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FFmpeg/libavcodec/ac3enc.c

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  1. /*

  2.  * The simplest AC-3 encoder

  3.  * Copyright (c) 2000 Fabrice Bellard

  4.  *

  5.  * This file is part of FFmpeg.

  6.  *

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

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

  9.  * License as published by the Free Software Foundation; either

  10.  * version 2.1 of the License, or (at your option) any later version.

  11.  *

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

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

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

  15.  * Lesser General Public License for more details.

  16.  *

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

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

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

  20.  */

  21. 

  22. /**

  23.  * @file libavcodec/ac3enc.c

  24.  * The simplest AC-3 encoder.

  25.  */

  26. //#define DEBUG

  27. //#define DEBUG_BITALLOC

  28. #include "libavutil/crc.h"

  29. #include "avcodec.h"

  30. #include "bitstream.h"

  31. #include "ac3.h"

  32. 

  33. typedef struct AC3EncodeContext {

  34.     PutBitContext pb;

  35.     int nb_channels;

  36.     int nb_all_channels;

  37.     int lfe_channel;

  38.     int bit_rate;

  39.     unsigned int sample_rate;

  40.     unsigned int bitstream_id;

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

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

  43.     unsigned int bits_written;

  44.     unsigned int samples_written;

  45.     int sr_shift;

  46.     unsigned int frame_size_code;

  47.     unsigned int sr_code; /* frequency */

  48.     unsigned int channel_mode;

  49.     int lfe;

  50.     unsigned int bitstream_mode;

  51.     short last_samples[AC3_MAX_CHANNELS][256];

  52.     unsigned int chbwcod[AC3_MAX_CHANNELS];

  53.     int nb_coefs[AC3_MAX_CHANNELS];

  54. 

  55.     /* bitrate allocation control */

  56.     int slow_gain_code, slow_decay_code, fast_decay_code, db_per_bit_code, floor_code;

  57.     AC3BitAllocParameters bit_alloc;

  58.     int coarse_snr_offset;

  59.     int fast_gain_code[AC3_MAX_CHANNELS];

  60.     int fine_snr_offset[AC3_MAX_CHANNELS];

  61.     /* mantissa encoding */

  62.     int mant1_cnt, mant2_cnt, mant4_cnt;

  63. } AC3EncodeContext;

  64. 

  65. static int16_t costab[64];

  66. static int16_t sintab[64];

  67. static int16_t xcos1[128];

  68. static int16_t xsin1[128];

  69. 

  70. #define MDCT_NBITS 9

  71. #define N         (1 << MDCT_NBITS)

  72. 

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

  74. #define EXP_DIFF_THRESHOLD 1000

  75. 

  76. static inline int16_t fix15(float a)

  77. {

  78.     int v;

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

  80.     if (v < -32767)

  81.         v = -32767;

  82.     else if (v > 32767)

  83.         v = 32767;

  84.     return v;

  85. }

  86. 

  87. typedef struct IComplex {

  88.     short re,im;

  89. } IComplex;

  90. 

  91. static av_cold void fft_init(int ln)

  92. {

  93.     int i, n;

  94.     float alpha;

  95. 

  96.     n = 1 << ln;

  97. 

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

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

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

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

  102.     }

  103. }

  104. 

  105. /* butter fly op */

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

  107. {\

  108.   int ax, ay, bx, by;\

  109.   bx=pre1;\

  110.   by=pim1;\

  111.   ax=qre1;\

  112.   ay=qim1;\

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

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

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

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

  117. }

  118. 

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

  120. {\

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

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

  123. }

  124. 

  125. 

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

  127. static void fft(IComplex *z, int ln)

  128. {

  129.     int        j, l, np, np2;

  130.     int        nblocks, nloops;

  131.     register IComplex *p,*q;

  132.     int tmp_re, tmp_im;

  133. 

  134.     np = 1 << ln;

  135. 

  136.     /* reverse */

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

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

  139.         if (k < j)

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

  141.     }

  142. 

  143.     /* pass 0 */

  144. 

  145.     p=&z[0];

  146.     j=(np >> 1);

  147.     do {

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

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

  150.         p+=2;

  151.     } while (--j != 0);

  152. 

  153.     /* pass 1 */

  154. 

  155.     p=&z[0];

  156.     j=np >> 2;

  157.     do {

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

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

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

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

  162.         p+=4;

  163.     } while (--j != 0);

  164. 

  165.     /* pass 2 .. ln-1 */

  166. 

  167.     nblocks = np >> 3;

  168.     nloops = 1 << 2;

  169.     np2 = np >> 1;

  170.     do {

  171.         p = z;

  172.         q = z + nloops;

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

  174. 

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

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

  177. 

  178.             p++;

  179.             q++;

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

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

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

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

  184.                 p++;

  185.                 q++;

  186.             }

  187.             p += nloops;

  188.             q += nloops;

  189.         }

  190.         nblocks = nblocks >> 1;

  191.         nloops = nloops << 1;

  192.     } while (nblocks != 0);

  193. }

  194. 

  195. /* do a 512 point mdct */

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

  197. {

  198.     int i, re, im, re1, im1;

  199.     int16_t rot[N];

  200.     IComplex x[N/4];

  201. 

  202.     /* shift to simplify computations */

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

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

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

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

  207. 

  208.     /* pre rotation */

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

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

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

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

  213.     }

  214. 

  215.     fft(x, MDCT_NBITS - 2);

  216. 

  217.     /* post rotation */

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

  219.         re = x[i].re;

  220.         im = x[i].im;

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

  222.         out[2*i] = im1;

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

  224.     }

  225. }

  226. 

  227. /* XXX: use another norm ? */

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

  229. {

  230.     int sum, i;

  231.     sum = 0;

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

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

  234.     }

  235.     return sum;

  236. }

  237. 

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

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

  240.                                  int ch, int is_lfe)

  241. {

  242.     int i, j;

  243.     int exp_diff;

  244. 

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

  246.        reused in the next frame */

  247.     exp_strategy[0][ch] = EXP_NEW;

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

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

  250. #ifdef DEBUG

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

  252. #endif

  253.         if (exp_diff > EXP_DIFF_THRESHOLD)

  254.             exp_strategy[i][ch] = EXP_NEW;

  255.         else

  256.             exp_strategy[i][ch] = EXP_REUSE;

  257.     }

  258.     if (is_lfe)

  259.         return;

  260. 

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

  262.        recoded, we use a coarse encoding */

  263.     i = 0;

  264.     while (i < NB_BLOCKS) {

  265.         j = i + 1;

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

  267.             j++;

  268.         switch(j - i) {

  269.         case 1:

  270.             exp_strategy[i][ch] = EXP_D45;

  271.             break;

  272.         case 2:

  273.         case 3:

  274.             exp_strategy[i][ch] = EXP_D25;

  275.             break;

  276.         default:

  277.             exp_strategy[i][ch] = EXP_D15;

  278.             break;

  279.         }

  280.         i = j;

  281.     }

  282. }

  283. 

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

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

  286. {

  287.     int i;

  288. 

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

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

  291.             exp[i] = exp1[i];

  292.     }

  293. }

  294. 

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

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

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

  298.                       uint8_t exp[N/2],

  299.                       int nb_exps,

  300.                       int exp_strategy)

  301. {

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

  303.     uint8_t exp1[N/2];

  304. 

  305.     switch(exp_strategy) {

  306.     case EXP_D15:

  307.         group_size = 1;

  308.         break;

  309.     case EXP_D25:

  310.         group_size = 2;

  311.         break;

  312.     default:

  313.     case EXP_D45:

  314.         group_size = 4;

  315.         break;

  316.     }

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

  318. 

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

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

  321.     k = 1;

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

  323.         exp_min = exp[k];

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

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

  326.             if (exp[k+j] < exp_min)

  327.                 exp_min = exp[k+j];

  328.         }

  329.         exp1[i] = exp_min;

  330.         k += group_size;

  331.     }

  332. 

  333.     /* constraint for DC exponent */

  334.     if (exp1[0] > 15)

  335.         exp1[0] = 15;

  336. 

  337.     /* Decrease the delta between each groups to within 2

  338.      * so that they can be differentially encoded */

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

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

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

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

  343. 

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

  345.     encoded_exp[0] = exp1[0];

  346.     k = 1;

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

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

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

  350.         }

  351.         k += group_size;

  352.     }

  353. 

  354. #if defined(DEBUG)

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

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

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

  358.     }

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

  360. #endif

  361. 

  362.     return 4 + (nb_groups / 3) * 7;

  363. }

  364. 

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

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

  367. {

  368.     int bits, mant, i;

  369. 

  370.     bits = 0;

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

  372.         mant = m[i];

  373.         switch(mant) {

  374.         case 0:

  375.             /* nothing */

  376.             break;

  377.         case 1:

  378.             /* 3 mantissa in 5 bits */

  379.             if (s->mant1_cnt == 0)

  380.                 bits += 5;

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

  382.                 s->mant1_cnt = 0;

  383.             break;

  384.         case 2:

  385.             /* 3 mantissa in 7 bits */

  386.             if (s->mant2_cnt == 0)

  387.                 bits += 7;

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

  389.                 s->mant2_cnt = 0;

  390.             break;

  391.         case 3:

  392.             bits += 3;

  393.             break;

  394.         case 4:

  395.             /* 2 mantissa in 7 bits */

  396.             if (s->mant4_cnt == 0)

  397.                 bits += 7;

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

  399.                 s->mant4_cnt = 0;

  400.             break;

  401.         case 14:

  402.             bits += 14;

  403.             break;

  404.         case 15:

  405.             bits += 16;

  406.             break;

  407.         default:

  408.             bits += mant - 1;

  409.             break;

  410.         }

  411.     }

  412.     return bits;

  413. }

  414. 

  415. 

  416. static void bit_alloc_masking(AC3EncodeContext *s,

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

  418.                               uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

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

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

  421. {

  422.     int blk, ch;

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

  424. 

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

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

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

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

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

  430.             } else {

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

  432.                                           s->nb_coefs[ch],

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

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

  435.                                            0, s->nb_coefs[ch],

  436.                                            ff_ac3_fast_gain_tab[s->fast_gain_code[ch]],

  437.                                            ch == s->lfe_channel,

  438.                                            DBA_NONE, 0, NULL, NULL, NULL,

  439.                                            mask[blk][ch]);

  440.             }

  441.         }

  442.     }

  443. }

  444. 

  445. static int bit_alloc(AC3EncodeContext *s,

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

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

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

  449.                      int frame_bits, int coarse_snr_offset, int fine_snr_offset)

  450. {

  451.     int i, ch;

  452.     int snr_offset;

  453. 

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

  455. 

  456.     /* compute size */

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

  458.         s->mant1_cnt = 0;

  459.         s->mant2_cnt = 0;

  460.         s->mant4_cnt = 0;

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

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

  463.                                       s->nb_coefs[ch], snr_offset,

  464.                                       s->bit_alloc.floor, ff_ac3_bap_tab,

  465.                                       bap[i][ch]);

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

  467.                                                  s->nb_coefs[ch]);

  468.         }

  469.     }

  470. #if 0

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

  472.            coarse_snr_offset, fine_snr_offset, frame_bits,

  473.            16 * s->frame_size - ((frame_bits + 7) & ~7));

  474. #endif

  475.     return 16 * s->frame_size - frame_bits;

  476. }

  477. 

  478. #define SNR_INC1 4

  479. 

  480. static int compute_bit_allocation(AC3EncodeContext *s,

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

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

  483.                                   uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  484.                                   int frame_bits)

  485. {

  486.     int i, ch;

  487.     int coarse_snr_offset, fine_snr_offset;

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

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

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

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

  492. 

  493.     /* init default parameters */

  494.     s->slow_decay_code = 2;

  495.     s->fast_decay_code = 1;

  496.     s->slow_gain_code = 1;

  497.     s->db_per_bit_code = 2;

  498.     s->floor_code = 4;

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

  500.         s->fast_gain_code[ch] = 4;

  501. 

  502.     /* compute real values */

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

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

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

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

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

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

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

  510. 

  511.     /* header size */

  512.     frame_bits += 65;

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

  514.     //    frame_bits += 2;

  515.     frame_bits += frame_bits_inc[s->channel_mode];

  516. 

  517.     /* audio blocks */

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

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

  520.         if (s->channel_mode == AC3_CHMODE_STEREO) {

  521.             frame_bits++; /* rematstr */

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

  523.         }

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

  525.         if (s->lfe)

  526.             frame_bits++; /* lfeexpstr */

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

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

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

  530.         }

  531.         frame_bits++; /* baie */

  532.         frame_bits++; /* snr */

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

  534.     }

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

  536.     /* bit alloc info */

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

  538.     /* csnroffset[6] */

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

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

  541. 

  542.     /* auxdatae, crcrsv */

  543.     frame_bits += 2;

  544. 

  545.     /* CRC */

  546.     frame_bits += 16;

  547. 

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

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

  550. 

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

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

  553. 

  554.     coarse_snr_offset = s->coarse_snr_offset;

  555.     while (coarse_snr_offset >= 0 &&

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

  557.         coarse_snr_offset -= SNR_INC1;

  558.     if (coarse_snr_offset < 0) {

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

  560.         return -1;

  561.     }

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

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

  564.                      coarse_snr_offset + SNR_INC1, 0) >= 0) {

  565.         coarse_snr_offset += SNR_INC1;

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

  567.     }

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

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

  570.         coarse_snr_offset++;

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

  572.     }

  573. 

  574.     fine_snr_offset = 0;

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

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

  577.                      coarse_snr_offset, fine_snr_offset + SNR_INC1) >= 0) {

  578.         fine_snr_offset += SNR_INC1;

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

  580.     }

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

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

  583.                      coarse_snr_offset, fine_snr_offset + 1) >= 0) {

  584.         fine_snr_offset++;

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

  586.     }

  587. 

  588.     s->coarse_snr_offset = coarse_snr_offset;

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

  590.         s->fine_snr_offset[ch] = fine_snr_offset;

  591. #if defined(DEBUG_BITALLOC)

  592.     {

  593.         int j;

  594. 

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

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

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

  598.                 printf("bap=");

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

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

  601.                 }

  602.                 printf("\n");

  603.             }

  604.         }

  605.     }

  606. #endif

  607.     return 0;

  608. }

  609. 

  610. static av_cold int AC3_encode_init(AVCodecContext *avctx)

  611. {

  612.     int freq = avctx->sample_rate;

  613.     int bitrate = avctx->bit_rate;

  614.     int channels = avctx->channels;

  615.     AC3EncodeContext *s = avctx->priv_data;

  616.     int i, j, ch;

  617.     float alpha;

  618.     int bw_code;

  619.     static const uint8_t channel_mode_defs[6] = {

  620.         0x01, /* C */

  621.         0x02, /* L R */

  622.         0x03, /* L C R */

  623.         0x06, /* L R SL SR */

  624.         0x07, /* L C R SL SR */

  625.         0x07, /* L C R SL SR (+LFE) */

  626.     };

  627. 

  628.     avctx->frame_size = AC3_FRAME_SIZE;

  629. 

  630.     ac3_common_init();

  631. 

  632.     /* number of channels */

  633.     if (channels < 1 || channels > 6)

  634.         return -1;

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

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

  637.     s->nb_all_channels = channels;

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

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

  640. 

  641.     /* frequency */

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

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

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

  645.                 goto found;

  646.     }

  647.     return -1;

  648.  found:

  649.     s->sample_rate = freq;

  650.     s->sr_shift = i;

  651.     s->sr_code = j;

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

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

  654. 

  655.     /* bitrate & frame size */

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

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

  658.             break;

  659.     }

  660.     if (i == 19)

  661.         return -1;

  662.     s->bit_rate = bitrate;

  663.     s->frame_size_code = i << 1;

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

  665.     s->bits_written = 0;

  666.     s->samples_written = 0;

  667.     s->frame_size = s->frame_size_min;

  668. 

  669.     /* bit allocation init */

  670.     if(avctx->cutoff) {

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

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

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

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

  675.     } else {

  676.         /* use default bandwidth setting */

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

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

  679.         bw_code = 50;

  680.     }

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

  682.         /* bandwidth for each channel */

  683.         s->chbwcod[ch] = bw_code;

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

  685.     }

  686.     if (s->lfe) {

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

  688.     }

  689.     /* initial snr offset */

  690.     s->coarse_snr_offset = 40;

  691. 

  692.     /* mdct init */

  693.     fft_init(MDCT_NBITS - 2);

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

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

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

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

  698.     }

  699. 

  700.     avctx->coded_frame= avcodec_alloc_frame();

  701.     avctx->coded_frame->key_frame= 1;

  702. 

  703.     return 0;

  704. }

  705. 

  706. /* output the AC-3 frame header */

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

  708. {

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

  710. 

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

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

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

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

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

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

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

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

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

  720.     if (s->channel_mode & 0x04)

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

  722.     if (s->channel_mode == AC3_CHMODE_STEREO)

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

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

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

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

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

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

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

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

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

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

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

  734. }

  735. 

  736. /* symetric quantization on 'levels' levels */

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

  738. {

  739.     int v;

  740. 

  741.     if (c >= 0) {

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

  743.         v = (v + 1) >> 1;

  744.         v = (levels >> 1) + v;

  745.     } else {

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

  747.         v = (v + 1) >> 1;

  748.         v = (levels >> 1) - v;

  749.     }

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

  751.     return v;

  752. }

  753. 

  754. /* asymetric quantization on 2^qbits levels */

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

  756. {

  757.     int lshift, m, v;

  758. 

  759.     lshift = e + qbits - 24;

  760.     if (lshift >= 0)

  761.         v = c << lshift;

  762.     else

  763.         v = c >> (-lshift);

  764.     /* rounding */

  765.     v = (v + 1) >> 1;

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

  767.     if (v >= m)

  768.         v = m - 1;

  769.     assert(v >= -m);

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

  771. }

  772. 

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

  774.    frame */

  775. static void output_audio_block(AC3EncodeContext *s,

  776.                                uint8_t exp_strategy[AC3_MAX_CHANNELS],

  777.                                uint8_t encoded_exp[AC3_MAX_CHANNELS][N/2],

  778.                                uint8_t bap[AC3_MAX_CHANNELS][N/2],

  779.                                int32_t mdct_coefs[AC3_MAX_CHANNELS][N/2],

  780.                                int8_t global_exp[AC3_MAX_CHANNELS],

  781.                                int block_num)

  782. {

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

  784.     uint8_t *p;

  785.     uint16_t qmant[AC3_MAX_CHANNELS][N/2];

  786.     int exp0, exp1;

  787.     int mant1_cnt, mant2_cnt, mant4_cnt;

  788.     uint16_t *qmant1_ptr, *qmant2_ptr, *qmant4_ptr;

  789.     int delta0, delta1, delta2;

  790. 

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

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

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

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

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

  796.     if (block_num == 0) {

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

  798.            waste of bit :-) */

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

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

  801.     } else {

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

  803.     }

  804. 

  805.     if (s->channel_mode == AC3_CHMODE_STEREO)

  806.       {

  807.         if(block_num==0)

  808.           {

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

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

  811. 

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

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

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

  815.           }

  816.         else

  817.           {

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

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

  820.           }

  821.       }

  822. 

  823. #if defined(DEBUG)

  824.     {

  825.       static int count = 0;

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

  827.     }

  828. #endif

  829.     /* exponent strategy */

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

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

  832.     }

  833. 

  834.     if (s->lfe) {

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

  836.     }

  837. 

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

  839.         if (exp_strategy[ch] != EXP_REUSE)

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

  841.     }

  842. 

  843.     /* exponents */

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

  845.         switch(exp_strategy[ch]) {

  846.         case EXP_REUSE:

  847.             continue;

  848.         case EXP_D15:

  849.             group_size = 1;

  850.             break;

  851.         case EXP_D25:

  852.             group_size = 2;

  853.             break;

  854.         default:

  855.         case EXP_D45:

  856.             group_size = 4;

  857.             break;

  858.         }

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

  860.         p = encoded_exp[ch];

  861. 

  862.         /* first exponent */

  863.         exp1 = *p++;

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

  865. 

  866.         /* next ones are delta encoded */

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

  868.             /* merge three delta in one code */

  869.             exp0 = exp1;

  870.             exp1 = p[0];

  871.             p += group_size;

  872.             delta0 = exp1 - exp0 + 2;

  873. 

  874.             exp0 = exp1;

  875.             exp1 = p[0];

  876.             p += group_size;

  877.             delta1 = exp1 - exp0 + 2;

  878. 

  879.             exp0 = exp1;

  880.             exp1 = p[0];

  881.             p += group_size;

  882.             delta2 = exp1 - exp0 + 2;

  883. 

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

  885.         }

  886. 

  887.         if (ch != s->lfe_channel)

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

  889.     }

  890. 

  891.     /* bit allocation info */

  892.     baie = (block_num == 0);

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

  894.     if (baie) {

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

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

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

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

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

  900.     }

  901. 

  902.     /* snr offset */

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

  904.     if (baie) {

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

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

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

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

  909.         }

  910.     }

  911. 

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

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

  914. 

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

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

  917.        modify the output stream. */

  918. 

  919.     /* first pass: quantize */

  920.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  921.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  922. 

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

  924.         int b, c, e, v;

  925. 

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

  927.             c = mdct_coefs[ch][i];

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

  929.             b = bap[ch][i];

  930.             switch(b) {

  931.             case 0:

  932.                 v = 0;

  933.                 break;

  934.             case 1:

  935.                 v = sym_quant(c, e, 3);

  936.                 switch(mant1_cnt) {

  937.                 case 0:

  938.                     qmant1_ptr = &qmant[ch][i];

  939.                     v = 9 * v;

  940.                     mant1_cnt = 1;

  941.                     break;

  942.                 case 1:

  943.                     *qmant1_ptr += 3 * v;

  944.                     mant1_cnt = 2;

  945.                     v = 128;

  946.                     break;

  947.                 default:

  948.                     *qmant1_ptr += v;

  949.                     mant1_cnt = 0;

  950.                     v = 128;

  951.                     break;

  952.                 }

  953.                 break;

  954.             case 2:

  955.                 v = sym_quant(c, e, 5);

  956.                 switch(mant2_cnt) {

  957.                 case 0:

  958.                     qmant2_ptr = &qmant[ch][i];

  959.                     v = 25 * v;

  960.                     mant2_cnt = 1;

  961.                     break;

  962.                 case 1:

  963.                     *qmant2_ptr += 5 * v;

  964.                     mant2_cnt = 2;

  965.                     v = 128;

  966.                     break;

  967.                 default:

  968.                     *qmant2_ptr += v;

  969.                     mant2_cnt = 0;

  970.                     v = 128;

  971.                     break;

  972.                 }

  973.                 break;

  974.             case 3:

  975.                 v = sym_quant(c, e, 7);

  976.                 break;

  977.             case 4:

  978.                 v = sym_quant(c, e, 11);

  979.                 switch(mant4_cnt) {

  980.                 case 0:

  981.                     qmant4_ptr = &qmant[ch][i];

  982.                     v = 11 * v;

  983.                     mant4_cnt = 1;

  984.                     break;

  985.                 default:

  986.                     *qmant4_ptr += v;

  987.                     mant4_cnt = 0;

  988.                     v = 128;

  989.                     break;

  990.                 }

  991.                 break;

  992.             case 5:

  993.                 v = sym_quant(c, e, 15);

  994.                 break;

  995.             case 14:

  996.                 v = asym_quant(c, e, 14);

  997.                 break;

  998.             case 15:

  999.                 v = asym_quant(c, e, 16);

  1000.                 break;

  1001.             default:

  1002.                 v = asym_quant(c, e, b - 1);

  1003.                 break;

  1004.             }

  1005.             qmant[ch][i] = v;

  1006.         }

  1007.     }

  1008. 

  1009.     /* second pass : output the values */

  1010.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1011.         int b, q;

  1012. 

  1013.         for(i=0;i<s->nb_coefs[ch];i++) {

  1014.             q = qmant[ch][i];

  1015.             b = bap[ch][i];

  1016.             switch(b) {

  1017.             case 0:

  1018.                 break;

  1019.             case 1:

  1020.                 if (q != 128)

  1021.                     put_bits(&s->pb, 5, q);

  1022.                 break;

  1023.             case 2:

  1024.                 if (q != 128)

  1025.                     put_bits(&s->pb, 7, q);

  1026.                 break;

  1027.             case 3:

  1028.                 put_bits(&s->pb, 3, q);

  1029.                 break;

  1030.             case 4:

  1031.                 if (q != 128)

  1032.                     put_bits(&s->pb, 7, q);

  1033.                 break;

  1034.             case 14:

  1035.                 put_bits(&s->pb, 14, q);

  1036.                 break;

  1037.             case 15:

  1038.                 put_bits(&s->pb, 16, q);

  1039.                 break;

  1040.             default:

  1041.                 put_bits(&s->pb, b - 1, q);

  1042.                 break;

  1043.             }

  1044.         }

  1045.     }

  1046. }

  1047. 

  1048. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1049. 

  1050. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1051. {

  1052.     unsigned int c;

  1053. 

  1054.     c = 0;

  1055.     while (a) {

  1056.         if (a & 1)

  1057.             c ^= b;

  1058.         a = a >> 1;

  1059.         b = b << 1;

  1060.         if (b & (1 << 16))

  1061.             b ^= poly;

  1062.     }

  1063.     return c;

  1064. }

  1065. 

  1066. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1067. {

  1068.     unsigned int r;

  1069.     r = 1;

  1070.     while (n) {

  1071.         if (n & 1)

  1072.             r = mul_poly(r, a, poly);

  1073.         a = mul_poly(a, a, poly);

  1074.         n >>= 1;

  1075.     }

  1076.     return r;

  1077. }

  1078. 

  1079. 

  1080. /* compute log2(max(abs(tab[]))) */

  1081. static int log2_tab(int16_t *tab, int n)

  1082. {

  1083.     int i, v;

  1084. 

  1085.     v = 0;

  1086.     for(i=0;i<n;i++) {

  1087.         v |= abs(tab[i]);

  1088.     }

  1089.     return av_log2(v);

  1090. }

  1091. 

  1092. static void lshift_tab(int16_t *tab, int n, int lshift)

  1093. {

  1094.     int i;

  1095. 

  1096.     if (lshift > 0) {

  1097.         for(i=0;i<n;i++) {

  1098.             tab[i] <<= lshift;

  1099.         }

  1100.     } else if (lshift < 0) {

  1101.         lshift = -lshift;

  1102.         for(i=0;i<n;i++) {

  1103.             tab[i] >>= lshift;

  1104.         }

  1105.     }

  1106. }

  1107. 

  1108. /* fill the end of the frame and compute the two crcs */

  1109. static int output_frame_end(AC3EncodeContext *s)

  1110. {

  1111.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1112.     uint8_t *frame;

  1113. 

  1114.     frame_size = s->frame_size; /* frame size in words */

  1115.     /* align to 8 bits */

  1116.     flush_put_bits(&s->pb);

  1117.     /* add zero bytes to reach the frame size */

  1118.     frame = s->pb.buf;

  1119.     n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;

  1120.     assert(n >= 0);

  1121.     if(n>0)

  1122.       memset(pbBufPtr(&s->pb), 0, n);

  1123. 

  1124.     /* Now we must compute both crcs : this is not so easy for crc1

  1125.        because it is at the beginning of the data... */

  1126.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1127.     crc1 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

  1128.                            frame + 4, 2 * frame_size_58 - 4));

  1129.     /* XXX: could precompute crc_inv */

  1130.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1131.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1132.     AV_WB16(frame+2,crc1);

  1133. 

  1134.     crc2 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

  1135.                            frame + 2 * frame_size_58,

  1136.                            (frame_size - frame_size_58) * 2 - 2));

  1137.     AV_WB16(frame+2*frame_size-2,crc2);

  1138. 

  1139.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1140.     return frame_size * 2;

  1141. }

  1142. 

  1143. static int AC3_encode_frame(AVCodecContext *avctx,

  1144.                             unsigned char *frame, int buf_size, void *data)

  1145. {

  1146.     AC3EncodeContext *s = avctx->priv_data;

  1147.     int16_t *samples = data;

  1148.     int i, j, k, v, ch;

  1149.     int16_t input_samples[N];

  1150.     int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1151.     uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1152.     uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

  1153.     uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1154.     uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1155.     int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

  1156.     int frame_bits;

  1157. 

  1158.     frame_bits = 0;

  1159.     for(ch=0;ch<s->nb_all_channels;ch++) {

  1160.         /* fixed mdct to the six sub blocks & exponent computation */

  1161.         for(i=0;i<NB_BLOCKS;i++) {

  1162.             int16_t *sptr;

  1163.             int sinc;

  1164. 

  1165.             /* compute input samples */

  1166.             memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(int16_t));

  1167.             sinc = s->nb_all_channels;

  1168.             sptr = samples + (sinc * (N/2) * i) + ch;

  1169.             for(j=0;j<N/2;j++) {

  1170.                 v = *sptr;

  1171.                 input_samples[j + N/2] = v;

  1172.                 s->last_samples[ch][j] = v;

  1173.                 sptr += sinc;

  1174.             }

  1175. 

  1176.             /* apply the MDCT window */

  1177.             for(j=0;j<N/2;j++) {

  1178.                 input_samples[j] = MUL16(input_samples[j],

  1179.                                          ff_ac3_window[j]) >> 15;

  1180.                 input_samples[N-j-1] = MUL16(input_samples[N-j-1],

  1181.                                              ff_ac3_window[j]) >> 15;

  1182.             }

  1183. 

  1184.             /* Normalize the samples to use the maximum available

  1185.                precision */

  1186.             v = 14 - log2_tab(input_samples, N);

  1187.             if (v < 0)

  1188.                 v = 0;

  1189.             exp_samples[i][ch] = v - 9;

  1190.             lshift_tab(input_samples, N, v);

  1191. 

  1192.             /* do the MDCT */

  1193.             mdct512(mdct_coef[i][ch], input_samples);

  1194. 

  1195.             /* compute "exponents". We take into account the

  1196.                normalization there */

  1197.             for(j=0;j<N/2;j++) {

  1198.                 int e;

  1199.                 v = abs(mdct_coef[i][ch][j]);

  1200.                 if (v == 0)

  1201.                     e = 24;

  1202.                 else {

  1203.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1204.                     if (e >= 24) {

  1205.                         e = 24;

  1206.                         mdct_coef[i][ch][j] = 0;

  1207.                     }

  1208.                 }

  1209.                 exp[i][ch][j] = e;

  1210.             }

  1211.         }

  1212. 

  1213.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1214. 

  1215.         /* compute the exponents as the decoder will see them. The

  1216.            EXP_REUSE case must be handled carefully : we select the

  1217.            min of the exponents */

  1218.         i = 0;

  1219.         while (i < NB_BLOCKS) {

  1220.             j = i + 1;

  1221.             while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1222.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1223.                 j++;

  1224.             }

  1225.             frame_bits += encode_exp(encoded_exp[i][ch],

  1226.                                      exp[i][ch], s->nb_coefs[ch],

  1227.                                      exp_strategy[i][ch]);

  1228.             /* copy encoded exponents for reuse case */

  1229.             for(k=i+1;k<j;k++) {

  1230.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch],

  1231.                        s->nb_coefs[ch] * sizeof(uint8_t));

  1232.             }

  1233.             i = j;

  1234.         }

  1235.     }

  1236. 

  1237.     /* adjust for fractional frame sizes */

  1238.     while(s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {

  1239.         s->bits_written -= s->bit_rate;

  1240.         s->samples_written -= s->sample_rate;

  1241.     }

  1242.     s->frame_size = s->frame_size_min + (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);

  1243.     s->bits_written += s->frame_size * 16;

  1244.     s->samples_written += AC3_FRAME_SIZE;

  1245. 

  1246.     compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

  1247.     /* everything is known... let's output the frame */

  1248.     output_frame_header(s, frame);

  1249. 

  1250.     for(i=0;i<NB_BLOCKS;i++) {

  1251.         output_audio_block(s, exp_strategy[i], encoded_exp[i],

  1252.                            bap[i], mdct_coef[i], exp_samples[i], i);

  1253.     }

  1254.     return output_frame_end(s);

  1255. }

  1256. 

  1257. static av_cold int AC3_encode_close(AVCodecContext *avctx)

  1258. {

  1259.     av_freep(&avctx->coded_frame);

  1260.     return 0;

  1261. }

  1262. 

  1263. #if 0

  1264. /*************************************************************************/

  1265. /* TEST */

  1266. 

  1267. #undef random

  1268. #define FN (N/4)

  1269. 

  1270. void fft_test(void)

  1271. {

  1272.     IComplex in[FN], in1[FN];

  1273.     int k, n, i;

  1274.     float sum_re, sum_im, a;

  1275. 

  1276.     /* FFT test */

  1277. 

  1278.     for(i=0;i<FN;i++) {

  1279.         in[i].re = random() % 65535 - 32767;

  1280.         in[i].im = random() % 65535 - 32767;

  1281.         in1[i] = in[i];

  1282.     }

  1283.     fft(in, 7);

  1284. 

  1285.     /* do it by hand */

  1286.     for(k=0;k<FN;k++) {

  1287.         sum_re = 0;

  1288.         sum_im = 0;

  1289.         for(n=0;n<FN;n++) {

  1290.             a = -2 * M_PI * (n * k) / FN;

  1291.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1292.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1293.         }

  1294.         printf("%3d: %6d,%6d %6.0f,%6.0f\n",

  1295.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);

  1296.     }

  1297. }

  1298. 

  1299. void mdct_test(void)

  1300. {

  1301.     int16_t input[N];

  1302.     int32_t output[N/2];

  1303.     float input1[N];

  1304.     float output1[N/2];

  1305.     float s, a, err, e, emax;

  1306.     int i, k, n;

  1307. 

  1308.     for(i=0;i<N;i++) {

  1309.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1310.         input1[i] = input[i];

  1311.     }

  1312. 

  1313.     mdct512(output, input);

  1314. 

  1315.     /* do it by hand */

  1316.     for(k=0;k<N/2;k++) {

  1317.         s = 0;

  1318.         for(n=0;n<N;n++) {

  1319.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1320.             s += input1[n] * cos(a);

  1321.         }

  1322.         output1[k] = -2 * s / N;

  1323.     }

  1324. 

  1325.     err = 0;

  1326.     emax = 0;

  1327.     for(i=0;i<N/2;i++) {

  1328.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1329.         e = output[i] - output1[i];

  1330.         if (e > emax)

  1331.             emax = e;

  1332.         err += e * e;

  1333.     }

  1334.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1335. }

  1336. 

  1337. void test_ac3(void)

  1338. {

  1339.     AC3EncodeContext ctx;

  1340.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1341.     short samples[AC3_FRAME_SIZE];

  1342.     int ret, i;

  1343. 

  1344.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1345. 

  1346.     fft_test();

  1347.     mdct_test();

  1348. 

  1349.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1350.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1351.     ret = AC3_encode_frame(&ctx, frame, samples);

  1352.     printf("ret=%d\n", ret);

  1353. }

  1354. #endif

  1355. 

  1356. AVCodec ac3_encoder = {

  1357.     "ac3",

  1358.     CODEC_TYPE_AUDIO,

  1359.     CODEC_ID_AC3,

  1360.     sizeof(AC3EncodeContext),

  1361.     AC3_encode_init,

  1362.     AC3_encode_frame,

  1363.     AC3_encode_close,

  1364.     NULL,

  1365.     .sample_fmts = (enum SampleFormat[]){SAMPLE_FMT_S16,SAMPLE_FMT_NONE},

  1366.     .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),

  1367. };