libavcodec/ac3dec.c File Reference

#include <stdio.h>
#include <stddef.h>
#include <math.h>
#include <string.h>
#include "libavutil/crc.h"
#include "internal.h"
#include "aac_ac3_parser.h"
#include "ac3_parser.h"
#include "ac3dec.h"
#include "ac3dec_data.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...

Defines

#define AC3_FRAME_BUFFER_SIZE   32768

Large enough for maximum possible frame size when the specification limit is ignored.

#define LEVEL_PLUS_3DB   1.4142135623730950

Adjustments in dB gain.

#define LEVEL_PLUS_1POINT5DB   1.1892071150027209

#define LEVEL_MINUS_1POINT5DB   0.8408964152537145

#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

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.

void ff_ac3_downmix_c (float(*samples)[256], float(*matrix)[2], int out_ch, int in_ch, int len)

Downmix the output to mono or stereo.

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 *data_size, 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]

static const uint8_t center_levels [4] = { 4, 5, 6, 5 }

Table for center mix levels reference: Section 5.4.2.4 cmixlev.

static const uint8_t surround_levels [4] = { 4, 6, 7, 6 }

Table for surround mix levels reference: Section 5.4.2.5 surmixlev.

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.

AVCodec ac3_decoder

Define Documentation

#define AC3_FRAME_BUFFER_SIZE 32768

Large enough for maximum possible frame size when the specification limit is ignored.

Definition at line 40 of file ac3dec.c.

Referenced by ac3_decode_frame(), and ac3_decode_init().

#define LEVEL_MINUS_1POINT5DB 0.8408964152537145

Definition at line 71 of file ac3dec.c.

#define LEVEL_MINUS_3DB 0.7071067811865476

Definition at line 72 of file ac3dec.c.

Referenced by do_imdct(), and set_downmix_coeffs().

#define LEVEL_MINUS_4POINT5DB 0.5946035575013605

Definition at line 73 of file ac3dec.c.

#define LEVEL_MINUS_6DB 0.5000000000000000

Definition at line 74 of file ac3dec.c.

#define LEVEL_MINUS_9DB 0.3535533905932738

Definition at line 75 of file ac3dec.c.

#define LEVEL_ONE 1.0000000000000000

Definition at line 77 of file ac3dec.c.

#define LEVEL_PLUS_1POINT5DB 1.1892071150027209

Definition at line 70 of file ac3dec.c.

#define LEVEL_PLUS_3DB 1.4142135623730950

Adjustments in dB gain.

Definition at line 69 of file ac3dec.c.

#define LEVEL_ZERO 0.0000000000000000

Definition at line 76 of file ac3dec.c.

Function Documentation

static av_cold int ac3_decode_end ( AVCodecContext * avctx ) [static]

Uninitialize the AC-3 decoder.

Definition at line 1429 of file ac3dec.c.

static int ac3_decode_frame	(	AVCodecContext *	avctx,
		void *	data,
		int *	data_size,
		AVPacket *	avpkt
	)			`[static]`

Decode a single AC-3 frame.

Definition at line 1313 of file ac3dec.c.

static av_cold int ac3_decode_init ( AVCodecContext * avctx ) [static]

AVCodec initialization.

Definition at line 185 of file ac3dec.c.

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 453 of file ac3dec.c.

Referenced by decode_transform_coeffs_ch().

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 231 of file ac3dec.c.

Referenced by parse_frame_header().

static av_cold void ac3_tables_init ( void ) [static]

Definition at line 132 of file ac3dec.c.

Referenced by ac3_decode_init().

static void ac3_upmix_delay ( AC3DecodeContext * s ) [static]

Upmix delay samples from stereo to original channel layout.

Definition at line 682 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 413 of file ac3dec.c.

Referenced by decode_transform_coeffs().

static int decode_audio_block	(	AC3DecodeContext *	s,
		int	blk
	)			`[static]`

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

Definition at line 775 of file ac3dec.c.

Referenced by ac3_decode_frame().

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]`	gbc	bit reader context
`[in]`	blk	block number
`[in]`	eac3	flag to indicate E-AC-3
`[in]`	ecpl	flag to indicate enhanced coupling
`[in]`	start_subband	subband number for start of range
`[in]`	end_subband	subband number for end of range
`[in]`	default_band_struct	default band structure table
`[out]`	num_bands	number of bands (optionally NULL)
`[out]`	band_sizes	array containing the number of bins in each band (optionally NULL)

Definition at line 723 of file ac3dec.c.

Referenced by decode_audio_block().

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 376 of file ac3dec.c.

Referenced by decode_audio_block().

static void decode_transform_coeffs	(	AC3DecodeContext *	s,
		int	blk
	)			`[static]`

Decode the transform coefficients.

Definition at line 566 of file ac3dec.c.

Referenced by decode_audio_block().

static void decode_transform_coeffs_ch	(	AC3DecodeContext *	s,
		int	blk,
		int	ch,
		mant_groups *	m
	)			`[static]`

Definition at line 546 of file ac3dec.c.

Referenced by decode_transform_coeffs().

static void do_imdct	(	AC3DecodeContext *	s,
		int	channels
	)			`[inline, static]`

Inverse MDCT Transform.

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

Definition at line 626 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 602 of file ac3dec.c.

Referenced by decode_audio_block().

void ff_ac3_downmix_c	(	float(*)	samples[256],
		float(*)	matrix[2],
		int	out_ch,
		int	in_ch,
		int	len
	)

Downmix the output to mono or stereo.

Definition at line 655 of file ac3dec.c.

Referenced by dsputil_init().

static int parse_frame_header ( AC3DecodeContext * s ) [static]

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

Definition at line 271 of file ac3dec.c.

Referenced by ac3_decode_frame().

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 533 of file ac3dec.c.

Referenced by decode_transform_coeffs().

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 330 of file ac3dec.c.

Referenced by ac3_decode_frame().

static int symmetric_dequant	(	int	code,
		int	levels
	)			`[inline, static]`

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

Definition at line 124 of file ac3dec.c.

Referenced by ac3_tables_init().

Variable Documentation

AVCodec ac3_decoder

Initial value:

 {
    .name = "ac3",
    .type = AVMEDIA_TYPE_AUDIO,
    .id = CODEC_ID_AC3,
    .priv_data_size = sizeof (AC3DecodeContext),
    .init = ac3_decode_init,
    .close = ac3_decode_end,
    .decode = ac3_decode_frame,
    .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
}

Definition at line 1440 of file ac3dec.c.

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 107 of file ac3dec.c.

Referenced by set_downmix_coeffs().

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 center_levels[4] = { 4, 5, 6, 5 } [static]

Table for center mix levels reference: Section 5.4.2.4 cmixlev.

Definition at line 95 of file ac3dec.c.

Referenced by set_downmix_coeffs().

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(), and decode_audio_block().

const float gain_levels[9] [static]

Initial value:

 {
    LEVEL_PLUS_3DB,
    LEVEL_PLUS_1POINT5DB,
    LEVEL_ONE,
    LEVEL_MINUS_1POINT5DB,
    LEVEL_MINUS_3DB,
    LEVEL_MINUS_4POINT5DB,
    LEVEL_MINUS_6DB,
    LEVEL_ZERO,
    LEVEL_MINUS_9DB
}

Definition at line 79 of file ac3dec.c.

Referenced by set_downmix_coeffs().

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().

const uint8_t surround_levels[4] = { 4, 6, 7, 6 } [static]

Table for surround mix levels reference: Section 5.4.2.5 surmixlev.

Definition at line 101 of file ac3dec.c.

Referenced by set_downmix_coeffs().

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 46 of file ac3dec.c.

Referenced by ac3_tables_init(), and decode_exponents().


Data Structures
struct	mant_groups
	Grouped mantissas for 3-level 5-level and 11-level quantization. More...
Defines
#define	AC3_FRAME_BUFFER_SIZE 32768
	Large enough for maximum possible frame size when the specification limit is ignored.
#define	LEVEL_PLUS_3DB 1.4142135623730950
	Adjustments in dB gain.
#define	LEVEL_PLUS_1POINT5DB 1.1892071150027209
#define	LEVEL_MINUS_1POINT5DB 0.8408964152537145
#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
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.
void	ff_ac3_downmix_c (float(samples)[256], float(matrix)[2], int out_ch, int in_ch, int len)
	Downmix the output to mono or stereo.
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 data_size, 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]
static const uint8_t	center_levels [4] = { 4, 5, 6, 5 }
	Table for center mix levels reference: Section 5.4.2.4 cmixlev.
static const uint8_t	surround_levels [4] = { 4, 6, 7, 6 }
	Table for surround mix levels reference: Section 5.4.2.5 surmixlev.
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.
AVCodec	ac3_decoder