libavcodec/ac3dec.c File Reference

#include <stdio.h>
#include <stddef.h>
#include <math.h>
#include <string.h>
#include "libavutil/crc.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...

Defines

#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.

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 *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 uint8_t ac3_default_coeffs [8][5][2]

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

static const AVOption options []

static const AVClass ac3_decoder_class

AVCodec ff_ac3_decoder

Define Documentation

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

Definition at line 1454 of file ac3dec.c.

#define PAR (AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_AUDIO_PARAM)

Definition at line 1455 of file ac3dec.c.

Function Documentation

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

Uninitialize the AC-3 decoder.

Definition at line 1445 of file ac3dec.c.

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 1293 of file ac3dec.c.

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

AVCodec initialization.

Definition at line 160 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 428 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 203 of file ac3dec.c.

Referenced by parse_frame_header().

static av_cold void ac3_tables_init ( void ) [static]

Definition at line 108 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 654 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 387 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 747 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 695 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 350 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 538 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 518 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 598 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 574 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 626 of file ac3dec.c.

Referenced by ff_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 243 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 505 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 303 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 100 of file ac3dec.c.

Referenced by ac3_tables_init().

Variable Documentation

const AVClass ac3_decoder_class [static]

Initial value:

 {
    .class_name = "AC3 decoder",
    .item_name  = av_default_item_name,
    .option     = options,
    .version    = LIBAVUTIL_VERSION_INT,
}

Definition at line 1468 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 83 of file ac3dec.c.

Referenced by set_downmix_coeffs().

int b1_mantissas[32][3] [static]

tables for ungrouping mantissas

Definition at line 48 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b2_mantissas[128][3] [static]

Definition at line 49 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b3_mantissas[8] [static]

Definition at line 50 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b4_mantissas[128][2] [static]

Definition at line 51 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b5_mantissas[16] [static]

Definition at line 52 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

float dynamic_range_tab[256] [static]

dynamic range table.

converts codes to scale factors.

Definition at line 64 of file ac3dec.c.

Referenced by ac3_tables_init(), and decode_audio_block().

AVCodec ff_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,
    .capabilities   = CODEC_CAP_DR1,
    .long_name      = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
    .sample_fmts    = (const enum AVSampleFormat[]) { AV_SAMPLE_FMT_FLT,
                                                      AV_SAMPLE_FMT_S16,
                                                      AV_SAMPLE_FMT_NONE },
    .priv_class     = &ac3_decoder_class,
}

Definition at line 1475 of file ac3dec.c.

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
}

Adjustments in dB gain.

Definition at line 67 of file ac3dec.c.

Referenced by ac3_decode_frame(), and set_downmix_coeffs().

const AVOption options[] [static]

Initial value:

 {
    { "drc_scale", "percentage of dynamic range compression to apply", OFFSET(drc_scale), AV_OPT_TYPE_FLOAT, {1.0}, 0.0, 1.0, PAR },

{"dmix_mode", "Preferred Stereo Downmix Mode", OFFSET(preferred_stereo_downmix), AV_OPT_TYPE_INT, {.dbl = -1 }, -1, 2, 0, "dmix_mode"},
{"ltrt_cmixlev",   "Lt/Rt Center Mix Level",   OFFSET(ltrt_center_mix_level),    AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"ltrt_surmixlev", "Lt/Rt Surround Mix Level", OFFSET(ltrt_surround_mix_level),  AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"loro_cmixlev",   "Lo/Ro Center Mix Level",   OFFSET(loro_center_mix_level),    AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"loro_surmixlev", "Lo/Ro Surround Mix Level", OFFSET(loro_surround_mix_level),  AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},

    { NULL},
}

Definition at line 1456 of file ac3dec.c.

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 58 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch().

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 45 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	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.
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 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 uint8_t	ac3_default_coeffs [8][5][2]
	Table for default stereo downmixing coefficients reference: Section 7.8.2 Downmixing Into Two Channels.
static const AVOption	options []
static const AVClass	ac3_decoder_class
AVCodec	ff_ac3_decoder