#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... | |
Defines | |
| #define | AC3_MAX_CODED_FRAME_SIZE 3840 |
| #define | AC3_MAX_CHANNELS 6 |
| #define | NB_BLOCKS 6 |
| #define | AC3_FRAME_SIZE (NB_BLOCKS * 256) |
| #define | EXP_REUSE 0 |
| #define | EXP_NEW 1 |
| #define | EXP_D15 1 |
| #define | EXP_D25 2 |
| #define | EXP_D45 3 |
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 | 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 *band_psd) |
| Calculates 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) |
| Calculates the masking curve. | |
| void | ff_ac3_bit_alloc_calc_bap (int16_t *mask, int16_t *psd, int start, int end, int snr_offset, int floor, const uint8_t *bap_tab, 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 snr_offset, int fast_gain, int is_lfe, int dba_mode, int dba_nsegs, uint8_t *dba_offsets, uint8_t *dba_lengths, uint8_t *dba_values) |
Common code between the AC-3 and E-AC-3 decoders.
Definition in file ac3.h.
| #define AC3_FRAME_SIZE (NB_BLOCKS * 256) |
| #define AC3_MAX_CHANNELS 6 |
| #define AC3_MAX_CODED_FRAME_SIZE 3840 |
| #define EXP_D15 1 |
Definition at line 42 of file ac3.h.
Referenced by compute_exp_strategy(), encode_exp(), and output_audio_block().
| #define EXP_D25 2 |
Definition at line 43 of file ac3.h.
Referenced by compute_exp_strategy(), encode_exp(), and output_audio_block().
| #define EXP_D45 3 |
Definition at line 44 of file ac3.h.
Referenced by compute_exp_strategy(), decode_exponents(), encode_exp(), and output_audio_block().
| #define EXP_NEW 1 |
| #define EXP_REUSE 0 |
Definition at line 39 of file ac3.h.
Referenced by AC3_encode_frame(), bit_alloc_masking(), compute_bit_allocation(), compute_exp_strategy(), decode_audio_block(), ff_eac3_parse_header(), and output_audio_block().
| #define NB_BLOCKS 6 |
Definition at line 35 of file ac3.h.
Referenced by AC3_encode_frame(), bit_alloc(), bit_alloc_masking(), compute_bit_allocation(), and compute_exp_strategy().
| enum AC3ChannelMode |
| enum AC3DeltaStrategy |
| enum EAC3FrameType |
| 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 233 of file ac3.c.
Referenced by ac3_decode_init(), and AC3_encode_init().
| void ac3_parametric_bit_allocation | ( | AC3BitAllocParameters * | s, | |
| uint8_t * | bap, | |||
| int8_t * | exp, | |||
| int | start, | |||
| int | end, | |||
| int | snr_offset, | |||
| int | fast_gain, | |||
| int | is_lfe, | |||
| int | dba_mode, | |||
| int | dba_nsegs, | |||
| uint8_t * | dba_offsets, | |||
| uint8_t * | dba_lengths, | |||
| uint8_t * | dba_values | |||
| ) |
| void ff_ac3_bit_alloc_calc_bap | ( | int16_t * | mask, | |
| int16_t * | psd, | |||
| int | start, | |||
| int | end, | |||
| int | snr_offset, | |||
| int | floor, | |||
| const uint8_t * | bap_tab, | |||
| 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.
| [in] | mask | masking curve |
| [in] | psd | signal power for each frequency bin |
| [in] | start | starting bin location |
| [in] | end | ending bin location |
| [in] | snr_offset | SNR adjustment |
| [in] | floor | noise floor |
| [in] | bap_tab | look-up table for bit allocation pointers |
| [out] | bap | bit allocation pointers |
Definition at line 180 of file ac3.c.
Referenced by ac3_parametric_bit_allocation(), bit_alloc(), 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 | |||
| ) |
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.
| [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 |
Definition at line 83 of file ac3.c.
Referenced by ac3_parametric_bit_allocation(), bit_alloc_masking(), and decode_audio_block().
| void ff_ac3_bit_alloc_calc_psd | ( | int8_t * | exp, | |
| int | start, | |||
| int | end, | |||
| int16_t * | psd, | |||
| int16_t * | band_psd | |||
| ) |
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.
| [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 55 of file ac3.c.
Referenced by ac3_parametric_bit_allocation(), bit_alloc_masking(), and decode_audio_block().
1.5.8