ac3dec.c File Reference

#include <stdio.h>
#include <stddef.h>
#include <math.h>
#include <string.h>
#include "libavutil/crc.h"
#include "libavutil/random.h"
#include "avcodec.h"
#include "ac3_parser.h"
#include "bitstream.h"
#include "dsputil.h"
#include "ac3dec.h"
#include "ac3dec_data.h"

Go to the source code of this file.

Data Structures
struct	mant_groups
Defines
#define	AC3_MAX_FRAME_SIZE   21695
#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
Functions
static int	symmetric_dequant (int code, int levels)
static av_cold void	ac3_tables_init (void)
static av_cold int	ac3_decode_init (AVCodecContext *avctx)
static int	ac3_parse_header (AC3DecodeContext *s)
static int	parse_frame_header (AC3DecodeContext *s)
static void	set_downmix_coeffs (AC3DecodeContext *s)
static void	decode_exponents (GetBitContext *gbc, int exp_strategy, int ngrps, uint8_t absexp, int8_t *dexps)
static void	uncouple_channels (AC3DecodeContext *s)
static void	get_transform_coeffs_ch (AC3DecodeContext *s, int ch_index, mant_groups *m)
static void	remove_dithering (AC3DecodeContext *s)
static void	get_transform_coeffs (AC3DecodeContext *s)
static void	do_rematrixing (AC3DecodeContext *s)
static void	do_imdct_256 (AC3DecodeContext *s, int chindex)
static void	do_imdct (AC3DecodeContext *s, int channels)
static void	ac3_downmix (AC3DecodeContext *s, float samples[AC3_MAX_CHANNELS][256], int ch_offset)
static void	ac3_upmix_delay (AC3DecodeContext *s)
static int	ac3_parse_audio_block (AC3DecodeContext *s, int blk)
static int	ac3_decode_frame (AVCodecContext *avctx, void *data, int *data_size, const uint8_t *buf, int buf_size)
static av_cold int	ac3_decode_end (AVCodecContext *avctx)
Variables
static uint8_t	exp_ungroup_tab [128][3]
static int	b1_mantissas [32][3]
static int	b2_mantissas [128][3]
static int	b3_mantissas [8]
static int	b4_mantissas [128][2]
static int	b5_mantissas [16]
static const uint8_t	quantization_tab [16]
static float	dynamic_range_tab [256]
static const float	gain_levels [9]
static const uint8_t	center_levels [4] = { 4, 5, 6, 5 }
static const uint8_t	surround_levels [4] = { 4, 6, 7, 6 }
static const uint8_t	ac3_default_coeffs [8][5][2]
AVCodec	ac3_decoder

---

Define Documentation

#define AC3_MAX_FRAME_SIZE   21695

Maximum possible frame size when the specification limit is ignored

Definition at line 45 of file ac3dec.c.

Referenced by ac3_decode_frame(), and ac3_decode_init().

#define LEVEL_MINUS_1POINT5DB   0.8408964152537145

Definition at line 73 of file ac3dec.c.

#define LEVEL_MINUS_3DB   0.7071067811865476

Definition at line 74 of file ac3dec.c.

Referenced by ac3_downmix().

#define LEVEL_MINUS_4POINT5DB   0.5946035575013605

Definition at line 75 of file ac3dec.c.

#define LEVEL_MINUS_6DB   0.5000000000000000

Definition at line 76 of file ac3dec.c.

#define LEVEL_MINUS_9DB   0.3535533905932738

Definition at line 77 of file ac3dec.c.

#define LEVEL_ONE   1.0000000000000000

Definition at line 79 of file ac3dec.c.

#define LEVEL_PLUS_1POINT5DB   1.1892071150027209

Definition at line 72 of file ac3dec.c.

#define LEVEL_PLUS_3DB   1.4142135623730950

Adjustments in dB gain

Definition at line 71 of file ac3dec.c.

#define LEVEL_ZERO   0.0000000000000000

Definition at line 78 of file ac3dec.c.

---

Function Documentation

static av_cold int ac3_decode_end

(

AVCodecContext *

avctx

)

[static]

Uninitialize the AC-3 decoder.

Definition at line 1182 of file ac3dec.c.

References av_freep(), ff_mdct_end(), AC3DecodeContext::imdct_256, AC3DecodeContext::imdct_512, AC3DecodeContext::input_buffer, and AVCodecContext::priv_data.

{
    AC3DecodeContext *s = avctx->priv_data;
    ff_mdct_end(&s->imdct_512);
    ff_mdct_end(&s->imdct_256);

    av_freep(&s->input_buffer);

    return 0;
}

static int ac3_decode_frame	(	AVCodecContext *	avctx,
		void *	data,
		int *	data_size,
		const uint8_t *	buf,
		int	buf_size
	)			[static]

Decode a single AC-3 frame.

Definition at line 1071 of file ac3dec.c.

References AC3_CHMODE_MONO, AC3_CHMODE_STEREO, AC3_MAX_FRAME_SIZE, AC3_OUTPUT_LFEON, ac3_parse_audio_block(), AC3_PARSE_ERROR_BSID, AC3_PARSE_ERROR_CRC, AC3_PARSE_ERROR_FRAME_SIZE, AC3_PARSE_ERROR_FRAME_TYPE, AC3_PARSE_ERROR_SAMPLE_RATE, AC3_PARSE_ERROR_SYNC, av_crc(), AV_CRC_16_ANSI, av_crc_get_table(), av_log(), AV_LOG_ERROR, AC3DecodeContext::bit_rate, AVCodecContext::bit_rate, blk, AC3DecodeContext::channel_mode, AVCodecContext::channels, AC3DecodeContext::channels, EAC3_FRAME_TYPE_DEPENDENT, AVCodecContext::error_resilience, AC3DecodeContext::fbw_channels, FF_ER_CAREFUL, FFMIN, AC3DecodeContext::frame_size, AC3DecodeContext::frame_type, AC3DecodeContext::gbc, init_get_bits(), AC3DecodeContext::input_buffer, AC3DecodeContext::lfe_on, AC3DecodeContext::num_blocks, AC3DecodeContext::out_channels, AC3DecodeContext::output_mode, parse_frame_header(), AVCodecContext::priv_data, AVCodecContext::request_channels, AC3DecodeContext::sample_rate, AVCodecContext::sample_rate, set_downmix_coeffs(), and AC3DecodeContext::substreamid.

{
    AC3DecodeContext *s = avctx->priv_data;
    int16_t *out_samples = (int16_t *)data;
    int i, blk, ch, err;

    /* initialize the GetBitContext with the start of valid AC-3 Frame */
    if (s->input_buffer) {
        /* copy input buffer to decoder context to avoid reading past the end
           of the buffer, which can be caused by a damaged input stream. */
        memcpy(s->input_buffer, buf, FFMIN(buf_size, AC3_MAX_FRAME_SIZE));
        init_get_bits(&s->gbc, s->input_buffer, buf_size * 8);
    } else {
        init_get_bits(&s->gbc, buf, buf_size * 8);
    }

    /* parse the syncinfo */
    *data_size = 0;
    err = parse_frame_header(s);

    /* check that reported frame size fits in input buffer */
    if(s->frame_size > buf_size) {
        av_log(avctx, AV_LOG_ERROR, "incomplete frame\n");
        err = AC3_PARSE_ERROR_FRAME_SIZE;
    }

    /* check for crc mismatch */
    if(err != AC3_PARSE_ERROR_FRAME_SIZE && avctx->error_resilience >= FF_ER_CAREFUL) {
        if(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, &buf[2], s->frame_size-2)) {
            av_log(avctx, AV_LOG_ERROR, "frame CRC mismatch\n");
            err = AC3_PARSE_ERROR_CRC;
        }
    }

    if(err && err != AC3_PARSE_ERROR_CRC) {
        switch(err) {
            case AC3_PARSE_ERROR_SYNC:
                av_log(avctx, AV_LOG_ERROR, "frame sync error\n");
                return -1;
            case AC3_PARSE_ERROR_BSID:
                av_log(avctx, AV_LOG_ERROR, "invalid bitstream id\n");
                break;
            case AC3_PARSE_ERROR_SAMPLE_RATE:
                av_log(avctx, AV_LOG_ERROR, "invalid sample rate\n");
                break;
            case AC3_PARSE_ERROR_FRAME_SIZE:
                av_log(avctx, AV_LOG_ERROR, "invalid frame size\n");
                break;
            case AC3_PARSE_ERROR_FRAME_TYPE:
                /* skip frame if CRC is ok. otherwise use error concealment. */
                /* TODO: add support for substreams and dependent frames */
                if(s->frame_type == EAC3_FRAME_TYPE_DEPENDENT || s->substreamid) {
                    av_log(avctx, AV_LOG_ERROR, "unsupported frame type : skipping frame\n");
                    return s->frame_size;
                } else {
                    av_log(avctx, AV_LOG_ERROR, "invalid frame type\n");
                }
                break;
            default:
                av_log(avctx, AV_LOG_ERROR, "invalid header\n");
                break;
        }
    }

    /* if frame is ok, set audio parameters */
    if (!err) {
        avctx->sample_rate = s->sample_rate;
        avctx->bit_rate = s->bit_rate;

        /* channel config */
        s->out_channels = s->channels;
        s->output_mode = s->channel_mode;
        if(s->lfe_on)
            s->output_mode |= AC3_OUTPUT_LFEON;
        if (avctx->request_channels > 0 && avctx->request_channels <= 2 &&
                avctx->request_channels < s->channels) {
            s->out_channels = avctx->request_channels;
            s->output_mode  = avctx->request_channels == 1 ? AC3_CHMODE_MONO : AC3_CHMODE_STEREO;
        }
        avctx->channels = s->out_channels;

        /* set downmixing coefficients if needed */
        if(s->channels != s->out_channels && !((s->output_mode & AC3_OUTPUT_LFEON) &&
                s->fbw_channels == s->out_channels)) {
            set_downmix_coeffs(s);
        }
    } else if (!s->out_channels) {
        s->out_channels = avctx->channels;
        if(s->out_channels < s->channels)
            s->output_mode  = s->out_channels == 1 ? AC3_CHMODE_MONO : AC3_CHMODE_STEREO;
    }

    /* parse the audio blocks */
    for (blk = 0; blk < s->num_blocks; blk++) {
        if (!err && ac3_parse_audio_block(s, blk)) {
            av_log(avctx, AV_LOG_ERROR, "error parsing the audio block\n");
        }

        /* interleave output samples */
        for (i = 0; i < 256; i++)
            for (ch = 0; ch < s->out_channels; ch++)
                *(out_samples++) = s->int_output[ch][i];
    }
    *data_size = s->num_blocks * 256 * avctx->channels * sizeof (int16_t);
    return s->frame_size;
}

static av_cold int ac3_decode_init

(

AVCodecContext *

avctx

)

[static]

AVCodec initialization

Definition at line 187 of file ac3dec.c.

References ac3_common_init(), AC3_MAX_FRAME_SIZE, ac3_tables_init(), AC3DecodeContext::add_bias, av_init_random(), av_mallocz(), AC3DecodeContext::avctx, AVERROR_NOMEM, AVCodecContext::channels, AC3DecodeContext::dith_state, AC3DecodeContext::downmixed, AC3DecodeContext::dsp, dsputil_init(), AVCodecContext::error_resilience, FF_ER_CAREFUL, ff_float_to_int16_c(), FF_INPUT_BUFFER_PADDING_SIZE, ff_kbd_window_init(), ff_mdct_init(), DSPContext::float_to_int16, AC3DecodeContext::imdct_256, AC3DecodeContext::imdct_512, AC3DecodeContext::input_buffer, AC3DecodeContext::mul_bias, AVCodecContext::priv_data, and AVCodecContext::request_channels.

{
    AC3DecodeContext *s = avctx->priv_data;
    s->avctx = avctx;

    ac3_common_init();
    ac3_tables_init();
    ff_mdct_init(&s->imdct_256, 8, 1);
    ff_mdct_init(&s->imdct_512, 9, 1);
    ff_kbd_window_init(s->window, 5.0, 256);
    dsputil_init(&s->dsp, avctx);
    av_init_random(0, &s->dith_state);

    /* set bias values for float to int16 conversion */
    if(s->dsp.float_to_int16 == ff_float_to_int16_c) {
        s->add_bias = 385.0f;
        s->mul_bias = 1.0f;
    } else {
        s->add_bias = 0.0f;
        s->mul_bias = 32767.0f;
    }

    /* allow downmixing to stereo or mono */
    if (avctx->channels > 0 && avctx->request_channels > 0 &&
            avctx->request_channels < avctx->channels &&
            avctx->request_channels <= 2) {
        avctx->channels = avctx->request_channels;
    }
    s->downmixed = 1;

    /* allocate context input buffer */
    if (avctx->error_resilience >= FF_ER_CAREFUL) {
        s->input_buffer = av_mallocz(AC3_MAX_FRAME_SIZE + FF_INPUT_BUFFER_PADDING_SIZE);
        if (!s->input_buffer)
            return AVERROR_NOMEM;
    }

    return 0;
}

static void ac3_downmix	(	AC3DecodeContext *	s,
		float	samples[AC3_MAX_CHANNELS][256],
		int	ch_offset
	)			[static]

Downmix the output to mono or stereo.

Definition at line 659 of file ac3dec.c.

References AC3_CHMODE_MONO, AC3_CHMODE_STEREO, AC3DecodeContext::downmix_coeff_adjust, AC3DecodeContext::downmix_coeffs, AC3DecodeContext::fbw_channels, LEVEL_MINUS_3DB, AC3DecodeContext::output_mode, samples, and v0.

{
    int i, j;
    float v0, v1;

    for(i=0; i<256; i++) {
        v0 = v1 = 0.0f;
        for(j=0; j<s->fbw_channels; j++) {
            v0 += samples[j+ch_offset][i] * s->downmix_coeffs[j][0];
            v1 += samples[j+ch_offset][i] * s->downmix_coeffs[j][1];
        }
        v0 *= s->downmix_coeff_adjust[0];
        v1 *= s->downmix_coeff_adjust[1];
        if(s->output_mode == AC3_CHMODE_MONO) {
            samples[ch_offset][i] = (v0 + v1) * LEVEL_MINUS_3DB;
        } else if(s->output_mode == AC3_CHMODE_STEREO) {
            samples[  ch_offset][i] = v0;
            samples[1+ch_offset][i] = v1;
        }
    }
}

static int ac3_parse_audio_block	(	AC3DecodeContext *	s,
		int	blk
	)			[static]

Parse an audio block from AC-3 bitstream.

Definition at line 713 of file ac3dec.c.

References AC3_CHMODE_STEREO, AC3_MAX_CHANNELS, av_log(), AV_LOG_ERROR, AC3DecodeContext::avctx, AC3DecodeContext::block_switch, AC3DecodeContext::channel_in_cpl, AC3DecodeContext::channel_mode, AC3DecodeContext::cpl_band_struct, CPL_CH, AC3DecodeContext::cpl_coords, AC3DecodeContext::cpl_in_use, AC3DecodeContext::dither_all, AC3DecodeContext::dither_flag, AVCodecContext::drc_scale, AC3DecodeContext::dynamic_range, dynamic_range_tab, AC3DecodeContext::end_freq, AC3DecodeContext::fbw_channels, AC3DecodeContext::gbc, get_bits(), get_bits1(), AC3DecodeContext::num_cpl_bands, AC3DecodeContext::num_cpl_subbands, AC3DecodeContext::phase_flags, AC3DecodeContext::phase_flags_in_use, and AC3DecodeContext::start_freq.

Referenced by ac3_decode_frame().

{
    int fbw_channels = s->fbw_channels;
    int channel_mode = s->channel_mode;
    int i, bnd, seg, ch;
    int different_transforms;
    int downmix_output;
    int cpl_in_use;
    GetBitContext *gbc = &s->gbc;
    uint8_t bit_alloc_stages[AC3_MAX_CHANNELS];

    memset(bit_alloc_stages, 0, AC3_MAX_CHANNELS);

    /* block switch flags */
    different_transforms = 0;
    for (ch = 1; ch <= fbw_channels; ch++) {
        s->block_switch[ch] = get_bits1(gbc);
        if(ch > 1 && s->block_switch[ch] != s->block_switch[1])
            different_transforms = 1;
    }

    /* dithering flags */
    s->dither_all = 1;
    for (ch = 1; ch <= fbw_channels; ch++) {
        s->dither_flag[ch] = get_bits1(gbc);
        if(!s->dither_flag[ch])
            s->dither_all = 0;
    }

    /* dynamic range */
    i = !(s->channel_mode);
    do {
        if(get_bits1(gbc)) {
            s->dynamic_range[i] = ((dynamic_range_tab[get_bits(gbc, 8)]-1.0) *
                                  s->avctx->drc_scale)+1.0;
        } else if(blk == 0) {
            s->dynamic_range[i] = 1.0f;
        }
    } while(i--);

    /* coupling strategy */
    if (get_bits1(gbc)) {
        memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
        s->cpl_in_use[blk] = get_bits1(gbc);
        if (s->cpl_in_use[blk]) {
            /* coupling in use */
            int cpl_begin_freq, cpl_end_freq;

            if (channel_mode < AC3_CHMODE_STEREO) {
                av_log(s->avctx, AV_LOG_ERROR, "coupling not allowed in mono or dual-mono\n");
                return -1;
            }

            /* determine which channels are coupled */
            for (ch = 1; ch <= fbw_channels; ch++)
                s->channel_in_cpl[ch] = get_bits1(gbc);

            /* phase flags in use */
            if (channel_mode == AC3_CHMODE_STEREO)
                s->phase_flags_in_use = get_bits1(gbc);

            /* coupling frequency range and band structure */
            cpl_begin_freq = get_bits(gbc, 4);
            cpl_end_freq = get_bits(gbc, 4);
            if (3 + cpl_end_freq - cpl_begin_freq < 0) {
                av_log(s->avctx, AV_LOG_ERROR, "3+cplendf = %d < cplbegf = %d\n", 3+cpl_end_freq, cpl_begin_freq);
                return -1;
            }
            s->num_cpl_bands = s->num_cpl_subbands = 3 + cpl_end_freq - cpl_begin_freq;
            s->start_freq[CPL_CH] = cpl_begin_freq * 12 + 37;
            s->end_freq[CPL_CH] = cpl_end_freq * 12 + 73;
            for (bnd = 0; bnd < s->num_cpl_subbands - 1; bnd++) {
                if (get_bits1(gbc)) {
                    s->cpl_band_struct[bnd] = 1;
                    s->num_cpl_bands--;
                }
            }
            s->cpl_band_struct[s->num_cpl_subbands-1] = 0;
        } else {
            /* coupling not in use */
            for (ch = 1; ch <= fbw_channels; ch++)
                s->channel_in_cpl[ch] = 0;
        }
    } else if (!blk) {
        av_log(s->avctx, AV_LOG_ERROR, "new coupling strategy must be present in block 0\n");
        return -1;
    } else {
        s->cpl_in_use[blk] = s->cpl_in_use[blk-1];
    }
    cpl_in_use = s->cpl_in_use[blk];

    /* coupling coordinates */
    if (cpl_in_use) {
        int cpl_coords_exist = 0;

        for (ch = 1; ch <= fbw_channels; ch++) {
            if (s->channel_in_cpl[ch]) {
                if (get_bits1(gbc)) {
                    int master_cpl_coord, cpl_coord_exp, cpl_coord_mant;
                    cpl_coords_exist = 1;
                    master_cpl_coord = 3 * get_bits(gbc, 2);
                    for (bnd = 0; bnd < s->num_cpl_bands; bnd++) {
                        cpl_coord_exp = get_bits(gbc, 4);
                        cpl_coord_mant = get_bits(gbc, 4);
                        if (cpl_coord_exp == 15)
                            s->cpl_coords[ch][bnd] = cpl_coord_mant << 22;
                        else
                            s->cpl_coords[ch][bnd] = (cpl_coord_mant + 16) << 21;
                        s->cpl_coords[ch][bnd] >>= (cpl_coord_exp + master_cpl_coord);
                    }
                } else if (!blk) {
                    av_log(s->avctx, AV_LOG_ERROR, "new coupling coordinates must be present in block 0\n");
                    return -1;
                }
            }
        }
        /* phase flags */
        if (channel_mode == AC3_CHMODE_STEREO && cpl_coords_exist) {
            for (bnd = 0; bnd < s->num_cpl_bands; bnd++) {
                s->phase_flags[bnd] = s->phase_flags_in_use? get_bits1(gbc) : 0;
            }
        }
    }

    /* stereo rematrixing strategy and band structure */
    if (channel_mode == AC3_CHMODE_STEREO) {
        if (get_bits1(gbc)) {
            s->num_rematrixing_bands = 4;
            if(cpl_in_use && s->start_freq[CPL_CH] <= 61)
                s->num_rematrixing_bands -= 1 + (s->start_freq[CPL_CH] == 37);
            for(bnd=0; bnd<s->num_rematrixing_bands; bnd++)
                s->rematrixing_flags[bnd] = get_bits1(gbc);
        } else if (!blk) {
            av_log(s->avctx, AV_LOG_ERROR, "new rematrixing strategy must be present in block 0\n");
            return -1;
        }
    }

    /* exponent strategies for each channel */
    s->exp_strategy[blk][CPL_CH] = EXP_REUSE;
    s->exp_strategy[blk][s->lfe_ch] = EXP_REUSE;
    for (ch = !cpl_in_use; ch <= s->channels; ch++) {
        s->exp_strategy[blk][ch] = get_bits(gbc, 2 - (ch == s->lfe_ch));
        if(s->exp_strategy[blk][ch] != EXP_REUSE)
            bit_alloc_stages[ch] = 3;
    }

    /* channel bandwidth */
    for (ch = 1; ch <= fbw_channels; ch++) {
        s->start_freq[ch] = 0;
        if (s->exp_strategy[blk][ch] != EXP_REUSE) {
            int group_size;
            int prev = s->end_freq[ch];
            if (s->channel_in_cpl[ch])
                s->end_freq[ch] = s->start_freq[CPL_CH];
            else {
                int bandwidth_code = get_bits(gbc, 6);
                if (bandwidth_code > 60) {
                    av_log(s->avctx, AV_LOG_ERROR, "bandwidth code = %d > 60", bandwidth_code);
                    return -1;
                }
                s->end_freq[ch] = bandwidth_code * 3 + 73;
            }
            group_size = 3 << (s->exp_strategy[blk][ch] - 1);
            s->num_exp_groups[ch] = (s->end_freq[ch]+group_size-4) / group_size;
            if(blk > 0 && s->end_freq[ch] != prev)
                memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
        }
    }
    if (cpl_in_use && s->exp_strategy[blk][CPL_CH] != EXP_REUSE) {
        s->num_exp_groups[CPL_CH] = (s->end_freq[CPL_CH] - s->start_freq[CPL_CH]) /
                                    (3 << (s->exp_strategy[blk][CPL_CH] - 1));
    }

    /* decode exponents for each channel */
    for (ch = !cpl_in_use; ch <= s->channels; ch++) {
        if (s->exp_strategy[blk][ch] != EXP_REUSE) {
            s->dexps[ch][0] = get_bits(gbc, 4) << !ch;
            decode_exponents(gbc, s->exp_strategy[blk][ch],
                             s->num_exp_groups[ch], s->dexps[ch][0],
                             &s->dexps[ch][s->start_freq[ch]+!!ch]);
            if(ch != CPL_CH && ch != s->lfe_ch)
                skip_bits(gbc, 2); /* skip gainrng */
        }
    }

    /* bit allocation information */
    if (get_bits1(gbc)) {
        s->bit_alloc_params.slow_decay = ff_ac3_slow_decay_tab[get_bits(gbc, 2)] >> s->bit_alloc_params.sr_shift;
        s->bit_alloc_params.fast_decay = ff_ac3_fast_decay_tab[get_bits(gbc, 2)] >> s->bit_alloc_params.sr_shift;
        s->bit_alloc_params.slow_gain  = ff_ac3_slow_gain_tab[get_bits(gbc, 2)];
        s->bit_alloc_params.db_per_bit = ff_ac3_db_per_bit_tab[get_bits(gbc, 2)];
        s->bit_alloc_params.floor  = ff_ac3_floor_tab[get_bits(gbc, 3)];
        for(ch=!cpl_in_use; ch<=s->channels; ch++)
            bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
    } else if (!blk) {
        av_log(s->avctx, AV_LOG_ERROR, "new bit allocation info must be present in block 0\n");
        return -1;
    }

    /* signal-to-noise ratio offsets and fast gains (signal-to-mask ratios) */
    if (get_bits1(gbc)) {
        int csnr;
        csnr = (get_bits(gbc, 6) - 15) << 4;
        for (ch = !cpl_in_use; ch <= s->channels; ch++) { /* snr offset and fast gain */
            s->snr_offset[ch] = (csnr + get_bits(gbc, 4)) << 2;
            s->fast_gain[ch] = ff_ac3_fast_gain_tab[get_bits(gbc, 3)];
        }
        memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
    } else if (!blk) {
        av_log(s->avctx, AV_LOG_ERROR, "new snr offsets must be present in block 0\n");
        return -1;
    }

    /* coupling leak information */
    if (cpl_in_use) {
        if (get_bits1(gbc)) {
            s->bit_alloc_params.cpl_fast_leak = get_bits(gbc, 3);
            s->bit_alloc_params.cpl_slow_leak = get_bits(gbc, 3);
            bit_alloc_stages[CPL_CH] = FFMAX(bit_alloc_stages[CPL_CH], 2);
        } else if (!blk) {
            av_log(s->avctx, AV_LOG_ERROR, "new coupling leak info must be present in block 0\n");
            return -1;
        }
    }

    /* delta bit allocation information */
    if (get_bits1(gbc)) {
        /* delta bit allocation exists (strategy) */
        for (ch = !cpl_in_use; ch <= fbw_channels; ch++) {
            s->dba_mode[ch] = get_bits(gbc, 2);
            if (s->dba_mode[ch] == DBA_RESERVED) {
                av_log(s->avctx, AV_LOG_ERROR, "delta bit allocation strategy reserved\n");
                return -1;
            }
            bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
        }
        /* channel delta offset, len and bit allocation */
        for (ch = !cpl_in_use; ch <= fbw_channels; ch++) {
            if (s->dba_mode[ch] == DBA_NEW) {
                s->dba_nsegs[ch] = get_bits(gbc, 3);
                for (seg = 0; seg <= s->dba_nsegs[ch]; seg++) {
                    s->dba_offsets[ch][seg] = get_bits(gbc, 5);
                    s->dba_lengths[ch][seg] = get_bits(gbc, 4);
                    s->dba_values[ch][seg] = get_bits(gbc, 3);
                }
                /* run last 2 bit allocation stages if new dba values */
                bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
            }
        }
    } else if(blk == 0) {
        for(ch=0; ch<=s->channels; ch++) {
            s->dba_mode[ch] = DBA_NONE;
        }
    }

    /* Bit allocation */
    for(ch=!cpl_in_use; ch<=s->channels; ch++) {
        if(bit_alloc_stages[ch] > 2) {
            /* Exponent mapping into PSD and PSD integration */
            ff_ac3_bit_alloc_calc_psd(s->dexps[ch],
                                      s->start_freq[ch], s->end_freq[ch],
                                      s->psd[ch], s->band_psd[ch]);
        }
        if(bit_alloc_stages[ch] > 1) {
            /* Compute excitation function, Compute masking curve, and
               Apply delta bit allocation */
            ff_ac3_bit_alloc_calc_mask(&s->bit_alloc_params, s->band_psd[ch],
                                       s->start_freq[ch], s->end_freq[ch],
                                       s->fast_gain[ch], (ch == s->lfe_ch),
                                       s->dba_mode[ch], s->dba_nsegs[ch],
                                       s->dba_offsets[ch], s->dba_lengths[ch],
                                       s->dba_values[ch], s->mask[ch]);
        }
        if(bit_alloc_stages[ch] > 0) {
            /* Compute bit allocation */
            ff_ac3_bit_alloc_calc_bap(s->mask[ch], s->psd[ch],
                                      s->start_freq[ch], s->end_freq[ch],
                                      s->snr_offset[ch],
                                      s->bit_alloc_params.floor,
                                      ff_ac3_bap_tab, s->bap[ch]);
        }
    }

    /* unused dummy data */
    if (get_bits1(gbc)) {
        int skipl = get_bits(gbc, 9);
        while(skipl--)
            skip_bits(gbc, 8);
    }

    /* unpack the transform coefficients
       this also uncouples channels if coupling is in use. */
    get_transform_coeffs(s);

    /* recover coefficients if rematrixing is in use */
    if(s->channel_mode == AC3_CHMODE_STEREO)
        do_rematrixing(s);

    /* apply scaling to coefficients (headroom, dynrng) */
    for(ch=1; ch<=s->channels; ch++) {
        float gain = s->mul_bias / 4194304.0f;
        if(s->channel_mode == AC3_CHMODE_DUALMONO) {
            gain *= s->dynamic_range[ch-1];
        } else {
            gain *= s->dynamic_range[0];
        }
        for(i=0; i<256; i++) {
            s->transform_coeffs[ch][i] = s->fixed_coeffs[ch][i] * gain;
        }
    }

    /* downmix and MDCT. order depends on whether block switching is used for
       any channel in this block. this is because coefficients for the long
       and short transforms cannot be mixed. */
    downmix_output = s->channels != s->out_channels &&
                     !((s->output_mode & AC3_OUTPUT_LFEON) &&
                     s->fbw_channels == s->out_channels);
    if(different_transforms) {
        /* the delay samples have already been downmixed, so we upmix the delay
           samples in order to reconstruct all channels before downmixing. */
        if(s->downmixed) {
            s->downmixed = 0;
            ac3_upmix_delay(s);
        }

        do_imdct(s, s->channels);

        if(downmix_output) {
            ac3_downmix(s, s->output, 0);
        }
    } else {
        if(downmix_output) {
            ac3_downmix(s, s->transform_coeffs, 1);
        }

        if(!s->downmixed) {
            s->downmixed = 1;
            ac3_downmix(s, s->delay, 0);
        }

        do_imdct(s, s->out_channels);
    }

    /* convert float to 16-bit integer */
    for(ch=0; ch<s->out_channels; ch++) {
        for(i=0; i<256; i++) {
            s->output[ch][i] += s->add_bias;
        }
        s->dsp.float_to_int16(s->int_output[ch], s->output[ch], 256);
    }

    return 0;
}

static int ac3_parse_header

(

AC3DecodeContext *

s

)

[static]

Parse the 'sync info' and 'bit stream info' from the AC-3 bitstream. GetBitContext within AC3DecodeContext must point to start of the synchronized ac3 bitstream.

Definition at line 232 of file ac3dec.c.

References AC3DecodeContext::channel_mode, AC3DecodeContext::gbc, get_bits(), get_bits1(), and skip_bits().

Referenced by parse_frame_header().

{
    GetBitContext *gbc = &s->gbc;
    int i;

    /* read the rest of the bsi. read twice for dual mono mode. */
    i = !(s->channel_mode);
    do {
        skip_bits(gbc, 5); // skip dialog normalization
        if (get_bits1(gbc))
            skip_bits(gbc, 8); //skip compression
        if (get_bits1(gbc))
            skip_bits(gbc, 8); //skip language code
        if (get_bits1(gbc))
            skip_bits(gbc, 7); //skip audio production information
    } while (i--);

    skip_bits(gbc, 2); //skip copyright bit and original bitstream bit

    /* skip the timecodes (or extra bitstream information for Alternate Syntax)
       TODO: read & use the xbsi1 downmix levels */
    if (get_bits1(gbc))
        skip_bits(gbc, 14); //skip timecode1 / xbsi1
    if (get_bits1(gbc))
        skip_bits(gbc, 14); //skip timecode2 / xbsi2

    /* skip additional bitstream info */
    if (get_bits1(gbc)) {
        i = get_bits(gbc, 6);
        do {
            skip_bits(gbc, 8);
        } while(i--);
    }

    return 0;
}

static av_cold void ac3_tables_init

(

void

)

[static]

Definition at line 134 of file ac3dec.c.

References b1_mantissas, b2_mantissas, b3_mantissas, b4_mantissas, b5_mantissas, dynamic_range_tab, exp_ungroup_tab, and symmetric_dequant().

Referenced by ac3_decode_init().

{
    int i;

    /* generate grouped mantissa tables
       reference: Section 7.3.5 Ungrouping of Mantissas */
    for(i=0; i<32; i++) {
        /* bap=1 mantissas */
        b1_mantissas[i][0] = symmetric_dequant( i / 9     , 3);
        b1_mantissas[i][1] = symmetric_dequant((i % 9) / 3, 3);
        b1_mantissas[i][2] = symmetric_dequant((i % 9) % 3, 3);
    }
    for(i=0; i<128; i++) {
        /* bap=2 mantissas */
        b2_mantissas[i][0] = symmetric_dequant( i / 25     , 5);
        b2_mantissas[i][1] = symmetric_dequant((i % 25) / 5, 5);
        b2_mantissas[i][2] = symmetric_dequant((i % 25) % 5, 5);

        /* bap=4 mantissas */
        b4_mantissas[i][0] = symmetric_dequant(i / 11, 11);
        b4_mantissas[i][1] = symmetric_dequant(i % 11, 11);
    }
    /* generate ungrouped mantissa tables
       reference: Tables 7.21 and 7.23 */
    for(i=0; i<7; i++) {
        /* bap=3 mantissas */
        b3_mantissas[i] = symmetric_dequant(i, 7);
    }
    for(i=0; i<15; i++) {
        /* bap=5 mantissas */
        b5_mantissas[i] = symmetric_dequant(i, 15);
    }