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FFmpeg/libavcodec/ac3dec.c
Justin Ruggles 1408352ada Add option for user to scale the amount of dynamic range compression which is 
applied by the audio decoder, and use that option in the AC3 decoder.

Originally committed as revision 11280 to svn://svn.ffmpeg.org/ffmpeg/trunk
2007-12-20 00:55:08 +00:00

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/*
* AC-3 Audio Decoder
* This code is developed as part of Google Summer of Code 2006 Program.
*
* Copyright (c) 2006 Kartikey Mahendra BHATT (bhattkm at gmail dot com).
* Copyright (c) 2007 Justin Ruggles
*
* Portions of this code are derived from liba52
* http://liba52.sourceforge.net
* Copyright (C) 2000-2003 Michel Lespinasse <walken@zoy.org>
* Copyright (C) 1999-2000 Aaron Holtzman <aholtzma@ess.engr.uvic.ca>
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <stdio.h>
#include <stddef.h>
#include <math.h>
#include <string.h>
#include "avcodec.h"
#include "ac3_parser.h"
#include "bitstream.h"
#include "dsputil.h"
#include "random.h"
/**
* Table of bin locations for rematrixing bands
* reference: Section 7.5.2 Rematrixing : Frequency Band Definitions
*/
static const uint8_t rematrix_band_tab[5] = { 13, 25, 37, 61, 253 };
/**
* table for exponent to scale_factor mapping
* scale_factors[i] = 2 ^ -i
*/
static float scale_factors[25];
/** table for grouping exponents */
static uint8_t exp_ungroup_tab[128][3];
/** tables for ungrouping mantissas */
static float b1_mantissas[32][3];
static float b2_mantissas[128][3];
static float b3_mantissas[8];
static float b4_mantissas[128][2];
static float b5_mantissas[16];
/**
* Quantization table: levels for symmetric. bits for asymmetric.
* reference: Table 7.18 Mapping of bap to Quantizer
*/
static const uint8_t quantization_tab[16] = {
0, 3, 5, 7, 11, 15,
5, 6, 7, 8, 9, 10, 11, 12, 14, 16
};
/** dynamic range table. converts codes to scale factors. */
static float dynamic_range_tab[256];
/** Adjustments in dB gain */
#define LEVEL_MINUS_3DB 0.7071067811865476
#define LEVEL_MINUS_4POINT5DB 0.5946035575013605
#define LEVEL_MINUS_6DB 0.5000000000000000
#define LEVEL_MINUS_9DB 0.3535533905932738
#define LEVEL_ZERO 0.0000000000000000
#define LEVEL_ONE 1.0000000000000000
static const float gain_levels[6] = {
LEVEL_ZERO,
LEVEL_ONE,
LEVEL_MINUS_3DB,
LEVEL_MINUS_4POINT5DB,
LEVEL_MINUS_6DB,
LEVEL_MINUS_9DB
};
/**
* Table for center mix levels
* reference: Section 5.4.2.4 cmixlev
*/
static const uint8_t center_levels[4] = { 2, 3, 4, 3 };
/**
* Table for surround mix levels
* reference: Section 5.4.2.5 surmixlev
*/
static const uint8_t surround_levels[4] = { 2, 4, 0, 4 };
/**
* Table for default stereo downmixing coefficients
* reference: Section 7.8.2 Downmixing Into Two Channels
*/
static const uint8_t ac3_default_coeffs[8][5][2] = {
{ { 1, 0 }, { 0, 1 }, },
{ { 2, 2 }, },
{ { 1, 0 }, { 0, 1 }, },
{ { 1, 0 }, { 3, 3 }, { 0, 1 }, },
{ { 1, 0 }, { 0, 1 }, { 4, 4 }, },
{ { 1, 0 }, { 3, 3 }, { 0, 1 }, { 5, 5 }, },
{ { 1, 0 }, { 0, 1 }, { 4, 0 }, { 0, 4 }, },
{ { 1, 0 }, { 3, 3 }, { 0, 1 }, { 4, 0 }, { 0, 4 }, },
};
/* override ac3.h to include coupling channel */
#undef AC3_MAX_CHANNELS
#define AC3_MAX_CHANNELS 7
#define CPL_CH 0
#define AC3_OUTPUT_LFEON 8
typedef struct {
int channel_mode; ///< channel mode (acmod)
int dolby_surround_mode; ///< dolby surround mode
int block_switch[AC3_MAX_CHANNELS]; ///< block switch flags
int dither_flag[AC3_MAX_CHANNELS]; ///< dither flags
int dither_all; ///< true if all channels are dithered
int cpl_in_use; ///< coupling in use
int channel_in_cpl[AC3_MAX_CHANNELS]; ///< channel in coupling
int phase_flags_in_use; ///< phase flags in use
int cpl_band_struct[18]; ///< coupling band structure
int rematrixing_strategy; ///< rematrixing strategy
int num_rematrixing_bands; ///< number of rematrixing bands
int rematrixing_flags[4]; ///< rematrixing flags
int exp_strategy[AC3_MAX_CHANNELS]; ///< exponent strategies
int snr_offset[AC3_MAX_CHANNELS]; ///< signal-to-noise ratio offsets
int fast_gain[AC3_MAX_CHANNELS]; ///< fast gain values (signal-to-mask ratio)
int dba_mode[AC3_MAX_CHANNELS]; ///< delta bit allocation mode
int dba_nsegs[AC3_MAX_CHANNELS]; ///< number of delta segments
uint8_t dba_offsets[AC3_MAX_CHANNELS][8]; ///< delta segment offsets
uint8_t dba_lengths[AC3_MAX_CHANNELS][8]; ///< delta segment lengths
uint8_t dba_values[AC3_MAX_CHANNELS][8]; ///< delta values for each segment
int sampling_rate; ///< sample frequency, in Hz
int bit_rate; ///< stream bit rate, in bits-per-second
int frame_size; ///< current frame size, in bytes
int channels; ///< number of total channels
int fbw_channels; ///< number of full-bandwidth channels
int lfe_on; ///< lfe channel in use
int lfe_ch; ///< index of LFE channel
int output_mode; ///< output channel configuration
int out_channels; ///< number of output channels
float downmix_coeffs[AC3_MAX_CHANNELS][2]; ///< stereo downmix coefficients
float dynamic_range[2]; ///< dynamic range
float cpl_coords[AC3_MAX_CHANNELS][18]; ///< coupling coordinates
int num_cpl_bands; ///< number of coupling bands
int num_cpl_subbands; ///< number of coupling sub bands
int start_freq[AC3_MAX_CHANNELS]; ///< start frequency bin
int end_freq[AC3_MAX_CHANNELS]; ///< end frequency bin
AC3BitAllocParameters bit_alloc_params; ///< bit allocation parameters
int8_t dexps[AC3_MAX_CHANNELS][256]; ///< decoded exponents
uint8_t bap[AC3_MAX_CHANNELS][256]; ///< bit allocation pointers
int16_t psd[AC3_MAX_CHANNELS][256]; ///< scaled exponents
int16_t band_psd[AC3_MAX_CHANNELS][50]; ///< interpolated exponents
int16_t mask[AC3_MAX_CHANNELS][50]; ///< masking curve values
DECLARE_ALIGNED_16(float, transform_coeffs[AC3_MAX_CHANNELS][256]); ///< transform coefficients
/* For IMDCT. */
MDCTContext imdct_512; ///< for 512 sample IMDCT
MDCTContext imdct_256; ///< for 256 sample IMDCT
DSPContext dsp; ///< for optimization
float add_bias; ///< offset for float_to_int16 conversion
float mul_bias; ///< scaling for float_to_int16 conversion
DECLARE_ALIGNED_16(float, output[AC3_MAX_CHANNELS-1][256]); ///< output after imdct transform and windowing
DECLARE_ALIGNED_16(short, int_output[AC3_MAX_CHANNELS-1][256]); ///< final 16-bit integer output
DECLARE_ALIGNED_16(float, delay[AC3_MAX_CHANNELS-1][256]); ///< delay - added to the next block
DECLARE_ALIGNED_16(float, tmp_imdct[256]); ///< temporary storage for imdct transform
DECLARE_ALIGNED_16(float, tmp_output[512]); ///< temporary storage for output before windowing
DECLARE_ALIGNED_16(float, window[256]); ///< window coefficients
/* Miscellaneous. */
GetBitContext gb; ///< bitstream reader
AVRandomState dith_state; ///< for dither generation
AVCodecContext *avctx; ///< parent context
} AC3DecodeContext;
/**
* Generate a Kaiser-Bessel Derived Window.
*/
static void ac3_window_init(float *window)
{
int i, j;
double sum = 0.0, bessel, tmp;
double local_window[256];
double alpha2 = (5.0 * M_PI / 256.0) * (5.0 * M_PI / 256.0);
for (i = 0; i < 256; i++) {
tmp = i * (256 - i) * alpha2;
bessel = 1.0;
for (j = 100; j > 0; j--) /* default to 100 iterations */
bessel = bessel * tmp / (j * j) + 1;
sum += bessel;
local_window[i] = sum;
}
sum++;
for (i = 0; i < 256; i++)
window[i] = sqrt(local_window[i] / sum);
}
/**
* Symmetrical Dequantization
* reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization
* Tables 7.19 to 7.23
*/
static inline float
symmetric_dequant(int code, int levels)
{
return (code - (levels >> 1)) * (2.0f / levels);
}
/*
* Initialize tables at runtime.
*/
static void ac3_tables_init(void)
{
int i;
/* generate grouped mantissa tables
reference: Section 7.3.5 Ungrouping of Mantissas */
for(i=0; i<32; i++) {
/* bap=1 mantissas */
b1_mantissas[i][0] = symmetric_dequant( i / 9 , 3);
b1_mantissas[i][1] = symmetric_dequant((i % 9) / 3, 3);
b1_mantissas[i][2] = symmetric_dequant((i % 9) % 3, 3);
}
for(i=0; i<128; i++) {
/* bap=2 mantissas */
b2_mantissas[i][0] = symmetric_dequant( i / 25 , 5);
b2_mantissas[i][1] = symmetric_dequant((i % 25) / 5, 5);
b2_mantissas[i][2] = symmetric_dequant((i % 25) % 5, 5);
/* bap=4 mantissas */
b4_mantissas[i][0] = symmetric_dequant(i / 11, 11);
b4_mantissas[i][1] = symmetric_dequant(i % 11, 11);
}
/* generate ungrouped mantissa tables
reference: Tables 7.21 and 7.23 */
for(i=0; i<7; i++) {
/* bap=3 mantissas */
b3_mantissas[i] = symmetric_dequant(i, 7);
}
for(i=0; i<15; i++) {
/* bap=5 mantissas */
b5_mantissas[i] = symmetric_dequant(i, 15);
}
/* generate dynamic range table
reference: Section 7.7.1 Dynamic Range Control */
for(i=0; i<256; i++) {
int v = (i >> 5) - ((i >> 7) << 3) - 5;
dynamic_range_tab[i] = powf(2.0f, v) * ((i & 0x1F) | 0x20);
}
/* generate scale factors for exponents and asymmetrical dequantization
reference: Section 7.3.2 Expansion of Mantissas for Asymmetric Quantization */
for (i = 0; i < 25; i++)
scale_factors[i] = pow(2.0, -i);
/* generate exponent tables
reference: Section 7.1.3 Exponent Decoding */
for(i=0; i<128; i++) {
exp_ungroup_tab[i][0] = i / 25;
exp_ungroup_tab[i][1] = (i % 25) / 5;
exp_ungroup_tab[i][2] = (i % 25) % 5;
}
}
/**
* AVCodec initialization
*/
static int ac3_decode_init(AVCodecContext *avctx)
{
AC3DecodeContext *ctx = avctx->priv_data;
ctx->avctx = avctx;
ac3_common_init();
ac3_tables_init();
ff_mdct_init(&ctx->imdct_256, 8, 1);
ff_mdct_init(&ctx->imdct_512, 9, 1);
ac3_window_init(ctx->window);
dsputil_init(&ctx->dsp, avctx);
av_init_random(0, &ctx->dith_state);
/* set bias values for float to int16 conversion */
if(ctx->dsp.float_to_int16 == ff_float_to_int16_c) {
ctx->add_bias = 385.0f;
ctx->mul_bias = 1.0f;
} else {
ctx->add_bias = 0.0f;
ctx->mul_bias = 32767.0f;
}
return 0;
}
/**
* Parse the 'sync info' and 'bit stream info' from the AC-3 bitstream.
* GetBitContext within AC3DecodeContext must point to
* start of the synchronized ac3 bitstream.
*/
static int ac3_parse_header(AC3DecodeContext *ctx)
{
AC3HeaderInfo hdr;
GetBitContext *gb = &ctx->gb;
float center_mix_level, surround_mix_level;
int err, i;
err = ff_ac3_parse_header(gb->buffer, &hdr);
if(err)
return err;
/* get decoding parameters from header info */
ctx->bit_alloc_params.sr_code = hdr.sr_code;
ctx->channel_mode = hdr.channel_mode;
center_mix_level = gain_levels[center_levels[hdr.center_mix_level]];
surround_mix_level = gain_levels[surround_levels[hdr.surround_mix_level]];
ctx->dolby_surround_mode = hdr.dolby_surround_mode;
ctx->lfe_on = hdr.lfe_on;
ctx->bit_alloc_params.sr_shift = hdr.sr_shift;
ctx->sampling_rate = hdr.sample_rate;
ctx->bit_rate = hdr.bit_rate;
ctx->channels = hdr.channels;
ctx->fbw_channels = ctx->channels - ctx->lfe_on;
ctx->lfe_ch = ctx->fbw_channels + 1;
ctx->frame_size = hdr.frame_size;
/* set default output to all source channels */
ctx->out_channels = ctx->channels;
ctx->output_mode = ctx->channel_mode;
if(ctx->lfe_on)
ctx->output_mode |= AC3_OUTPUT_LFEON;
/* skip over portion of header which has already been read */
skip_bits(gb, 16); // skip the sync_word
skip_bits(gb, 16); // skip crc1
skip_bits(gb, 8); // skip fscod and frmsizecod
skip_bits(gb, 11); // skip bsid, bsmod, and acmod
if(ctx->channel_mode == AC3_CHMODE_STEREO) {
skip_bits(gb, 2); // skip dsurmod
} else {
if((ctx->channel_mode & 1) && ctx->channel_mode != AC3_CHMODE_MONO)
skip_bits(gb, 2); // skip cmixlev
if(ctx->channel_mode & 4)
skip_bits(gb, 2); // skip surmixlev
}
skip_bits1(gb); // skip lfeon
/* read the rest of the bsi. read twice for dual mono mode. */
i = !(ctx->channel_mode);
do {
skip_bits(gb, 5); // skip dialog normalization
if (get_bits1(gb))
skip_bits(gb, 8); //skip compression
if (get_bits1(gb))
skip_bits(gb, 8); //skip language code
if (get_bits1(gb))
skip_bits(gb, 7); //skip audio production information
} while (i--);
skip_bits(gb, 2); //skip copyright bit and original bitstream bit
/* skip the timecodes (or extra bitstream information for Alternate Syntax)
TODO: read & use the xbsi1 downmix levels */
if (get_bits1(gb))
skip_bits(gb, 14); //skip timecode1 / xbsi1
if (get_bits1(gb))
skip_bits(gb, 14); //skip timecode2 / xbsi2
/* skip additional bitstream info */
if (get_bits1(gb)) {
i = get_bits(gb, 6);
do {
skip_bits(gb, 8);
} while(i--);
}
/* set stereo downmixing coefficients
reference: Section 7.8.2 Downmixing Into Two Channels */
for(i=0; i<ctx->fbw_channels; i++) {
ctx->downmix_coeffs[i][0] = gain_levels[ac3_default_coeffs[ctx->channel_mode][i][0]];
ctx->downmix_coeffs[i][1] = gain_levels[ac3_default_coeffs[ctx->channel_mode][i][1]];
}
if(ctx->channel_mode > 1 && ctx->channel_mode & 1) {
ctx->downmix_coeffs[1][0] = ctx->downmix_coeffs[1][1] = center_mix_level;
}
if(ctx->channel_mode == AC3_CHMODE_2F1R || ctx->channel_mode == AC3_CHMODE_3F1R) {
int nf = ctx->channel_mode - 2;
ctx->downmix_coeffs[nf][0] = ctx->downmix_coeffs[nf][1] = surround_mix_level * LEVEL_MINUS_3DB;
}
if(ctx->channel_mode == AC3_CHMODE_2F2R || ctx->channel_mode == AC3_CHMODE_3F2R) {
int nf = ctx->channel_mode - 4;
ctx->downmix_coeffs[nf][0] = ctx->downmix_coeffs[nf+1][1] = surround_mix_level;
}
return 0;
}
/**
* Decode the grouped exponents according to exponent strategy.
* reference: Section 7.1.3 Exponent Decoding
*/
static void decode_exponents(GetBitContext *gb, int exp_strategy, int ngrps,
uint8_t absexp, int8_t *dexps)
{
int i, j, grp, group_size;
int dexp[256];
int expacc, prevexp;
/* unpack groups */
group_size = exp_strategy + (exp_strategy == EXP_D45);
for(grp=0,i=0; grp<ngrps; grp++) {
expacc = get_bits(gb, 7);
dexp[i++] = exp_ungroup_tab[expacc][0];
dexp[i++] = exp_ungroup_tab[expacc][1];
dexp[i++] = exp_ungroup_tab[expacc][2];
}
/* convert to absolute exps and expand groups */
prevexp = absexp;
for(i=0; i<ngrps*3; i++) {
prevexp = av_clip(prevexp + dexp[i]-2, 0, 24);
for(j=0; j<group_size; j++) {
dexps[(i*group_size)+j] = prevexp;
}
}
}
/**
* Generate 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->start_freq[CPL_CH];
for(bnd=0; bnd<ctx->num_cpl_bands; bnd++) {
do {
subbnd++;
for(j=0; j<12; j++) {
for(ch=1; ch<=ctx->fbw_channels; ch++) {
if(ctx->channel_in_cpl[ch])
ctx->transform_coeffs[ch][i] = ctx->transform_coeffs[CPL_CH][i] * ctx->cpl_coords[ch][bnd] * 8.0f;
}
i++;
}
} while(ctx->cpl_band_struct[subbnd]);
}
}
/**
* Grouped mantissas for 3-level 5-level and 11-level quantization
*/
typedef struct {
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 a particular channel
* reference: Section 7.3 Quantization and Decoding of Mantissas
*/
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->start_freq[ch_index];
end = ctx->end_freq[ch_index];
for (i = start; i < end; i++) {
tbap = bap[i];
switch (tbap) {
case 0:
coeffs[i] = ((av_random(&ctx->dith_state) & 0xFFFF) / 65535.0f) - 0.5f;
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:
/* asymmetric dequantization */
coeffs[i] = get_sbits(gb, quantization_tab[tbap]) * scale_factors[quantization_tab[tbap]-1];
break;
}
coeffs[i] *= scale_factors[exps[i]];
}
return 0;
}
/**
* Remove 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->fbw_channels; ch++) {
if(!ctx->dither_flag[ch]) {
coeffs = ctx->transform_coeffs[ch];
bap = ctx->bap[ch];
if(ctx->channel_in_cpl[ch])
end = ctx->start_freq[CPL_CH];
else
end = ctx->end_freq[ch];
for(i=0; i<end; i++) {
if(bap[i] == 0)
coeffs[i] = 0.0f;
}
if(ctx->channel_in_cpl[ch]) {
bap = ctx->bap[CPL_CH];
for(; i<ctx->end_freq[CPL_CH]; i++) {
if(bap[i] == 0)
coeffs[i] = 0.0f;
}
}
}
}
}
/**
* Get the transform coefficients.
*/
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->channels; ch++) {
/* transform coefficients for full-bandwidth channel */
if (get_transform_coeffs_ch(ctx, ch, &m))
return -1;
/* tranform coefficients for coupling channel come right after the
coefficients for the first coupled channel*/
if (ctx->channel_in_cpl[ch]) {
if (!got_cplchan) {
if (get_transform_coeffs_ch(ctx, CPL_CH, &m)) {
av_log(ctx->avctx, AV_LOG_ERROR, "error in decoupling channels\n");
return -1;
}
uncouple_channels(ctx);
got_cplchan = 1;
}
end = ctx->end_freq[CPL_CH];
} else {
end = ctx->end_freq[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;
}
/**
* 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->end_freq[1], ctx->end_freq[2]);
for(bnd=0; bnd<ctx->num_rematrixing_bands; bnd++) {
if(ctx->rematrixing_flags[bnd]) {
bndend = FFMIN(end, rematrix_band_tab[bnd+1]);
for(i=rematrix_band_tab[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;
}
}
}
}
/**
* Perform the 256-point IMDCT
*/
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;
}
}
/**
* Inverse MDCT Transform.
* Convert frequency domain coefficients to time-domain audio samples.
* reference: Section 7.9.4 Transformation Equations
*/
static inline void do_imdct(AC3DecodeContext *ctx)
{
int ch;
int channels;
/* Don't perform the IMDCT on the LFE channel unless it's used in the output */
channels = ctx->fbw_channels;
if(ctx->output_mode & AC3_OUTPUT_LFEON)
channels++;
for (ch=1; ch<=channels; ch++) {
if (ctx->block_switch[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);
}
/* For the first half of the block, apply the window, add the delay
from the previous block, and send to output */
ctx->dsp.vector_fmul_add_add(ctx->output[ch-1], ctx->tmp_output,
ctx->window, ctx->delay[ch-1], 0, 256, 1);
/* For the second half of the block, apply the window and store the
samples to delay, to be combined with the next block */
ctx->dsp.vector_fmul_reverse(ctx->delay[ch-1], ctx->tmp_output+256,
ctx->window, 256);
}
}
/**
* Downmix the output to mono or stereo.
*/
static void ac3_downmix(float samples[AC3_MAX_CHANNELS][256], int fbw_channels,
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<fbw_channels; 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_CHMODE_MONO) {
samples[0][i] = (v0 + v1) * LEVEL_MINUS_3DB;
} else if(output_mode == AC3_CHMODE_STEREO) {
samples[0][i] = v0;
samples[1][i] = v1;
}
}
}
/**
* Parse an audio block from AC-3 bitstream.
*/
static int ac3_parse_audio_block(AC3DecodeContext *ctx, int blk)
{
int fbw_channels = ctx->fbw_channels;
int channel_mode = ctx->channel_mode;
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);
/* block switch flags */
for (ch = 1; ch <= fbw_channels; ch++)
ctx->block_switch[ch] = get_bits1(gb);
/* dithering flags */
ctx->dither_all = 1;
for (ch = 1; ch <= fbw_channels; ch++) {
ctx->dither_flag[ch] = get_bits1(gb);
if(!ctx->dither_flag[ch])
ctx->dither_all = 0;
}
/* dynamic range */
i = !(ctx->channel_mode);
do {
if(get_bits1(gb)) {
ctx->dynamic_range[i] = ((dynamic_range_tab[get_bits(gb, 8)]-1.0) *
ctx->avctx->drc_scale)+1.0;
} else if(blk == 0) {
ctx->dynamic_range[i] = 1.0f;
}
} while(i--);
/* coupling strategy */
if (get_bits1(gb)) {
memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
ctx->cpl_in_use = get_bits1(gb);
if (ctx->cpl_in_use) {
/* coupling in use */
int cpl_begin_freq, cpl_end_freq;
/* determine which channels are coupled */
for (ch = 1; ch <= fbw_channels; ch++)
ctx->channel_in_cpl[ch] = get_bits1(gb);
/* phase flags in use */
if (channel_mode == AC3_CHMODE_STEREO)
ctx->phase_flags_in_use = get_bits1(gb);
/* coupling frequency range and band structure */
cpl_begin_freq = get_bits(gb, 4);
cpl_end_freq = get_bits(gb, 4);
if (3 + cpl_end_freq - cpl_begin_freq < 0) {
av_log(ctx->avctx, AV_LOG_ERROR, "3+cplendf = %d < cplbegf = %d\n", 3+cpl_end_freq, cpl_begin_freq);
return -1;
}
ctx->num_cpl_bands = ctx->num_cpl_subbands = 3 + cpl_end_freq - cpl_begin_freq;
ctx->start_freq[CPL_CH] = cpl_begin_freq * 12 + 37;
ctx->end_freq[CPL_CH] = cpl_end_freq * 12 + 73;
for (bnd = 0; bnd < ctx->num_cpl_subbands - 1; bnd++) {
if (get_bits1(gb)) {
ctx->cpl_band_struct[bnd] = 1;
ctx->num_cpl_bands--;
}
}
} else {
/* coupling not in use */
for (ch = 1; ch <= fbw_channels; ch++)
ctx->channel_in_cpl[ch] = 0;
}
}
/* coupling coordinates */
if (ctx->cpl_in_use) {
int cpl_coords_exist = 0;
for (ch = 1; ch <= fbw_channels; ch++) {
if (ctx->channel_in_cpl[ch]) {
if (get_bits1(gb)) {
int master_cpl_coord, cpl_coord_exp, cpl_coord_mant;
cpl_coords_exist = 1;
master_cpl_coord = 3 * get_bits(gb, 2);
for (bnd = 0; bnd < ctx->num_cpl_bands; bnd++) {
cpl_coord_exp = get_bits(gb, 4);
cpl_coord_mant = get_bits(gb, 4);
if (cpl_coord_exp == 15)
ctx->cpl_coords[ch][bnd] = cpl_coord_mant / 16.0f;
else
ctx->cpl_coords[ch][bnd] = (cpl_coord_mant + 16.0f) / 32.0f;
ctx->cpl_coords[ch][bnd] *= scale_factors[cpl_coord_exp + master_cpl_coord];
}
}
}
}
/* phase flags */
if (channel_mode == AC3_CHMODE_STEREO && ctx->phase_flags_in_use && cpl_coords_exist) {
for (bnd = 0; bnd < ctx->num_cpl_bands; bnd++) {
if (get_bits1(gb))
ctx->cpl_coords[2][bnd] = -ctx->cpl_coords[2][bnd];
}
}
}
/* stereo rematrixing strategy and band structure */
if (channel_mode == AC3_CHMODE_STEREO) {
ctx->rematrixing_strategy = get_bits1(gb);
if (ctx->rematrixing_strategy) {
ctx->num_rematrixing_bands = 4;
if(ctx->cpl_in_use && ctx->start_freq[CPL_CH] <= 61)
ctx->num_rematrixing_bands -= 1 + (ctx->start_freq[CPL_CH] == 37);
for(bnd=0; bnd<ctx->num_rematrixing_bands; bnd++)
ctx->rematrixing_flags[bnd] = get_bits1(gb);
}
}
/* exponent strategies for each channel */
ctx->exp_strategy[CPL_CH] = EXP_REUSE;
ctx->exp_strategy[ctx->lfe_ch] = EXP_REUSE;
for (ch = !ctx->cpl_in_use; ch <= ctx->channels; ch++) {
if(ch == ctx->lfe_ch)
ctx->exp_strategy[ch] = get_bits(gb, 1);
else
ctx->exp_strategy[ch] = get_bits(gb, 2);
if(ctx->exp_strategy[ch] != EXP_REUSE)
bit_alloc_stages[ch] = 3;
}
/* channel bandwidth */
for (ch = 1; ch <= fbw_channels; ch++) {
ctx->start_freq[ch] = 0;
if (ctx->exp_strategy[ch] != EXP_REUSE) {
int prev = ctx->end_freq[ch];
if (ctx->channel_in_cpl[ch])
ctx->end_freq[ch] = ctx->start_freq[CPL_CH];
else {
int bandwidth_code = get_bits(gb, 6);
if (bandwidth_code > 60) {
av_log(ctx->avctx, AV_LOG_ERROR, "bandwidth code = %d > 60", bandwidth_code);
return -1;
}
ctx->end_freq[ch] = bandwidth_code * 3 + 73;
}
if(blk > 0 && ctx->end_freq[ch] != prev)
memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
}
}
ctx->start_freq[ctx->lfe_ch] = 0;
ctx->end_freq[ctx->lfe_ch] = 7;
/* decode exponents for each channel */
for (ch = !ctx->cpl_in_use; ch <= ctx->channels; ch++) {
if (ctx->exp_strategy[ch] != EXP_REUSE) {
int group_size, num_groups;
group_size = 3 << (ctx->exp_strategy[ch] - 1);
if(ch == CPL_CH)
num_groups = (ctx->end_freq[ch] - ctx->start_freq[ch]) / group_size;
else if(ch == ctx->lfe_ch)
num_groups = 2;
else
num_groups = (ctx->end_freq[ch] + group_size - 4) / group_size;
ctx->dexps[ch][0] = get_bits(gb, 4) << !ch;
decode_exponents(gb, ctx->exp_strategy[ch], num_groups, ctx->dexps[ch][0],
&ctx->dexps[ch][ctx->start_freq[ch]+!!ch]);
if(ch != CPL_CH && ch != ctx->lfe_ch)
skip_bits(gb, 2); /* skip gainrng */
}
}
/* bit allocation information */
if (get_bits1(gb)) {
ctx->bit_alloc_params.slow_decay = ff_ac3_slow_decay_tab[get_bits(gb, 2)] >> ctx->bit_alloc_params.sr_shift;
ctx->bit_alloc_params.fast_decay = ff_ac3_fast_decay_tab[get_bits(gb, 2)] >> ctx->bit_alloc_params.sr_shift;
ctx->bit_alloc_params.slow_gain = ff_ac3_slow_gain_tab[get_bits(gb, 2)];
ctx->bit_alloc_params.db_per_bit = ff_ac3_db_per_bit_tab[get_bits(gb, 2)];
ctx->bit_alloc_params.floor = ff_ac3_floor_tab[get_bits(gb, 3)];
for(ch=!ctx->cpl_in_use; ch<=ctx->channels; ch++) {
bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
}
}
/* signal-to-noise ratio offsets and fast gains (signal-to-mask ratios) */
if (get_bits1(gb)) {
int csnr;
csnr = (get_bits(gb, 6) - 15) << 4;
for (ch = !ctx->cpl_in_use; ch <= ctx->channels; ch++) { /* snr offset and fast gain */
ctx->snr_offset[ch] = (csnr + get_bits(gb, 4)) << 2;
ctx->fast_gain[ch] = ff_ac3_fast_gain_tab[get_bits(gb, 3)];
}
memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
}
/* coupling leak information */
if (ctx->cpl_in_use && get_bits1(gb)) {
ctx->bit_alloc_params.cpl_fast_leak = get_bits(gb, 3);
ctx->bit_alloc_params.cpl_slow_leak = get_bits(gb, 3);
bit_alloc_stages[CPL_CH] = FFMAX(bit_alloc_stages[CPL_CH], 2);
}
/* delta bit allocation information */
if (get_bits1(gb)) {
/* delta bit allocation exists (strategy) */
for (ch = !ctx->cpl_in_use; ch <= fbw_channels; ch++) {
ctx->dba_mode[ch] = get_bits(gb, 2);
if (ctx->dba_mode[ch] == DBA_RESERVED) {
av_log(ctx->avctx, AV_LOG_ERROR, "delta bit allocation strategy reserved\n");
return -1;
}
bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
}
/* channel delta offset, len and bit allocation */
for (ch = !ctx->cpl_in_use; ch <= fbw_channels; ch++) {
if (ctx->dba_mode[ch] == DBA_NEW) {
ctx->dba_nsegs[ch] = get_bits(gb, 3);
for (seg = 0; seg <= ctx->dba_nsegs[ch]; seg++) {
ctx->dba_offsets[ch][seg] = get_bits(gb, 5);
ctx->dba_lengths[ch][seg] = get_bits(gb, 4);
ctx->dba_values[ch][seg] = get_bits(gb, 3);
}
}
}
} else if(blk == 0) {
for(ch=0; ch<=ctx->channels; ch++) {
ctx->dba_mode[ch] = DBA_NONE;
}
}
/* Bit allocation */
for(ch=!ctx->cpl_in_use; ch<=ctx->channels; ch++) {
if(bit_alloc_stages[ch] > 2) {
/* Exponent mapping into PSD and PSD integration */
ff_ac3_bit_alloc_calc_psd(ctx->dexps[ch],
ctx->start_freq[ch], ctx->end_freq[ch],
ctx->psd[ch], ctx->band_psd[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->band_psd[ch],
ctx->start_freq[ch], ctx->end_freq[ch],
ctx->fast_gain[ch], (ch == ctx->lfe_ch),
ctx->dba_mode[ch], ctx->dba_nsegs[ch],
ctx->dba_offsets[ch], ctx->dba_lengths[ch],
ctx->dba_values[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->start_freq[ch], ctx->end_freq[ch],
ctx->snr_offset[ch],
ctx->bit_alloc_params.floor,
ctx->bap[ch]);
}
}
/* unused dummy data */
if (get_bits1(gb)) {
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(ctx->avctx, AV_LOG_ERROR, "Error in routine get_transform_coeffs\n");
return -1;
}
/* recover coefficients if rematrixing is in use */
if(ctx->channel_mode == AC3_CHMODE_STEREO)
do_rematrixing(ctx);
/* apply scaling to coefficients (headroom, dynrng) */
for(ch=1; ch<=ctx->channels; ch++) {
float gain = 2.0f * ctx->mul_bias;
if(ctx->channel_mode == AC3_CHMODE_DUALMONO) {
gain *= ctx->dynamic_range[ch-1];
} else {
gain *= ctx->dynamic_range[0];
}
for(i=0; i<ctx->end_freq[ch]; i++) {
ctx->transform_coeffs[ch][i] *= gain;
}
}
do_imdct(ctx);
/* downmix output if needed */
if(ctx->channels != ctx->out_channels && !((ctx->output_mode & AC3_OUTPUT_LFEON) &&
ctx->fbw_channels == ctx->out_channels)) {
ac3_downmix(ctx->output, ctx->fbw_channels, 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 a single AC-3 frame.
*/
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, err;
/* initialize the GetBitContext with the start of valid AC-3 Frame */
init_get_bits(&ctx->gb, buf, buf_size * 8);
/* parse the syncinfo */
err = ac3_parse_header(ctx);
if(err) {
switch(err) {
case AC3_PARSE_ERROR_SYNC:
av_log(avctx, AV_LOG_ERROR, "frame sync error\n");
break;
case AC3_PARSE_ERROR_BSID:
av_log(avctx, AV_LOG_ERROR, "invalid bitstream id\n");
break;
case AC3_PARSE_ERROR_SAMPLE_RATE:
av_log(avctx, AV_LOG_ERROR, "invalid sample rate\n");
break;
case AC3_PARSE_ERROR_FRAME_SIZE:
av_log(avctx, AV_LOG_ERROR, "invalid frame size\n");
break;
default:
av_log(avctx, AV_LOG_ERROR, "invalid header\n");
break;
}
return -1;
}
avctx->sample_rate = ctx->sampling_rate;
avctx->bit_rate = ctx->bit_rate;
/* check that reported frame size fits in input buffer */
if(ctx->frame_size > buf_size) {
av_log(avctx, AV_LOG_ERROR, "incomplete frame\n");
return -1;
}
/* channel config */
ctx->out_channels = ctx->channels;
if (avctx->request_channels > 0 && avctx->request_channels <= 2 &&
avctx->request_channels < ctx->channels) {
ctx->out_channels = avctx->request_channels;
ctx->output_mode = avctx->request_channels == 1 ? AC3_CHMODE_MONO : AC3_CHMODE_STEREO;
}
avctx->channels = ctx->out_channels;
/* 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 the AC-3 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,
};
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