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ac3dec.c File Reference
#include <stdio.h>
#include <stddef.h>
#include <math.h>
#include <string.h>
#include "libavutil/channel_layout.h"
#include "libavutil/crc.h"
#include "libavutil/downmix_info.h"
#include "libavutil/opt.h"
#include "internal.h"
#include "aac_ac3_parser.h"
#include "ac3_parser.h"
#include "ac3dec.h"
#include "ac3dec_data.h"
#include "kbdwin.h"

Go to the source code of this file.

Data Structures

struct  mant_groups
 Grouped mantissas for 3-level 5-level and 11-level quantization. More...
 

Macros

#define OFFSET(x)   offsetof(AC3DecodeContext, x)
 
#define PAR   (AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_AUDIO_PARAM)
 

Functions

static int symmetric_dequant (int code, int levels)
 Symmetrical Dequantization reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization Tables 7.19 to 7.23.
 
static av_cold void ac3_tables_init (void)
 
static av_cold int ac3_decode_init (AVCodecContext *avctx)
 AVCodec initialization.
 
static int ac3_parse_header (AC3DecodeContext *s)
 Parse the 'sync info' and 'bit stream info' from the AC-3 bitstream.
 
static int parse_frame_header (AC3DecodeContext *s)
 Common function to parse AC-3 or E-AC-3 frame header.
 
static void set_downmix_coeffs (AC3DecodeContext *s)
 Set stereo downmixing coefficients based on frame header info.
 
static int decode_exponents (GetBitContext *gbc, int exp_strategy, int ngrps, uint8_t absexp, int8_t *dexps)
 Decode the grouped exponents according to exponent strategy.
 
static void calc_transform_coeffs_cpl (AC3DecodeContext *s)
 Generate transform coefficients for each coupled channel in the coupling range using the coupling coefficients and coupling coordinates.
 
static void ac3_decode_transform_coeffs_ch (AC3DecodeContext *s, int ch_index, mant_groups *m)
 Decode the transform coefficients for a particular channel reference: Section 7.3 Quantization and Decoding of Mantissas.
 
static void remove_dithering (AC3DecodeContext *s)
 Remove random dithering from coupling range coefficients with zero-bit mantissas for coupled channels which do not use dithering.
 
static void decode_transform_coeffs_ch (AC3DecodeContext *s, int blk, int ch, mant_groups *m)
 
static void decode_transform_coeffs (AC3DecodeContext *s, int blk)
 Decode the transform coefficients.
 
static void do_rematrixing (AC3DecodeContext *s)
 Stereo rematrixing.
 
static void do_imdct (AC3DecodeContext *s, int channels)
 Inverse MDCT Transform.
 
static void ac3_upmix_delay (AC3DecodeContext *s)
 Upmix delay samples from stereo to original channel layout.
 
static void decode_band_structure (GetBitContext *gbc, int blk, int eac3, int ecpl, int start_subband, int end_subband, const uint8_t *default_band_struct, int *num_bands, uint8_t *band_sizes)
 Decode band structure for coupling, spectral extension, or enhanced coupling.
 
static int decode_audio_block (AC3DecodeContext *s, int blk)
 Decode a single audio block from the AC-3 bitstream.
 
static int ac3_decode_frame (AVCodecContext *avctx, void *data, int *got_frame_ptr, AVPacket *avpkt)
 Decode a single AC-3 frame.
 
static av_cold int ac3_decode_end (AVCodecContext *avctx)
 Uninitialize the AC-3 decoder.
 

Variables

static uint8_t ungroup_3_in_7_bits_tab [128][3]
 table for ungrouping 3 values in 7 bits.
 
static int b1_mantissas [32][3]
 tables for ungrouping mantissas
 
static int b2_mantissas [128][3]
 
static int b3_mantissas [8]
 
static int b4_mantissas [128][2]
 
static int b5_mantissas [16]
 
static const uint8_t quantization_tab [16]
 Quantization table: levels for symmetric.
 
static float dynamic_range_tab [256]
 dynamic range table.
 
static const float gain_levels [9]
 Adjustments in dB gain.
 
static const float gain_levels_lfe [32]
 Adjustments in dB gain (LFE, +10 to -21 dB)
 
static const uint8_t ac3_default_coeffs [8][5][2]
 Table for default stereo downmixing coefficients reference: Section 7.8.2 Downmixing Into Two Channels.
 

Macro Definition Documentation

#define OFFSET (   x)    offsetof(AC3DecodeContext, x)

Definition at line 1618 of file ac3dec.c.

Definition at line 1619 of file ac3dec.c.

Function Documentation

static int symmetric_dequant ( int  code,
int  levels 
)
inlinestatic

Symmetrical Dequantization reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization Tables 7.19 to 7.23.

Definition at line 111 of file ac3dec.c.

Referenced by ac3_tables_init().

static av_cold void ac3_tables_init ( void  )
static

Definition at line 119 of file ac3dec.c.

Referenced by ac3_decode_init().

static av_cold int ac3_decode_init ( AVCodecContext avctx)
static

AVCodec initialization.

Definition at line 171 of file ac3dec.c.

static int ac3_parse_header ( AC3DecodeContext s)
static

Parse the 'sync info' and 'bit stream info' from the AC-3 bitstream.

GetBitContext within AC3DecodeContext must point to the start of the synchronized AC-3 bitstream.

Definition at line 230 of file ac3dec.c.

Referenced by parse_frame_header().

static int parse_frame_header ( AC3DecodeContext s)
static

Common function to parse AC-3 or E-AC-3 frame header.

Definition at line 284 of file ac3dec.c.

Referenced by ac3_decode_frame().

static void set_downmix_coeffs ( AC3DecodeContext s)
static

Set stereo downmixing coefficients based on frame header info.

reference: Section 7.8.2 Downmixing Into Two Channels

Definition at line 351 of file ac3dec.c.

Referenced by ac3_decode_frame().

static int decode_exponents ( GetBitContext gbc,
int  exp_strategy,
int  ngrps,
uint8_t  absexp,
int8_t *  dexps 
)
static

Decode the grouped exponents according to exponent strategy.

reference: Section 7.1.3 Exponent Decoding

Definition at line 403 of file ac3dec.c.

Referenced by decode_audio_block().

static void calc_transform_coeffs_cpl ( AC3DecodeContext s)
static

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

Definition at line 440 of file ac3dec.c.

Referenced by decode_transform_coeffs().

static void ac3_decode_transform_coeffs_ch ( AC3DecodeContext s,
int  ch_index,
mant_groups m 
)
static

Decode the transform coefficients for a particular channel reference: Section 7.3 Quantization and Decoding of Mantissas.

Definition at line 481 of file ac3dec.c.

Referenced by decode_transform_coeffs_ch().

static void remove_dithering ( AC3DecodeContext s)
static

Remove random dithering from coupling range coefficients with zero-bit mantissas for coupled channels which do not use dithering.

reference: Section 7.3.4 Dither for Zero Bit Mantissas (bap=0)

Definition at line 563 of file ac3dec.c.

Referenced by decode_transform_coeffs().

static void decode_transform_coeffs_ch ( AC3DecodeContext s,
int  blk,
int  ch,
mant_groups m 
)
static

Definition at line 576 of file ac3dec.c.

Referenced by decode_transform_coeffs().

static void decode_transform_coeffs ( AC3DecodeContext s,
int  blk 
)
static

Decode the transform coefficients.

Definition at line 596 of file ac3dec.c.

Referenced by decode_audio_block().

static void do_rematrixing ( AC3DecodeContext s)
static

Stereo rematrixing.

reference: Section 7.5.4 Rematrixing : Decoding Technique

Definition at line 632 of file ac3dec.c.

Referenced by decode_audio_block().

static void do_imdct ( AC3DecodeContext s,
int  channels 
)
inlinestatic

Inverse MDCT Transform.

Convert frequency domain coefficients to time-domain audio samples. reference: Section 7.9.4 Transformation Equations

Definition at line 656 of file ac3dec.c.

Referenced by decode_audio_block().

static void ac3_upmix_delay ( AC3DecodeContext s)
static

Upmix delay samples from stereo to original channel layout.

Definition at line 694 of file ac3dec.c.

Referenced by decode_audio_block().

static void decode_band_structure ( GetBitContext gbc,
int  blk,
int  eac3,
int  ecpl,
int  start_subband,
int  end_subband,
const uint8_t default_band_struct,
int *  num_bands,
uint8_t band_sizes 
)
static

Decode band structure for coupling, spectral extension, or enhanced coupling.

The band structure defines how many subbands are in each band. For each subband in the range, 1 means it is combined with the previous band, and 0 means that it starts a new band.

Parameters
[in]gbcbit reader context
[in]blkblock number
[in]eac3flag to indicate E-AC-3
[in]ecplflag to indicate enhanced coupling
[in]start_subbandsubband number for start of range
[in]end_subbandsubband number for end of range
[in]default_band_structdefault band structure table
[out]num_bandsnumber of bands (optionally NULL)
[out]band_sizesarray containing the number of bins in each band (optionally NULL)

Definition at line 735 of file ac3dec.c.

Referenced by decode_audio_block().

static int decode_audio_block ( AC3DecodeContext s,
int  blk 
)
static

Decode a single audio block from the AC-3 bitstream.

Definition at line 787 of file ac3dec.c.

Referenced by ac3_decode_frame().

static int ac3_decode_frame ( AVCodecContext avctx,
void data,
int *  got_frame_ptr,
AVPacket avpkt 
)
static

Decode a single AC-3 frame.

Definition at line 1382 of file ac3dec.c.

static av_cold int ac3_decode_end ( AVCodecContext avctx)
static

Uninitialize the AC-3 decoder.

Definition at line 1606 of file ac3dec.c.

Variable Documentation

uint8_t ungroup_3_in_7_bits_tab[128][3]
static

table for ungrouping 3 values in 7 bits.

used for exponents and bap=2 mantissas

Definition at line 47 of file ac3dec.c.

Referenced by ac3_tables_init(), and decode_exponents().

int b1_mantissas[32][3]
static

tables for ungrouping mantissas

Definition at line 50 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b2_mantissas[128][3]
static

Definition at line 51 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b3_mantissas[8]
static

Definition at line 52 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b4_mantissas[128][2]
static

Definition at line 53 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b5_mantissas[16]
static

Definition at line 54 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

const uint8_t quantization_tab[16]
static
Initial value:
= {
0, 3, 5, 7, 11, 15,
5, 6, 7, 8, 9, 10, 11, 12, 14, 16
}

Quantization table: levels for symmetric.

bits for asymmetric. reference: Table 7.18 Mapping of bap to Quantizer

Definition at line 60 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch().

float dynamic_range_tab[256]
static

dynamic range table.

converts codes to scale factors.

Definition at line 66 of file ac3dec.c.

Referenced by ac3_tables_init().

const float gain_levels[9]
static
const float gain_levels_lfe[32]
static
Initial value:
= {
3.162275, 2.818382, 2.511886, 2.238719, 1.995261, 1.778278, 1.584893,
1.412536, 1.258924, 1.122018, 1.000000, 0.891251, 0.794328, 0.707946,
0.630957, 0.562341, 0.501187, 0.446683, 0.398107, 0.354813, 0.316227,
0.281838, 0.251188, 0.223872, 0.199526, 0.177828, 0.158489, 0.141253,
0.125892, 0.112201, 0.100000, 0.089125
}

Adjustments in dB gain (LFE, +10 to -21 dB)

Definition at line 82 of file ac3dec.c.

Referenced by ac3_decode_frame().

const uint8_t ac3_default_coeffs[8][5][2]
static
Initial value:
= {
{ { 2, 7 }, { 7, 2 }, },
{ { 4, 4 }, },
{ { 2, 7 }, { 7, 2 }, },
{ { 2, 7 }, { 5, 5 }, { 7, 2 }, },
{ { 2, 7 }, { 7, 2 }, { 6, 6 }, },
{ { 2, 7 }, { 5, 5 }, { 7, 2 }, { 8, 8 }, },
{ { 2, 7 }, { 7, 2 }, { 6, 7 }, { 7, 6 }, },
{ { 2, 7 }, { 5, 5 }, { 7, 2 }, { 6, 7 }, { 7, 6 }, },
}

Table for default stereo downmixing coefficients reference: Section 7.8.2 Downmixing Into Two Channels.

Definition at line 94 of file ac3dec.c.

Referenced by set_downmix_coeffs().