ac3.h File Reference

Common code between the AC-3 encoder and decoder. More...

#include "libavutil/opt.h"
#include "avcodec.h"
#include "ac3tab.h"

Go to the source code of this file.

Data Structures
struct	AC3BitAllocParameters
struct	AC3HeaderInfo
	Coded AC-3 header values up to the lfeon element, plus derived values. More...

Macros
#define	AC3_MAX_CODED_FRAME_SIZE   3840 /* in bytes */
#define	AC3_MAX_CHANNELS   7
	maximum number of channels, including coupling channel
#define	CPL_CH   0
	coupling channel index
#define	AC3_MAX_COEFS   256
#define	AC3_BLOCK_SIZE   256
#define	AC3_MAX_BLOCKS   6
#define	AC3_FRAME_SIZE   (AC3_MAX_BLOCKS * 256)
#define	AC3_WINDOW_SIZE   (AC3_BLOCK_SIZE * 2)
#define	AC3_CRITICAL_BANDS   50
#define	AC3_MAX_CPL_BANDS   18
#define	EXP_REUSE   0
#define	EXP_NEW   1
#define	EXP_D15   1
#define	EXP_D25   2
#define	EXP_D45   3
#define	LEVEL_PLUS_3DB   1.4142135623730950
#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

Enumerations
enum	AC3DeltaStrategy { DBA_REUSE = 0, DBA_NEW, DBA_NONE, DBA_RESERVED }
	Delta bit allocation strategy. More...
enum	AC3ChannelMode {   AC3_CHMODE_DUALMONO = 0, AC3_CHMODE_MONO, AC3_CHMODE_STEREO, AC3_CHMODE_3F,   AC3_CHMODE_2F1R, AC3_CHMODE_3F1R, AC3_CHMODE_2F2R, AC3_CHMODE_3F2R }
	Channel mode (audio coding mode) More...
enum	EAC3FrameType { EAC3_FRAME_TYPE_INDEPENDENT = 0, EAC3_FRAME_TYPE_DEPENDENT, EAC3_FRAME_TYPE_AC3_CONVERT, EAC3_FRAME_TYPE_RESERVED }

Functions
void	ff_ac3_common_init (void)
	Initialize some tables.
void	ff_ac3_bit_alloc_calc_psd (int8_t *exp, int start, int end, int16_t *psd, int16_t *band_psd)
	Calculate the log power-spectral density of the input signal.
int	ff_ac3_bit_alloc_calc_mask (AC3BitAllocParameters *s, int16_t *band_psd, int start, int end, int fast_gain, int is_lfe, int dba_mode, int dba_nsegs, uint8_t *dba_offsets, uint8_t *dba_lengths, uint8_t *dba_values, int16_t *mask)
	Calculate the masking curve.

Detailed Description

Common code between the AC-3 encoder and decoder.

Definition in file ac3.h.

Macro Definition Documentation

#define AC3_MAX_CODED_FRAME_SIZE   3840 /* in bytes */

Definition at line 30 of file ac3.h.

Referenced by ff_ac3_output_frame().

#define AC3_MAX_CHANNELS   7

maximum number of channels, including coupling channel

Definition at line 31 of file ac3.h.

Referenced by ac3_decode_frame(), ac3_decode_init(), apply_channel_coupling(), decode_audio_block(), ff_eac3_set_cpl_states(), and set_channel_info().

#define CPL_CH   0

coupling channel index

Definition at line 32 of file ac3.h.

Referenced by ac3_decode_transform_coeffs_ch(), apply_channel_coupling(), calc_transform_coeffs_cpl(), compute_exp_strategy(), compute_rematrixing_strategy(), count_exponent_bits(), count_mantissa_bits_update_ch(), decode_audio_block(), decode_transform_coeffs(), encode_exponents(), ff_ac3_compute_coupling_strategy(), ff_ac3_group_exponents(), ff_ac3_quantize_mantissas(), ff_eac3_parse_header(), output_audio_block(), remove_dithering(), and set_bandwidth().

#define AC3_MAX_COEFS   256

Definition at line 34 of file ac3.h.

Referenced by ac3_bit_alloc_calc_bap_c(), allocate_buffers(), compute_exp_strategy(), encode_exponents(), encode_frame(), extract_exponents(), ff_eac3_decode_transform_coeffs_aht_ch(), reset_block_bap(), scale_coefficients(), and set_bandwidth().

#define AC3_BLOCK_SIZE   256

Definition at line 35 of file ac3.h.

Referenced by ac3_decode_frame(), allocate_sample_buffers(), apply_mdct(), copy_input_samples(), ff_ac3_adjust_frame_size(), ff_ac3_encode_init(), and validate_options().

#define AC3_MAX_BLOCKS   6

Definition at line 36 of file ac3.h.

Referenced by ac3_compute_mantissa_size_c(), apply_channel_coupling(), count_mantissa_bits(), and count_mantissa_bits_init().

#define AC3_FRAME_SIZE   (AC3_MAX_BLOCKS * 256)

Definition at line 37 of file ac3.h.

Referenced by allocate_sample_buffers(), spdif_get_offset_and_codec(), spdif_header_ac3(), and validate_options().

#define AC3_WINDOW_SIZE   (AC3_BLOCK_SIZE * 2)

Definition at line 38 of file ac3.h.

Referenced by allocate_sample_buffers(), apply_mdct(), and normalize_samples().

#define AC3_CRITICAL_BANDS   50

Definition at line 39 of file ac3.h.

Referenced by ff_ac3_bit_alloc_calc_mask(), and ff_ac3_common_init().

#define AC3_MAX_CPL_BANDS   18

Definition at line 40 of file ac3.h.

#define EXP_REUSE   0

Definition at line 47 of file ac3.h.

Referenced by bit_alloc(), bit_alloc_masking(), compute_exp_strategy(), count_exponent_bits(), count_frame_bits(), decode_audio_block(), encode_exponents(), ff_ac3_group_exponents(), ff_eac3_parse_header(), and output_audio_block().

#define EXP_NEW   1

Definition at line 48 of file ac3.h.

Referenced by compute_exp_strategy().

#define EXP_D15   1

Definition at line 50 of file ac3.h.

Referenced by compute_exp_strategy(), and exponent_init().

#define EXP_D25   2

Definition at line 51 of file ac3.h.

Referenced by encode_exponents_blk_ch().

#define EXP_D45   3

Definition at line 52 of file ac3.h.

Referenced by decode_exponents(), encode_exponents_blk_ch(), exponent_init(), and ff_ac3_group_exponents().

#define LEVEL_PLUS_3DB   1.4142135623730950

Definition at line 55 of file ac3.h.

#define LEVEL_PLUS_1POINT5DB   1.1892071150027209

Definition at line 56 of file ac3.h.

#define LEVEL_MINUS_1POINT5DB   0.8408964152537145

Definition at line 57 of file ac3.h.

#define LEVEL_MINUS_3DB   0.7071067811865476

Definition at line 58 of file ac3.h.

Referenced by ac3_decode_frame(), and set_downmix_coeffs().

#define LEVEL_MINUS_4POINT5DB   0.5946035575013605

Definition at line 59 of file ac3.h.

#define LEVEL_MINUS_6DB   0.5000000000000000

Definition at line 60 of file ac3.h.

#define LEVEL_MINUS_9DB   0.3535533905932738

Definition at line 61 of file ac3.h.

#define LEVEL_ZERO   0.0000000000000000

Definition at line 62 of file ac3.h.

#define LEVEL_ONE   1.0000000000000000

Definition at line 63 of file ac3.h.

Enumeration Type Documentation

enum AC3DeltaStrategy

Delta bit allocation strategy.

Enumerator:

DBA_REUSE
DBA_NEW
DBA_NONE
DBA_RESERVED

Definition at line 66 of file ac3.h.

enum AC3ChannelMode

Channel mode (audio coding mode)

Enumerator:

AC3_CHMODE_DUALMONO
AC3_CHMODE_MONO
AC3_CHMODE_STEREO
AC3_CHMODE_3F
AC3_CHMODE_2F1R
AC3_CHMODE_3F1R
AC3_CHMODE_2F2R
AC3_CHMODE_3F2R

Definition at line 74 of file ac3.h.

enum EAC3FrameType

Enumerator:

EAC3_FRAME_TYPE_INDEPENDENT
EAC3_FRAME_TYPE_DEPENDENT
EAC3_FRAME_TYPE_AC3_CONVERT
EAC3_FRAME_TYPE_RESERVED

Definition at line 127 of file ac3.h.

Function Documentation

void ff_ac3_common_init

(

void

)

Initialize some tables.

note: This function must remain thread safe because it is called by the AVParser init code.

Definition at line 220 of file ac3.c.

Referenced by ac3_decode_init(), and ff_ac3_encode_init().

void ff_ac3_bit_alloc_calc_psd	(	int8_t *	exp,
		int	start,
		int	end,
		int16_t *	psd,
		int16_t *	band_psd
	)

Calculate the log power-spectral density of the input signal.

This gives a rough estimate of signal power in the frequency domain by using the spectral envelope (exponents). The psd is also separately grouped into critical bands for use in the calculating the masking curve. 128 units in psd = -6 dB. The dbknee parameter in AC3BitAllocParameters determines the reference level.

Parameters

[in]	exp	frequency coefficient exponents
[in]	start	starting bin location
[in]	end	ending bin location
[out]	psd	signal power for each frequency bin
[out]	band_psd	signal power for each critical band

Definition at line 97 of file ac3.c.

Referenced by bit_alloc_masking(), and decode_audio_block().

int ff_ac3_bit_alloc_calc_mask	(	AC3BitAllocParameters *	s,
		int16_t *	band_psd,
		int	start,
		int	end,
		int	fast_gain,
		int	is_lfe,
		int	dba_mode,
		int	dba_nsegs,
		uint8_t *	dba_offsets,
		uint8_t *	dba_lengths,
		uint8_t *	dba_values,
		int16_t *	mask
	)

Calculate the masking curve.

First, the excitation is calculated using parameters in s and the signal power in each critical band. The excitation is compared with a predefined hearing threshold table to produce the masking curve. If delta bit allocation information is provided, it is used for adjusting the masking curve, usually to give a closer match to a better psychoacoustic model.

Parameters

[in]	s	adjustable bit allocation parameters
[in]	band_psd	signal power for each critical band
[in]	start	starting bin location
[in]	end	ending bin location
[in]	fast_gain	fast gain (estimated signal-to-mask ratio)
[in]	is_lfe	whether or not the channel being processed is the LFE
[in]	dba_mode	delta bit allocation mode (none, reuse, or new)
[in]	dba_nsegs	number of delta segments
[in]	dba_offsets	location offsets for each segment
[in]	dba_lengths	length of each segment
[in]	dba_values	delta bit allocation for each segment
[out]	mask	calculated masking curve

Returns

returns 0 for success, non-zero for error

Definition at line 123 of file ac3.c.

Referenced by bit_alloc_masking(), and decode_audio_block().