS];
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int dithflag[AC3_MAX_CHANNELS];
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int dither_all;
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int cplinu;
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int chincpl[AC3_MAX_CHANNELS];
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int phsflginu;
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int cplbndstrc[18];
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int rematstr;
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int nrematbnd;
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int rematflg[4];
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int expstr[AC3_MAX_CHANNELS];
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int snroffst[AC3_MAX_CHANNELS];
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int fgain[AC3_MAX_CHANNELS];
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int deltbae[AC3_MAX_CHANNELS];
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int deltnseg[AC3_MAX_CHANNELS];
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uint8_t deltoffst[AC3_MAX_CHANNELS][8];
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uint8_t deltlen[AC3_MAX_CHANNELS][8];
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uint8_t deltba[AC3_MAX_CHANNELS][8];
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/* Derived Attributes. */
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int sampling_rate;
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int bit_rate;
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int frame_size;
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int nchans; //number of total channels
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int nfchans; //number of full-bandwidth channels
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int lfeon; //lfe channel in use
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int lfe_ch; ///< index of LFE channel
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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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float downmix_coeffs[AC3_MAX_CHANNELS][2]; ///< stereo downmix coefficients
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float dialnorm[2]; ///< dialogue normalization
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float dynrng[2]; ///< dynamic range
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float cplco[AC3_MAX_CHANNELS][18]; //coupling coordinates
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int ncplbnd; //number of coupling bands
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int ncplsubnd; //number of coupling sub bands
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int startmant[AC3_MAX_CHANNELS]; ///< start frequency bin
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int endmant[AC3_MAX_CHANNELS]; //channel end mantissas
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AC3BitAllocParameters bit_alloc_params; ///< bit allocation parameters
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int8_t dexps[AC3_MAX_CHANNELS][256]; ///< decoded exponents
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uint8_t bap[AC3_MAX_CHANNELS][256]; ///< bit allocation pointers
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int16_t psd[AC3_MAX_CHANNELS][256]; ///< scaled exponents
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int16_t bndpsd[AC3_MAX_CHANNELS][50]; ///< interpolated exponents
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int16_t mask[AC3_MAX_CHANNELS][50]; ///< masking curve values
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DECLARE_ALIGNED_16(float, transform_coeffs[AC3_MAX_CHANNELS][256]); //transform coefficients
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/* For IMDCT. */
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MDCTContext imdct_512; //for 512 sample imdct transform
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MDCTContext imdct_256; //for 256 sample imdct transform
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DSPContext dsp; //for optimization
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float add_bias; ///< offset for float_to_int16 conversion
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float mul_bias; ///< scaling for float_to_int16 conversion
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DECLARE_ALIGNED_16(float, output[AC3_MAX_CHANNELS-1][256]); //output after imdct transform and windowing
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DECLARE_ALIGNED_16(short, int_output[AC3_MAX_CHANNELS-1][256]); ///< final 16-bit integer output
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DECLARE_ALIGNED_16(float, delay[AC3_MAX_CHANNELS-1][256]); //delay - added to the next block
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DECLARE_ALIGNED_16(float, tmp_imdct[256]); //temporary storage for imdct transform
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DECLARE_ALIGNED_16(float, tmp_output[512]); //temporary storage for output before windowing
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DECLARE_ALIGNED_16(float, window[256]); //window coefficients
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/* Miscellaneous. */
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GetBitContext gb;
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AVRandomState dith_state; //for dither generation
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} AC3DecodeContext;
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/*********** BEGIN INIT HELPER FUNCTIONS ***********/
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/**
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* Generate a Kaiser-Bessel Derived Window.
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*/
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static void ac3_window_init(float *window)
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{
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int i, j;
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double sum = 0.0, bessel, tmp;
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double local_window[256];
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double alpha2 = (5.0 * M_PI / 256.0) * (5.0 * M_PI / 256.0);
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for (i = 0; i < 256; i++) {
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tmp = i * (256 - i) * alpha2;
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bessel = 1.0;
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for (j = 100; j > 0; j--) /* defaul to 100 iterations */
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bessel = bessel * tmp / (j * j) + 1;
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sum += bessel;
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local_window[i] = sum;
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}
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sum++;
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for (i = 0; i < 256; i++)
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window[i] = sqrt(local_window[i] / sum);
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}
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static inline float
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symmetric_dequant(int code, int levels)
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{
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return (code - (levels >> 1)) * (2.0f / levels);
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}
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/*
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* Initialize tables at runtime.
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*/
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static void ac3_tables_init(void)
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{
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int i;
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/* generate grouped mantissa tables
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reference: Section 7.3.5 Ungrouping of Mantissas */
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for(i=0; i<32; i++) {
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/* bap=1 mantissas */
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b1_mantissas[i][0] = symmetric_dequant( i / 9 , 3);
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b1_mantissas[i][1] = symmetric_dequant((i % 9) / 3, 3);
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b1_mantissas[i][2] = symmetric_dequant((i % 9) % 3, 3);
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}
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for(i=0; i<128; i++) {
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/* bap=2 mantissas */
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b2_mantissas[i][0] = symmetric_dequant( i / 25 , 5);
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b2_mantissas[i][1] = symmetric_dequant((i % 25) / 5, 5);
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b2_mantissas[i][2] = symmetric_dequant((i % 25) % 5, 5);
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/* bap=4 mantissas */
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b4_mantissas[i][0] = symmetric_dequant(i / 11, 11);
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b4_mantissas[i][1] = symmetric_dequant(i % 11, 11);
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}
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/* generate ungrouped mantissa tables
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reference: Tables 7.21 and 7.23 */
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for(i=0; i<7; i++) {
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/* bap=3 mantissas */
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b3_mantissas[i] = symmetric_dequant(i, 7);
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}
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for(i=0; i<15; i++) {
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/* bap=5 mantissas */
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b5_mantissas[i] = symmetric_dequant(i, 15);
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}
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/* generate dynamic range table
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reference: Section 7.7.1 Dynamic Range Control */
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for(i=0; i<256; i++) {
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int v = (i >> 5) - ((i >> 7) << 3) - 5;
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dynrng_tbl[i] = powf(2.0f, v) * ((i & 0x1F) | 0x20);
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}
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/* generate dialogue normalization table
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references: Section 5.4.2.8 dialnorm
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Section 7.6 Dialogue Normalization */
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for(i=1; i<32; i++) {
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dialnorm_tbl[i] = expf((i-31) * M_LN10 / 20.0f);
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}
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dialnorm_tbl[0] = dialnorm_tbl[31];
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//generate scale factors
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for (i = 0; i < 25; i++)
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scale_factors[i] = pow(2.0, -i);
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/* generate exponent tables
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reference: Section 7.1.3 Exponent Decoding */
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for(i=0; i<128; i++) {
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exp_ungroup_tbl[i][0] = i / 25;
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exp_ungroup_tbl[i][1] = (i % 25) / 5;
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exp_ungroup_tbl[i][2] = (i % 25) % 5;
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}
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}
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static int ac3_decode_init(AVCodecContext *avctx)
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{
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AC3DecodeContext *ctx = avctx->priv_data;
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ac3_common_init();
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ac3_tables_init();
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ff_mdct_init(&ctx->imdct_256, 8, 1);
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ff_mdct_init(&ctx->imdct_512, 9, 1);
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ac3_window_init(ctx->window);
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dsputil_init(&ctx->dsp, avctx);
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av_init_random(0, &ctx->dith_state);
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if(ctx->dsp.float_to_int16 == ff_float_to_int16_c) {
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ctx->add_bias = 385.0f;
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ctx->mul_bias = 1.0f;
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} else {
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ctx->add_bias = 0.0f;
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ctx->mul_bias = 32767.0f;
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}
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return 0;
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}
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/*********** END INIT FUNCTIONS ***********/
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/**
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* Parses the 'sync info' and 'bit stream info' from the AC-3 bitstream.
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* GetBitContext within AC3DecodeContext must point to
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* start of the synchronized ac3 bitstream.
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*/
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static int ac3_parse_header(AC3DecodeContext *ctx)
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{
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AC3HeaderInfo hdr;
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GetBitContext *gb = &ctx->gb;
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float cmixlev, surmixlev;
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int err, i;
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err = ff_ac3_parse_header(gb->buffer, &hdr);
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if(err)
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return err;
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/* get decoding parameters from header info */
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ctx->bit_alloc_params.fscod = hdr.fscod;
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ctx->acmod = hdr.acmod;
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cmixlev = gain_levels[clevs[hdr.cmixlev]];
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surmixlev = gain_levels[slevs[hdr.surmixlev]];
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ctx->dsurmod = hdr.dsurmod;
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ctx->lfeon = hdr.lfeon;
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ctx->bit_alloc_params.halfratecod = hdr.halfratecod;
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ctx->sampling_rate = hdr.sample_rate;
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ctx->bit_rate = hdr.bit_rate;
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ctx->nchans = hdr.channels;
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ctx->nfchans = ctx->nchans - ctx->lfeon;
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ctx->lfe_ch = ctx->nfchans + 1;
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ctx->frame_size = hdr.frame_size;
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/* set default output to all source channels */
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ctx->out_channels = ctx->nchans;
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ctx->output_mode = ctx->acmod;
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if(ctx->lfeon)
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ctx->output_mode |= AC3_OUTPUT_LFEON;
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/* skip over portion of header which has already been read */
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skip_bits(gb, 16); //skip the sync_word, sync_info->sync_word = get_bits(gb, 16);
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skip_bits(gb, 16); // skip crc1
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skip_bits(gb, 8); // skip fscod and frmsizecod
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skip_bits(gb, 11); // skip bsid, bsmod, and acmod
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if(ctx->acmod == AC3_ACMOD_STEREO) {
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skip_bits(gb, 2); // skip dsurmod
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} else {
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if((ctx->acmod & 1) && ctx->acmod != AC3_ACMOD_MONO)
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skip_bits(gb, 2); // skip cmixlev
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if(ctx->acmod & 4)
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skip_bits(gb, 2); // skip surmixlev
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}
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skip_bits1(gb); // skip lfeon
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/* read the rest of the bsi. read twice for dual mono mode. */
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i = !(ctx->acmod);
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do {
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ctx->dialnorm[i] = dialnorm_tbl[get_bits(gb, 5)]; // dialogue normalization
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if (get_bits1(gb))
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skip_bits(gb, 8); //skip compression
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if (get_bits1(gb))
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skip_bits(gb, 8); //skip language code
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if (get_bits1(gb))
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skip_bits(gb, 7); //skip audio production information
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} while (i--);
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skip_bits(gb, 2); //skip copyright bit and original bitstream bit
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/* FIXME: read & use the xbsi1 downmix levels */
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if (get_bits1(gb))
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skip_bits(gb, 14); //skip timecode1
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if (get_bits1(gb))
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skip_bits(gb, 14); //skip timecode2
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if (get_bits1(gb)) {
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i = get_bits(gb, 6); //additional bsi length
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do {
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skip_bits(gb, 8);
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} while(i--);
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}
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/* set stereo downmixing coefficients
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reference: Section 7.8.2 Downmixing Into Two Channels */
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for(i=0; i<ctx->nfchans; i++) {
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ctx->downmix_coeffs[i][0] = gain_levels[ac3_default_coeffs[ctx->acmod][i][0]];
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ctx->downmix_coeffs[i][1] = gain_levels[ac3_default_coeffs[ctx->acmod][i][1]];
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}
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if(ctx->acmod > 1 && ctx->acmod & 1) {
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ctx->downmix_coeffs[1][0] = ctx->downmix_coeffs[1][1] = cmixlev;
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}
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if(ctx->acmod == AC3_ACMOD_2F1R || ctx->acmod == AC3_ACMOD_3F1R) {
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int nf = ctx->acmod - 2;
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ctx->downmix_coeffs[nf][0] = ctx->downmix_coeffs[nf][1] = surmixlev * LEVEL_MINUS_3DB;
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}
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if(ctx->acmod == AC3_ACMOD_2F2R || ctx->acmod == AC3_ACMOD_3F2R) {
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int nf = ctx->acmod - 4;
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ctx->downmix_coeffs[nf][0] = ctx->downmix_coeffs[nf+1][1] = surmixlev;
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}
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return 0;
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}
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/**
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* Decodes the grouped exponents.
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* This function decodes the coded exponents according to exponent strategy
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* and stores them in the decoded exponents buffer.
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*
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* @param[in] gb GetBitContext which points to start of coded exponents
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* @param[in] expstr Exponent coding strategy
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* @param[in] ngrps Number of grouped exponents
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* @param[in] absexp Absolute exponent or DC exponent
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* @param[out] dexps Decoded exponents are stored in dexps
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*/
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static void decode_exponents(GetBitContext *gb, int expstr, int ngrps,
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uint8_t absexp, int8_t *dexps)
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{
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int i, j, grp, grpsize;
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int dexp[256];
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int expacc, prevexp;
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/* unpack groups */
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grpsize = expstr + (expstr == EXP_D45);
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for(grp=0,i=0; grp<ngrps; grp++) {
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expacc = get_bits(gb, 7);
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dexp[i++] = exp_ungroup_tbl[expacc][0];
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dexp[i++] = exp_ungroup_tbl[expacc][1];
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dexp[i++] = exp_ungroup_tbl[expacc][2];
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}
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/* convert to absolute exps and expand groups */
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prevexp = absexp;
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for(i=0; i<ngrps*3; i++) {
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prevexp = av_clip(prevexp + dexp[i]-2, 0, 24);
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for(j=0; j<grpsize; j++) {
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dexps[(i*grpsize)+j] = prevexp;
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Generates transform coefficients for each coupled channel in the coupling
|
|
* range using the coupling coefficients and coupling coordinates.
|
|
* reference: Section 7.4.3 Coupling Coordinate Format
|
|
*/
|
|
static void uncouple_channels(AC3DecodeContext *ctx)
|
|
{
|
|
int i, j, ch, bnd, subbnd;
|
|
|
|
subbnd = -1;
|
|
i = ctx->startmant[CPL_CH];
|
|
for(bnd=0; bnd<ctx->ncplbnd; bnd++) {
|
|
do {
|
|
subbnd++;
|
|
for(j=0; j<12; j++) {
|
|
for(ch=1; ch<=ctx->nfchans; ch++) {
|
|
if(ctx->chincpl[ch])
|
|
ctx->transform_coeffs[ch][i] = ctx->transform_coeffs[CPL_CH][i] * ctx->cplco[ch][bnd] * 8.0f;
|
|
}
|
|
i++;
|
|
}
|
|
} while(ctx->cplbndstrc[subbnd]);
|
|
}
|
|
}
|
|
|
|
typedef struct { /* grouped mantissas for 3-level 5-leve and 11-level quantization */
|
|
float b1_mant[3];
|
|
float b2_mant[3];
|
|
float b4_mant[2];
|
|
int b1ptr;
|
|
int b2ptr;
|
|
int b4ptr;
|
|
} mant_groups;
|
|
|
|
/* Get the transform coefficients for particular channel */
|
|
static int get_transform_coeffs_ch(AC3DecodeContext *ctx, int ch_index, mant_groups *m)
|
|
{
|
|
GetBitContext *gb = &ctx->gb;
|
|
int i, gcode, tbap, start, end;
|
|
uint8_t *exps;
|
|
uint8_t *bap;
|
|
float *coeffs;
|
|
|
|
exps = ctx->dexps[ch_index];
|
|
bap = ctx->bap[ch_index];
|
|
coeffs = ctx->transform_coeffs[ch_index];
|
|
start = ctx->startmant[ch_index];
|
|
end = ctx->endmant[ch_index];
|
|
|
|
|
|
for (i = start; i < end; i++) {
|
|
tbap = bap[i];
|
|
switch (tbap) {
|
|
case 0:
|
|
coeffs[i] = ((av_random(&ctx->dith_state) & 0xFFFF) * LEVEL_MINUS_3DB) / 32768.0f;
|
|
break;
|
|
|
|
case 1:
|
|
if(m->b1ptr > 2) {
|
|
gcode = get_bits(gb, 5);
|
|
m->b1_mant[0] = b1_mantissas[gcode][0];
|
|
m->b1_mant[1] = b1_mantissas[gcode][1];
|
|
m->b1_mant[2] = b1_mantissas[gcode][2];
|
|
m->b1ptr = 0;
|
|
}
|
|
coeffs[i] = m->b1_mant[m->b1ptr++];
|
|
break;
|
|
|
|
case 2:
|
|
if(m->b2ptr > 2) {
|
|
gcode = get_bits(gb, 7);
|
|
m->b2_mant[0] = b2_mantissas[gcode][0];
|
|
m->b2_mant[1] = b2_mantissas[gcode][1];
|
|
m->b2_mant[2] = b2_mantissas[gcode][2];
|
|
m->b2ptr = 0;
|
|
}
|
|
coeffs[i] = m->b2_mant[m->b2ptr++];
|
|
break;
|
|
|
|
case 3:
|
|
coeffs[i] = b3_mantissas[get_bits(gb, 3)];
|
|
break;
|
|
|
|
case 4:
|
|
if(m->b4ptr > 1) {
|
|
gcode = get_bits(gb, 7);
|
|
m->b4_mant[0] = b4_mantissas[gcode][0];
|
|
m->b4_mant[1] = b4_mantissas[gcode][1];
|
|
m->b4ptr = 0;
|
|
}
|
|
coeffs[i] = m->b4_mant[m->b4ptr++];
|
|
break;
|
|
|
|
case 5:
|
|
coeffs[i] = b5_mantissas[get_bits(gb, 4)];
|
|
break;
|
|
|
|
default:
|
|
coeffs[i] = get_sbits(gb, qntztab[tbap]) * scale_factors[qntztab[tbap]-1];
|
|
break;
|
|
}
|
|
coeffs[i] *= scale_factors[exps[i]];
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* Removes random dithering from coefficients with zero-bit mantissas
|
|
* reference: Section 7.3.4 Dither for Zero Bit Mantissas (bap=0)
|
|
*/
|
|
static void remove_dithering(AC3DecodeContext *ctx) {
|
|
int ch, i;
|
|
int end=0;
|
|
float *coeffs;
|
|
uint8_t *bap;
|
|
|
|
for(ch=1; ch<=ctx->nfchans; ch++) {
|
|
if(!ctx->dithflag[ch]) {
|
|
coeffs = ctx->transform_coeffs[ch];
|
|
bap = ctx->bap[ch];
|
|
if(ctx->chincpl[ch])
|
|
end = ctx->startmant[CPL_CH];
|
|
else
|
|
end = ctx->endmant[ch];
|
|
for(i=0; i<end; i++) {
|
|
if(bap[i] == 0)
|
|
coeffs[i] = 0.0f;
|
|
}
|
|
if(ctx->chincpl[ch]) {
|
|
bap = ctx->bap[CPL_CH];
|
|
for(; i<ctx->endmant[CPL_CH]; i++) {
|
|
if(bap[i] == 0)
|
|
coeffs[i] = 0.0f;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Get the transform coefficients.
|
|
* This function extracts the tranform coefficients form the ac3 bitstream.
|
|
* This function is called after bit allocation is performed.
|
|
*/
|
|
static int get_transform_coeffs(AC3DecodeContext * ctx)
|
|
{
|
|
int ch, end;
|
|
int got_cplchan = 0;
|
|
mant_groups m;
|
|
|
|
m.b1ptr = m.b2ptr = m.b4ptr = 3;
|
|
|
|
for (ch = 1; ch <= ctx->nchans; ch++) {
|
|
/* transform coefficients for individual channel */
|
|
if (get_transform_coeffs_ch(ctx, ch, &m))
|
|
return -1;
|
|
/* tranform coefficients for coupling channels */
|
|
if (ctx->chincpl[ch]) {
|
|
if (!got_cplchan) {
|
|
if (get_transform_coeffs_ch(ctx, CPL_CH, &m)) {
|
|
av_log(NULL, AV_LOG_ERROR, "error in decoupling channels\n");
|
|
return -1;
|
|
}
|
|
uncouple_channels(ctx);
|
|
got_cplchan = 1;
|
|
}
|
|
end = ctx->endmant[CPL_CH];
|
|
} else {
|
|
end = ctx->endmant[ch];
|
|
}
|
|
do
|
|
ctx->transform_coeffs[ch][end] = 0;
|
|
while(++end < 256);
|
|
}
|
|
|
|
/* if any channel doesn't use dithering, zero appropriate coefficients */
|
|
if(!ctx->dither_all)
|
|
remove_dithering(ctx);
|
|
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* Performs stereo rematrixing.
|
|
* reference: Section 7.5.4 Rematrixing : Decoding Technique
|
|
*/
|
|
static void do_rematrixing(AC3DecodeContext *ctx)
|
|
{
|
|
int bnd, i;
|
|
int end, bndend;
|
|
float tmp0, tmp1;
|
|
|
|
end = FFMIN(ctx->endmant[1], ctx->endmant[2]);
|
|
|
|
for(bnd=0; bnd<ctx->nrematbnd; bnd++) {
|
|
if(ctx->rematflg[bnd]) {
|
|
bndend = FFMIN(end, rematrix_band_tbl[bnd+1]);
|
|
for(i=rematrix_band_tbl[bnd]; i<bndend; i++) {
|
|
tmp0 = ctx->transform_coeffs[1][i];
|
|
tmp1 = ctx->transform_coeffs[2][i];
|
|
ctx->transform_coeffs[1][i] = tmp0 + tmp1;
|
|
ctx->transform_coeffs[2][i] = tmp0 - tmp1;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/* This function performs the imdct on 256 sample transform
|
|
* coefficients.
|
|
*/
|
|
static void do_imdct_256(AC3DecodeContext *ctx, int chindex)
|
|
{
|
|
int i, k;
|
|
DECLARE_ALIGNED_16(float, x[128]);
|
|
FFTComplex z[2][64];
|
|
float *o_ptr = ctx->tmp_output;
|
|
|
|
for(i=0; i<2; i++) {
|
|
/* de-interleave coefficients */
|
|
for(k=0; k<128; k++) {
|
|
x[k] = ctx->transform_coeffs[chindex][2*k+i];
|
|
}
|
|
|
|
/* run standard IMDCT */
|
|
ctx->imdct_256.fft.imdct_calc(&ctx->imdct_256, o_ptr, x, ctx->tmp_imdct);
|
|
|
|
/* reverse the post-rotation & reordering from standard IMDCT */
|
|
for(k=0; k<32; k++) {
|
|
z[i][32+k].re = -o_ptr[128+2*k];
|
|
z[i][32+k].im = -o_ptr[2*k];
|
|
z[i][31-k].re = o_ptr[2*k+1];
|
|
z[i][31-k].im = o_ptr[128+2*k+1];
|
|
}
|
|
}
|
|
|
|
/* apply AC-3 post-rotation & reordering */
|
|
for(k=0; k<64; k++) {
|
|
o_ptr[ 2*k ] = -z[0][ k].im;
|
|
o_ptr[ 2*k+1] = z[0][63-k].re;
|
|
o_ptr[128+2*k ] = -z[0][ k].re;
|
|
o_ptr[128+2*k+1] = z[0][63-k].im;
|
|
o_ptr[256+2*k ] = -z[1][ k].re;
|
|
o_ptr[256+2*k+1] = z[1][63-k].im;
|
|
o_ptr[384+2*k ] = z[1][ k].im;
|
|
o_ptr[384+2*k+1] = -z[1][63-k].re;
|
|
}
|
|
}
|
|
|
|
/* IMDCT Transform. */
|
|
static inline void do_imdct(AC3DecodeContext *ctx)
|
|
{
|
|
int ch;
|
|
int nchans;
|
|
|
|
nchans = ctx->nfchans;
|
|
if(ctx->output_mode & AC3_OUTPUT_LFEON)
|
|
nchans++;
|
|
|
|
for (ch=1; ch<=nchans; ch++) {
|
|
if (ctx->blksw[ch]) {
|
|
do_imdct_256(ctx, ch);
|
|
} else {
|
|
ctx->imdct_512.fft.imdct_calc(&ctx->imdct_512, ctx->tmp_output,
|
|
ctx->transform_coeffs[ch],
|
|
ctx->tmp_imdct);
|
|
}
|
|
ctx->dsp.vector_fmul_add_add(ctx->output[ch-1], ctx->tmp_output,
|
|
ctx->window, ctx->delay[ch-1], 0, 256, 1);
|
|
ctx->dsp.vector_fmul_reverse(ctx->delay[ch-1], ctx->tmp_output+256,
|
|
ctx->window, 256);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Downmixes the output to stereo.
|
|
*/
|
|
static void ac3_downmix(float samples[AC3_MAX_CHANNELS][256], int nfchans,
|
|
int output_mode, float coef[AC3_MAX_CHANNELS][2])
|
|
{
|
|
int i, j;
|
|
float v0, v1, s0, s1;
|
|
|
|
for(i=0; i<256; i++) {
|
|
v0 = v1 = s0 = s1 = 0.0f;
|
|
for(j=0; j<nfchans; j++) {
|
|
v0 += samples[j][i] * coef[j][0];
|
|
v1 += samples[j][i] * coef[j][1];
|
|
s0 += coef[j][0];
|
|
s1 += coef[j][1];
|
|
}
|
|
v0 /= s0;
|
|
v1 /= s1;
|
|
if(output_mode == AC3_ACMOD_MONO) {
|
|
samples[0][i] = (v0 + v1) * LEVEL_MINUS_3DB;
|
|
} else if(output_mode == AC3_ACMOD_STEREO) {
|
|
samples[0][i] = v0;
|
|
samples[1][i] = v1;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Parse the audio block from ac3 bitstream.
|
|
* This function extract the audio block from the ac3 bitstream
|
|
* and produces the output for the block. This function must
|
|
* be called for each of the six audio block in the ac3 bitstream.
|
|
*/
|
|
static int ac3_parse_audio_block(AC3DecodeContext *ctx, int blk)
|
|
{
|
|
int nfchans = ctx->nfchans;
|
|
int acmod = ctx->acmod;
|
|
int i, bnd, seg, ch;
|
|
GetBitContext *gb = &ctx->gb;
|
|
uint8_t bit_alloc_stages[AC3_MAX_CHANNELS];
|
|
|
|
memset(bit_alloc_stages, 0, AC3_MAX_CHANNELS);
|
|
|
|
for (ch = 1; ch <= nfchans; ch++) /*block switch flag */
|
|
ctx->blksw[ch] = get_bits1(gb);
|
|
|
|
ctx->dither_all = 1;
|
|
for (ch = 1; ch <= nfchans; ch++) { /* dithering flag */
|
|
ctx->dithflag[ch] = get_bits1(gb);
|
|
if(!ctx->dithflag[ch])
|
|
ctx->dither_all = 0;
|
|
}
|
|
|
|
/* dynamic range */
|
|
i = !(ctx->acmod);
|
|
do {
|
|
if(get_bits1(gb)) {
|
|
ctx->dynrng[i] = dynrng_tbl[get_bits(gb, 8)];
|
|
} else if(blk == 0) {
|
|
ctx->dynrng[i] = 1.0f;
|
|
}
|
|
} while(i--);
|
|
|
|
if (get_bits1(gb)) { /* coupling strategy */
|
|
memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
|
|
ctx->cplinu = get_bits1(gb);
|
|
if (ctx->cplinu) { /* coupling in use */
|
|
int cplbegf, cplendf;
|
|
|
|
for (ch = 1; ch <= nfchans; ch++)
|
|
ctx->chincpl[ch] = get_bits1(gb);
|
|
|
|
if (acmod == AC3_ACMOD_STEREO)
|
|
ctx->phsflginu = get_bits1(gb); //phase flag in use
|
|
|
|
cplbegf = get_bits(gb, 4);
|
|
cplendf = get_bits(gb, 4);
|
|
|
|
if (3 + cplendf - cplbegf < 0) {
|
|
av_log(NULL, AV_LOG_ERROR, "cplendf = %d < cplbegf = %d\n", cplendf, cplbegf);
|
|
return -1;
|
|
}
|
|
|
|
ctx->ncplbnd = ctx->ncplsubnd = 3 + cplendf - cplbegf;
|
|
ctx->startmant[CPL_CH] = cplbegf * 12 + 37;
|
|
ctx->endmant[CPL_CH] = cplendf * 12 + 73;
|
|
for (bnd = 0; bnd < ctx->ncplsubnd - 1; bnd++) { /* coupling band structure */
|
|
if (get_bits1(gb)) {
|
|
ctx->cplbndstrc[bnd] = 1;
|
|
ctx->ncplbnd--;
|
|
}
|
|
}
|
|
} else {
|
|
for (ch = 1; ch <= nfchans; ch++)
|
|
ctx->chincpl[ch] = 0;
|
|
}
|
|
}
|
|
|
|
if (ctx->cplinu) {
|
|
int cplcoe = 0;
|
|
|
|
for (ch = 1; ch <= nfchans; ch++) {
|
|
if (ctx->chincpl[ch]) {
|
|
if (get_bits1(gb)) { /* coupling co-ordinates */
|
|
int mstrcplco, cplcoexp, cplcomant;
|
|
cplcoe = 1;
|
|
mstrcplco = 3 * get_bits(gb, 2);
|
|
for (bnd = 0; bnd < ctx->ncplbnd; bnd++) {
|
|
cplcoexp = get_bits(gb, 4);
|
|
cplcomant = get_bits(gb, 4);
|
|
if (cplcoexp == 15)
|
|
ctx->cplco[ch][bnd] = cplcomant / 16.0f;
|
|
else
|
|
ctx->cplco[ch][bnd] = (cplcomant + 16.0f) / 32.0f;
|
|
ctx->cplco[ch][bnd] *= scale_factors[cplcoexp + mstrcplco];
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
if (acmod == AC3_ACMOD_STEREO && ctx->phsflginu && cplcoe) {
|
|
for (bnd = 0; bnd < ctx->ncplbnd; bnd++) {
|
|
if (get_bits1(gb))
|
|
ctx->cplco[2][bnd] = -ctx->cplco[2][bnd];
|
|
}
|
|
}
|
|
}
|
|
|
|
if (acmod == AC3_ACMOD_STEREO) {/* rematrixing */
|
|
ctx->rematstr = get_bits1(gb);
|
|
if (ctx->rematstr) {
|
|
ctx->nrematbnd = 4;
|
|
if(ctx->cplinu && ctx->startmant[CPL_CH] <= 61)
|
|
ctx->nrematbnd -= 1 + (ctx->startmant[CPL_CH] == 37);
|
|
for(bnd=0; bnd<ctx->nrematbnd; bnd++)
|
|
ctx->rematflg[bnd] = get_bits1(gb);
|
|
}
|
|
}
|
|
|
|
ctx->expstr[CPL_CH] = EXP_REUSE;
|
|
ctx->expstr[ctx->lfe_ch] = EXP_REUSE;
|
|
for (ch = !ctx->cplinu; ch <= ctx->nchans; ch++) {
|
|
if(ch == ctx->lfe_ch)
|
|
ctx->expstr[ch] = get_bits(gb, 1);
|
|
else
|
|
ctx->expstr[ch] = get_bits(gb, 2);
|
|
if(ctx->expstr[ch] != EXP_REUSE)
|
|
bit_alloc_stages[ch] = 3;
|
|
}
|
|
|
|
for (ch = 1; ch <= nfchans; ch++) { /* channel bandwidth code */
|
|
ctx->startmant[ch] = 0;
|
|
if (ctx->expstr[ch] != EXP_REUSE) {
|
|
int prev = ctx->endmant[ch];
|
|
if (ctx->chincpl[ch])
|
|
ctx->endmant[ch] = ctx->startmant[CPL_CH];
|
|
else {
|
|
int chbwcod = get_bits(gb, 6);
|
|
if (chbwcod > 60) {
|
|
av_log(NULL, AV_LOG_ERROR, "chbwcod = %d > 60", chbwcod);
|
|
return -1;
|
|
}
|
|
ctx->endmant[ch] = chbwcod * 3 + 73;
|
|
}
|
|
if(blk > 0 && ctx->endmant[ch] != prev)
|
|
memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
|
|
}
|
|
}
|
|
ctx->startmant[ctx->lfe_ch] = 0;
|
|
ctx->endmant[ctx->lfe_ch] = 7;
|
|
|
|
for (ch = !ctx->cplinu; ch <= ctx->nchans; ch++) {
|
|
if (ctx->expstr[ch] != EXP_REUSE) {
|
|
int grpsize, ngrps;
|
|
grpsize = 3 << (ctx->expstr[ch] - 1);
|
|
if(ch == CPL_CH)
|
|
ngrps = (ctx->endmant[ch] - ctx->startmant[ch]) / grpsize;
|
|
else if(ch == ctx->lfe_ch)
|
|
ngrps = 2;
|
|
else
|
|
ngrps = (ctx->endmant[ch] + grpsize - 4) / grpsize;
|
|
ctx->dexps[ch][0] = get_bits(gb, 4) << !ch;
|
|
decode_exponents(gb, ctx->expstr[ch], ngrps, ctx->dexps[ch][0],
|
|
&ctx->dexps[ch][ctx->startmant[ch]+!!ch]);
|
|
if(ch != CPL_CH && ch != ctx->lfe_ch)
|
|
skip_bits(gb, 2); /* skip gainrng */
|
|
}
|
|
}
|
|
|
|
if (get_bits1(gb)) { /* bit allocation information */
|
|
ctx->bit_alloc_params.sdecay = ff_sdecaytab[get_bits(gb, 2)];
|
|
ctx->bit_alloc_params.fdecay = ff_fdecaytab[get_bits(gb, 2)];
|
|
ctx->bit_alloc_params.sgain = ff_sgaintab[get_bits(gb, 2)];
|
|
ctx->bit_alloc_params.dbknee = ff_dbkneetab[get_bits(gb, 2)];
|
|
ctx->bit_alloc_params.floor = ff_floortab[get_bits(gb, 3)];
|
|
for(ch=!ctx->cplinu; ch<=ctx->nchans; ch++) {
|
|
bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
|
|
}
|
|
}
|
|
|
|
if (get_bits1(gb)) { /* snroffset */
|
|
int csnr;
|
|
csnr = (get_bits(gb, 6) - 15) << 4;
|
|
for (ch = !ctx->cplinu; ch <= ctx->nchans; ch++) { /* snr offset and fast gain */
|
|
ctx->snroffst[ch] = (csnr + get_bits(gb, 4)) << 2;
|
|
ctx->fgain[ch] = ff_fgaintab[get_bits(gb, 3)];
|
|
}
|
|
memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
|
|
}
|
|
|
|
if (ctx->cplinu && get_bits1(gb)) { /* coupling leak information */
|
|
ctx->bit_alloc_params.cplfleak = get_bits(gb, 3);
|
|
ctx->bit_alloc_params.cplsleak = get_bits(gb, 3);
|
|
bit_alloc_stages[CPL_CH] = FFMAX(bit_alloc_stages[CPL_CH], 2);
|
|
}
|
|
|
|
if (get_bits1(gb)) { /* delta bit allocation information */
|
|
for (ch = !ctx->cplinu; ch <= nfchans; ch++) {
|
|
ctx->deltbae[ch] = get_bits(gb, 2);
|
|
if (ctx->deltbae[ch] == DBA_RESERVED) {
|
|
av_log(NULL, AV_LOG_ERROR, "delta bit allocation strategy reserved\n");
|
|
return -1;
|
|
}
|
|
bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
|
|
}
|
|
|
|
for (ch = !ctx->cplinu; ch <= nfchans; ch++) {
|
|
if (ctx->deltbae[ch] == DBA_NEW) {/*channel delta offset, len and bit allocation */
|
|
ctx->deltnseg[ch] = get_bits(gb, 3);
|
|
for (seg = 0; seg <= ctx->deltnseg[ch]; seg++) {
|
|
ctx->deltoffst[ch][seg] = get_bits(gb, 5);
|
|
ctx->deltlen[ch][seg] = get_bits(gb, 4);
|
|
ctx->deltba[ch][seg] = get_bits(gb, 3);
|
|
}
|
|
}
|
|
}
|
|
} else if(blk == 0) {
|
|
for(ch=0; ch<=ctx->nchans; ch++) {
|
|
ctx->deltbae[ch] = DBA_NONE;
|
|
}
|
|
}
|
|
|
|
for(ch=!ctx->cplinu; ch<=ctx->nchans; ch++) {
|
|
if(bit_alloc_stages[ch] > 2) {
|
|
/* Exponent mapping into PSD and PSD integration */
|
|
ff_ac3_bit_alloc_calc_psd(ctx->dexps[ch],
|
|
ctx->startmant[ch], ctx->endmant[ch],
|
|
ctx->psd[ch], ctx->bndpsd[ch]);
|
|
}
|
|
if(bit_alloc_stages[ch] > 1) {
|
|
/* Compute excitation function, Compute masking curve, and
|
|
Apply delta bit allocation */
|
|
ff_ac3_bit_alloc_calc_mask(&ctx->bit_alloc_params, ctx->bndpsd[ch],
|
|
ctx->startmant[ch], ctx->endmant[ch],
|
|
ctx->fgain[ch], (ch == ctx->lfe_ch),
|
|
ctx->deltbae[ch], ctx->deltnseg[ch],
|
|
ctx->deltoffst[ch], ctx->deltlen[ch],
|
|
ctx->deltba[ch], ctx->mask[ch]);
|
|
}
|
|
if(bit_alloc_stages[ch] > 0) {
|
|
/* Compute bit allocation */
|
|
ff_ac3_bit_alloc_calc_bap(ctx->mask[ch], ctx->psd[ch],
|
|
ctx->startmant[ch], ctx->endmant[ch],
|
|
ctx->snroffst[ch],
|
|
ctx->bit_alloc_params.floor,
|
|
ctx->bap[ch]);
|
|
}
|
|
}
|
|
|
|
if (get_bits1(gb)) { /* unused dummy data */
|
|
int skipl = get_bits(gb, 9);
|
|
while(skipl--)
|
|
skip_bits(gb, 8);
|
|
}
|
|
/* unpack the transform coefficients
|
|
* * this also uncouples channels if coupling is in use.
|
|
*/
|
|
if (get_transform_coeffs(ctx)) {
|
|
av_log(NULL, AV_LOG_ERROR, "Error in routine get_transform_coeffs\n");
|
|
return -1;
|
|
}
|
|
|
|
/* recover coefficients if rematrixing is in use */
|
|
if(ctx->acmod == AC3_ACMOD_STEREO)
|
|
do_rematrixing(ctx);
|
|
|
|
/* apply scaling to coefficients (headroom, dialnorm, dynrng) */
|
|
for(ch=1; ch<=ctx->nchans; ch++) {
|
|
float gain = 2.0f * ctx->mul_bias;
|
|
if(ctx->acmod == AC3_ACMOD_DUALMONO) {
|
|
gain *= ctx->dialnorm[ch-1] * ctx->dynrng[ch-1];
|
|
} else {
|
|
gain *= ctx->dialnorm[0] * ctx->dynrng[0];
|
|
}
|
|
for(i=0; i<ctx->endmant[ch]; i++) {
|
|
ctx->transform_coeffs[ch][i] *= gain;
|
|
}
|
|
}
|
|
|
|
do_imdct(ctx);
|
|
|
|
/* downmix output if needed */
|
|
if(ctx->nchans != ctx->out_channels && !((ctx->output_mode & AC3_OUTPUT_LFEON) &&
|
|
ctx->nfchans == ctx->out_channels)) {
|
|
ac3_downmix(ctx->output, ctx->nfchans, ctx->output_mode,
|
|
ctx->downmix_coeffs);
|
|
}
|
|
|
|
/* convert float to 16-bit integer */
|
|
for(ch=0; ch<ctx->out_channels; ch++) {
|
|
for(i=0; i<256; i++) {
|
|
ctx->output[ch][i] += ctx->add_bias;
|
|
}
|
|
ctx->dsp.float_to_int16(ctx->int_output[ch], ctx->output[ch], 256);
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
/* Decode ac3 frame.
|
|
*
|
|
* @param avctx Pointer to AVCodecContext
|
|
* @param data Pointer to pcm smaples
|
|
* @param data_size Set to number of pcm samples produced by decoding
|
|
* @param buf Data to be decoded
|
|
* @param buf_size Size of the buffer
|
|
*/
|
|
static int ac3_decode_frame(AVCodecContext * avctx, void *data, int *data_size, uint8_t *buf, int buf_size)
|
|
{
|
|
AC3DecodeContext *ctx = (AC3DecodeContext *)avctx->priv_data;
|
|
int16_t *out_samples = (int16_t *)data;
|
|
int i, blk, ch;
|
|
|
|
//Initialize the GetBitContext with the start of valid AC3 Frame.
|
|
init_get_bits(&ctx->gb, buf, buf_size * 8);
|
|
|
|
//Parse the syncinfo.
|
|
if (ac3_parse_header(ctx)) {
|
|
av_log(avctx, AV_LOG_ERROR, "\n");
|
|
*data_size = 0;
|
|
return buf_size;
|
|
}
|
|
|
|
avctx->sample_rate = ctx->sampling_rate;
|
|
avctx->bit_rate = ctx->bit_rate;
|
|
|
|
/* channel config */
|
|
ctx->out_channels = ctx->nchans;
|
|
if (avctx->channels == 0) {
|
|
avctx->channels = ctx->out_channels;
|
|
} else if(ctx->out_channels < avctx->channels) {
|
|
av_log(avctx, AV_LOG_ERROR, "Cannot upmix AC3 from %d to %d channels.\n",
|
|
ctx->out_channels, avctx->channels);
|
|
return -1;
|
|
}
|
|
if(avctx->channels == 2) {
|
|
ctx->output_mode = AC3_ACMOD_STEREO;
|
|
} else if(avctx->channels == 1) {
|
|
ctx->output_mode = AC3_ACMOD_MONO;
|
|
} else if(avctx->channels != ctx->out_channels) {
|
|
av_log(avctx, AV_LOG_ERROR, "Cannot downmix AC3 from %d to %d channels.\n",
|
|
ctx->out_channels, avctx->channels);
|
|
return -1;
|
|
}
|
|
ctx->out_channels = avctx->channels;
|
|
|
|
//av_log(avctx, AV_LOG_INFO, "channels = %d \t bit rate = %d \t sampling rate = %d \n", avctx->channels, avctx->bit_rate * 1000, avctx->sample_rate);
|
|
|
|
//Parse the Audio Blocks.
|
|
for (blk = 0; blk < NB_BLOCKS; blk++) {
|
|
if (ac3_parse_audio_block(ctx, blk)) {
|
|
av_log(avctx, AV_LOG_ERROR, "error parsing the audio block\n");
|
|
*data_size = 0;
|
|
return ctx->frame_size;
|
|
}
|
|
for (i = 0; i < 256; i++)
|
|
for (ch = 0; ch < ctx->out_channels; ch++)
|
|
*(out_samples++) = ctx->int_output[ch][i];
|
|
}
|
|
*data_size = NB_BLOCKS * 256 * avctx->channels * sizeof (int16_t);
|
|
return ctx->frame_size;
|
|
}
|
|
|
|
/* Uninitialize ac3 decoder.
|
|
*/
|
|
static int ac3_decode_end(AVCodecContext *avctx)
|
|
{
|
|
AC3DecodeContext *ctx = (AC3DecodeContext *)avctx->priv_data;
|
|
ff_mdct_end(&ctx->imdct_512);
|
|
ff_mdct_end(&ctx->imdct_256);
|
|
|
|
return 0;
|
|
}
|
|
|
|
AVCodec ac3_decoder = {
|
|
.name = "ac3",
|
|
.type = CODEC_TYPE_AUDIO,
|
|
.id = CODEC_ID_AC3,
|
|
.priv_data_size = sizeof (AC3DecodeContext),
|
|
.init = ac3_decode_init,
|
|
.close = ac3_decode_end,
|
|
.decode = ac3_decode_frame,
|
|
};
|
|
|