PeerStreamer

/*

 * The simplest AC-3 encoder

 * Copyright (c) 2000 Fabrice Bellard

 *

 * This file is part of FFmpeg.

 *

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

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 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

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser 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

 */

/**

 * @file libavcodec/ac3enc.c

 * The simplest AC-3 encoder.

 */

//#define DEBUG

//#define DEBUG_BITALLOC

#include "libavutil/crc.h"

#include "avcodec.h"

#include "bitstream.h" // for ff_reverse

#include "put_bits.h"

#include "ac3.h"

typedef struct AC3EncodeContext {

    PutBitContext pb;

    int nb_channels;

    int nb_all_channels;

    int lfe_channel;

    int bit_rate;

    unsigned int sample_rate;

    unsigned int bitstream_id;

    unsigned int frame_size_min; /* minimum frame size in case rounding is necessary */

    unsigned int frame_size; /* current frame size in words */

    unsigned int bits_written;

    unsigned int samples_written;

    int sr_shift;

    unsigned int frame_size_code;

    unsigned int sr_code; /* frequency */

    unsigned int channel_mode;

    int lfe;

    unsigned int bitstream_mode;

    short last_samples[AC3_MAX_CHANNELS][256];

    unsigned int chbwcod[AC3_MAX_CHANNELS];

    int nb_coefs[AC3_MAX_CHANNELS];

    /* bitrate allocation control */

    int slow_gain_code, slow_decay_code, fast_decay_code, db_per_bit_code, floor_code;

    AC3BitAllocParameters bit_alloc;

    int coarse_snr_offset;

    int fast_gain_code[AC3_MAX_CHANNELS];

    int fine_snr_offset[AC3_MAX_CHANNELS];

    /* mantissa encoding */

    int mant1_cnt, mant2_cnt, mant4_cnt;

} AC3EncodeContext;

static int16_t costab[64];

static int16_t sintab[64];

static int16_t xcos1[128];

static int16_t xsin1[128];

#define MDCT_NBITS 9

#define N         (1 << MDCT_NBITS)

/* new exponents are sent if their Norm 1 exceed this number */

#define EXP_DIFF_THRESHOLD 1000

static inline int16_t fix15(float a)

{

    int v;

    v = (int)(a * (float)(1 << 15));

    if (v < -32767)

        v = -32767;

    else if (v > 32767)

        v = 32767;

    return v;

}

typedef struct IComplex {

    short re,im;

} IComplex;

static av_cold void fft_init(int ln)

{

    int i, n;

    float alpha;

    n = 1 << ln;

    for(i=0;i<(n/2);i++) {

        alpha = 2 * M_PI * (float)i / (float)n;

        costab[i] = fix15(cos(alpha));

        sintab[i] = fix15(sin(alpha));

    }

}

/* butter fly op */

#define BF(pre, pim, qre, qim, pre1, pim1, qre1, qim1) \

{\

  int ax, ay, bx, by;\

  bx=pre1;\

  by=pim1;\

  ax=qre1;\

  ay=qim1;\

  pre = (bx + ax) >> 1;\

  pim = (by + ay) >> 1;\

  qre = (bx - ax) >> 1;\

  qim = (by - ay) >> 1;\

}

#define CMUL(pre, pim, are, aim, bre, bim) \

{\

   pre = (MUL16(are, bre) - MUL16(aim, bim)) >> 15;\

   pim = (MUL16(are, bim) + MUL16(bre, aim)) >> 15;\

}

/* do a 2^n point complex fft on 2^ln points. */

static void fft(IComplex *z, int ln)

{

    int        j, l, np, np2;

    int        nblocks, nloops;

    register IComplex *p,*q;

    int tmp_re, tmp_im;

    np = 1 << ln;

    /* reverse */

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

        int k = ff_reverse[j] >> (8 - ln);

        if (k < j)

            FFSWAP(IComplex, z[k], z[j]);

    }

    /* pass 0 */

    p=&z[0];

    j=(np >> 1);

    do {

        BF(p[0].re, p[0].im, p[1].re, p[1].im,

           p[0].re, p[0].im, p[1].re, p[1].im);

        p+=2;

    } while (--j != 0);

    /* pass 1 */

    p=&z[0];

    j=np >> 2;

    do {

        BF(p[0].re, p[0].im, p[2].re, p[2].im,

           p[0].re, p[0].im, p[2].re, p[2].im);

        BF(p[1].re, p[1].im, p[3].re, p[3].im,

           p[1].re, p[1].im, p[3].im, -p[3].re);

        p+=4;

    } while (--j != 0);

    /* pass 2 .. ln-1 */

    nblocks = np >> 3;

    nloops = 1 << 2;

    np2 = np >> 1;

    do {

        p = z;

        q = z + nloops;

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

            BF(p->re, p->im, q->re, q->im,

               p->re, p->im, q->re, q->im);

            p++;

            q++;

            for(l = nblocks; l < np2; l += nblocks) {

                CMUL(tmp_re, tmp_im, costab[l], -sintab[l], q->re, q->im);

                BF(p->re, p->im, q->re, q->im,

                   p->re, p->im, tmp_re, tmp_im);

                p++;

                q++;

            }

            p += nloops;

            q += nloops;

        }

        nblocks = nblocks >> 1;

        nloops = nloops << 1;

    } while (nblocks != 0);

}

/* do a 512 point mdct */

static void mdct512(int32_t *out, int16_t *in)

{

    int i, re, im, re1, im1;

    int16_t rot[N];

    IComplex x[N/4];

    /* shift to simplify computations */

    for(i=0;i<N/4;i++)

        rot[i] = -in[i + 3*N/4];

    for(i=N/4;i<N;i++)

        rot[i] = in[i - N/4];

    /* pre rotation */

    for(i=0;i<N/4;i++) {

        re = ((int)rot[2*i] - (int)rot[N-1-2*i]) >> 1;

        im = -((int)rot[N/2+2*i] - (int)rot[N/2-1-2*i]) >> 1;

        CMUL(x[i].re, x[i].im, re, im, -xcos1[i], xsin1[i]);

    }

    fft(x, MDCT_NBITS - 2);

    /* post rotation */

    for(i=0;i<N/4;i++) {

        re = x[i].re;

        im = x[i].im;

        CMUL(re1, im1, re, im, xsin1[i], xcos1[i]);

        out[2*i] = im1;

        out[N/2-1-2*i] = re1;

    }

}

/* XXX: use another norm ? */

static int calc_exp_diff(uint8_t *exp1, uint8_t *exp2, int n)

{

    int sum, i;

    sum = 0;

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

        sum += abs(exp1[i] - exp2[i]);

    }

    return sum;

}

static void compute_exp_strategy(uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

                                 uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                                 int ch, int is_lfe)

{

    int i, j;

    int exp_diff;

    /* estimate if the exponent variation & decide if they should be

       reused in the next frame */

    exp_strategy[0][ch] = EXP_NEW;

    for(i=1;i<NB_BLOCKS;i++) {

        exp_diff = calc_exp_diff(exp[i][ch], exp[i-1][ch], N/2);

#ifdef DEBUG

        av_log(NULL, AV_LOG_DEBUG, "exp_diff=%d\n", exp_diff);

#endif

        if (exp_diff > EXP_DIFF_THRESHOLD)

            exp_strategy[i][ch] = EXP_NEW;

        else

            exp_strategy[i][ch] = EXP_REUSE;

    }

    if (is_lfe)

        return;

    /* now select the encoding strategy type : if exponents are often

       recoded, we use a coarse encoding */

    i = 0;

    while (i < NB_BLOCKS) {

        j = i + 1;

        while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE)

            j++;

        switch(j - i) {

        case 1:

            exp_strategy[i][ch] = EXP_D45;

            break;

        case 2:

        case 3:

            exp_strategy[i][ch] = EXP_D25;

            break;

        default:

            exp_strategy[i][ch] = EXP_D15;

            break;

        }

        i = j;

    }

}

/* set exp[i] to min(exp[i], exp1[i]) */

static void exponent_min(uint8_t exp[N/2], uint8_t exp1[N/2], int n)

{

    int i;

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

        if (exp1[i] < exp[i])

            exp[i] = exp1[i];

    }

}

/* update the exponents so that they are the ones the decoder will

   decode. Return the number of bits used to code the exponents */

static int encode_exp(uint8_t encoded_exp[N/2],

                      uint8_t exp[N/2],

                      int nb_exps,

                      int exp_strategy)

{

    int group_size, nb_groups, i, j, k, exp_min;

    uint8_t exp1[N/2];

    switch(exp_strategy) {

    case EXP_D15:

        group_size = 1;

        break;

    case EXP_D25:

        group_size = 2;

        break;

    default:

    case EXP_D45:

        group_size = 4;

        break;

    }

    nb_groups = ((nb_exps + (group_size * 3) - 4) / (3 * group_size)) * 3;

    /* for each group, compute the minimum exponent */

    exp1[0] = exp[0]; /* DC exponent is handled separately */

    k = 1;

    for(i=1;i<=nb_groups;i++) {

        exp_min = exp[k];

        assert(exp_min >= 0 && exp_min <= 24);

        for(j=1;j<group_size;j++) {

            if (exp[k+j] < exp_min)

                exp_min = exp[k+j];

        }

        exp1[i] = exp_min;

        k += group_size;

    }

    /* constraint for DC exponent */

    if (exp1[0] > 15)

        exp1[0] = 15;

    /* Decrease the delta between each groups to within 2

     * so that they can be differentially encoded */

    for (i=1;i<=nb_groups;i++)

        exp1[i] = FFMIN(exp1[i], exp1[i-1] + 2);

    for (i=nb_groups-1;i>=0;i--)

        exp1[i] = FFMIN(exp1[i], exp1[i+1] + 2);

    /* now we have the exponent values the decoder will see */

    encoded_exp[0] = exp1[0];

    k = 1;

    for(i=1;i<=nb_groups;i++) {

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

            encoded_exp[k+j] = exp1[i];

        }

        k += group_size;

    }

#if defined(DEBUG)

    av_log(NULL, AV_LOG_DEBUG, "exponents: strategy=%d\n", exp_strategy);

    for(i=0;i<=nb_groups * group_size;i++) {

        av_log(NULL, AV_LOG_DEBUG, "%d ", encoded_exp[i]);

    }

    av_log(NULL, AV_LOG_DEBUG, "\n");

#endif

    return 4 + (nb_groups / 3) * 7;

}

/* return the size in bits taken by the mantissa */

static int compute_mantissa_size(AC3EncodeContext *s, uint8_t *m, int nb_coefs)

{

    int bits, mant, i;

    bits = 0;

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

        mant = m[i];

        switch(mant) {

        case 0:

            /* nothing */

            break;

        case 1:

            /* 3 mantissa in 5 bits */

            if (s->mant1_cnt == 0)

                bits += 5;

            if (++s->mant1_cnt == 3)

                s->mant1_cnt = 0;

            break;

        case 2:

            /* 3 mantissa in 7 bits */

            if (s->mant2_cnt == 0)

                bits += 7;

            if (++s->mant2_cnt == 3)

                s->mant2_cnt = 0;

            break;

        case 3:

            bits += 3;

            break;

        case 4:

            /* 2 mantissa in 7 bits */

            if (s->mant4_cnt == 0)

                bits += 7;

            if (++s->mant4_cnt == 2)

                s->mant4_cnt = 0;

            break;

        case 14:

            bits += 14;

            break;

        case 15:

            bits += 16;

            break;

        default:

            bits += mant - 1;

            break;

        }

    }

    return bits;

}

static void bit_alloc_masking(AC3EncodeContext *s,

                              uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                              uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

                              int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                              int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50])

{

    int blk, ch;

    int16_t band_psd[NB_BLOCKS][AC3_MAX_CHANNELS][50];

    for(blk=0; blk<NB_BLOCKS; blk++) {

        for(ch=0;ch<s->nb_all_channels;ch++) {

            if(exp_strategy[blk][ch] == EXP_REUSE) {

                memcpy(psd[blk][ch], psd[blk-1][ch], (N/2)*sizeof(int16_t));

                memcpy(mask[blk][ch], mask[blk-1][ch], 50*sizeof(int16_t));

            } else {

                ff_ac3_bit_alloc_calc_psd(encoded_exp[blk][ch], 0,

                                          s->nb_coefs[ch],

                                          psd[blk][ch], band_psd[blk][ch]);

                ff_ac3_bit_alloc_calc_mask(&s->bit_alloc, band_psd[blk][ch],

                                           0, s->nb_coefs[ch],

                                           ff_ac3_fast_gain_tab[s->fast_gain_code[ch]],

                                           ch == s->lfe_channel,

                                           DBA_NONE, 0, NULL, NULL, NULL,

                                           mask[blk][ch]);

            }

        }

    }

}

static int bit_alloc(AC3EncodeContext *s,

                     int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50],

                     int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                     uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                     int frame_bits, int coarse_snr_offset, int fine_snr_offset)

{

    int i, ch;

    int snr_offset;

    snr_offset = (((coarse_snr_offset - 15) << 4) + fine_snr_offset) << 2;

    /* compute size */

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

        s->mant1_cnt = 0;

        s->mant2_cnt = 0;

        s->mant4_cnt = 0;

        for(ch=0;ch<s->nb_all_channels;ch++) {

            ff_ac3_bit_alloc_calc_bap(mask[i][ch], psd[i][ch], 0,

                                      s->nb_coefs[ch], snr_offset,

                                      s->bit_alloc.floor, ff_ac3_bap_tab,

                                      bap[i][ch]);

            frame_bits += compute_mantissa_size(s, bap[i][ch],

                                                 s->nb_coefs[ch]);

        }

    }

#if 0

    printf("csnr=%d fsnr=%d frame_bits=%d diff=%d\n",

           coarse_snr_offset, fine_snr_offset, frame_bits,

           16 * s->frame_size - ((frame_bits + 7) & ~7));

#endif

    return 16 * s->frame_size - frame_bits;

}

#define SNR_INC1 4

static int compute_bit_allocation(AC3EncodeContext *s,

                                  uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                                  uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                                  uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

                                  int frame_bits)

{

    int i, ch;

    int coarse_snr_offset, fine_snr_offset;

    uint8_t bap1[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

    int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

    int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50];

    static const int frame_bits_inc[8] = { 0, 0, 2, 2, 2, 4, 2, 4 };

    /* init default parameters */

    s->slow_decay_code = 2;

    s->fast_decay_code = 1;

    s->slow_gain_code = 1;

    s->db_per_bit_code = 2;

    s->floor_code = 4;

    for(ch=0;ch<s->nb_all_channels;ch++)

        s->fast_gain_code[ch] = 4;

    /* compute real values */

    s->bit_alloc.sr_code = s->sr_code;

    s->bit_alloc.sr_shift = s->sr_shift;

    s->bit_alloc.slow_decay = ff_ac3_slow_decay_tab[s->slow_decay_code] >> s->sr_shift;

    s->bit_alloc.fast_decay = ff_ac3_fast_decay_tab[s->fast_decay_code] >> s->sr_shift;

    s->bit_alloc.slow_gain = ff_ac3_slow_gain_tab[s->slow_gain_code];

    s->bit_alloc.db_per_bit = ff_ac3_db_per_bit_tab[s->db_per_bit_code];

    s->bit_alloc.floor = ff_ac3_floor_tab[s->floor_code];

    /* header size */

    frame_bits += 65;

    // if (s->channel_mode == 2)

    //    frame_bits += 2;

    frame_bits += frame_bits_inc[s->channel_mode];

    /* audio blocks */

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

        frame_bits += s->nb_channels * 2 + 2; /* blksw * c, dithflag * c, dynrnge, cplstre */

        if (s->channel_mode == AC3_CHMODE_STEREO) {

            frame_bits++; /* rematstr */

            if(i==0) frame_bits += 4;

        }

        frame_bits += 2 * s->nb_channels; /* chexpstr[2] * c */

        if (s->lfe)

            frame_bits++; /* lfeexpstr */

        for(ch=0;ch<s->nb_channels;ch++) {

            if (exp_strategy[i][ch] != EXP_REUSE)

                frame_bits += 6 + 2; /* chbwcod[6], gainrng[2] */

        }

        frame_bits++; /* baie */

        frame_bits++; /* snr */

        frame_bits += 2; /* delta / skip */

    }

    frame_bits++; /* cplinu for block 0 */

    /* bit alloc info */

    /* sdcycod[2], fdcycod[2], sgaincod[2], dbpbcod[2], floorcod[3] */

    /* csnroffset[6] */

    /* (fsnoffset[4] + fgaincod[4]) * c */

    frame_bits += 2*4 + 3 + 6 + s->nb_all_channels * (4 + 3);

    /* auxdatae, crcrsv */

    frame_bits += 2;

    /* CRC */

    frame_bits += 16;

    /* calculate psd and masking curve before doing bit allocation */

    bit_alloc_masking(s, encoded_exp, exp_strategy, psd, mask);

    /* now the big work begins : do the bit allocation. Modify the snr

       offset until we can pack everything in the requested frame size */

    coarse_snr_offset = s->coarse_snr_offset;

    while (coarse_snr_offset >= 0 &&

           bit_alloc(s, mask, psd, bap, frame_bits, coarse_snr_offset, 0) < 0)

        coarse_snr_offset -= SNR_INC1;

    if (coarse_snr_offset < 0) {

        av_log(NULL, AV_LOG_ERROR, "Bit allocation failed. Try increasing the bitrate.\n");

        return -1;

    }

    while ((coarse_snr_offset + SNR_INC1) <= 63 &&

           bit_alloc(s, mask, psd, bap1, frame_bits,

                     coarse_snr_offset + SNR_INC1, 0) >= 0) {

        coarse_snr_offset += SNR_INC1;

        memcpy(bap, bap1, sizeof(bap1));

    }

    while ((coarse_snr_offset + 1) <= 63 &&

           bit_alloc(s, mask, psd, bap1, frame_bits, coarse_snr_offset + 1, 0) >= 0) {

        coarse_snr_offset++;

        memcpy(bap, bap1, sizeof(bap1));

    }

    fine_snr_offset = 0;

    while ((fine_snr_offset + SNR_INC1) <= 15 &&

           bit_alloc(s, mask, psd, bap1, frame_bits,

                     coarse_snr_offset, fine_snr_offset + SNR_INC1) >= 0) {

        fine_snr_offset += SNR_INC1;

        memcpy(bap, bap1, sizeof(bap1));

    }

    while ((fine_snr_offset + 1) <= 15 &&

           bit_alloc(s, mask, psd, bap1, frame_bits,

                     coarse_snr_offset, fine_snr_offset + 1) >= 0) {

        fine_snr_offset++;

        memcpy(bap, bap1, sizeof(bap1));

    }

    s->coarse_snr_offset = coarse_snr_offset;

    for(ch=0;ch<s->nb_all_channels;ch++)

        s->fine_snr_offset[ch] = fine_snr_offset;

#if defined(DEBUG_BITALLOC)

    {

        int j;

        for(i=0;i<6;i++) {

            for(ch=0;ch<s->nb_all_channels;ch++) {

                printf("Block #%d Ch%d:\n", i, ch);

                printf("bap=");

                for(j=0;j<s->nb_coefs[ch];j++) {

                    printf("%d ",bap[i][ch][j]);

                }

                printf("\n");

            }

        }

    }

#endif

    return 0;

}

static av_cold int AC3_encode_init(AVCodecContext *avctx)

{

    int freq = avctx->sample_rate;

    int bitrate = avctx->bit_rate;

    int channels = avctx->channels;

    AC3EncodeContext *s = avctx->priv_data;

    int i, j, ch;

    float alpha;

    int bw_code;

    static const uint8_t channel_mode_defs[6] = {

        0x01, /* C */

        0x02, /* L R */

        0x03, /* L C R */

        0x06, /* L R SL SR */

        0x07, /* L C R SL SR */

        0x07, /* L C R SL SR (+LFE) */

    };

    avctx->frame_size = AC3_FRAME_SIZE;

    ac3_common_init();

    /* number of channels */

    if (channels < 1 || channels > 6)

        return -1;

    s->channel_mode = channel_mode_defs[channels - 1];

    s->lfe = (channels == 6) ? 1 : 0;

    s->nb_all_channels = channels;

    s->nb_channels = channels > 5 ? 5 : channels;

    s->lfe_channel = s->lfe ? 5 : -1;

    /* frequency */

    for(i=0;i<3;i++) {

        for(j=0;j<3;j++)

            if ((ff_ac3_sample_rate_tab[j] >> i) == freq)

                goto found;

    }

    return -1;

 found:

    s->sample_rate = freq;

    s->sr_shift = i;

    s->sr_code = j;

    s->bitstream_id = 8 + s->sr_shift;

    s->bitstream_mode = 0; /* complete main audio service */

    /* bitrate & frame size */

    for(i=0;i<19;i++) {

        if ((ff_ac3_bitrate_tab[i] >> s->sr_shift)*1000 == bitrate)

            break;

    }

    if (i == 19)

        return -1;

    s->bit_rate = bitrate;

    s->frame_size_code = i << 1;

    s->frame_size_min = ff_ac3_frame_size_tab[s->frame_size_code][s->sr_code];

    s->bits_written = 0;

    s->samples_written = 0;

    s->frame_size = s->frame_size_min;

    /* bit allocation init */

    if(avctx->cutoff) {

        /* calculate bandwidth based on user-specified cutoff frequency */

        int cutoff = av_clip(avctx->cutoff, 1, s->sample_rate >> 1);

        int fbw_coeffs = cutoff * 512 / s->sample_rate;

        bw_code = av_clip((fbw_coeffs - 73) / 3, 0, 60);

    } else {

        /* use default bandwidth setting */

        /* XXX: should compute the bandwidth according to the frame

           size, so that we avoid annoying high frequency artifacts */

        bw_code = 50;

    }

    for(ch=0;ch<s->nb_channels;ch++) {

        /* bandwidth for each channel */

        s->chbwcod[ch] = bw_code;

        s->nb_coefs[ch] = bw_code * 3 + 73;

    }

    if (s->lfe) {

        s->nb_coefs[s->lfe_channel] = 7; /* fixed */

    }

    /* initial snr offset */

    s->coarse_snr_offset = 40;

    /* mdct init */

    fft_init(MDCT_NBITS - 2);

    for(i=0;i<N/4;i++) {

        alpha = 2 * M_PI * (i + 1.0 / 8.0) / (float)N;

        xcos1[i] = fix15(-cos(alpha));

        xsin1[i] = fix15(-sin(alpha));

    }

    avctx->coded_frame= avcodec_alloc_frame();

    avctx->coded_frame->key_frame= 1;

    return 0;

}

/* output the AC-3 frame header */

static void output_frame_header(AC3EncodeContext *s, unsigned char *frame)

{

    init_put_bits(&s->pb, frame, AC3_MAX_CODED_FRAME_SIZE);

    put_bits(&s->pb, 16, 0x0b77); /* frame header */

    put_bits(&s->pb, 16, 0); /* crc1: will be filled later */

    put_bits(&s->pb, 2, s->sr_code);

    put_bits(&s->pb, 6, s->frame_size_code + (s->frame_size - s->frame_size_min));

    put_bits(&s->pb, 5, s->bitstream_id);

    put_bits(&s->pb, 3, s->bitstream_mode);

    put_bits(&s->pb, 3, s->channel_mode);

    if ((s->channel_mode & 0x01) && s->channel_mode != AC3_CHMODE_MONO)

        put_bits(&s->pb, 2, 1); /* XXX -4.5 dB */

    if (s->channel_mode & 0x04)

        put_bits(&s->pb, 2, 1); /* XXX -6 dB */

    if (s->channel_mode == AC3_CHMODE_STEREO)

        put_bits(&s->pb, 2, 0); /* surround not indicated */

    put_bits(&s->pb, 1, s->lfe); /* LFE */

    put_bits(&s->pb, 5, 31); /* dialog norm: -31 db */

    put_bits(&s->pb, 1, 0); /* no compression control word */

    put_bits(&s->pb, 1, 0); /* no lang code */

    put_bits(&s->pb, 1, 0); /* no audio production info */

    put_bits(&s->pb, 1, 0); /* no copyright */

    put_bits(&s->pb, 1, 1); /* original bitstream */

    put_bits(&s->pb, 1, 0); /* no time code 1 */

    put_bits(&s->pb, 1, 0); /* no time code 2 */

    put_bits(&s->pb, 1, 0); /* no additional bit stream info */

}

/* symetric quantization on 'levels' levels */

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

{

    int v;

    if (c >= 0) {

        v = (levels * (c << e)) >> 24;

        v = (v + 1) >> 1;

        v = (levels >> 1) + v;

    } else {

        v = (levels * ((-c) << e)) >> 24;

        v = (v + 1) >> 1;

        v = (levels >> 1) - v;

    }

    assert (v >= 0 && v < levels);

    return v;

}

/* asymetric quantization on 2^qbits levels */

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

{

    int lshift, m, v;

    lshift = e + qbits - 24;

    if (lshift >= 0)

        v = c << lshift;

    else

        v = c >> (-lshift);

    /* rounding */

    v = (v + 1) >> 1;

    m = (1 << (qbits-1));

    if (v >= m)

        v = m - 1;

    assert(v >= -m);

    return v & ((1 << qbits)-1);

}

/* Output one audio block. There are NB_BLOCKS audio blocks in one AC-3

   frame */

static void output_audio_block(AC3EncodeContext *s,

                               uint8_t exp_strategy[AC3_MAX_CHANNELS],

                               uint8_t encoded_exp[AC3_MAX_CHANNELS][N/2],

                               uint8_t bap[AC3_MAX_CHANNELS][N/2],

                               int32_t mdct_coefs[AC3_MAX_CHANNELS][N/2],

                               int8_t global_exp[AC3_MAX_CHANNELS],

                               int block_num)

{

    int ch, nb_groups, group_size, i, baie, rbnd;

    uint8_t *p;

    uint16_t qmant[AC3_MAX_CHANNELS][N/2];

    int exp0, exp1;

    int mant1_cnt, mant2_cnt, mant4_cnt;

    uint16_t *qmant1_ptr, *qmant2_ptr, *qmant4_ptr;

    int delta0, delta1, delta2;

    for(ch=0;ch<s->nb_channels;ch++)

        put_bits(&s->pb, 1, 0); /* 512 point MDCT */

    for(ch=0;ch<s->nb_channels;ch++)

        put_bits(&s->pb, 1, 1); /* no dither */

    put_bits(&s->pb, 1, 0); /* no dynamic range */

    if (block_num == 0) {

        /* for block 0, even if no coupling, we must say it. This is a

           waste of bit :-) */

        put_bits(&s->pb, 1, 1); /* coupling strategy present */

        put_bits(&s->pb, 1, 0); /* no coupling strategy */

    } else {

        put_bits(&s->pb, 1, 0); /* no new coupling strategy */

    }

    if (s->channel_mode == AC3_CHMODE_STEREO)

      {

        if(block_num==0)

          {

            /* first block must define rematrixing (rematstr)  */

            put_bits(&s->pb, 1, 1);

            /* dummy rematrixing rematflg(1:4)=0 */

            for (rbnd=0;rbnd<4;rbnd++)

              put_bits(&s->pb, 1, 0);

          }

        else

          {

            /* no matrixing (but should be used in the future) */

            put_bits(&s->pb, 1, 0);

          }

      }

#if defined(DEBUG)

    {

      static int count = 0;

      av_log(NULL, AV_LOG_DEBUG, "Block #%d (%d)\n", block_num, count++);

    }

#endif

    /* exponent strategy */

    for(ch=0;ch<s->nb_channels;ch++) {

        put_bits(&s->pb, 2, exp_strategy[ch]);

    }

    if (s->lfe) {

        put_bits(&s->pb, 1, exp_strategy[s->lfe_channel]);

    }

    for(ch=0;ch<s->nb_channels;ch++) {

        if (exp_strategy[ch] != EXP_REUSE)

            put_bits(&s->pb, 6, s->chbwcod[ch]);

    }

    /* exponents */

    for (ch = 0; ch < s->nb_all_channels; ch++) {

        switch(exp_strategy[ch]) {

        case EXP_REUSE:

            continue;

        case EXP_D15:

            group_size = 1;

            break;

        case EXP_D25:

            group_size = 2;

            break;

        default:

        case EXP_D45:

            group_size = 4;

            break;

        }

        nb_groups = (s->nb_coefs[ch] + (group_size * 3) - 4) / (3 * group_size);

        p = encoded_exp[ch];

        /* first exponent */

        exp1 = *p++;

        put_bits(&s->pb, 4, exp1);

        /* next ones are delta encoded */

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

            /* merge three delta in one code */

            exp0 = exp1;

            exp1 = p[0];

            p += group_size;

            delta0 = exp1 - exp0 + 2;

            exp0 = exp1;

            exp1 = p[0];

            p += group_size;

            delta1 = exp1 - exp0 + 2;

            exp0 = exp1;

            exp1 = p[0];

            p += group_size;

            delta2 = exp1 - exp0 + 2;

            put_bits(&s->pb, 7, ((delta0 * 5 + delta1) * 5) + delta2);

        }

        if (ch != s->lfe_channel)

            put_bits(&s->pb, 2, 0); /* no gain range info */

    }

    /* bit allocation info */

    baie = (block_num == 0);

    put_bits(&s->pb, 1, baie);

    if (baie) {

        put_bits(&s->pb, 2, s->slow_decay_code);

        put_bits(&s->pb, 2, s->fast_decay_code);

        put_bits(&s->pb, 2, s->slow_gain_code);

        put_bits(&s->pb, 2, s->db_per_bit_code);

        put_bits(&s->pb, 3, s->floor_code);

    }

    /* snr offset */

    put_bits(&s->pb, 1, baie); /* always present with bai */

    if (baie) {

        put_bits(&s->pb, 6, s->coarse_snr_offset);

        for(ch=0;ch<s->nb_all_channels;ch++) {

            put_bits(&s->pb, 4, s->fine_snr_offset[ch]);

            put_bits(&s->pb, 3, s->fast_gain_code[ch]);

        }

    }

    put_bits(&s->pb, 1, 0); /* no delta bit allocation */

    put_bits(&s->pb, 1, 0); /* no data to skip */

    /* mantissa encoding : we use two passes to handle the grouping. A

       one pass method may be faster, but it would necessitate to

       modify the output stream. */

    /* first pass: quantize */

    mant1_cnt = mant2_cnt = mant4_cnt = 0;

    qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

    for (ch = 0; ch < s->nb_all_channels; ch++) {

        int b, c, e, v;

        for(i=0;i<s->nb_coefs[ch];i++) {

            c = mdct_coefs[ch][i];

            e = encoded_exp[ch][i] - global_exp[ch];

            b = bap[ch][i];

            switch(b) {

            case 0:

                v = 0;

                break;

            case 1:

                v = sym_quant(c, e, 3);

                switch(mant1_cnt) {

                case 0:

                    qmant1_ptr = &qmant[ch][i];

                    v = 9 * v;

                    mant1_cnt = 1;

                    break;

                case 1:

                    *qmant1_ptr += 3 * v;

                    mant1_cnt = 2;

                    v = 128;

                    break;

                default:

                    *qmant1_ptr += v;

                    mant1_cnt = 0;

                    v = 128;

                    break;

                }

                break;

            case 2:

                v = sym_quant(c, e, 5);

                switch(mant2_cnt) {

                case 0:

                    qmant2_ptr = &qmant[ch][i];

                    v = 25 * v;

                    mant2_cnt = 1;

                    break;

                case 1:

                    *qmant2_ptr += 5 * v;

                    mant2_cnt = 2;

                    v = 128;

                    break;

                default:

                    *qmant2_ptr += v;

                    mant2_cnt = 0;

                    v = 128;

                    break;

                }

                break;

            case 3:

                v = sym_quant(c, e, 7);

                break;

            case 4:

                v = sym_quant(c, e, 11);

                switch(mant4_cnt) {

                case 0:

                    qmant4_ptr = &qmant[ch][i];

                    v = 11 * v;

                    mant4_cnt = 1;

                    break;

                default:

                    *qmant4_ptr += v;

                    mant4_cnt = 0;

                    v = 128;

                    break;

                }

                break;

            case 5:

                v = sym_quant(c, e, 15);

                break;

            case 14:

                v = asym_quant(c, e, 14);

                break;

            case 15:

                v = asym_quant(c, e, 16);

                break;

            default:

                v = asym_quant(c, e, b - 1);

                break;

            }

            qmant[ch][i] = v;

        }

    }

    /* second pass : output the values */

    for (ch = 0; ch < s->nb_all_channels; ch++) {

        int b, q;

        for(i=0;i<s->nb_coefs[ch];i++) {

            q = qmant[ch][i];

            b = bap[ch][i];

            switch(b) {

            case 0:

                break;

            case 1:

                if (q != 128)

                    put_bits(&s->pb, 5, q);

                break;

            case 2:

                if (q != 128)

                    put_bits(&s->pb, 7, q);

                break;

            case 3:

                put_bits(&s->pb, 3, q);

                break;

            case 4:

                if (q != 128)

                    put_bits(&s->pb, 7, q);

                break;

            case 14:

                put_bits(&s->pb, 14, q);

                break;

            case 15:

                put_bits(&s->pb, 16, q);

                break;

            default:

                put_bits(&s->pb, b - 1, q);

                break;

            }

        }

    }

}

#define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

{

    unsigned int c;

    c = 0;

    while (a) {

        if (a & 1)

            c ^= b;

        a = a >> 1;

        b = b << 1;

        if (b & (1 << 16))

            b ^= poly;

    }

    return c;

}

static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

{

    unsigned int r;

    r = 1;

    while (n) {

        if (n & 1)

            r = mul_poly(r, a, poly);

        a = mul_poly(a, a, poly);

        n >>= 1;

    }

    return r;

}

/* compute log2(max(abs(tab[]))) */

static int log2_tab(int16_t *tab, int n)

{

    int i, v;

    v = 0;

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

        v |= abs(tab[i]);

    }

    return av_log2(v);

}

static void lshift_tab(int16_t *tab, int n, int lshift)

{

    int i;

    if (lshift > 0) {

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

            tab[i] <<= lshift;

        }

    } else if (lshift < 0) {

        lshift = -lshift;

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

            tab[i] >>= lshift;

        }

    }

}

/* fill the end of the frame and compute the two crcs */

static int output_frame_end(AC3EncodeContext *s)

{

    int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

    uint8_t *frame;

    frame_size = s->frame_size; /* frame size in words */

    /* align to 8 bits */

    flush_put_bits(&s->pb);

    /* add zero bytes to reach the frame size */

    frame = s->pb.buf;

    n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;

    assert(n >= 0);

    if(n>0)

      memset(pbBufPtr(&s->pb), 0, n);

    /* Now we must compute both crcs : this is not so easy for crc1

       because it is at the beginning of the data... */

    frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

    crc1 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

                           frame + 4, 2 * frame_size_58 - 4));

    /* XXX: could precompute crc_inv */

    crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

    crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

    AV_WB16(frame+2,crc1);

    crc2 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

                           frame + 2 * frame_size_58,

                           (frame_size - frame_size_58) * 2 - 2));

    AV_WB16(frame+2*frame_size-2,crc2);

    //    printf("n=%d frame_size=%d\n", n, frame_size);

    return frame_size * 2;

}

static int AC3_encode_frame(AVCodecContext *avctx,

                            unsigned char *frame, int buf_size, void *data)

{

    AC3EncodeContext *s = avctx->priv_data;

    int16_t *samples = data;

    int i, j, k, v, ch;

    int16_t input_samples[N];

    int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

    uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

    uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

    uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

    uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

    int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

    int frame_bits;

    frame_bits = 0;

    for(ch=0;ch<s->nb_all_channels;ch++) {

        /* fixed mdct to the six sub blocks & exponent computation */

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

            int16_t *sptr;

            int sinc;

            /* compute input samples */

            memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(int16_t));

            sinc = s->nb_all_channels;

            sptr = samples + (sinc * (N/2) * i) + ch;

            for(j=0;j<N/2;j++) {

                v = *sptr;

                input_samples[j + N/2] = v;

                s->last_samples[ch][j] = v;

                sptr += sinc;

            }

            /* apply the MDCT window */

            for(j=0;j<N/2;j++) {

                input_samples[j] = MUL16(input_samples[j],

                                         ff_ac3_window[j]) >> 15;

                input_samples[N-j-1] = MUL16(input_samples[N-j-1],

                                             ff_ac3_window[j]) >> 15;

            }

            /* Normalize the samples to use the maximum available

               precision */

            v = 14 - log2_tab(input_samples, N);

            if (v < 0)

                v = 0;

            exp_samples[i][ch] = v - 9;

            lshift_tab(input_samples, N, v);

            /* do the MDCT */

            mdct512(mdct_coef[i][ch], input_samples);

            /* compute "exponents". We take into account the

               normalization there */

            for(j=0;j<N/2;j++) {

                int e;

                v = abs(mdct_coef[i][ch][j]);

                if (v == 0)

                    e = 24;

                else {

                    e = 23 - av_log2(v) + exp_samples[i][ch];

                    if (e >= 24) {

                        e = 24;

                        mdct_coef[i][ch][j] = 0;

                    }

                }

                exp[i][ch][j] = e;

            }

        }

        compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

        /* compute the exponents as the decoder will see them. The

           EXP_REUSE case must be handled carefully : we select the

           min of the exponents */

        i = 0;

        while (i < NB_BLOCKS) {

            j = i + 1;

            while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

                exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

                j++;

            }

            frame_bits += encode_exp(encoded_exp[i][ch],

                                     exp[i][ch], s->nb_coefs[ch],

                                     exp_strategy[i][ch]);

            /* copy encoded exponents for reuse case */

            for(k=i+1;k<j;k++) {

                memcpy(encoded_exp[k][ch], encoded_exp[i][ch],

                       s->nb_coefs[ch] * sizeof(uint8_t));

            }

            i = j;

        }

    }

    /* adjust for fractional frame sizes */

    while(s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {

        s->bits_written -= s->bit_rate;

        s->samples_written -= s->sample_rate;

    }

    s->frame_size = s->frame_size_min + (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);

    s->bits_written += s->frame_size * 16;

    s->samples_written += AC3_FRAME_SIZE;

    compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

    /* everything is known... let's output the frame */

    output_frame_header(s, frame);

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

        output_audio_block(s, exp_strategy[i], encoded_exp[i],

                           bap[i], mdct_coef[i], exp_samples[i], i);

    }

    return output_frame_end(s);

}

static av_cold int AC3_encode_close(AVCodecContext *avctx)

{

    av_freep(&avctx->coded_frame);

    return 0;

}

#if 0

/*************************************************************************/

/* TEST */

#undef random

#define FN (N/4)

void fft_test(void)

{

    IComplex in[FN], in1[FN];

    int k, n, i;

    float sum_re, sum_im, a;

    /* FFT test */

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

        in[i].re = random() % 65535 - 32767;

        in[i].im = random() % 65535 - 32767;

        in1[i] = in[i];

    }

    fft(in, 7);

    /* do it by hand */

    for(k=0;k<FN;k++) {

        sum_re = 0;

        sum_im = 0;

        for(n=0;n<FN;n++) {

            a = -2 * M_PI * (n * k) / FN;

            sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

            sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

        }

        printf("%3d: %6d,%6d %6.0f,%6.0f\n",

               k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);

    }

}

void mdct_test(void)

{

    int16_t input[N];

    int32_t output[N/2];

    float input1[N];

    float output1[N/2];

    float s, a, err, e, emax;

    int i, k, n;

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

        input[i] = (random() % 65535 - 32767) * 9 / 10;

        input1[i] = input[i];

    }