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.
static const AVOption	options []
static const AVClass	ac3_decoder_class
AVCodec	ff_ac3_decoder

Macro Definition Documentation

#define OFFSET

(

x

)

offsetof(AC3DecodeContext, x)

Definition at line 1547 of file ac3dec.c.

#define PAR   (AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_AUDIO_PARAM)

Definition at line 1548 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 221 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 275 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 342 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 389 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 426 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 467 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 549 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 562 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 582 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 618 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 642 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 670 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]	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 711 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 763 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 1314 of file ac3dec.c.

static av_cold int ac3_decode_end ( AVCodecContext *  avctx )

static

Uninitialize the AC-3 decoder.

Definition at line 1538 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(), 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
}

Adjustments in dB gain.

Definition at line 69 of file ac3dec.c.

Referenced by ac3_decode_frame(), and set_downmix_coeffs().

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().

const AVOption options[]

static

Initial value:

= {
    { "drc_scale", "percentage of dynamic range compression to apply", OFFSET(drc_scale), AV_OPT_TYPE_FLOAT, {.dbl = 1.0}, 0.0, 6.0, PAR },

{"dmix_mode", "Preferred Stereo Downmix Mode", OFFSET(preferred_stereo_downmix), AV_OPT_TYPE_INT, {.i64 = -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 1549 of file ac3dec.c.

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 1561 of file ac3dec.c.

AVCodec ff_ac3_decoder

Initial value:

= {
    .name           = "ac3",
    .long_name      = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
    .type           = AVMEDIA_TYPE_AUDIO,
    .id             = AV_CODEC_ID_AC3,
    .priv_data_size = sizeof (AC3DecodeContext),
    .init           = ac3_decode_init,
    .close          = ac3_decode_end,
    .decode         = ac3_decode_frame,
    .capabilities   = CODEC_CAP_DR1,
    .sample_fmts    = (const enum AVSampleFormat[]) { AV_SAMPLE_FMT_FLTP,
                                                      AV_SAMPLE_FMT_NONE },
    .priv_class     = &ac3_decoder_class,
}

Definition at line 1568 of file ac3dec.c.