ac3.h File Reference

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

#include <math.h>
#include <stdint.h>
#include "ac3tab.h"
#include "libavutil/libm.h"

Go to the source code of this file.

Data Structures
struct	AC3BitAllocParameters

Macros
#define	USE_FIXED   0
#define	FIXR(x)
#define	FIXR12(x)
#define	FIXR15(x)
#define	ROUND15(x)
#define	AC3_RENAME(x)
#define	AC3_NORM(norm)
#define	AC3_MUL(a, b)
#define	AC3_RANGE(x)
#define	AC3_HEAVY_RANGE(x)
#define	AC3_DYNAMIC_RANGE(x)
#define	AC3_SPX_BLEND(x)
#define	AC3_DYNAMIC_RANGE1   1.0f
#define	AC3_LEVEL(x)

Functions
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

USE_FIXED

#define USE_FIXED   0

Definition at line 36 of file ac3.h.

FIXR

#define FIXR

(

x

)

Value:

((float)(x))

Definition at line 62 of file ac3.h.

FIXR12

#define FIXR12

(

x

)

Value:

((float)(x))

Definition at line 63 of file ac3.h.

Referenced by set_downmix_coeffs().

FIXR15

#define FIXR15

(

x

)

Value:

((float)(x))

Definition at line 64 of file ac3.h.

ROUND15

#define ROUND15

(

x

)

Value:

(x)

Definition at line 65 of file ac3.h.

AC3_RENAME

#define AC3_RENAME

(

x

)

Value:

x

Definition at line 67 of file ac3.h.

Referenced by ac3_decode_flush(), ac3_decode_init(), and decode_audio_block().

AC3_NORM

#define AC3_NORM

(

norm

)

Value:

(1.0f/(norm))

Definition at line 68 of file ac3.h.

AC3_MUL

#define AC3_MUL	(		a,
			b )

Value:

((a) * (b))

Definition at line 69 of file ac3.h.

AC3_RANGE

#define AC3_RANGE

(

x

)

Value:

(dynamic_range_tab[(x)])

Definition at line 70 of file ac3.h.

Referenced by decode_audio_block().

AC3_HEAVY_RANGE

#define AC3_HEAVY_RANGE

(

x

)

Value:

(ff_ac3_heavy_dynamic_range_tab[(x)])

Definition at line 71 of file ac3.h.

Referenced by ff_eac3_parse_header(), and parse_frame_header().

AC3_DYNAMIC_RANGE

#define AC3_DYNAMIC_RANGE

(

x

)

Value:

(powf(x,  s->drc_scale))

Definition at line 72 of file ac3.h.

Referenced by decode_audio_block().

AC3_SPX_BLEND

#define AC3_SPX_BLEND

(

x

)

Value:

(x)* (1.0f/32)

Definition at line 73 of file ac3.h.

Referenced by spx_coordinates().

AC3_DYNAMIC_RANGE1

#define AC3_DYNAMIC_RANGE1   1.0f

Definition at line 74 of file ac3.h.

Referenced by decode_audio_block().

AC3_LEVEL

#define AC3_LEVEL

(

x

)

Value:

ROUND15((x) * FIXR15(M_SQRT1_2))

Definition at line 82 of file ac3.h.

Function Documentation

ff_ac3_bit_alloc_calc_psd()

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 175 of file ac3.c.

Referenced by bit_alloc_masking(), and decode_audio_block().

ff_ac3_bit_alloc_calc_mask()

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 201 of file ac3.c.

Referenced by bit_alloc_masking(), and decode_audio_block().