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FFmpeg/libavcodec/ac3enc.c

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  1. /*

  2.  * The simplest AC3 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 ac3enc.c

  24.  * The simplest AC3 encoder.

  25.  */

  26. //#define DEBUG

  27. //#define DEBUG_BITALLOC

  28. #include "avcodec.h"

  29. #include "bitstream.h"

  30. #include "crc.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 bsid;

  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 halfratecod;

  46.     unsigned int frmsizecod;

  47.     unsigned int fscod; /* frequency */

  48.     unsigned int acmod;

  49.     int lfe;

  50.     unsigned int bsmod;

  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 sgaincod, sdecaycod, fdecaycod, dbkneecod, floorcod;

  57.     AC3BitAllocParameters bit_alloc;

  58.     int csnroffst;

  59.     int fgaincod[AC3_MAX_CHANNELS];

  60.     int fsnroffst[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 fft_rev[512];

  68. static int16_t xcos1[128];

  69. static int16_t xsin1[128];

  70. 

  71. #define MDCT_NBITS 9

  72. #define N         (1 << MDCT_NBITS)

  73. 

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

  75. #define EXP_DIFF_THRESHOLD 1000

  76. 

  77. static void fft_init(int ln);

  78. 

  79. static inline int16_t fix15(float a)

  80. {

  81.     int v;

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

  83.     if (v < -32767)

  84.         v = -32767;

  85.     else if (v > 32767)

  86.         v = 32767;

  87.     return v;

  88. }

  89. 

  90. typedef struct IComplex {

  91.     short re,im;

  92. } IComplex;

  93. 

  94. static void fft_init(int ln)

  95. {

  96.     int i, j, m, n;

  97.     float alpha;

  98. 

  99.     n = 1 << ln;

  100. 

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

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

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

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

  105.     }

  106. 

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

  108.         m=0;

  109.         for(j=0;j<ln;j++) {

  110.             m |= ((i >> j) & 1) << (ln-j-1);

  111.         }

  112.         fft_rev[i]=m;

  113.     }

  114. }

  115. 

  116. /* butter fly op */

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

  118. {\

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

  120.   bx=pre1;\

  121.   by=pim1;\

  122.   ax=qre1;\

  123.   ay=qim1;\

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

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

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

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

  128. }

  129. 

  130. #define MUL16(a,b) ((a) * (b))

  131. 

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

  133. {\

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

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

  136. }

  137. 

  138. 

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

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

  141. {

  142.     int        j, l, np, np2;

  143.     int        nblocks, nloops;

  144.     register IComplex *p,*q;

  145.     int tmp_re, tmp_im;

  146. 

  147.     np = 1 << ln;

  148. 

  149.     /* reverse */

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

  151.         int k;

  152.         IComplex tmp;

  153.         k = fft_rev[j];

  154.         if (k < j) {

  155.             tmp = z[k];

  156.             z[k] = z[j];

  157.             z[j] = tmp;

  158.         }

  159.     }

  160. 

  161.     /* pass 0 */

  162. 

  163.     p=&z[0];

  164.     j=(np >> 1);

  165.     do {

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

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

  168.         p+=2;

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

  170. 

  171.     /* pass 1 */

  172. 

  173.     p=&z[0];

  174.     j=np >> 2;

  175.     do {

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

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

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

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

  180.         p+=4;

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

  182. 

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

  184. 

  185.     nblocks = np >> 3;

  186.     nloops = 1 << 2;

  187.     np2 = np >> 1;

  188.     do {

  189.         p = z;

  190.         q = z + nloops;

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

  192. 

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

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

  195. 

  196.             p++;

  197.             q++;

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

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

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

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

  202.                 p++;

  203.                 q++;

  204.             }

  205.             p += nloops;

  206.             q += nloops;

  207.         }

  208.         nblocks = nblocks >> 1;

  209.         nloops = nloops << 1;

  210.     } while (nblocks != 0);

  211. }

  212. 

  213. /* do a 512 point mdct */

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

  215. {

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

  217.     int16_t rot[N];

  218.     IComplex x[N/4];

  219. 

  220.     /* shift to simplify computations */

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

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

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

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

  225. 

  226.     /* pre rotation */

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

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

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

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

  231.     }

  232. 

  233.     fft(x, MDCT_NBITS - 2);

  234. 

  235.     /* post rotation */

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

  237.         re = x[i].re;

  238.         im = x[i].im;

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

  240.         out[2*i] = im1;

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

  242.     }

  243. }

  244. 

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

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

  247. {

  248.     int sum, i;

  249.     sum = 0;

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

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

  252.     }

  253.     return sum;

  254. }

  255. 

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

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

  258.                                  int ch, int is_lfe)

  259. {

  260.     int i, j;

  261.     int exp_diff;

  262. 

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

  264.        reused in the next frame */

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

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

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

  268. #ifdef DEBUG

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

  270. #endif

  271.         if (exp_diff > EXP_DIFF_THRESHOLD)

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

  273.         else

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

  275.     }

  276.     if (is_lfe)

  277.         return;

  278. 

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

  280.        recoded, we use a coarse encoding */

  281.     i = 0;

  282.     while (i < NB_BLOCKS) {

  283.         j = i + 1;

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

  285.             j++;

  286.         switch(j - i) {

  287.         case 1:

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

  289.             break;

  290.         case 2:

  291.         case 3:

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

  293.             break;

  294.         default:

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

  296.             break;

  297.         }

  298.         i = j;

  299.     }

  300. }

  301. 

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

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

  304. {

  305.     int i;

  306. 

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

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

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

  310.     }

  311. }

  312. 

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

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

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

  316.                       uint8_t exp[N/2],

  317.                       int nb_exps,

  318.                       int exp_strategy)

  319. {

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

  321.     uint8_t exp1[N/2];

  322. 

  323.     switch(exp_strategy) {

  324.     case EXP_D15:

  325.         group_size = 1;

  326.         break;

  327.     case EXP_D25:

  328.         group_size = 2;

  329.         break;

  330.     default:

  331.     case EXP_D45:

  332.         group_size = 4;

  333.         break;

  334.     }

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

  336. 

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

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

  339.     k = 1;

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

  341.         exp_min = exp[k];

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

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

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

  345.                 exp_min = exp[k+j];

  346.         }

  347.         exp1[i] = exp_min;

  348.         k += group_size;

  349.     }

  350. 

  351.     /* constraint for DC exponent */

  352.     if (exp1[0] > 15)

  353.         exp1[0] = 15;

  354. 

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

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

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

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

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

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

  361. 

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

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

  364.     k = 1;

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

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

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

  368.         }

  369.         k += group_size;

  370.     }

  371. 

  372. #if defined(DEBUG)

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

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

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

  376.     }

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

  378. #endif

  379. 

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

  381. }

  382. 

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

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

  385. {

  386.     int bits, mant, i;

  387. 

  388.     bits = 0;

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

  390.         mant = m[i];

  391.         switch(mant) {

  392.         case 0:

  393.             /* nothing */

  394.             break;

  395.         case 1:

  396.             /* 3 mantissa in 5 bits */

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

  398.                 bits += 5;

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

  400.                 s->mant1_cnt = 0;

  401.             break;

  402.         case 2:

  403.             /* 3 mantissa in 7 bits */

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

  405.                 bits += 7;

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

  407.                 s->mant2_cnt = 0;

  408.             break;

  409.         case 3:

  410.             bits += 3;

  411.             break;

  412.         case 4:

  413.             /* 2 mantissa in 7 bits */

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

  415.                 bits += 7;

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

  417.                 s->mant4_cnt = 0;

  418.             break;

  419.         case 14:

  420.             bits += 14;

  421.             break;

  422.         case 15:

  423.             bits += 16;

  424.             break;

  425.         default:

  426.             bits += mant - 1;

  427.             break;

  428.         }

  429.     }

  430.     return bits;

  431. }

  432. 

  433. 

  434. static void bit_alloc_masking(AC3EncodeContext *s,

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

  436.                               uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

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

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

  439. {

  440.     int blk, ch;

  441.     int16_t bndpsd[NB_BLOCKS][AC3_MAX_CHANNELS][50];

  442. 

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

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

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

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

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

  448.             } else {

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

  450.                                           s->nb_coefs[ch],

  451.                                           psd[blk][ch], bndpsd[blk][ch]);

  452.                 ff_ac3_bit_alloc_calc_mask(&s->bit_alloc, bndpsd[blk][ch],

  453.                                            0, s->nb_coefs[ch],

  454.                                            ff_fgaintab[s->fgaincod[ch]],

  455.                                            ch == s->lfe_channel,

  456.                                            DBA_NONE, 0, NULL, NULL, NULL,

  457.                                            mask[blk][ch]);

  458.             }

  459.         }

  460.     }

  461. }

  462. 

  463. static int bit_alloc(AC3EncodeContext *s,

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

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

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

  467.                      int frame_bits, int csnroffst, int fsnroffst)

  468. {

  469.     int i, ch;

  470.     int snroffset;

  471. 

  472.     snroffset = (((csnroffst - 15) << 4) + fsnroffst) << 2;

  473. 

  474.     /* compute size */

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

  476.         s->mant1_cnt = 0;

  477.         s->mant2_cnt = 0;

  478.         s->mant4_cnt = 0;

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

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

  481.                                       s->nb_coefs[ch], snroffset,

  482.                                       s->bit_alloc.floor, bap[i][ch]);

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

  484.                                                  s->nb_coefs[ch]);

  485.         }

  486.     }

  487. #if 0

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

  489.            csnroffst, fsnroffst, frame_bits,

  490.            16 * s->frame_size - ((frame_bits + 7) & ~7));

  491. #endif

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

  493. }

  494. 

  495. #define SNR_INC1 4

  496. 

  497. static int compute_bit_allocation(AC3EncodeContext *s,

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

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

  500.                                   uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  501.                                   int frame_bits)

  502. {

  503.     int i, ch;

  504.     int csnroffst, fsnroffst;

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

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

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

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

  509. 

  510.     /* init default parameters */

  511.     s->sdecaycod = 2;

  512.     s->fdecaycod = 1;

  513.     s->sgaincod = 1;

  514.     s->dbkneecod = 2;

  515.     s->floorcod = 4;

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

  517.         s->fgaincod[ch] = 4;

  518. 

  519.     /* compute real values */

  520.     s->bit_alloc.fscod = s->fscod;

  521.     s->bit_alloc.halfratecod = s->halfratecod;

  522.     s->bit_alloc.sdecay = ff_sdecaytab[s->sdecaycod] >> s->halfratecod;

  523.     s->bit_alloc.fdecay = ff_fdecaytab[s->fdecaycod] >> s->halfratecod;

  524.     s->bit_alloc.sgain = ff_sgaintab[s->sgaincod];

  525.     s->bit_alloc.dbknee = ff_dbkneetab[s->dbkneecod];

  526.     s->bit_alloc.floor = ff_floortab[s->floorcod];

  527. 

  528.     /* header size */

  529.     frame_bits += 65;

  530.     // if (s->acmod == 2)

  531.     //    frame_bits += 2;

  532.     frame_bits += frame_bits_inc[s->acmod];

  533. 

  534.     /* audio blocks */

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

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

  537.         if (s->acmod == AC3_ACMOD_STEREO) {

  538.             frame_bits++; /* rematstr */

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

  540.         }

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

  542.         if (s->lfe)

  543.             frame_bits++; /* lfeexpstr */

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

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

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

  547.         }

  548.         frame_bits++; /* baie */

  549.         frame_bits++; /* snr */

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

  551.     }

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

  553.     /* bit alloc info */

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

  555.     /* csnroffset[6] */

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

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

  558. 

  559.     /* auxdatae, crcrsv */

  560.     frame_bits += 2;

  561. 

  562.     /* CRC */

  563.     frame_bits += 16;

  564. 

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

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

  567. 

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

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

  570. 

  571.     csnroffst = s->csnroffst;

  572.     while (csnroffst >= 0 &&

  573.            bit_alloc(s, mask, psd, bap, frame_bits, csnroffst, 0) < 0)

  574.         csnroffst -= SNR_INC1;

  575.     if (csnroffst < 0) {

  576.         av_log(NULL, AV_LOG_ERROR, "Bit allocation failed, try increasing the bitrate, -ab 384 for example!\n");

  577.         return -1;

  578.     }

  579.     while ((csnroffst + SNR_INC1) <= 63 &&

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

  581.                      csnroffst + SNR_INC1, 0) >= 0) {

  582.         csnroffst += SNR_INC1;

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

  584.     }

  585.     while ((csnroffst + 1) <= 63 &&

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

  587.         csnroffst++;

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

  589.     }

  590. 

  591.     fsnroffst = 0;

  592.     while ((fsnroffst + SNR_INC1) <= 15 &&

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

  594.                      csnroffst, fsnroffst + SNR_INC1) >= 0) {

  595.         fsnroffst += SNR_INC1;

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

  597.     }

  598.     while ((fsnroffst + 1) <= 15 &&

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

  600.                      csnroffst, fsnroffst + 1) >= 0) {

  601.         fsnroffst++;

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

  603.     }

  604. 

  605.     s->csnroffst = csnroffst;

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

  607.         s->fsnroffst[ch] = fsnroffst;

  608. #if defined(DEBUG_BITALLOC)

  609.     {

  610.         int j;

  611. 

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

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

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

  615.                 printf("bap=");

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

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

  618.                 }

  619.                 printf("\n");

  620.             }

  621.         }

  622.     }

  623. #endif

  624.     return 0;

  625. }

  626. 

  627. static int AC3_encode_init(AVCodecContext *avctx)

  628. {

  629.     int freq = avctx->sample_rate;

  630.     int bitrate = avctx->bit_rate;

  631.     int channels = avctx->channels;

  632.     AC3EncodeContext *s = avctx->priv_data;

  633.     int i, j, ch;

  634.     float alpha;

  635.     static const uint8_t acmod_defs[6] = {

  636.         0x01, /* C */

  637.         0x02, /* L R */

  638.         0x03, /* L C R */

  639.         0x06, /* L R SL SR */

  640.         0x07, /* L C R SL SR */

  641.         0x07, /* L C R SL SR (+LFE) */

  642.     };

  643. 

  644.     avctx->frame_size = AC3_FRAME_SIZE;

  645. 

  646.     ac3_common_init();

  647. 

  648.     /* number of channels */

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

  650.         return -1;

  651.     s->acmod = acmod_defs[channels - 1];

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

  653.     s->nb_all_channels = channels;

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

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

  656. 

  657.     /* frequency */

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

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

  660.             if ((ff_ac3_freqs[j] >> i) == freq)

  661.                 goto found;

  662.     }

  663.     return -1;

  664.  found:

  665.     s->sample_rate = freq;

  666.     s->halfratecod = i;

  667.     s->fscod = j;

  668.     s->bsid = 8 + s->halfratecod;

  669.     s->bsmod = 0; /* complete main audio service */

  670. 

  671.     /* bitrate & frame size */

  672.     bitrate /= 1000;

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

  674.         if ((ff_ac3_bitratetab[i] >> s->halfratecod) == bitrate)

  675.             break;

  676.     }

  677.     if (i == 19)

  678.         return -1;

  679.     s->bit_rate = bitrate;

  680.     s->frmsizecod = i << 1;

  681.     s->frame_size_min = ff_ac3_frame_sizes[s->frmsizecod][s->fscod];

  682.     s->bits_written = 0;

  683.     s->samples_written = 0;

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

  685. 

  686.     /* bit allocation init */

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

  688.         /* bandwidth for each channel */

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

  690.            size, so that we avoid anoying high freq artefacts */

  691.         s->chbwcod[ch] = 50; /* sample bandwidth as mpeg audio layer 2 table 0 */

  692.         s->nb_coefs[ch] = ((s->chbwcod[ch] + 12) * 3) + 37;

  693.     }

  694.     if (s->lfe) {

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

  696.     }

  697.     /* initial snr offset */

  698.     s->csnroffst = 40;

  699. 

  700.     /* mdct init */

  701.     fft_init(MDCT_NBITS - 2);

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

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

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

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

  706.     }

  707. 

  708.     avctx->coded_frame= avcodec_alloc_frame();

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

  710. 

  711.     return 0;

  712. }

  713. 

  714. /* output the AC3 frame header */

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

  716. {

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

  718. 

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

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

  721.     put_bits(&s->pb, 2, s->fscod);

  722.     put_bits(&s->pb, 6, s->frmsizecod + (s->frame_size - s->frame_size_min));

  723.     put_bits(&s->pb, 5, s->bsid);

  724.     put_bits(&s->pb, 3, s->bsmod);

  725.     put_bits(&s->pb, 3, s->acmod);

  726.     if ((s->acmod & 0x01) && s->acmod != AC3_ACMOD_MONO)

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

  728.     if (s->acmod & 0x04)

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

  730.     if (s->acmod == AC3_ACMOD_STEREO)

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

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

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

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

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

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

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

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

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

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

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

  742. }

  743. 

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

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

  746. {

  747.     int v;

  748. 

  749.     if (c >= 0) {

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

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

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

  753.     } else {

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

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

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

  757.     }

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

  759.     return v;

  760. }

  761. 

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

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

  764. {

  765.     int lshift, m, v;

  766. 

  767.     lshift = e + qbits - 24;

  768.     if (lshift >= 0)

  769.         v = c << lshift;

  770.     else

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

  772.     /* rounding */

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

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

  775.     if (v >= m)

  776.         v = m - 1;

  777.     assert(v >= -m);

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

  779. }

  780. 

  781. /* Output one audio block. There are NB_BLOCKS audio blocks in one AC3

  782.    frame */

  783. static void output_audio_block(AC3EncodeContext *s,

  784.                                uint8_t exp_strategy[AC3_MAX_CHANNELS],

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

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

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

  788.                                int8_t global_exp[AC3_MAX_CHANNELS],

  789.                                int block_num)

  790. {

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

  792.     uint8_t *p;

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

  794.     int exp0, exp1;

  795.     int mant1_cnt, mant2_cnt, mant4_cnt;

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

  797.     int delta0, delta1, delta2;

  798. 

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

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

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

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

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

  804.     if (block_num == 0) {

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

  806.            waste of bit :-) */

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

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

  809.     } else {

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

  811.     }

  812. 

  813.     if (s->acmod == AC3_ACMOD_STEREO)

  814.       {

  815.         if(block_num==0)

  816.           {

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

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

  819. 

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

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

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

  823.           }

  824.         else

  825.           {

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

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

  828.           }

  829.       }

  830. 

  831. #if defined(DEBUG)

  832.     {

  833.       static int count = 0;

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

  835.     }

  836. #endif

  837.     /* exponent strategy */

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

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

  840.     }

  841. 

  842.     if (s->lfe) {

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

  844.     }

  845. 

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

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

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

  849.     }

  850. 

  851.     /* exponents */

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

  853.         switch(exp_strategy[ch]) {

  854.         case EXP_REUSE:

  855.             continue;

  856.         case EXP_D15:

  857.             group_size = 1;

  858.             break;

  859.         case EXP_D25:

  860.             group_size = 2;

  861.             break;

  862.         default:

  863.         case EXP_D45:

  864.             group_size = 4;

  865.             break;

  866.         }

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

  868.         p = encoded_exp[ch];

  869. 

  870.         /* first exponent */

  871.         exp1 = *p++;

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

  873. 

  874.         /* next ones are delta encoded */

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

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

  877.             exp0 = exp1;

  878.             exp1 = p[0];

  879.             p += group_size;

  880.             delta0 = exp1 - exp0 + 2;

  881. 

  882.             exp0 = exp1;

  883.             exp1 = p[0];

  884.             p += group_size;

  885.             delta1 = exp1 - exp0 + 2;

  886. 

  887.             exp0 = exp1;

  888.             exp1 = p[0];

  889.             p += group_size;

  890.             delta2 = exp1 - exp0 + 2;

  891. 

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

  893.         }

  894. 

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

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

  897.     }

  898. 

  899.     /* bit allocation info */

  900.     baie = (block_num == 0);

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

  902.     if (baie) {

  903.         put_bits(&s->pb, 2, s->sdecaycod);

  904.         put_bits(&s->pb, 2, s->fdecaycod);

  905.         put_bits(&s->pb, 2, s->sgaincod);

  906.         put_bits(&s->pb, 2, s->dbkneecod);

  907.         put_bits(&s->pb, 3, s->floorcod);

  908.     }

  909. 

  910.     /* snr offset */

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

  912.     if (baie) {

  913.         put_bits(&s->pb, 6, s->csnroffst);

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

  915.             put_bits(&s->pb, 4, s->fsnroffst[ch]);

  916.             put_bits(&s->pb, 3, s->fgaincod[ch]);

  917.         }

  918.     }

  919. 

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

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

  922. 

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

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

  925.        modify the output stream. */

  926. 

  927.     /* first pass: quantize */

  928.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  929.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  930. 

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

  932.         int b, c, e, v;

  933. 

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

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

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

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

  938.             switch(b) {

  939.             case 0:

  940.                 v = 0;

  941.                 break;

  942.             case 1:

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

  944.                 switch(mant1_cnt) {

  945.                 case 0:

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

  947.                     v = 9 * v;

  948.                     mant1_cnt = 1;

  949.                     break;

  950.                 case 1:

  951.                     *qmant1_ptr += 3 * v;

  952.                     mant1_cnt = 2;

  953.                     v = 128;

  954.                     break;

  955.                 default:

  956.                     *qmant1_ptr += v;

  957.                     mant1_cnt = 0;

  958.                     v = 128;

  959.                     break;

  960.                 }

  961.                 break;

  962.             case 2:

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

  964.                 switch(mant2_cnt) {

  965.                 case 0:

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

  967.                     v = 25 * v;

  968.                     mant2_cnt = 1;

  969.                     break;

  970.                 case 1:

  971.                     *qmant2_ptr += 5 * v;

  972.                     mant2_cnt = 2;

  973.                     v = 128;

  974.                     break;

  975.                 default:

  976.                     *qmant2_ptr += v;

  977.                     mant2_cnt = 0;

  978.                     v = 128;

  979.                     break;

  980.                 }

  981.                 break;

  982.             case 3:

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

  984.                 break;

  985.             case 4:

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

  987.                 switch(mant4_cnt) {

  988.                 case 0:

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

  990.                     v = 11 * v;

  991.                     mant4_cnt = 1;

  992.                     break;

  993.                 default:

  994.                     *qmant4_ptr += v;

  995.                     mant4_cnt = 0;

  996.                     v = 128;

  997.                     break;

  998.                 }

  999.                 break;

  1000.             case 5:

  1001.                 v = sym_quant(c, e, 15);

  1002.                 break;

  1003.             case 14:

  1004.                 v = asym_quant(c, e, 14);

  1005.                 break;

  1006.             case 15:

  1007.                 v = asym_quant(c, e, 16);

  1008.                 break;

  1009.             default:

  1010.                 v = asym_quant(c, e, b - 1);

  1011.                 break;

  1012.             }

  1013.             qmant[ch][i] = v;

  1014.         }

  1015.     }

  1016. 

  1017.     /* second pass : output the values */

  1018.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1019.         int b, q;

  1020. 

  1021.         for(i=0;i<s->nb_coefs[ch];i++) {

  1022.             q = qmant[ch][i];

  1023.             b = bap[ch][i];

  1024.             switch(b) {

  1025.             case 0:

  1026.                 break;

  1027.             case 1:

  1028.                 if (q != 128)

  1029.                     put_bits(&s->pb, 5, q);

  1030.                 break;

  1031.             case 2:

  1032.                 if (q != 128)

  1033.                     put_bits(&s->pb, 7, q);

  1034.                 break;

  1035.             case 3:

  1036.                 put_bits(&s->pb, 3, q);

  1037.                 break;

  1038.             case 4:

  1039.                 if (q != 128)

  1040.                     put_bits(&s->pb, 7, q);

  1041.                 break;

  1042.             case 14:

  1043.                 put_bits(&s->pb, 14, q);

  1044.                 break;

  1045.             case 15:

  1046.                 put_bits(&s->pb, 16, q);

  1047.                 break;

  1048.             default:

  1049.                 put_bits(&s->pb, b - 1, q);

  1050.                 break;

  1051.             }

  1052.         }

  1053.     }

  1054. }

  1055. 

  1056. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1057. 

  1058. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1059. {

  1060.     unsigned int c;

  1061. 

  1062.     c = 0;

  1063.     while (a) {

  1064.         if (a & 1)

  1065.             c ^= b;

  1066.         a = a >> 1;

  1067.         b = b << 1;

  1068.         if (b & (1 << 16))

  1069.             b ^= poly;

  1070.     }

  1071.     return c;

  1072. }

  1073. 

  1074. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1075. {

  1076.     unsigned int r;

  1077.     r = 1;

  1078.     while (n) {

  1079.         if (n & 1)

  1080.             r = mul_poly(r, a, poly);

  1081.         a = mul_poly(a, a, poly);

  1082.         n >>= 1;

  1083.     }

  1084.     return r;

  1085. }

  1086. 

  1087. 

  1088. /* compute log2(max(abs(tab[]))) */

  1089. static int log2_tab(int16_t *tab, int n)

  1090. {

  1091.     int i, v;

  1092. 

  1093.     v = 0;

  1094.     for(i=0;i<n;i++) {

  1095.         v |= abs(tab[i]);

  1096.     }

  1097.     return av_log2(v);

  1098. }

  1099. 

  1100. static void lshift_tab(int16_t *tab, int n, int lshift)

  1101. {

  1102.     int i;

  1103. 

  1104.     if (lshift > 0) {

  1105.         for(i=0;i<n;i++) {

  1106.             tab[i] <<= lshift;

  1107.         }

  1108.     } else if (lshift < 0) {

  1109.         lshift = -lshift;

  1110.         for(i=0;i<n;i++) {

  1111.             tab[i] >>= lshift;

  1112.         }

  1113.     }

  1114. }

  1115. 

  1116. /* fill the end of the frame and compute the two crcs */

  1117. static int output_frame_end(AC3EncodeContext *s)

  1118. {

  1119.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1120.     uint8_t *frame;

  1121. 

  1122.     frame_size = s->frame_size; /* frame size in words */

  1123.     /* align to 8 bits */

  1124.     flush_put_bits(&s->pb);

  1125.     /* add zero bytes to reach the frame size */

  1126.     frame = s->pb.buf;

  1127.     n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;

  1128.     assert(n >= 0);

  1129.     if(n>0)

  1130.       memset(pbBufPtr(&s->pb), 0, n);

  1131. 

  1132.     /* Now we must compute both crcs : this is not so easy for crc1

  1133.        because it is at the beginning of the data... */

  1134.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1135.     crc1 = bswap_16(av_crc(av_crc8005, 0, frame + 4, 2 * frame_size_58 - 4));

  1136.     /* XXX: could precompute crc_inv */

  1137.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1138.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1139.     AV_WB16(frame+2,crc1);

  1140. 

  1141.     crc2 = bswap_16(av_crc(av_crc8005, 0, frame + 2 * frame_size_58, (frame_size - frame_size_58) * 2 - 2));

  1142.     AV_WB16(frame+2*frame_size-2,crc2);

  1143. 

  1144.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1145.     return frame_size * 2;

  1146. }

  1147. 

  1148. static int AC3_encode_frame(AVCodecContext *avctx,

  1149.                             unsigned char *frame, int buf_size, void *data)

  1150. {

  1151.     AC3EncodeContext *s = avctx->priv_data;

  1152.     int16_t *samples = data;

  1153.     int i, j, k, v, ch;

  1154.     int16_t input_samples[N];

  1155.     int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1156.     uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1157.     uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

  1158.     uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1159.     uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1160.     int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

  1161.     int frame_bits;

  1162. 

  1163.     frame_bits = 0;

  1164.     for(ch=0;ch<s->nb_all_channels;ch++) {

  1165.         /* fixed mdct to the six sub blocks & exponent computation */

  1166.         for(i=0;i<NB_BLOCKS;i++) {

  1167.             int16_t *sptr;

  1168.             int sinc;

  1169. 

  1170.             /* compute input samples */

  1171.             memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(int16_t));

  1172.             sinc = s->nb_all_channels;

  1173.             sptr = samples + (sinc * (N/2) * i) + ch;

  1174.             for(j=0;j<N/2;j++) {

  1175.                 v = *sptr;

  1176.                 input_samples[j + N/2] = v;

  1177.                 s->last_samples[ch][j] = v;

  1178.                 sptr += sinc;

  1179.             }

  1180. 

  1181.             /* apply the MDCT window */

  1182.             for(j=0;j<N/2;j++) {

  1183.                 input_samples[j] = MUL16(input_samples[j],

  1184.                                          ff_ac3_window[j]) >> 15;

  1185.                 input_samples[N-j-1] = MUL16(input_samples[N-j-1],

  1186.                                              ff_ac3_window[j]) >> 15;

  1187.             }

  1188. 

  1189.             /* Normalize the samples to use the maximum available

  1190.                precision */

  1191.             v = 14 - log2_tab(input_samples, N);

  1192.             if (v < 0)

  1193.                 v = 0;

  1194.             exp_samples[i][ch] = v - 9;

  1195.             lshift_tab(input_samples, N, v);

  1196. 

  1197.             /* do the MDCT */

  1198.             mdct512(mdct_coef[i][ch], input_samples);

  1199. 

  1200.             /* compute "exponents". We take into account the

  1201.                normalization there */

  1202.             for(j=0;j<N/2;j++) {

  1203.                 int e;

  1204.                 v = abs(mdct_coef[i][ch][j]);

  1205.                 if (v == 0)

  1206.                     e = 24;

  1207.                 else {

  1208.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1209.                     if (e >= 24) {

  1210.                         e = 24;

  1211.                         mdct_coef[i][ch][j] = 0;

  1212.                     }

  1213.                 }

  1214.                 exp[i][ch][j] = e;

  1215.             }

  1216.         }

  1217. 

  1218.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1219. 

  1220.         /* compute the exponents as the decoder will see them. The

  1221.            EXP_REUSE case must be handled carefully : we select the

  1222.            min of the exponents */

  1223.         i = 0;

  1224.         while (i < NB_BLOCKS) {

  1225.             j = i + 1;

  1226.             while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1227.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1228.                 j++;

  1229.             }

  1230.             frame_bits += encode_exp(encoded_exp[i][ch],

  1231.                                      exp[i][ch], s->nb_coefs[ch],

  1232.                                      exp_strategy[i][ch]);

  1233.             /* copy encoded exponents for reuse case */

  1234.             for(k=i+1;k<j;k++) {

  1235.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch],

  1236.                        s->nb_coefs[ch] * sizeof(uint8_t));

  1237.             }

  1238.             i = j;

  1239.         }

  1240.     }

  1241. 

  1242.     /* adjust for fractional frame sizes */

  1243.     while(s->bits_written >= s->bit_rate*1000 && s->samples_written >= s->sample_rate) {

  1244.         s->bits_written -= s->bit_rate*1000;

  1245.         s->samples_written -= s->sample_rate;

  1246.     }

  1247.     s->frame_size = s->frame_size_min + (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate*1000);

  1248.     s->bits_written += s->frame_size * 16;

  1249.     s->samples_written += AC3_FRAME_SIZE;

  1250. 

  1251.     compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

  1252.     /* everything is known... let's output the frame */

  1253.     output_frame_header(s, frame);

  1254. 

  1255.     for(i=0;i<NB_BLOCKS;i++) {

  1256.         output_audio_block(s, exp_strategy[i], encoded_exp[i],

  1257.                            bap[i], mdct_coef[i], exp_samples[i], i);

  1258.     }

  1259.     return output_frame_end(s);

  1260. }

  1261. 

  1262. static int AC3_encode_close(AVCodecContext *avctx)

  1263. {

  1264.     av_freep(&avctx->coded_frame);

  1265.     return 0;

  1266. }

  1267. 

  1268. #if 0

  1269. /*************************************************************************/

  1270. /* TEST */

  1271. 

  1272. #undef random

  1273. #define FN (N/4)

  1274. 

  1275. void fft_test(void)

  1276. {

  1277.     IComplex in[FN], in1[FN];

  1278.     int k, n, i;

  1279.     float sum_re, sum_im, a;

  1280. 

  1281.     /* FFT test */

  1282. 

  1283.     for(i=0;i<FN;i++) {

  1284.         in[i].re = random() % 65535 - 32767;

  1285.         in[i].im = random() % 65535 - 32767;

  1286.         in1[i] = in[i];

  1287.     }

  1288.     fft(in, 7);

  1289. 

  1290.     /* do it by hand */

  1291.     for(k=0;k<FN;k++) {

  1292.         sum_re = 0;

  1293.         sum_im = 0;

  1294.         for(n=0;n<FN;n++) {

  1295.             a = -2 * M_PI * (n * k) / FN;

  1296.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1297.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1298.         }

  1299.         printf("%3d: %6d,%6d %6.0f,%6.0f\n",

  1300.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);

  1301.     }

  1302. }

  1303. 

  1304. void mdct_test(void)

  1305. {

  1306.     int16_t input[N];

  1307.     int32_t output[N/2];

  1308.     float input1[N];

  1309.     float output1[N/2];

  1310.     float s, a, err, e, emax;

  1311.     int i, k, n;

  1312. 

  1313.     for(i=0;i<N;i++) {

  1314.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1315.         input1[i] = input[i];

  1316.     }

  1317. 

  1318.     mdct512(output, input);

  1319. 

  1320.     /* do it by hand */

  1321.     for(k=0;k<N/2;k++) {

  1322.         s = 0;

  1323.         for(n=0;n<N;n++) {

  1324.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1325.             s += input1[n] * cos(a);

  1326.         }

  1327.         output1[k] = -2 * s / N;

  1328.     }

  1329. 

  1330.     err = 0;

  1331.     emax = 0;

  1332.     for(i=0;i<N/2;i++) {

  1333.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1334.         e = output[i] - output1[i];

  1335.         if (e > emax)

  1336.             emax = e;

  1337.         err += e * e;

  1338.     }

  1339.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1340. }

  1341. 

  1342. void test_ac3(void)

  1343. {

  1344.     AC3EncodeContext ctx;

  1345.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1346.     short samples[AC3_FRAME_SIZE];

  1347.     int ret, i;

  1348. 

  1349.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1350. 

  1351.     fft_test();

  1352.     mdct_test();

  1353. 

  1354.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1355.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1356.     ret = AC3_encode_frame(&ctx, frame, samples);

  1357.     printf("ret=%d\n", ret);

  1358. }

  1359. #endif

  1360. 

  1361. AVCodec ac3_encoder = {

  1362.     "ac3",

  1363.     CODEC_TYPE_AUDIO,

  1364.     CODEC_ID_AC3,

  1365.     sizeof(AC3EncodeContext),

  1366.     AC3_encode_init,

  1367.     AC3_encode_frame,

  1368.     AC3_encode_close,

  1369.     NULL,

  1370. };