ac3.h File Reference

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Detailed Description

Common code between AC3 encoder and decoder.

Definition in file ac3.h.

Go to the source code of this file.

Classes
struct	AC3BitAllocParameters
struct	AC3HeaderInfo
	Coded AC-3 header values up to the lfeon element, plus derived values. More...
Enumerations
enum	AC3DeltaStrategy { DBA_REUSE = 0, DBA_NEW, DBA_NONE, DBA_RESERVED }
	Delta bit allocation strategy. More...
enum	AC3ChannelMode {   AC3_ACMOD_DUALMONO = 0, AC3_ACMOD_MONO, AC3_ACMOD_STEREO, AC3_ACMOD_3F,   AC3_ACMOD_2F1R, AC3_ACMOD_3F1R, AC3_ACMOD_2F2R, AC3_ACMOD_3F2R }
	Channel mode (audio coding mode). More...
Functions
void	ac3_common_init (void)
	Initializes some tables.
void	ff_ac3_bit_alloc_calc_psd (int8_t *exp, int start, int end, int16_t *psd, int16_t *bndpsd)
	Calculates the log power-spectral density of the input signal.
void	ff_ac3_bit_alloc_calc_mask (AC3BitAllocParameters *s, int16_t *bndpsd, int start, int end, int fgain, int is_lfe, int deltbae, int deltnseg, uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba, int16_t *mask)
	Calculates the masking curve.
void	ff_ac3_bit_alloc_calc_bap (int16_t *mask, int16_t *psd, int start, int end, int snroffset, int floor, uint8_t *bap)
	Calculates bit allocation pointers.
void	ac3_parametric_bit_allocation (AC3BitAllocParameters *s, uint8_t *bap, int8_t *exp, int start, int end, int snroffset, int fgain, int is_lfe, int deltbae, int deltnseg, uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba)

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Enumeration Type Documentation

enum AC3DeltaStrategy

Delta bit allocation strategy.

Enumerator:

DBA_REUSE
DBA_NEW
DBA_NONE
DBA_RESERVED

Definition at line 47 of file ac3.h.

enum AC3ChannelMode

Channel mode (audio coding mode).

Enumerator:

AC3_ACMOD_DUALMONO
AC3_ACMOD_MONO
AC3_ACMOD_STEREO
AC3_ACMOD_3F
AC3_ACMOD_2F1R
AC3_ACMOD_3F1R
AC3_ACMOD_2F2R
AC3_ACMOD_3F2R

Definition at line 55 of file ac3.h.

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Function Documentation

void ac3_common_init

(

void

)

Initializes some tables.

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

Definition at line 226 of file ac3.c.

Referenced by ac3_decode_init(), and AC3_encode_init().

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

Calculates 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]	bndpsd	signal power for each critical band

Definition at line 55 of file ac3.c.

Referenced by ac3_parametric_bit_allocation(), ac3_parse_audio_block(), and bit_alloc_masking().

void ff_ac3_bit_alloc_calc_mask	(	AC3BitAllocParameters *	s,
		int16_t *	bndpsd,
		int	start,
		int	end,
		int	fgain,
		int	is_lfe,
		int	deltbae,
		int	deltnseg,
		uint8_t *	deltoffst,
		uint8_t *	deltlen,
		uint8_t *	deltba,
		int16_t *	mask
	)

Calculates 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]	bndpsd	signal power for each critical band
[in]	start	starting bin location
[in]	end	ending bin location
[in]	fgain	fast gain (estimated signal-to-mask ratio)
[in]	is_lfe	whether or not the channel being processed is the LFE
[in]	deltbae	delta bit allocation exists (none, reuse, or new)
[in]	deltnseg	number of delta segments
[in]	deltoffst	location offsets for each segment
[in]	deltlen	length of each segment
[in]	deltba	delta bit allocation for each segment
[out]	mask	calculated masking curve

Definition at line 83 of file ac3.c.

Referenced by ac3_parametric_bit_allocation(), ac3_parse_audio_block(), and bit_alloc_masking().

void ff_ac3_bit_alloc_calc_bap	(	int16_t *	mask,
		int16_t *	psd,
		int	start,
		int	end,
		int	snroffset,
		int	floor,
		uint8_t *	bap
	)

Calculates bit allocation pointers.

The SNR is the difference between the masking curve and the signal. AC-3 uses this value for each frequency bin to allocate bits. The snroffset parameter is a global adjustment to the SNR for all bins.

Parameters:

[in]	mask	masking curve
[in]	psd	signal power for each frequency bin
[in]	start	starting bin location
[in]	end	ending bin location
[in]	snroffset	SNR adjustment
[in]	floor	noise floor
[out]	bap	bit allocation pointers

Definition at line 175 of file ac3.c.

Referenced by ac3_parametric_bit_allocation(), ac3_parse_audio_block(), and bit_alloc().

void ac3_parametric_bit_allocation	(	AC3BitAllocParameters *	s,
		uint8_t *	bap,
		int8_t *	exp,
		int	start,
		int	end,
		int	snroffset,
		int	fgain,
		int	is_lfe,
		int	deltbae,
		int	deltnseg,
		uint8_t *	deltoffst,
		uint8_t *	deltlen,
		uint8_t *	deltba
	)

Definition at line 201 of file ac3.c.