PeerStreamer

/*

 * AC-3 Audio Decoder

 * This code was developed as part of Google Summer of Code 2006.

 * E-AC-3 support was added as part of Google Summer of Code 2007.

 *

 * Copyright (c) 2006 Kartikey Mahendra BHATT (bhattkm at gmail dot com)

 * Copyright (c) 2007-2008 Bartlomiej Wolowiec <bartek.wolowiec@gmail.com>

 * Copyright (c) 2007 Justin Ruggles <justin.ruggles@gmail.com>

 *

 * Portions of this code are derived from liba52

 * http://liba52.sourceforge.net

 * Copyright (C) 2000-2003 Michel Lespinasse <walken@zoy.org>

 * Copyright (C) 1999-2000 Aaron Holtzman <aholtzma@ess.engr.uvic.ca>

 *

 * This file is part of FFmpeg.

 *

 * FFmpeg is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public

 * License as published by the Free Software Foundation; either

 * version 2 of the License, or (at your option) any later version.

 *

 * FFmpeg is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * General Public License for more details.

 *

 * You should have received a copy of the GNU General Public

 * License along with FFmpeg; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

#include <stdio.h>

#include <stddef.h>

#include <math.h>

#include <string.h>

#include "libavutil/crc.h"

#include "internal.h"

#include "aac_ac3_parser.h"

#include "ac3_parser.h"

#include "ac3dec.h"

#include "ac3dec_data.h"

/** Large enough for maximum possible frame size when the specification limit is ignored */

#define AC3_FRAME_BUFFER_SIZE 32768

/**

 * table for ungrouping 3 values in 7 bits.

 * used for exponents and bap=2 mantissas

 */

static uint8_t ungroup_3_in_7_bits_tab[128][3];

/** tables for ungrouping mantissas */

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];

/**

 * Quantization table: levels for symmetric. bits for asymmetric.

 * reference: Table 7.18 Mapping of bap to Quantizer

 */

static const uint8_t quantization_tab[16] = {

    0, 3, 5, 7, 11, 15,

    5, 6, 7, 8, 9, 10, 11, 12, 14, 16

};

/** dynamic range table. converts codes to scale factors. */

static float dynamic_range_tab[256];

/** Adjustments in dB gain */

#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

static const float gain_levels[9] = {

    LEVEL_PLUS_3DB,

    LEVEL_PLUS_1POINT5DB,

    LEVEL_ONE,

    LEVEL_MINUS_1POINT5DB,

    LEVEL_MINUS_3DB,

    LEVEL_MINUS_4POINT5DB,

    LEVEL_MINUS_6DB,

    LEVEL_ZERO,

    LEVEL_MINUS_9DB

};

/**

 * Table for center mix levels

 * reference: Section 5.4.2.4 cmixlev

 */

static const uint8_t center_levels[4] = { 4, 5, 6, 5 };

/**

 * Table for surround mix levels

 * reference: Section 5.4.2.5 surmixlev

 */

static const uint8_t surround_levels[4] = { 4, 6, 7, 6 };

/**

 * Table for default stereo downmixing coefficients

 * reference: Section 7.8.2 Downmixing Into Two Channels

 */

static const uint8_t ac3_default_coeffs[8][5][2] = {

    { { 2, 7 }, { 7, 2 },                               },

    { { 4, 4 },                                         },

    { { 2, 7 }, { 7, 2 },                               },

    { { 2, 7 }, { 5, 5 }, { 7, 2 },                     },

    { { 2, 7 }, { 7, 2 }, { 6, 6 },                     },

    { { 2, 7 }, { 5, 5 }, { 7, 2 }, { 8, 8 },           },

    { { 2, 7 }, { 7, 2 }, { 6, 7 }, { 7, 6 },           },

    { { 2, 7 }, { 5, 5 }, { 7, 2 }, { 6, 7 }, { 7, 6 }, },

};

/**

 * Symmetrical Dequantization

 * reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization

 *            Tables 7.19 to 7.23

 */

static inline int

symmetric_dequant(int code, int levels)

{

    return ((code - (levels >> 1)) << 24) / levels;

}

/*

 * Initialize tables at runtime.

 */

static av_cold void ac3_tables_init(void)

{

    int i;

    /* generate table for ungrouping 3 values in 7 bits

       reference: Section 7.1.3 Exponent Decoding */

    for(i=0; i<128; i++) {

        ungroup_3_in_7_bits_tab[i][0] =  i / 25;

        ungroup_3_in_7_bits_tab[i][1] = (i % 25) / 5;

        ungroup_3_in_7_bits_tab[i][2] = (i % 25) % 5;

    }

    /* 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(ff_ac3_ungroup_3_in_5_bits_tab[i][0], 3);

        b1_mantissas[i][1] = symmetric_dequant(ff_ac3_ungroup_3_in_5_bits_tab[i][1], 3);

        b1_mantissas[i][2] = symmetric_dequant(ff_ac3_ungroup_3_in_5_bits_tab[i][2], 3);

    }

    for(i=0; i<128; i++) {

        /* bap=2 mantissas */

        b2_mantissas[i][0] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][0], 5);

        b2_mantissas[i][1] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][1], 5);

        b2_mantissas[i][2] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][2], 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);

    }

    /* generate dynamic range table

       reference: Section 7.7.1 Dynamic Range Control */

    for(i=0; i<256; i++) {

        int v = (i >> 5) - ((i >> 7) << 3) - 5;

        dynamic_range_tab[i] = powf(2.0f, v) * ((i & 0x1F) | 0x20);

    }

}

/**

 * AVCodec initialization

 */

static av_cold int ac3_decode_init(AVCodecContext *avctx)

{

    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_lfg_init(&s->dith_state, 0);

    /* set bias values for float to int16 conversion */

    if(s->dsp.float_to_int16_interleave == ff_float_to_int16_interleave_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_recognition >= FF_ER_CAREFUL) {

        s->input_buffer = av_mallocz(AC3_FRAME_BUFFER_SIZE + FF_INPUT_BUFFER_PADDING_SIZE);

        if (!s->input_buffer)

            return AVERROR_NOMEM;

    }

    avctx->sample_fmt = SAMPLE_FMT_S16;

    return 0;

}

/**

 * Parse the 'sync info' and 'bit stream info' from the AC-3 bitstream.

 * GetBitContext within AC3DecodeContext must point to

 * the start of the synchronized AC-3 bitstream.

 */

static int ac3_parse_header(AC3DecodeContext *s)

{

    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;

}

/**

 * Common function to parse AC-3 or E-AC-3 frame header

 */

static int parse_frame_header(AC3DecodeContext *s)

{

    AC3HeaderInfo hdr;

    int err;

    err = ff_ac3_parse_header(&s->gbc, &hdr);

    if(err)

        return err;

    /* get decoding parameters from header info */

    s->bit_alloc_params.sr_code     = hdr.sr_code;

    s->channel_mode                 = hdr.channel_mode;

    s->channel_layout               = hdr.channel_layout;

    s->lfe_on                       = hdr.lfe_on;

    s->bit_alloc_params.sr_shift    = hdr.sr_shift;

    s->sample_rate                  = hdr.sample_rate;

    s->bit_rate                     = hdr.bit_rate;

    s->channels                     = hdr.channels;

    s->fbw_channels                 = s->channels - s->lfe_on;

    s->lfe_ch                       = s->fbw_channels + 1;

    s->frame_size                   = hdr.frame_size;

    s->center_mix_level             = hdr.center_mix_level;

    s->surround_mix_level           = hdr.surround_mix_level;

    s->num_blocks                   = hdr.num_blocks;

    s->frame_type                   = hdr.frame_type;

    s->substreamid                  = hdr.substreamid;

    if(s->lfe_on) {

        s->start_freq[s->lfe_ch] = 0;

        s->end_freq[s->lfe_ch] = 7;

        s->num_exp_groups[s->lfe_ch] = 2;

        s->channel_in_cpl[s->lfe_ch] = 0;

    }

    if (hdr.bitstream_id <= 10) {

        s->eac3                  = 0;

        s->snr_offset_strategy   = 2;

        s->block_switch_syntax   = 1;

        s->dither_flag_syntax    = 1;

        s->bit_allocation_syntax = 1;

        s->fast_gain_syntax      = 0;

        s->first_cpl_leak        = 0;

        s->dba_syntax            = 1;

        s->skip_syntax           = 1;

        memset(s->channel_uses_aht, 0, sizeof(s->channel_uses_aht));

        return ac3_parse_header(s);

    } else {

        s->eac3 = 1;

        return ff_eac3_parse_header(s);

    }

}

/**

 * Set stereo downmixing coefficients based on frame header info.

 * reference: Section 7.8.2 Downmixing Into Two Channels

 */

static void set_downmix_coeffs(AC3DecodeContext *s)

{

    int i;

    float cmix = gain_levels[center_levels[s->center_mix_level]];

    float smix = gain_levels[surround_levels[s->surround_mix_level]];

    float norm0, norm1;

    for(i=0; i<s->fbw_channels; i++) {

        s->downmix_coeffs[i][0] = gain_levels[ac3_default_coeffs[s->channel_mode][i][0]];

        s->downmix_coeffs[i][1] = gain_levels[ac3_default_coeffs[s->channel_mode][i][1]];

    }

    if(s->channel_mode > 1 && s->channel_mode & 1) {

        s->downmix_coeffs[1][0] = s->downmix_coeffs[1][1] = cmix;

    }

    if(s->channel_mode == AC3_CHMODE_2F1R || s->channel_mode == AC3_CHMODE_3F1R) {

        int nf = s->channel_mode - 2;

        s->downmix_coeffs[nf][0] = s->downmix_coeffs[nf][1] = smix * LEVEL_MINUS_3DB;

    }

    if(s->channel_mode == AC3_CHMODE_2F2R || s->channel_mode == AC3_CHMODE_3F2R) {

        int nf = s->channel_mode - 4;

        s->downmix_coeffs[nf][0] = s->downmix_coeffs[nf+1][1] = smix;

    }

    /* renormalize */

    norm0 = norm1 = 0.0;

    for(i=0; i<s->fbw_channels; i++) {

        norm0 += s->downmix_coeffs[i][0];

        norm1 += s->downmix_coeffs[i][1];

    }

    norm0 = 1.0f / norm0;

    norm1 = 1.0f / norm1;

    for(i=0; i<s->fbw_channels; i++) {

        s->downmix_coeffs[i][0] *= norm0;

        s->downmix_coeffs[i][1] *= norm1;

    }

    if(s->output_mode == AC3_CHMODE_MONO) {

        for(i=0; i<s->fbw_channels; i++)

            s->downmix_coeffs[i][0] = (s->downmix_coeffs[i][0] + s->downmix_coeffs[i][1]) * LEVEL_MINUS_3DB;

    }

}

/**

 * Decode the grouped exponents according to exponent strategy.

 * reference: Section 7.1.3 Exponent Decoding

 */

static int decode_exponents(GetBitContext *gbc, int exp_strategy, int ngrps,

                            uint8_t absexp, int8_t *dexps)

{

    int i, j, grp, group_size;

    int dexp[256];

    int expacc, prevexp;

    /* unpack groups */

    group_size = exp_strategy + (exp_strategy == EXP_D45);

    for(grp=0,i=0; grp<ngrps; grp++) {

        expacc = get_bits(gbc, 7);

        dexp[i++] = ungroup_3_in_7_bits_tab[expacc][0];

        dexp[i++] = ungroup_3_in_7_bits_tab[expacc][1];

        dexp[i++] = ungroup_3_in_7_bits_tab[expacc][2];

    }

    /* convert to absolute exps and expand groups */

    prevexp = absexp;

    for(i=0,j=0; i<ngrps*3; i++) {

        prevexp += dexp[i] - 2;

        if (prevexp > 24U)

            return -1;

        switch (group_size) {

            case 4: dexps[j++] = prevexp;

                    dexps[j++] = prevexp;

            case 2: dexps[j++] = prevexp;

            case 1: dexps[j++] = prevexp;

        }

    }

    return 0;

}

/**

 * Generate transform coefficients for each coupled channel in the coupling

 * range using the coupling coefficients and coupling coordinates.

 * reference: Section 7.4.3 Coupling Coordinate Format

 */

static void calc_transform_coeffs_cpl(AC3DecodeContext *s)

{

    int i, j, ch, bnd, subbnd;

    subbnd = -1;

    i = s->start_freq[CPL_CH];

    for(bnd=0; bnd<s->num_cpl_bands; bnd++) {

        do {

            subbnd++;

            for(j=0; j<12; j++) {

                for(ch=1; ch<=s->fbw_channels; ch++) {

                    if(s->channel_in_cpl[ch]) {

                        s->fixed_coeffs[ch][i] = ((int64_t)s->fixed_coeffs[CPL_CH][i] * (int64_t)s->cpl_coords[ch][bnd]) >> 23;

                        if (ch == 2 && s->phase_flags[bnd])

                            s->fixed_coeffs[ch][i] = -s->fixed_coeffs[ch][i];

                    }

                }

                i++;

            }

        } while(s->cpl_band_struct[subbnd]);

    }

}

/**

 * Grouped mantissas for 3-level 5-level and 11-level quantization

 */

typedef struct {

    int b1_mant[3];

    int b2_mant[3];

    int b4_mant[2];

    int b1ptr;

    int b2ptr;

    int b4ptr;

} mant_groups;

/**

 * Decode the transform coefficients for a particular channel

 * reference: Section 7.3 Quantization and Decoding of Mantissas

 */

static void ac3_decode_transform_coeffs_ch(AC3DecodeContext *s, int ch_index, mant_groups *m)

{

    GetBitContext *gbc = &s->gbc;

    int i, gcode, tbap, start, end;

    uint8_t *exps;

    uint8_t *bap;

    int *coeffs;

    exps = s->dexps[ch_index];

    bap = s->bap[ch_index];

    coeffs = s->fixed_coeffs[ch_index];

    start = s->start_freq[ch_index];

    end = s->end_freq[ch_index];

    for (i = start; i < end; i++) {

        tbap = bap[i];

        switch (tbap) {

            case 0:

                coeffs[i] = (av_lfg_get(&s->dith_state) & 0x7FFFFF) - 0x400000;

                break;

            case 1:

                if(m->b1ptr > 2) {

                    gcode = get_bits(gbc, 5);

                    m->b1_mant[0] = b1_mantissas[gcode][0];

                    m->b1_mant[1] = b1_mantissas[gcode][1];

                    m->b1_mant[2] = b1_mantissas[gcode][2];

                    m->b1ptr = 0;

                }

                coeffs[i] = m->b1_mant[m->b1ptr++];

                break;

            case 2:

                if(m->b2ptr > 2) {

                    gcode = get_bits(gbc, 7);

                    m->b2_mant[0] = b2_mantissas[gcode][0];

                    m->b2_mant[1] = b2_mantissas[gcode][1];

                    m->b2_mant[2] = b2_mantissas[gcode][2];

                    m->b2ptr = 0;

                }

                coeffs[i] = m->b2_mant[m->b2ptr++];

                break;

            case 3:

                coeffs[i] = b3_mantissas[get_bits(gbc, 3)];

                break;

            case 4:

                if(m->b4ptr > 1) {

                    gcode = get_bits(gbc, 7);

                    m->b4_mant[0] = b4_mantissas[gcode][0];

                    m->b4_mant[1] = b4_mantissas[gcode][1];

                    m->b4ptr = 0;

                }

                coeffs[i] = m->b4_mant[m->b4ptr++];

                break;

            case 5:

                coeffs[i] = b5_mantissas[get_bits(gbc, 4)];

                break;

            default: {

                /* asymmetric dequantization */

                int qlevel = quantization_tab[tbap];

                coeffs[i] = get_sbits(gbc, qlevel) << (24 - qlevel);

                break;

            }

        }

        coeffs[i] >>= exps[i];

    }

}

/**

 * Remove random dithering from coefficients with zero-bit mantissas

 * reference: Section 7.3.4 Dither for Zero Bit Mantissas (bap=0)

 */

static void remove_dithering(AC3DecodeContext *s) {

    int ch, i;

    int end=0;

    int *coeffs;

    uint8_t *bap;

    for(ch=1; ch<=s->fbw_channels; ch++) {

        if(!s->dither_flag[ch]) {

            coeffs = s->fixed_coeffs[ch];

            bap = s->bap[ch];

            if(s->channel_in_cpl[ch])

                end = s->start_freq[CPL_CH];

            else

                end = s->end_freq[ch];

            for(i=0; i<end; i++) {

                if(!bap[i])

                    coeffs[i] = 0;

            }

            if(s->channel_in_cpl[ch]) {

                bap = s->bap[CPL_CH];

                for(; i<s->end_freq[CPL_CH]; i++) {

                    if(!bap[i])

                        coeffs[i] = 0;

                }

            }

        }

    }

}

static void decode_transform_coeffs_ch(AC3DecodeContext *s, int blk, int ch,

                                    mant_groups *m)

{

    if (!s->channel_uses_aht[ch]) {

        ac3_decode_transform_coeffs_ch(s, ch, m);

    } else {

        /* if AHT is used, mantissas for all blocks are encoded in the first

           block of the frame. */

        int bin;

        if (!blk)

            ff_eac3_decode_transform_coeffs_aht_ch(s, ch);

        for (bin = s->start_freq[ch]; bin < s->end_freq[ch]; bin++) {

            s->fixed_coeffs[ch][bin] = s->pre_mantissa[ch][bin][blk] >> s->dexps[ch][bin];

        }

    }

}

/**

 * Decode the transform coefficients.

 */

static void decode_transform_coeffs(AC3DecodeContext *s, int blk)

{

    int ch, end;

    int got_cplchan = 0;

    mant_groups m;

    m.b1ptr = m.b2ptr = m.b4ptr = 3;

    for (ch = 1; ch <= s->channels; ch++) {

        /* transform coefficients for full-bandwidth channel */

        decode_transform_coeffs_ch(s, blk, ch, &m);

        /* tranform coefficients for coupling channel come right after the

           coefficients for the first coupled channel*/

        if (s->channel_in_cpl[ch])  {

            if (!got_cplchan) {

                decode_transform_coeffs_ch(s, blk, CPL_CH, &m);

                calc_transform_coeffs_cpl(s);

                got_cplchan = 1;

            }

            end = s->end_freq[CPL_CH];

        } else {

            end = s->end_freq[ch];

        }

        do

            s->fixed_coeffs[ch][end] = 0;

        while(++end < 256);

    }

    /* zero the dithered coefficients for appropriate channels */

    remove_dithering(s);

}

/**

 * Stereo rematrixing.

 * reference: Section 7.5.4 Rematrixing : Decoding Technique

 */

static void do_rematrixing(AC3DecodeContext *s)

{

    int bnd, i;

    int end, bndend;

    int tmp0, tmp1;

    end = FFMIN(s->end_freq[1], s->end_freq[2]);

    for(bnd=0; bnd<s->num_rematrixing_bands; bnd++) {

        if(s->rematrixing_flags[bnd]) {

            bndend = FFMIN(end, ff_ac3_rematrix_band_tab[bnd+1]);

            for(i=ff_ac3_rematrix_band_tab[bnd]; i<bndend; i++) {

                tmp0 = s->fixed_coeffs[1][i];

                tmp1 = s->fixed_coeffs[2][i];

                s->fixed_coeffs[1][i] = tmp0 + tmp1;

                s->fixed_coeffs[2][i] = tmp0 - tmp1;

            }

        }

    }

}

/**

 * Inverse MDCT Transform.

 * Convert frequency domain coefficients to time-domain audio samples.

 * reference: Section 7.9.4 Transformation Equations

 */

static inline void do_imdct(AC3DecodeContext *s, int channels)

{

    int ch;

    float add_bias = s->add_bias;

    if(s->out_channels==1 && channels>1)

        add_bias *= LEVEL_MINUS_3DB; // compensate for the gain in downmix

    for (ch=1; ch<=channels; ch++) {

        if (s->block_switch[ch]) {

            int i;

            float *x = s->tmp_output+128;

            for(i=0; i<128; i++)

                x[i] = s->transform_coeffs[ch][2*i];

            ff_imdct_half(&s->imdct_256, s->tmp_output, x);

            s->dsp.vector_fmul_window(s->output[ch-1], s->delay[ch-1], s->tmp_output, s->window, add_bias, 128);

            for(i=0; i<128; i++)

                x[i] = s->transform_coeffs[ch][2*i+1];

            ff_imdct_half(&s->imdct_256, s->delay[ch-1], x);

        } else {

            ff_imdct_half(&s->imdct_512, s->tmp_output, s->transform_coeffs[ch]);

            s->dsp.vector_fmul_window(s->output[ch-1], s->delay[ch-1], s->tmp_output, s->window, add_bias, 128);

            memcpy(s->delay[ch-1], s->tmp_output+128, 128*sizeof(float));

        }

    }

}

/**

 * Downmix the output to mono or stereo.

 */

void ff_ac3_downmix_c(float (*samples)[256], float (*matrix)[2], int out_ch, int in_ch, int len)

{

    int i, j;

    float v0, v1;

    if(out_ch == 2) {

        for(i=0; i<len; i++) {

            v0 = v1 = 0.0f;

            for(j=0; j<in_ch; j++) {

                v0 += samples[j][i] * matrix[j][0];

                v1 += samples[j][i] * matrix[j][1];

            }

            samples[0][i] = v0;

            samples[1][i] = v1;

        }

    } else if(out_ch == 1) {

        for(i=0; i<len; i++) {

            v0 = 0.0f;

            for(j=0; j<in_ch; j++)

                v0 += samples[j][i] * matrix[j][0];

            samples[0][i] = v0;

        }

    }

}

/**

 * Upmix delay samples from stereo to original channel layout.

 */

static void ac3_upmix_delay(AC3DecodeContext *s)

{

    int channel_data_size = sizeof(s->delay[0]);

    switch(s->channel_mode) {

        case AC3_CHMODE_DUALMONO:

        case AC3_CHMODE_STEREO:

            /* upmix mono to stereo */

            memcpy(s->delay[1], s->delay[0], channel_data_size);

            break;

        case AC3_CHMODE_2F2R:

            memset(s->delay[3], 0, channel_data_size);

        case AC3_CHMODE_2F1R:

            memset(s->delay[2], 0, channel_data_size);

            break;

        case AC3_CHMODE_3F2R:

            memset(s->delay[4], 0, channel_data_size);

        case AC3_CHMODE_3F1R:

            memset(s->delay[3], 0, channel_data_size);

        case AC3_CHMODE_3F:

            memcpy(s->delay[2], s->delay[1], channel_data_size);

            memset(s->delay[1], 0, channel_data_size);

            break;

    }

}

/**

 * Decode band structure for coupling, spectral extension, or enhanced coupling.

 * @param[in] gbc bit reader context

 * @param[in] blk block number

 * @param[in] eac3 flag to indicate E-AC-3

 * @param[in] ecpl flag to indicate enhanced coupling

 * @param[in] start_subband subband number for start of range

 * @param[in] end_subband subband number for end of range

 * @param[in] default_band_struct default band structure table

 * @param[out] band_struct decoded band structure

 * @param[out] num_subbands number of subbands (optionally NULL)

 * @param[out] num_bands number of bands (optionally NULL)

 * @param[out] band_sizes array containing the number of bins in each band (optionally NULL)

 */

static void decode_band_structure(GetBitContext *gbc, int blk, int eac3,

                                  int ecpl, int start_subband, int end_subband,

                                  const uint8_t *default_band_struct,

                                  uint8_t *band_struct, int *num_subbands,

                                  int *num_bands, uint8_t *band_sizes)

{

    int subbnd, bnd, n_subbands, n_bands=0;

    uint8_t bnd_sz[22];

    n_subbands = end_subband - start_subband;

    /* decode band structure from bitstream or use default */

    if (!eac3 || get_bits1(gbc)) {

        for (subbnd = 0; subbnd < n_subbands - 1; subbnd++) {

            band_struct[subbnd] = get_bits1(gbc);

        }

    } else if (!blk) {

        memcpy(band_struct,

               &default_band_struct[start_subband+1],

               n_subbands-1);

    }

    band_struct[n_subbands-1] = 0;

    /* calculate number of bands and band sizes based on band structure.

       note that the first 4 subbands in enhanced coupling span only 6 bins

       instead of 12. */

    if (num_bands || band_sizes ) {

        n_bands = n_subbands;

        bnd_sz[0] = ecpl ? 6 : 12;

        for (bnd = 0, subbnd = 1; subbnd < n_subbands; subbnd++) {

            int subbnd_size = (ecpl && subbnd < 4) ? 6 : 12;

            if (band_struct[subbnd-1]) {

                n_bands--;

                bnd_sz[bnd] += subbnd_size;

            } else {

                bnd_sz[++bnd] = subbnd_size;

            }

        }

    }

    /* set optional output params */

    if (num_subbands)

        *num_subbands = n_subbands;

    if (num_bands)

        *num_bands = n_bands;

    if (band_sizes)

        memcpy(band_sizes, bnd_sz, n_bands);

}

/**

 * Decode a single audio block from the AC-3 bitstream.

 */

static int decode_audio_block(AC3DecodeContext *s, int blk)

{

    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;

    if (s->block_switch_syntax) {

        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 */

    if (s->dither_flag_syntax) {

        for (ch = 1; ch <= fbw_channels; ch++) {

            s->dither_flag[ch] = get_bits1(gbc);

        }

    }

    /* 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--);

    /* spectral extension strategy */

    if (s->eac3 && (!blk || get_bits1(gbc))) {

        if (get_bits1(gbc)) {

            ff_log_missing_feature(s->avctx, "Spectral extension", 1);

            return -1;

        }

        /* TODO: parse spectral extension strategy info */

    }

    /* TODO: spectral extension coordinates */

    /* coupling strategy */

    if (s->eac3 ? s->cpl_strategy_exists[blk] : get_bits1(gbc)) {

        memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);

        if (!s->eac3)

            s->cpl_in_use[blk] = get_bits1(gbc);

        if (s->cpl_in_use[blk]) {

            /* coupling in use */

            int cpl_start_subband, cpl_end_subband;

            if (channel_mode < AC3_CHMODE_STEREO) {

                av_log(s->avctx, AV_LOG_ERROR, "coupling not allowed in mono or dual-mono\n");

                return -1;

            }

            /* check for enhanced coupling */

            if (s->eac3 && get_bits1(gbc)) {

                /* TODO: parse enhanced coupling strategy info */

                ff_log_missing_feature(s->avctx, "Enhanced coupling", 1);

                return -1;

            }

            /* determine which channels are coupled */

            if (s->eac3 && s->channel_mode == AC3_CHMODE_STEREO) {

                s->channel_in_cpl[1] = 1;

                s->channel_in_cpl[2] = 1;

            } else {

                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 */

            /* TODO: modify coupling end freq if spectral extension is used */

            cpl_start_subband = get_bits(gbc, 4);

            cpl_end_subband   = get_bits(gbc, 4) + 3;

            s->num_cpl_subbands = cpl_end_subband - cpl_start_subband;

            if (s->num_cpl_subbands < 0) {

                av_log(s->avctx, AV_LOG_ERROR, "invalid coupling range (%d > %d)\n",

                       cpl_start_subband, cpl_end_subband);

                return -1;

            }

            s->start_freq[CPL_CH] = cpl_start_subband * 12 + 37;

            s->end_freq[CPL_CH]   = cpl_end_subband   * 12 + 37;

           decode_band_structure(gbc, blk, s->eac3, 0,

                                 cpl_start_subband, cpl_end_subband,

                                 ff_eac3_default_cpl_band_struct,

                                 s->cpl_band_struct, &s->num_cpl_subbands,

                                 &s->num_cpl_bands, NULL);

        } else {

            /* coupling not in use */

            for (ch = 1; ch <= fbw_channels; ch++) {

                s->channel_in_cpl[ch] = 0;

                s->first_cpl_coords[ch] = 1;

            }

            s->first_cpl_leak = s->eac3;

            s->phase_flags_in_use = 0;

        }

    } else if (!s->eac3) {

        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 ((s->eac3 && s->first_cpl_coords[ch]) || get_bits1(gbc)) {

                    int master_cpl_coord, cpl_coord_exp, cpl_coord_mant;

                    s->first_cpl_coords[ch] = 0;

                    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;

                }

            } else {

                /* channel not in coupling */

                s->first_cpl_coords[ch] = 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 ((s->eac3 && !blk) || 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 */

    for (ch = !cpl_in_use; ch <= s->channels; ch++) {

        if (!s->eac3)

            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\n", 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;

            if (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])) {

                av_log(s->avctx, AV_LOG_ERROR, "exponent out-of-range\n");

                return -1;

            }

            if(ch != CPL_CH && ch != s->lfe_ch)

                skip_bits(gbc, 2); /* skip gainrng */

        }

    }

    /* bit allocation information */

    if (s->bit_allocation_syntax) {

        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(!s->eac3 || !blk){

        if(s->snr_offset_strategy && get_bits1(gbc)) {

            int snr = 0;

            int csnr;

            csnr = (get_bits(gbc, 6) - 15) << 4;

            for (i = ch = !cpl_in_use; ch <= s->channels; ch++) {

                /* snr offset */

                if (ch == i || s->snr_offset_strategy == 2)

                    snr = (csnr + get_bits(gbc, 4)) << 2;

                /* run at least last bit allocation stage if snr offset changes */

                if(blk && s->snr_offset[ch] != snr) {

                    bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 1);

                }

                s->snr_offset[ch] = snr;

                /* fast gain (normal AC-3 only) */

                if (!s->eac3) {

                    int prev = s->fast_gain[ch];

                    s->fast_gain[ch] = ff_ac3_fast_gain_tab[get_bits(gbc, 3)];

                    /* run last 2 bit allocation stages if fast gain changes */

                    if(blk && prev != s->fast_gain[ch])

                        bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);

                }

            }

        } else if (!s->eac3 && !blk) {

            av_log(s->avctx, AV_LOG_ERROR, "new snr offsets must be present in block 0\n");

            return -1;

        }

    }

    /* fast gain (E-AC-3 only) */

    if (s->fast_gain_syntax && get_bits1(gbc)) {

        for (ch = !cpl_in_use; ch <= s->channels; ch++) {

            int prev = s->fast_gain[ch];

            s->fast_gain[ch] = ff_ac3_fast_gain_tab[get_bits(gbc, 3)];

            /* run last 2 bit allocation stages if fast gain changes */

            if(blk && prev != s->fast_gain[ch])

                bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);

        }

    } else if (s->eac3 && !blk) {

        for (ch = !cpl_in_use; ch <= s->channels; ch++)

            s->fast_gain[ch] = ff_ac3_fast_gain_tab[4];

    }

    /* E-AC-3 to AC-3 converter SNR offset */

    if (s->frame_type == EAC3_FRAME_TYPE_INDEPENDENT && get_bits1(gbc)) {

        skip_bits(gbc, 10); // skip converter snr offset

    }

    /* coupling leak information */

    if (cpl_in_use) {

        if (s->first_cpl_leak || get_bits1(gbc)) {

            int fl = get_bits(gbc, 3);

            int sl = get_bits(gbc, 3);

            /* run last 2 bit allocation stages for coupling channel if

               coupling leak changes */

            if(blk && (fl != s->bit_alloc_params.cpl_fast_leak ||

                       sl != s->bit_alloc_params.cpl_slow_leak)) {

                bit_alloc_stages[CPL_CH] = FFMAX(bit_alloc_stages[CPL_CH], 2);

            }

            s->bit_alloc_params.cpl_fast_leak = fl;

            s->bit_alloc_params.cpl_slow_leak = sl;

        } else if (!s->eac3 && !blk) {

            av_log(s->avctx, AV_LOG_ERROR, "new coupling leak info must be present in block 0\n");

            return -1;

        }

        s->first_cpl_leak = 0;

    }

    /* delta bit allocation information */

    if (s->dba_syntax && 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 */

            if (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])) {

                av_log(s->avctx, AV_LOG_ERROR, "error in bit allocation\n");

                return -1;

            }

        }

        if(bit_alloc_stages[ch] > 0) {

            /* Compute bit allocation */

            const uint8_t *bap_tab = s->channel_uses_aht[ch] ?

                                     ff_eac3_hebap_tab : ff_ac3_bap_tab;

            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,

                                      bap_tab, s->bap[ch]);

        }

    }

    /* unused dummy data */

    if (s->skip_syntax && 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. */

    decode_transform_coeffs(s, blk);

    /* TODO: generate enhanced coupling coordinates and uncouple */

    /* TODO: apply spectral extension */

    /* 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];

        }

        s->dsp.int32_to_float_fmul_scalar(s->transform_coeffs[ch], s->fixed_coeffs[ch], gain, 256);

    }

    /* 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) {

            s->dsp.ac3_downmix(s->output, s->downmix_coeffs, s->out_channels, s->fbw_channels, 256);

        }

    } else {

        if(downmix_output) {

            s->dsp.ac3_downmix(s->transform_coeffs+1, s->downmix_coeffs, s->out_channels, s->fbw_channels, 256);

        }

        if(downmix_output && !s->downmixed) {

            s->downmixed = 1;

            s->dsp.ac3_downmix(s->delay, s->downmix_coeffs, s->out_channels, s->fbw_channels, 128);

        }

        do_imdct(s, s->out_channels);

    }

    return 0;

}

/**

 * Decode a single AC-3 frame.

 */

static int ac3_decode_frame(AVCodecContext * avctx, void *data, int *data_size,

                            AVPacket *avpkt)

{

    const uint8_t *buf = avpkt->data;

    int buf_size = avpkt->size;

    AC3DecodeContext *s = avctx->priv_data;

    int16_t *out_samples = (int16_t *)data;

    int blk, ch, err;

    const uint8_t *channel_map;

    /* 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_FRAME_BUFFER_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 = AAC_AC3_PARSE_ERROR_FRAME_SIZE;

    }

    /* check for crc mismatch */

    if(err != AAC_AC3_PARSE_ERROR_FRAME_SIZE && avctx->error_recognition >= 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 = AAC_AC3_PARSE_ERROR_CRC;

        }

    }

    if(err && err != AAC_AC3_PARSE_ERROR_CRC) {

        switch(err) {

            case AAC_AC3_PARSE_ERROR_SYNC:

                av_log(avctx, AV_LOG_ERROR, "frame sync error\n");

                return -1;

            case AAC_AC3_PARSE_ERROR_BSID:

                av_log(avctx, AV_LOG_ERROR, "invalid bitstream id\n");

                break;

            case AAC_AC3_PARSE_ERROR_SAMPLE_RATE:

                av_log(avctx, AV_LOG_ERROR, "invalid sample rate\n");

                break;

            case AAC_AC3_PARSE_ERROR_FRAME_SIZE:

                av_log(avctx, AV_LOG_ERROR, "invalid frame size\n");

                break;

            case AAC_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 &&