ac3enc.c File Reference

The simplest AC-3 encoder. More...

#include <stdint.h>
#include "libavutil/attributes.h"
#include "libavutil/avassert.h"
#include "libavutil/avstring.h"
#include "libavutil/channel_layout.h"
#include "libavutil/crc.h"
#include "libavutil/internal.h"
#include "libavutil/opt.h"
#include "avcodec.h"
#include "internal.h"
#include "me_cmp.h"
#include "put_bits.h"
#include "audiodsp.h"
#include "ac3dsp.h"
#include "ac3.h"
#include "fft.h"
#include "ac3enc.h"
#include "eac3enc.h"

Go to the source code of this file.

Data Structures
struct	AC3Mant

Macros
#define	CMIXLEV_NUM_OPTIONS   3
#define	SURMIXLEV_NUM_OPTIONS   3
#define	EXTMIXLEV_NUM_OPTIONS   8
#define	EXP_DIFF_THRESHOLD   500
	Exponent Difference Threshold. More...
#define	CRC16_POLY   ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))
	CRC-16 Polynomial. More...
#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. More...
void	ff_ac3_compute_coupling_strategy (AC3EncodeContext *s)
	Set the initial coupling strategy parameters prior to coupling analysis. More...
void	ff_ac3_apply_rematrixing (AC3EncodeContext *s)
	Apply stereo rematrixing to coefficients based on rematrixing flags. More...
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. More...
static void	encode_exponents (AC3EncodeContext *s)
static int	count_exponent_bits (AC3EncodeContext *s)
void	ff_ac3_group_exponents (AC3EncodeContext *s)
	Group exponents. More...
void	ff_ac3_process_exponents (AC3EncodeContext *s)
	Calculate final exponents from the supplied MDCT coefficients and exponent shift. More...
static void	count_frame_bits_fixed (AC3EncodeContext *s)
static av_cold 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. More...
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. More...
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. More...
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. More...
static int	asym_quant (int c, int e, int qbits)
	Asymmetric quantization on 2^qbits levels. More...
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. More...
void	ff_ac3_quantize_mantissas (AC3EncodeContext *s)
	Quantize mantissas using coefficients, exponents, and bit allocation pointers. More...
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. More...
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. More...
av_cold int	ff_ac3_encode_close (AVCodecContext *avctx)
	Finalize encoding and free any memory allocated by the encoder. More...
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. More...
const uint64_t	ff_ac3_channel_layouts [19]
	List of supported channel layouts. More...
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. More...
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. More...
static const uint8_t	exp_strategy_reuse_tab [4][6]
	Table used to select exponent strategy based on exponent reuse block interval. More...

Detailed Description

The simplest AC-3 encoder.

Definition in file ac3enc.c.

Macro Definition Documentation

#define CMIXLEV_NUM_OPTIONS   3

Definition at line 54 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

#define SURMIXLEV_NUM_OPTIONS   3

Definition at line 59 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

#define EXTMIXLEV_NUM_OPTIONS   8

Definition at line 64 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

#define EXP_DIFF_THRESHOLD   500

Exponent Difference Threshold.

New exponents are sent if their SAD exceed this number.

Definition at line 342 of file ac3enc.c.

Referenced by compute_exp_strategy().

#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 FLT_OPTION_THRESHOLD   0.01

Definition at line 1791 of file ac3enc.c.

Referenced by validate_float_option().

Function Documentation

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 183 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 201 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 272 of file ac3enc.c.

Referenced by encode_frame().

static av_cold void exponent_init ( AC3EncodeContext *  s )

static

Definition at line 306 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

static void extract_exponents ( AC3EncodeContext *  s )

static

Definition at line 328 of file ac3enc.c.

Referenced by ff_ac3_process_exponents().

static void compute_exp_strategy ( AC3EncodeContext *  s )

static

Definition at line 358 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 424 of file ac3enc.c.

Referenced by encode_exponents().

static void encode_exponents ( AC3EncodeContext *  s )

static

Definition at line 497 of file ac3enc.c.

Referenced by ff_ac3_process_exponents().

static int count_exponent_bits ( AC3EncodeContext *  s )

static

Definition at line 547 of file ac3enc.c.

Referenced by ff_ac3_compute_bit_allocation().

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 579 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 637 of file ac3enc.c.

Referenced by encode_frame().

static void count_frame_bits_fixed ( AC3EncodeContext *  s )

static

Definition at line 653 of file ac3enc.c.

Referenced by bit_alloc_init().

static av_cold void bit_alloc_init ( AC3EncodeContext *  s )

static

Definition at line 759 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

static void count_frame_bits ( AC3EncodeContext *  s )

static

Definition at line 795 of file ac3enc.c.

Referenced by ff_ac3_compute_bit_allocation().

static void bit_alloc_masking ( AC3EncodeContext *  s )

static

Definition at line 941 of file ac3enc.c.

Referenced by ff_ac3_compute_bit_allocation().

static void reset_block_bap ( AC3EncodeContext *  s )

static

Definition at line 971 of file ac3enc.c.

Referenced by bit_alloc(), and cbr_bit_allocation().

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 996 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 1018 of file ac3enc.c.

Referenced by count_mantissa_bits().

static int count_mantissa_bits ( AC3EncodeContext *  s )

static

Definition at line 1038 of file ac3enc.c.

Referenced by bit_alloc().

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 1064 of file ac3enc.c.

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

static int cbr_bit_allocation ( AC3EncodeContext *  s )

static

Definition at line 1095 of file ac3enc.c.

Referenced by ff_ac3_compute_bit_allocation().

int ff_ac3_compute_bit_allocation

(

AC3EncodeContext *

s

)

Definition at line 1146 of file ac3enc.c.

Referenced by encode_frame().

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

inlinestatic

Symmetric quantization on 'levels' levels.

Parameters

c	unquantized coefficient
e	exponent
levels	number of quantization levels

Returns

quantized coefficient

Definition at line 1166 of file ac3enc.c.

Referenced by quantize_mantissas_blk_ch().

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

inlinestatic

Asymmetric quantization on 2^qbits levels.

Parameters

c	unquantized coefficient
e	exponent
qbits	number of quantization bits

Returns

quantized coefficient

Definition at line 1182 of file ac3enc.c.

Referenced by quantize_mantissas_blk_ch().

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 1206 of file ac3enc.c.

Referenced by ff_ac3_quantize_mantissas().

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 1300 of file ac3enc.c.

Referenced by encode_frame().

static void ac3_output_frame_header ( AC3EncodeContext *  s )

static

Definition at line 1329 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

static void output_audio_block ( AC3EncodeContext *  s, int  blk  )

static

Definition at line 1385 of file ac3enc.c.

Referenced by ff_ac3_output_frame().

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 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 output_frame_end ( AC3EncodeContext *  s )

static

Definition at line 1612 of file ac3enc.c.

Referenced by ff_ac3_output_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().

static void dprint_options ( AC3EncodeContext *  s )

static

Definition at line 1676 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

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().

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().

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().

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

static

Definition at line 2063 of file ac3enc.c.

Referenced by validate_options().

static av_cold int validate_options ( AC3EncodeContext *  s )

static

Definition at line 2108 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

static av_cold void set_bandwidth ( AC3EncodeContext *  s )

static

Definition at line 2253 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

static av_cold int allocate_buffers ( AC3EncodeContext *  s )

static

Definition at line 2323 of file ac3enc.c.

Referenced by ff_ac3_encode_init().

av_cold int ff_ac3_encode_init

(

AVCodecContext *

avctx

)

Definition at line 2425 of file ac3enc.c.

Referenced by ac3_fixed_encode_init(), and ff_ac3_float_encode_init().

Variable Documentation

const float cmixlev_options[CMIXLEV_NUM_OPTIONS]

static

Initial value:

= {
    LEVEL_MINUS_3DB, LEVEL_MINUS_4POINT5DB, LEVEL_MINUS_6DB
}

Definition at line 55 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

const float surmixlev_options[SURMIXLEV_NUM_OPTIONS]

static

Initial value:

= {
    LEVEL_MINUS_3DB, LEVEL_MINUS_6DB, LEVEL_ZERO
}

Definition at line 60 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

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 65 of file ac3enc.c.

Referenced by ff_ac3_validate_metadata().

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 75 of file ac3enc.c.

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

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 81 of file ac3enc.c.

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 109 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 142 of file ac3enc.c.

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 347 of file ac3enc.c.