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FFmpeg
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Common code between the AC-3 encoder and decoder. More...
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... | |
Macros | |
| #define | AC3_MAX_CODED_FRAME_SIZE 3840 /* in bytes */ |
| #define | AC3_MAX_CHANNELS 7 |
| maximum number of channels, including coupling channel More... | |
| #define | CPL_CH 0 |
| coupling channel index More... | |
| #define | AC3_MAX_COEFS 256 |
| #define | AC3_BLOCK_SIZE 256 |
| #define | AC3_MAX_BLOCKS 6 |
| #define | AC3_FRAME_SIZE (AC3_MAX_BLOCKS * 256) |
| #define | AC3_WINDOW_SIZE (AC3_BLOCK_SIZE * 2) |
| #define | AC3_CRITICAL_BANDS 50 |
| #define | AC3_MAX_CPL_BANDS 18 |
| #define | EXP_REUSE 0 |
| #define | EXP_NEW 1 |
| #define | EXP_D15 1 |
| #define | EXP_D25 2 |
| #define | EXP_D45 3 |
| #define | LEVEL_PLUS_3DB 1.4142135623730950 |
| #define | LEVEL_PLUS_1POINT5DB 1.1892071150027209 |
| #define | LEVEL_MINUS_1POINT5DB 0.8408964152537145 |
| #define | LEVEL_MINUS_3DB 0.7071067811865476 |
| #define | LEVEL_MINUS_4POINT5DB 0.5946035575013605 |
| #define | LEVEL_MINUS_6DB 0.5000000000000000 |
| #define | LEVEL_MINUS_9DB 0.3535533905932738 |
| #define | LEVEL_ZERO 0.0000000000000000 |
| #define | LEVEL_ONE 1.0000000000000000 |
Typedefs | |
| typedef struct AC3BitAllocParameters | AC3BitAllocParameters |
| typedef struct AC3HeaderInfo | AC3HeaderInfo |
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 | ff_ac3_common_init (void) |
| Initialize some tables. More... | |
| 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. More... | |
| 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. More... | |
Detailed Description
Common code between the AC-3 encoder and decoder.
Definition in file ac3.h.
Macro Definition Documentation
| #define AC3_BLOCK_SIZE 256 |
Definition at line 35 of file ac3.h.
Referenced by ac3_decode_frame(), allocate_sample_buffers(), apply_mdct(), copy_input_samples(), ff_ac3_adjust_frame_size(), ff_ac3_encode_init(), and validate_options().
| #define AC3_CRITICAL_BANDS 50 |
Definition at line 39 of file ac3.h.
Referenced by ff_ac3_bit_alloc_calc_mask(), and ff_ac3_common_init().
| #define AC3_FRAME_SIZE (AC3_MAX_BLOCKS * 256) |
Definition at line 37 of file ac3.h.
Referenced by allocate_sample_buffers(), spdif_get_offset_and_codec(), spdif_header_ac3(), and validate_options().
| #define AC3_MAX_BLOCKS 6 |
Definition at line 36 of file ac3.h.
Referenced by ac3_compute_mantissa_size_c(), apply_channel_coupling(), count_mantissa_bits(), and count_mantissa_bits_init().
| #define AC3_MAX_CHANNELS 7 |
maximum number of channels, including coupling channel
Definition at line 31 of file ac3.h.
Referenced by ac3_decode_frame(), ac3_decode_init(), apply_channel_coupling(), decode_audio_block(), ff_eac3_set_cpl_states(), and set_channel_info().
| #define AC3_MAX_CODED_FRAME_SIZE 3840 /* in bytes */ |
Definition at line 30 of file ac3.h.
Referenced by ff_ac3_output_frame().
| #define AC3_MAX_COEFS 256 |
Definition at line 34 of file ac3.h.
Referenced by ac3_bit_alloc_calc_bap_c(), allocate_buffers(), compute_exp_strategy(), encode_exponents(), encode_frame(), extract_exponents(), ff_eac3_decode_transform_coeffs_aht_ch(), reset_block_bap(), scale_coefficients(), and set_bandwidth().
| #define AC3_WINDOW_SIZE (AC3_BLOCK_SIZE * 2) |
Definition at line 38 of file ac3.h.
Referenced by allocate_sample_buffers(), apply_mdct(), and normalize_samples().
| #define CPL_CH 0 |
coupling channel index
Definition at line 32 of file ac3.h.
Referenced by ac3_decode_transform_coeffs_ch(), apply_channel_coupling(), calc_transform_coeffs_cpl(), compute_exp_strategy(), compute_rematrixing_strategy(), count_exponent_bits(), count_mantissa_bits_update_ch(), decode_audio_block(), decode_transform_coeffs(), encode_exponents(), ff_ac3_compute_coupling_strategy(), ff_ac3_group_exponents(), ff_ac3_quantize_mantissas(), ff_eac3_parse_header(), output_audio_block(), remove_dithering(), and set_bandwidth().
| #define EXP_D15 1 |
Definition at line 50 of file ac3.h.
Referenced by compute_exp_strategy(), and exponent_init().
| #define EXP_D25 2 |
Definition at line 51 of file ac3.h.
Referenced by encode_exponents_blk_ch().
| #define EXP_D45 3 |
Definition at line 52 of file ac3.h.
Referenced by decode_exponents(), encode_exponents_blk_ch(), exponent_init(), and ff_ac3_group_exponents().
| #define EXP_NEW 1 |
Definition at line 48 of file ac3.h.
Referenced by compute_exp_strategy().
| #define EXP_REUSE 0 |
Definition at line 47 of file ac3.h.
Referenced by bit_alloc(), bit_alloc_masking(), compute_exp_strategy(), count_exponent_bits(), count_frame_bits(), decode_audio_block(), encode_exponents(), ff_ac3_group_exponents(), ff_eac3_parse_header(), and output_audio_block().
| #define LEVEL_MINUS_3DB 0.7071067811865476 |
Definition at line 58 of file ac3.h.
Referenced by ac3_decode_frame(), and set_downmix_coeffs().
Typedef Documentation
| typedef struct AC3BitAllocParameters AC3BitAllocParameters |
| typedef struct AC3HeaderInfo AC3HeaderInfo |
Enumeration Type Documentation
| enum AC3ChannelMode |
| enum AC3DeltaStrategy |
| enum EAC3FrameType |
Function Documentation
| 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 123 of file ac3.c.
Referenced by 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 | ||
| ) |
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 97 of file ac3.c.
Referenced by bit_alloc_masking(), and decode_audio_block().
Initialize some tables.
note: This function must remain thread safe because it is called by the AVParser init code.
Definition at line 220 of file ac3.c.
Referenced by ac3_decode_init(), and ff_ac3_encode_init().
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