libavcodec/ac3enc.c File Reference

The simplest AC-3 encoder. More...

#include <stdint.h>
#include "libavutil/audioconvert.h"
#include "libavutil/avassert.h"
#include "libavutil/avstring.h"
#include "libavutil/crc.h"
#include "libavutil/opt.h"
#include "avcodec.h"
#include "put_bits.h"
#include "dsputil.h"
#include "ac3dsp.h"
#include "ac3.h"
#include "audioconvert.h"
#include "fft.h"
#include "ac3enc.h"
#include "eac3enc.h"

Go to the source code of this file.

Data Structures

struct AC3Mant

Defines

#define CMIXLEV_NUM_OPTIONS   3

#define SURMIXLEV_NUM_OPTIONS   3

#define EXTMIXLEV_NUM_OPTIONS   8

#define EXP_DIFF_THRESHOLD   500

Exponent Difference Threshold.

#define CRC16_POLY   ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

CRC-16 Polynomial.

#define FLT_OPTION_THRESHOLD   0.01

Functions

void ff_ac3_adjust_frame_size (AC3EncodeContext *s)

Adjust the frame size to make the average bit rate match the target bit rate.

void ff_ac3_compute_coupling_strategy (AC3EncodeContext *s)

Set the initial coupling strategy parameters prior to coupling analysis.

void ff_ac3_apply_rematrixing (AC3EncodeContext *s)

Apply stereo rematrixing to coefficients based on rematrixing flags.

static av_cold void exponent_init (AC3EncodeContext *s)

static void extract_exponents (AC3EncodeContext *s)

static void compute_exp_strategy (AC3EncodeContext *s)

static void encode_exponents_blk_ch (uint8_t *exp, int nb_exps, int exp_strategy, int cpl)

Update the exponents so that they are the ones the decoder will decode.

static void encode_exponents (AC3EncodeContext *s)

static int count_exponent_bits (AC3EncodeContext *s)

void ff_ac3_group_exponents (AC3EncodeContext *s)

Group exponents.

void ff_ac3_process_exponents (AC3EncodeContext *s)

Calculate final exponents from the supplied MDCT coefficients and exponent shift.

static void count_frame_bits_fixed (AC3EncodeContext *s)

static void bit_alloc_init (AC3EncodeContext *s)

static void count_frame_bits (AC3EncodeContext *s)

static void bit_alloc_masking (AC3EncodeContext *s)

static void reset_block_bap (AC3EncodeContext *s)

static void count_mantissa_bits_init (uint16_t mant_cnt[AC3_MAX_BLOCKS][16])

Initialize mantissa counts.

static void count_mantissa_bits_update_ch (AC3EncodeContext *s, int ch, uint16_t mant_cnt[AC3_MAX_BLOCKS][16], int start, int end)

Update mantissa bit counts for all blocks in 1 channel in a given bandwidth range.

static int count_mantissa_bits (AC3EncodeContext *s)

static int bit_alloc (AC3EncodeContext *s, int snr_offset)

Run the bit allocation with a given SNR offset.

static int cbr_bit_allocation (AC3EncodeContext *s)

int ff_ac3_compute_bit_allocation (AC3EncodeContext *s)

static int sym_quant (int c, int e, int levels)

Symmetric quantization on 'levels' levels.

static int asym_quant (int c, int e, int qbits)

Asymmetric quantization on 2^qbits levels.

static void quantize_mantissas_blk_ch (AC3Mant *s, int32_t *fixed_coef, uint8_t *exp, uint8_t *bap, int16_t *qmant, int start_freq, int end_freq)

Quantize a set of mantissas for a single channel in a single block.

void ff_ac3_quantize_mantissas (AC3EncodeContext *s)

Quantize mantissas using coefficients, exponents, and bit allocation pointers.

static void ac3_output_frame_header (AC3EncodeContext *s)

static void output_audio_block (AC3EncodeContext *s, int blk)

static unsigned int mul_poly (unsigned int a, unsigned int b, unsigned int poly)

static unsigned int pow_poly (unsigned int a, unsigned int n, unsigned int poly)

static void output_frame_end (AC3EncodeContext *s)

void ff_ac3_output_frame (AC3EncodeContext *s, unsigned char *frame)

Write the frame to the output bitstream.

static void dprint_options (AC3EncodeContext *s)

static int validate_float_option (float v, const float *v_list, int v_list_size)

static void validate_mix_level (void *log_ctx, const char *opt_name, float *opt_param, const float *list, int list_size, int default_value, int min_value, int *ctx_param)

int ff_ac3_validate_metadata (AC3EncodeContext *s)

Validate metadata options as set by AVOption system.

av_cold int ff_ac3_encode_close (AVCodecContext *avctx)

Finalize encoding and free any memory allocated by the encoder.

static av_cold int set_channel_info (AC3EncodeContext *s, int channels, uint64_t *channel_layout)

static av_cold int validate_options (AC3EncodeContext *s)

static av_cold void set_bandwidth (AC3EncodeContext *s)

static av_cold int allocate_buffers (AC3EncodeContext *s)

av_cold int ff_ac3_encode_init (AVCodecContext *avctx)

Variables

static const float cmixlev_options [CMIXLEV_NUM_OPTIONS]

static const float surmixlev_options [SURMIXLEV_NUM_OPTIONS]

static const float extmixlev_options [EXTMIXLEV_NUM_OPTIONS]

static uint8_t exponent_group_tab [2][3][256]

LUT for number of exponent groups.

const uint64_t ff_ac3_channel_layouts [19]

List of supported channel layouts.

static const uint8_t ac3_bandwidth_tab [5][3][19]

LUT to select the bandwidth code based on the bit rate, sample rate, and number of full-bandwidth channels.

static const int8_t ac3_coupling_start_tab [6][3][19]

LUT to select the coupling start band based on the bit rate, sample rate, and number of full-bandwidth channels.

static const uint8_t exp_strategy_reuse_tab [4][6]

Table used to select exponent strategy based on exponent reuse block interval.

Detailed Description

The simplest AC-3 encoder.

Definition in file ac3enc.c.

Define Documentation

#define CMIXLEV_NUM_OPTIONS 3

Definition at line 53 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

#define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

CRC-16 Polynomial.

Definition at line 1575 of file ac3enc.c.

Referenced by ff_ac3_encode_init(), and output_frame_end().

#define EXP_DIFF_THRESHOLD 500

Exponent Difference Threshold.

New exponents are sent if their SAD exceed this number.

Definition at line 341 of file ac3enc.c.

Referenced by compute_exp_strategy().

#define EXTMIXLEV_NUM_OPTIONS 8

Definition at line 63 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

#define FLT_OPTION_THRESHOLD 0.01

Definition at line 1791 of file ac3enc.c.

Referenced by validate_float_option().

#define SURMIXLEV_NUM_OPTIONS 3

Definition at line 58 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

Function Documentation

static void ac3_output_frame_header ( AC3EncodeContext * s ) [static]

Definition at line 1328 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

static av_cold int allocate_buffers ( AC3EncodeContext * s ) [static]

Definition at line 2305 of file ac3enc.c.

Referenced by alac_decode_init(), decode_frame(), ff_ac3_encode_init(), flac_decode_init(), parse_streaminfo(), and read_header().

static int asym_quant	(	int	c,
		int	e,
		int	qbits
	)			`[inline, static]`

Asymmetric quantization on 2^qbits levels.

Parameters:

	c	unquantized coefficient
	e	exponent
	qbits	number of quantization bits

Returns:: quantized coefficient

Definition at line 1181 of file ac3enc.c.

Referenced by quantize_mantissas_blk_ch().

static int bit_alloc	(	AC3EncodeContext *	s,
		int	snr_offset
	)			`[static]`

Run the bit allocation with a given SNR offset.

This calculates the bit allocation pointers that will be used to determine the quantization of each mantissa.

Parameters:

	s	AC-3 encoder private context
	snr_offset	SNR offset, 0 to 1023

Returns:: the number of bits needed for mantissas if the given SNR offset is is used.

Definition at line 1063 of file ac3enc.c.

Referenced by cbr_bit_allocation(), compute_bit_allocation(), encode_frame(), mp_decode_layer2(), and MPA_encode_frame().

static void bit_alloc_init ( AC3EncodeContext * s ) [static]

Definition at line 758 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

static void bit_alloc_masking ( AC3EncodeContext * s ) [static]

Definition at line 940 of file ac3enc.c.

Referenced by ff_ac3_compute_bit_allocation().

static int cbr_bit_allocation ( AC3EncodeContext * s ) [static]

Definition at line 1094 of file ac3enc.c.

Referenced by ff_ac3_compute_bit_allocation().

static void compute_exp_strategy ( AC3EncodeContext * s ) [static]

Definition at line 357 of file ac3enc.c.

Referenced by ff_ac3_process_exponents().

static int count_exponent_bits ( AC3EncodeContext * s ) [static]

Definition at line 546 of file ac3enc.c.

Referenced by ff_ac3_compute_bit_allocation().

static void count_frame_bits ( AC3EncodeContext * s ) [static]

Definition at line 794 of file ac3enc.c.

Referenced by ff_ac3_compute_bit_allocation().

static void count_frame_bits_fixed ( AC3EncodeContext * s ) [static]

Definition at line 652 of file ac3enc.c.

Referenced by bit_alloc_init().

static int count_mantissa_bits ( AC3EncodeContext * s ) [static]

Definition at line 1037 of file ac3enc.c.

Referenced by bit_alloc().

static void count_mantissa_bits_init ( uint16_t mant_cnt[AC3_MAX_BLOCKS][16] ) [static]

Initialize mantissa counts.

These are set so that they are padded to the next whole group size when bits are counted in compute_mantissa_size.

Parameters:

[in,out] mant_cnt running counts for each bap value for each block

Definition at line 995 of file ac3enc.c.

Referenced by count_mantissa_bits().

static void count_mantissa_bits_update_ch	(	AC3EncodeContext *	s,
		int	ch,
		uint16_t	mant_cnt[AC3_MAX_BLOCKS][16],
		int	start,
		int	end
	)			`[static]`

Update mantissa bit counts for all blocks in 1 channel in a given bandwidth range.

Parameters:

	s	AC-3 encoder private context
	ch	channel index
`[in,out]`	mant_cnt	running counts for each bap value for each block
	start	starting coefficient bin
	end	ending coefficient bin

Definition at line 1017 of file ac3enc.c.

Referenced by count_mantissa_bits().

static void dprint_options ( AC3EncodeContext * s ) [static]

Definition at line 1676 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

static void encode_exponents ( AC3EncodeContext * s ) [static]

Definition at line 496 of file ac3enc.c.

Referenced by ff_ac3_process_exponents().

static void encode_exponents_blk_ch	(	uint8_t *	exp,
		int	nb_exps,
		int	exp_strategy,
		int	cpl
	)			`[static]`

Update the exponents so that they are the ones the decoder will decode.

Parameters:

`[in,out]`	exp	array of exponents for 1 block in 1 channel
	nb_exps	number of exponents in active bandwidth
	exp_strategy	exponent strategy for the block
	cpl	indicates if the block is in the coupling channel

Definition at line 423 of file ac3enc.c.

Referenced by encode_exponents().

static av_cold void exponent_init ( AC3EncodeContext * s ) [static]

Definition at line 305 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

static void extract_exponents ( AC3EncodeContext * s ) [static]

Definition at line 327 of file ac3enc.c.

Referenced by ff_ac3_process_exponents().

void ff_ac3_adjust_frame_size ( AC3EncodeContext * s )

Adjust the frame size to make the average bit rate match the target bit rate.

This is only needed for 11025, 22050, and 44100 sample rates or any E-AC-3.

Parameters:

s

AC-3 encoder private context

Definition at line 182 of file ac3enc.c.

Referenced by encode_frame().

void ff_ac3_apply_rematrixing ( AC3EncodeContext * s )

Apply stereo rematrixing to coefficients based on rematrixing flags.

Parameters:

s

AC-3 encoder private context

Definition at line 271 of file ac3enc.c.

Referenced by encode_frame().

int ff_ac3_compute_bit_allocation ( AC3EncodeContext * s )

Definition at line 1145 of file ac3enc.c.

Referenced by encode_frame().

void ff_ac3_compute_coupling_strategy ( AC3EncodeContext * s )

Set the initial coupling strategy parameters prior to coupling analysis.

Parameters:

s

AC-3 encoder private context

Definition at line 200 of file ac3enc.c.

Referenced by encode_frame().

av_cold int ff_ac3_encode_close ( AVCodecContext * avctx )

Finalize encoding and free any memory allocated by the encoder.

Parameters:

avctx

Codec context

Definition at line 2017 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

av_cold int ff_ac3_encode_init ( AVCodecContext * avctx )

Definition at line 2407 of file ac3enc.c.

Referenced by ac3_fixed_encode_init().

void ff_ac3_group_exponents ( AC3EncodeContext * s )

Group exponents.

3 delta-encoded exponents are in each 7-bit group. The number of groups varies depending on exponent strategy and bandwidth.

Parameters:

s

AC-3 encoder private context

Definition at line 578 of file ac3enc.c.

Referenced by encode_frame().

void ff_ac3_output_frame	(	AC3EncodeContext *	s,
		unsigned char *	frame
	)

Write the frame to the output bitstream.

Parameters:

	s	AC-3 encoder private context
	frame	output data buffer

Definition at line 1661 of file ac3enc.c.

Referenced by encode_frame().

void ff_ac3_process_exponents ( AC3EncodeContext * s )

Calculate final exponents from the supplied MDCT coefficients and exponent shift.

Extract exponents from MDCT coefficients, calculate exponent strategies, and encode final exponents.

Parameters:

s

AC-3 encoder private context

Definition at line 636 of file ac3enc.c.

Referenced by encode_frame().

void ff_ac3_quantize_mantissas ( AC3EncodeContext * s )

Quantize mantissas using coefficients, exponents, and bit allocation pointers.

Parameters:

s

AC-3 encoder private context

Definition at line 1299 of file ac3enc.c.

Referenced by encode_frame().

int ff_ac3_validate_metadata ( AC3EncodeContext * s )

Validate metadata options as set by AVOption system.

These values can optionally be changed per-frame.

Parameters:

s

AC-3 encoder private context

Definition at line 1833 of file ac3enc.c.

Referenced by encode_frame(), and validate_options().

static unsigned int mul_poly	(	unsigned int	a,
		unsigned int	b,
		unsigned int	poly
	)			`[static]`

Definition at line 1578 of file ac3enc.c.

Referenced by output_frame_end(), and pow_poly().

static void output_audio_block	(	AC3EncodeContext *	s,
		int	blk
	)			`[static]`

Definition at line 1384 of file ac3enc.c.

Referenced by ff_ac3_output_frame().

static void output_frame_end ( AC3EncodeContext * s ) [static]

Definition at line 1612 of file ac3enc.c.

Referenced by ff_ac3_output_frame().

static unsigned int pow_poly	(	unsigned int	a,
		unsigned int	n,
		unsigned int	poly
	)			`[static]`

Definition at line 1595 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

static void quantize_mantissas_blk_ch	(	AC3Mant *	s,
		int32_t *	fixed_coef,
		uint8_t *	exp,
		uint8_t *	bap,
		int16_t *	qmant,
		int	start_freq,
		int	end_freq
	)			`[static]`

Quantize a set of mantissas for a single channel in a single block.

Parameters:

	s	Mantissa count context
	fixed_coef	unquantized fixed-point coefficients
	exp	exponents
	bap	bit allocation pointer indices
`[out]`	qmant	quantized coefficients
	start_freq	starting coefficient bin
	end_freq	ending coefficient bin

Definition at line 1205 of file ac3enc.c.

Referenced by ff_ac3_quantize_mantissas().

static void reset_block_bap ( AC3EncodeContext * s ) [static]

Definition at line 970 of file ac3enc.c.

Referenced by bit_alloc(), and cbr_bit_allocation().

static av_cold void set_bandwidth ( AC3EncodeContext * s ) [static]

Definition at line 2234 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

static av_cold int set_channel_info	(	AC3EncodeContext *	s,
		int	channels,
		uint64_t *	channel_layout
	)			`[static]`

Definition at line 2062 of file ac3enc.c.

Referenced by validate_options().

static int sym_quant	(	int	c,
		int	e,
		int	levels
	)			`[inline, static]`

Symmetric quantization on 'levels' levels.

Parameters:

	c	unquantized coefficient
	e	exponent
	levels	number of quantization levels

Returns:: quantized coefficient

Definition at line 1165 of file ac3enc.c.

Referenced by quantize_mantissas_blk_ch().

static int validate_float_option	(	float	v,
		const float *	v_list,
		int	v_list_size
	)			`[static]`

Definition at line 1793 of file ac3enc.c.

Referenced by validate_mix_level().

static void validate_mix_level	(	void *	log_ctx,
		const char *	opt_name,
		float *	opt_param,
		const float *	list,
		int	list_size,
		int	default_value,
		int	min_value,
		int *	ctx_param
	)			`[static]`

Definition at line 1809 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

static av_cold int validate_options ( AC3EncodeContext * s ) [static]

Definition at line 2107 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

Variable Documentation

const uint8_t ac3_bandwidth_tab[5][3][19] [static]

Initial value:

 {


    { {  0,  0,  0, 12, 16, 32, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0, 16, 20, 36, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0, 32, 40, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0, 20, 24, 32, 48, 48, 48, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  4, 24, 28, 36, 56, 56, 56, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0, 20, 44, 52, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0,  0,  0, 16, 24, 32, 40, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  4, 20, 28, 36, 44, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0,  0,  0, 20, 40, 48, 60, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 12, 24, 32, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 16, 28, 36, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 32, 48, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  8, 20, 32, 40, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 12, 24, 36, 44, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 28, 44, 60, 60, 60, 60, 60, 60 } }
}

LUT to select the bandwidth code based on the bit rate, sample rate, and number of full-bandwidth channels.

bandwidth_tab[fbw_channels-1][sample rate code][bit rate code]

Definition at line 108 of file ac3enc.c.

const int8_t ac3_coupling_start_tab[6][3][19] [static]

LUT to select the coupling start band based on the bit rate, sample rate, and number of full-bandwidth channels.

-1 = coupling off ac3_coupling_start_tab[channel_mode-2][sample rate code][bit rate code]

TODO: more testing for optimal parameters. multi-channel tests at 44.1kHz and 32kHz.

Definition at line 141 of file ac3enc.c.

const float cmixlev_options[CMIXLEV_NUM_OPTIONS] [static]

Initial value:

 {
    LEVEL_MINUS_3DB, LEVEL_MINUS_4POINT5DB, LEVEL_MINUS_6DB
}

Definition at line 54 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

const uint8_t exp_strategy_reuse_tab[4][6] [static]

Initial value:

 {
    { EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15 },
    { EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15 },
    { EXP_D25, EXP_D25, EXP_D15, EXP_D15, EXP_D15, EXP_D15 },
    { EXP_D45, EXP_D25, EXP_D25, EXP_D15, EXP_D15, EXP_D15 }
}

Table used to select exponent strategy based on exponent reuse block interval.

Definition at line 346 of file ac3enc.c.

uint8_t exponent_group_tab[2][3][256] [static]

LUT for number of exponent groups.

exponent_group_tab[coupling][exponent strategy-1][number of coefficients]

Definition at line 74 of file ac3enc.c.

Referenced by count_exponent_bits(), encode_exponents_blk_ch(), exponent_init(), ff_ac3_group_exponents(), and output_audio_block().

const float extmixlev_options[EXTMIXLEV_NUM_OPTIONS] [static]

Initial value:

 {
    LEVEL_PLUS_3DB,  LEVEL_PLUS_1POINT5DB,  LEVEL_ONE,       LEVEL_MINUS_4POINT5DB,
    LEVEL_MINUS_3DB, LEVEL_MINUS_4POINT5DB, LEVEL_MINUS_6DB, LEVEL_ZERO
}

Definition at line 64 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

const uint64_t ff_ac3_channel_layouts[19]

Initial value:

 {
     AV_CH_LAYOUT_MONO,
     AV_CH_LAYOUT_STEREO,
     AV_CH_LAYOUT_2_1,
     AV_CH_LAYOUT_SURROUND,
     AV_CH_LAYOUT_2_2,
     AV_CH_LAYOUT_QUAD,
     AV_CH_LAYOUT_4POINT0,
     AV_CH_LAYOUT_5POINT0,
     AV_CH_LAYOUT_5POINT0_BACK,
    (AV_CH_LAYOUT_MONO     | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_STEREO   | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_2_1      | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_SURROUND | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_2_2      | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_QUAD     | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_4POINT0  | AV_CH_LOW_FREQUENCY),
     AV_CH_LAYOUT_5POINT1,
     AV_CH_LAYOUT_5POINT1_BACK,
     0
}

List of supported channel layouts.

Definition at line 80 of file ac3enc.c.

const float surmixlev_options[SURMIXLEV_NUM_OPTIONS] [static]

Initial value:

 {
    LEVEL_MINUS_3DB, LEVEL_MINUS_6DB, LEVEL_ZERO
}

Definition at line 59 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().


Data Structures
struct	AC3Mant
Defines
#define	CMIXLEV_NUM_OPTIONS 3
#define	SURMIXLEV_NUM_OPTIONS 3
#define	EXTMIXLEV_NUM_OPTIONS 8
#define	EXP_DIFF_THRESHOLD 500
	Exponent Difference Threshold.
#define	CRC16_POLY ((1 << 0) \| (1 << 2) \| (1 << 15) \| (1 << 16))
	CRC-16 Polynomial.
#define	FLT_OPTION_THRESHOLD 0.01
Functions
void	ff_ac3_adjust_frame_size (AC3EncodeContext *s)
	Adjust the frame size to make the average bit rate match the target bit rate.
void	ff_ac3_compute_coupling_strategy (AC3EncodeContext *s)
	Set the initial coupling strategy parameters prior to coupling analysis.
void	ff_ac3_apply_rematrixing (AC3EncodeContext *s)
	Apply stereo rematrixing to coefficients based on rematrixing flags.
static av_cold void	exponent_init (AC3EncodeContext *s)
static void	extract_exponents (AC3EncodeContext *s)
static void	compute_exp_strategy (AC3EncodeContext *s)
static void	encode_exponents_blk_ch (uint8_t *exp, int nb_exps, int exp_strategy, int cpl)
	Update the exponents so that they are the ones the decoder will decode.
static void	encode_exponents (AC3EncodeContext *s)
static int	count_exponent_bits (AC3EncodeContext *s)
void	ff_ac3_group_exponents (AC3EncodeContext *s)
	Group exponents.
void	ff_ac3_process_exponents (AC3EncodeContext *s)
	Calculate final exponents from the supplied MDCT coefficients and exponent shift.
static void	count_frame_bits_fixed (AC3EncodeContext *s)
static void	bit_alloc_init (AC3EncodeContext *s)
static void	count_frame_bits (AC3EncodeContext *s)
static void	bit_alloc_masking (AC3EncodeContext *s)
static void	reset_block_bap (AC3EncodeContext *s)
static void	count_mantissa_bits_init (uint16_t mant_cnt[AC3_MAX_BLOCKS][16])
	Initialize mantissa counts.
static void	count_mantissa_bits_update_ch (AC3EncodeContext *s, int ch, uint16_t mant_cnt[AC3_MAX_BLOCKS][16], int start, int end)
	Update mantissa bit counts for all blocks in 1 channel in a given bandwidth range.
static int	count_mantissa_bits (AC3EncodeContext *s)
static int	bit_alloc (AC3EncodeContext *s, int snr_offset)
	Run the bit allocation with a given SNR offset.
static int	cbr_bit_allocation (AC3EncodeContext *s)
int	ff_ac3_compute_bit_allocation (AC3EncodeContext *s)
static int	sym_quant (int c, int e, int levels)
	Symmetric quantization on 'levels' levels.
static int	asym_quant (int c, int e, int qbits)
	Asymmetric quantization on 2^qbits levels.
static void	quantize_mantissas_blk_ch (AC3Mant s, int32_t fixed_coef, uint8_t exp, uint8_t bap, int16_t *qmant, int start_freq, int end_freq)
	Quantize a set of mantissas for a single channel in a single block.
void	ff_ac3_quantize_mantissas (AC3EncodeContext *s)
	Quantize mantissas using coefficients, exponents, and bit allocation pointers.
static void	ac3_output_frame_header (AC3EncodeContext *s)
static void	output_audio_block (AC3EncodeContext *s, int blk)
static unsigned int	mul_poly (unsigned int a, unsigned int b, unsigned int poly)
static unsigned int	pow_poly (unsigned int a, unsigned int n, unsigned int poly)
static void	output_frame_end (AC3EncodeContext *s)
void	ff_ac3_output_frame (AC3EncodeContext s, unsigned char frame)
	Write the frame to the output bitstream.
static void	dprint_options (AC3EncodeContext *s)
static int	validate_float_option (float v, const float *v_list, int v_list_size)
static void	validate_mix_level (void log_ctx, const char opt_name, float opt_param, const float list, int list_size, int default_value, int min_value, int *ctx_param)
int	ff_ac3_validate_metadata (AC3EncodeContext *s)
	Validate metadata options as set by AVOption system.
av_cold int	ff_ac3_encode_close (AVCodecContext *avctx)
	Finalize encoding and free any memory allocated by the encoder.
static av_cold int	set_channel_info (AC3EncodeContext s, int channels, uint64_t channel_layout)
static av_cold int	validate_options (AC3EncodeContext *s)
static av_cold void	set_bandwidth (AC3EncodeContext *s)
static av_cold int	allocate_buffers (AC3EncodeContext *s)
av_cold int	ff_ac3_encode_init (AVCodecContext *avctx)
Variables
static const float	cmixlev_options [CMIXLEV_NUM_OPTIONS]
static const float	surmixlev_options [SURMIXLEV_NUM_OPTIONS]
static const float	extmixlev_options [EXTMIXLEV_NUM_OPTIONS]
static uint8_t	exponent_group_tab [2][3][256]
	LUT for number of exponent groups.
const uint64_t	ff_ac3_channel_layouts [19]
	List of supported channel layouts.
static const uint8_t	ac3_bandwidth_tab [5][3][19]
	LUT to select the bandwidth code based on the bit rate, sample rate, and number of full-bandwidth channels.
static const int8_t	ac3_coupling_start_tab [6][3][19]
	LUT to select the coupling start band based on the bit rate, sample rate, and number of full-bandwidth channels.
static const uint8_t	exp_strategy_reuse_tab [4][6]
	Table used to select exponent strategy based on exponent reuse block interval.