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FFmpeg/libavcodec/ac3enc.c

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  1. /*

  2.  * The simplest AC3 encoder

  3.  * Copyright (c) 2000 Gerard Lantau.

  4.  *

  5.  * This program is free software; you can redistribute it and/or modify

  6.  * it under the terms of the GNU General Public License as published by

  7.  * the Free Software Foundation; either version 2 of the License, or

  8.  * (at your option) any later version.

  9.  *

  10.  * This program is distributed in the hope that it will be useful,

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

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

  13.  * GNU General Public License for more details.

  14.  *

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

  16.  * along with this program; if not, write to the Free Software

  17.  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

  18.  */

  19. //#define DEBUG

  20. //#define DEBUG_BITALLOC

  21. #include "avcodec.h"

  22. 

  23. #include "ac3enc.h"

  24. #include "ac3tab.h"

  25. 

  26. 

  27. #define MDCT_NBITS 9

  28. #define N         (1 << MDCT_NBITS)

  29. #define NB_BLOCKS 6 /* number of PCM blocks inside an AC3 frame */

  30. 

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

  32. #define EXP_DIFF_THRESHOLD 1000

  33. 

  34. /* exponent encoding strategy */

  35. #define EXP_REUSE 0

  36. #define EXP_NEW   1

  37. 

  38. #define EXP_D15   1

  39. #define EXP_D25   2

  40. #define EXP_D45   3

  41. 

  42. static void fft_init(int ln);

  43. static void ac3_crc_init(void);

  44. 

  45. static inline INT16 fix15(float a)

  46. {

  47.     int v;

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

  49.     if (v < -32767)

  50.         v = -32767;

  51.     else if (v > 32767) 

  52.         v = 32767;

  53.     return v;

  54. }

  55. 

  56. static inline int calc_lowcomp1(int a, int b0, int b1)

  57. {

  58.     if ((b0 + 256) == b1) {

  59.         a = 384 ;

  60.     } else if (b0 > b1) { 

  61.         a = a - 64;

  62.         if (a < 0) a=0;

  63.     }

  64.     return a;

  65. }

  66. 

  67. static inline int calc_lowcomp(int a, int b0, int b1, int bin)

  68. {

  69.     if (bin < 7) {

  70.         if ((b0 + 256) == b1) {

  71.             a = 384 ;

  72.         } else if (b0 > b1) { 

  73.             a = a - 64;

  74.             if (a < 0) a=0;

  75.         }

  76.     } else if (bin < 20) {

  77.         if ((b0 + 256) == b1) {

  78.             a = 320 ;

  79.         } else if (b0 > b1) {

  80.             a= a - 64;

  81.             if (a < 0) a=0;

  82.         }

  83.     } else {

  84.         a = a - 128;

  85.         if (a < 0) a=0;

  86.     }

  87.     return a;

  88. }

  89. 

  90. /* AC3 bit allocation. The algorithm is the one described in the AC3

  91.    spec with some optimizations because of our simplified encoding

  92.    assumptions. */

  93. void parametric_bit_allocation(AC3EncodeContext *s, UINT8 *bap,

  94.                                INT8 *exp, int start, int end,

  95.                                int snroffset, int fgain, int is_lfe)

  96. {

  97.     int bin,i,j,k,end1,v,v1,bndstrt,bndend,lowcomp,begin;

  98.     int fastleak,slowleak,address,tmp;

  99.     INT16 psd[256]; /* scaled exponents */

  100.     INT16 bndpsd[50]; /* interpolated exponents */

  101.     INT16 excite[50]; /* excitation */

  102.     INT16 mask[50];   /* masking value */

  103. 

  104.     /* exponent mapping to PSD */

  105.     for(bin=start;bin<end;bin++) {

  106.         psd[bin]=(3072 - (exp[bin] << 7));

  107.     }

  108. 

  109.     /* PSD integration */

  110.     j=start;

  111.     k=masktab[start];

  112.     do {

  113.         v=psd[j];

  114.         j++;

  115.         end1=bndtab[k+1];

  116.         if (end1 > end) end1=end;

  117.         for(i=j;i<end1;i++) {

  118.             int c,adr;

  119.             /* logadd */

  120.             v1=psd[j];

  121.             c=v-v1;

  122.             if (c >= 0) {

  123.                 adr=c >> 1;

  124.                 if (adr > 255) adr=255;

  125.                 v=v + latab[adr];

  126.             } else {

  127.                 adr=(-c) >> 1;

  128.                 if (adr > 255) adr=255;

  129.                 v=v1 + latab[adr];

  130.             }

  131.             j++;

  132.         }

  133.         bndpsd[k]=v;

  134.         k++;

  135.     } while (end > bndtab[k]);

  136. 

  137.     /* excitation function */

  138.     bndstrt = masktab[start];

  139.     bndend = masktab[end-1] + 1;

  140.     

  141.     lowcomp = 0;

  142.     lowcomp = calc_lowcomp1(lowcomp, bndpsd[0], bndpsd[1]) ;

  143.     excite[0] = bndpsd[0] - fgain - lowcomp ;

  144.     lowcomp = calc_lowcomp1(lowcomp, bndpsd[1], bndpsd[2]) ;

  145.     excite[1] = bndpsd[1] - fgain - lowcomp ;

  146.     begin = 7 ;

  147.     for (bin = 2; bin < 7; bin++) {

  148. 	if (!(is_lfe && bin == 6))

  149. 	    lowcomp = calc_lowcomp1(lowcomp, bndpsd[bin], bndpsd[bin+1]) ;

  150.         fastleak = bndpsd[bin] - fgain ;

  151.         slowleak = bndpsd[bin] - s->sgain ;

  152.         excite[bin] = fastleak - lowcomp ;

  153. 	if (!(is_lfe && bin == 6)) {

  154. 	    if (bndpsd[bin] <= bndpsd[bin+1]) {

  155. 		begin = bin + 1 ;

  156. 		break ;

  157. 	    }

  158. 	}

  159.     }

  160.     

  161.     end1=bndend;

  162.     if (end1 > 22) end1=22;

  163.     

  164.     for (bin = begin; bin < end1; bin++) {

  165. 	if (!(is_lfe && bin == 6))

  166. 	    lowcomp = calc_lowcomp(lowcomp, bndpsd[bin], bndpsd[bin+1], bin) ;

  167.         

  168.         fastleak -= s->fdecay ;

  169.         v = bndpsd[bin] - fgain;

  170.         if (fastleak < v) fastleak = v;

  171.         

  172.         slowleak -= s->sdecay ;

  173.         v = bndpsd[bin] - s->sgain;

  174.         if (slowleak < v) slowleak = v;

  175.         

  176.         v=fastleak - lowcomp;

  177.         if (slowleak > v) v=slowleak;

  178.         

  179.         excite[bin] = v;

  180.     }

  181. 

  182.     for (bin = 22; bin < bndend; bin++) {

  183.         fastleak -= s->fdecay ;

  184.         v = bndpsd[bin] - fgain;

  185.         if (fastleak < v) fastleak = v;

  186.         slowleak -= s->sdecay ;

  187.         v = bndpsd[bin] - s->sgain;

  188.         if (slowleak < v) slowleak = v;

  189. 

  190.         v=fastleak;

  191.         if (slowleak > v) v = slowleak;

  192.         excite[bin] = v;

  193.     }

  194. 

  195.     /* compute masking curve */

  196. 

  197.     for (bin = bndstrt; bin < bndend; bin++) {

  198.         v1 = excite[bin];

  199.         tmp = s->dbknee - bndpsd[bin];

  200.         if (tmp > 0) {

  201.             v1 += tmp >> 2;

  202.         }

  203.         v=hth[bin >> s->halfratecod][s->fscod];

  204.         if (v1 > v) v=v1;

  205.         mask[bin] = v;

  206.     }

  207. 

  208.     /* compute bit allocation */

  209.     

  210.     i = start ;

  211.     j = masktab[start] ;

  212.     do {

  213.         v=mask[j];

  214.         v -= snroffset ;

  215.         v -= s->floor ;

  216.         if (v < 0) v = 0;

  217.         v &= 0x1fe0 ;

  218.         v += s->floor ;

  219. 

  220.         end1=bndtab[j] + bndsz[j];

  221.         if (end1 > end) end1=end;

  222. 

  223.         for (k = i; k < end1; k++) {

  224.             address = (psd[i] - v) >> 5 ;

  225.             if (address < 0) address=0;

  226.             else if (address > 63) address=63;

  227.             bap[i] = baptab[address];

  228.             i++;

  229.         }

  230.     } while (end > bndtab[j++]) ;

  231. }

  232. 

  233. typedef struct IComplex {

  234.     short re,im;

  235. } IComplex;

  236. 

  237. static void fft_init(int ln)

  238. {

  239.     int i, j, m, n;

  240.     float alpha;

  241. 

  242.     n = 1 << ln;

  243. 

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

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

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

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

  248.     }

  249. 

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

  251.         m=0;

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

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

  254.         }

  255.         fft_rev[i]=m;

  256.     }

  257. }

  258. 

  259. /* butter fly op */

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

  261. {\

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

  263.   bx=pre1;\

  264.   by=pim1;\

  265.   ax=qre1;\

  266.   ay=qim1;\

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

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

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

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

  271. }

  272. 

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

  274. 

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

  276. {\

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

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

  279. }

  280. 

  281. 

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

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

  284. {

  285.     int	j, l, np, np2;

  286.     int	nblocks, nloops;

  287.     register IComplex *p,*q;

  288.     int tmp_re, tmp_im;

  289. 

  290.     np = 1 << ln;

  291. 

  292.     /* reverse */

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

  294.         int k;

  295.         IComplex tmp;

  296.         k = fft_rev[j];

  297.         if (k < j) {

  298.             tmp = z[k];

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

  300.             z[j] = tmp;

  301.         }

  302.     }

  303. 

  304.     /* pass 0 */

  305. 

  306.     p=&z[0];

  307.     j=(np >> 1);

  308.     do {

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

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

  311.         p+=2;

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

  313. 

  314.     /* pass 1 */

  315. 

  316.     p=&z[0];

  317.     j=np >> 2;

  318.     do {

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

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

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

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

  323.         p+=4;

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

  325. 

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

  327. 

  328.     nblocks = np >> 3;

  329.     nloops = 1 << 2;

  330.     np2 = np >> 1;

  331.     do {

  332.         p = z;

  333.         q = z + nloops;

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

  335. 

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

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

  338.             

  339.             p++;

  340.             q++;

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

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

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

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

  345.                 p++;

  346.                 q++;

  347.             }

  348.             p += nloops;

  349.             q += nloops;

  350.         }

  351.         nblocks = nblocks >> 1;

  352.         nloops = nloops << 1;

  353.     } while (nblocks != 0);

  354. }

  355. 

  356. /* do a 512 point mdct */

  357. static void mdct512(INT32 *out, INT16 *in)

  358. {

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

  360.     INT16 rot[N]; 

  361.     IComplex x[N/4];

  362. 

  363.     /* shift to simplify computations */

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

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

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

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

  368.         

  369.     /* pre rotation */

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

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

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

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

  374.     }

  375. 

  376.     fft(x, MDCT_NBITS - 2);

  377.   

  378.     /* post rotation */

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

  380.         re = x[i].re;

  381.         im = x[i].im;

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

  383.         out[2*i] = im1;

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

  385.     }

  386. }

  387. 

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

  389. static int calc_exp_diff(UINT8 *exp1, UINT8 *exp2, int n)

  390. {

  391.     int sum, i;

  392.     sum = 0;

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

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

  395.     }

  396.     return sum;

  397. }

  398. 

  399. static void compute_exp_strategy(UINT8 exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  400.                                  UINT8 exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

  401.                                  int ch, int is_lfe)

  402. {

  403.     int i, j;

  404.     int exp_diff;

  405.     

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

  407.        reused in the next frame */

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

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

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

  411. #ifdef DEBUG            

  412.         printf("exp_diff=%d\n", exp_diff);

  413. #endif

  414.         if (exp_diff > EXP_DIFF_THRESHOLD)

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

  416.         else

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

  418.     }

  419.     if (is_lfe)

  420. 	return;

  421. 

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

  423.        recoded, we use a coarse encoding */

  424.     i = 0;

  425.     while (i < NB_BLOCKS) {

  426.         j = i + 1;

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

  428.             j++;

  429.         switch(j - i) {

  430.         case 1:

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

  432.             break;

  433.         case 2:

  434.         case 3:

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

  436.             break;

  437.         default:

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

  439.             break;

  440.         }

  441. 	i = j;

  442.     }

  443. }

  444. 

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

  446. static void exponent_min(UINT8 exp[N/2], UINT8 exp1[N/2], int n)

  447. {

  448.     int i;

  449. 

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

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

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

  453.     }

  454. }

  455.                                  

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

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

  458. static int encode_exp(UINT8 encoded_exp[N/2], 

  459.                       UINT8 exp[N/2], 

  460.                       int nb_exps,

  461.                       int exp_strategy)

  462. {

  463.     int group_size, nb_groups, i, j, k, recurse, exp_min, delta;

  464.     UINT8 exp1[N/2];

  465. 

  466.     switch(exp_strategy) {

  467.     case EXP_D15:

  468.         group_size = 1;

  469.         break;

  470.     case EXP_D25:

  471.         group_size = 2;

  472.         break;

  473.     default:

  474.     case EXP_D45:

  475.         group_size = 4;

  476.         break;

  477.     }

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

  479. 

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

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

  482.     k = 1;

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

  484.         exp_min = exp[k];

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

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

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

  488.                 exp_min = exp[k+j];

  489.         }

  490.         exp1[i] = exp_min;

  491.         k += group_size;

  492.     }

  493. 

  494.     /* constraint for DC exponent */

  495.     if (exp1[0] > 15)

  496.         exp1[0] = 15;

  497. 

  498.     /* Iterate until the delta constraints between each groups are

  499.        satisfyed. I'm sure it is possible to find a better algorithm,

  500.        but I am lazy */

  501.     do {

  502.         recurse = 0;

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

  504.             delta = exp1[i] - exp1[i-1];

  505.             if (delta > 2) {

  506.                 /* if delta too big, we encode a smaller exponent */

  507.                 exp1[i] = exp1[i-1] + 2;

  508.             } else if (delta < -2) {

  509.                 /* if delta is too small, we must decrease the previous

  510.                exponent, which means we must recurse */

  511.                 recurse = 1;

  512.                 exp1[i-1] = exp1[i] + 2;

  513.             }

  514.         }

  515.     } while (recurse);

  516.     

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

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

  519.     k = 1;

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

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

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

  523.         }

  524.         k += group_size;

  525.     }

  526.     

  527. #if defined(DEBUG)

  528.     printf("exponents: strategy=%d\n", exp_strategy);

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

  530.         printf("%d ", encoded_exp[i]);

  531.     }

  532.     printf("\n");

  533. #endif

  534. 

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

  536. }

  537. 

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

  539. int compute_mantissa_size(AC3EncodeContext *s, UINT8 *m, int nb_coefs)

  540. {

  541.     int bits, mant, i;

  542. 

  543.     bits = 0;

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

  545.         mant = m[i];

  546.         switch(mant) {

  547.         case 0:

  548.             /* nothing */

  549.             break;

  550.         case 1:

  551.             /* 3 mantissa in 5 bits */

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

  553.                 bits += 5;

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

  555.                 s->mant1_cnt = 0;

  556.             break;

  557.         case 2:

  558.             /* 3 mantissa in 7 bits */

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

  560.                 bits += 7;

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

  562.                 s->mant2_cnt = 0;

  563.             break;

  564.         case 3:

  565.             bits += 3;

  566.             break;

  567.         case 4:

  568.             /* 2 mantissa in 7 bits */

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

  570.                 bits += 7;

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

  572.                 s->mant4_cnt = 0;

  573.             break;

  574.         case 14:

  575.             bits += 14;

  576.             break;

  577.         case 15:

  578.             bits += 16;

  579.             break;

  580.         default:

  581.             bits += mant - 1;

  582.             break;

  583.         }

  584.     }

  585.     return bits;

  586. }

  587. 

  588. 

  589. static int bit_alloc(AC3EncodeContext *s,

  590.                      UINT8 bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

  591.                      UINT8 encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

  592.                      UINT8 exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  593.                      int frame_bits, int csnroffst, int fsnroffst)

  594. {

  595.     int i, ch;

  596. 

  597.     /* compute size */

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

  599.         s->mant1_cnt = 0;

  600.         s->mant2_cnt = 0;

  601.         s->mant4_cnt = 0;

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

  603.             parametric_bit_allocation(s, bap[i][ch], (INT8 *)encoded_exp[i][ch], 

  604.                                       0, s->nb_coefs[ch], 

  605.                                       (((csnroffst-15) << 4) + 

  606.                                        fsnroffst) << 2, 

  607.                                       fgaintab[s->fgaincod[ch]],

  608. 				      ch == s->lfe_channel);

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

  610.                                                  s->nb_coefs[ch]);

  611.         }

  612.     }

  613. #if 0

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

  615.            csnroffst, fsnroffst, frame_bits, 

  616.            16 * s->frame_size - ((frame_bits + 7) & ~7));

  617. #endif

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

  619. }

  620. 

  621. #define SNR_INC1 4

  622. 

  623. static int compute_bit_allocation(AC3EncodeContext *s,

  624.                                   UINT8 bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

  625.                                   UINT8 encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

  626.                                   UINT8 exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  627.                                   int frame_bits)

  628. {

  629.     int i, ch;

  630.     int csnroffst, fsnroffst;

  631.     UINT8 bap1[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

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

  633. 

  634.     /* init default parameters */

  635.     s->sdecaycod = 2;

  636.     s->fdecaycod = 1;

  637.     s->sgaincod = 1;

  638.     s->dbkneecod = 2;

  639.     s->floorcod = 4;

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

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

  642.     

  643.     /* compute real values */

  644.     s->sdecay = sdecaytab[s->sdecaycod] >> s->halfratecod;

  645.     s->fdecay = fdecaytab[s->fdecaycod] >> s->halfratecod;

  646.     s->sgain = sgaintab[s->sgaincod];

  647.     s->dbknee = dbkneetab[s->dbkneecod];

  648.     s->floor = floortab[s->floorcod];

  649. 

  650.     /* header size */

  651.     frame_bits += 65;

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

  653.     //    frame_bits += 2;

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

  655. 

  656.     /* audio blocks */

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

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

  659.         if (s->acmod == 2)

  660.             frame_bits++; /* rematstr */

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

  662. 	if (s->lfe)

  663. 	    frame_bits++; /* lfeexpstr */

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

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

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

  667.         }

  668.         frame_bits++; /* baie */

  669.         frame_bits++; /* snr */

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

  671.     }

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

  673.     /* bit alloc info */

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

  675.     /* csnroffset[6] */

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

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

  678. 

  679.     /* CRC */

  680.     frame_bits += 16;

  681. 

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

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

  684. 

  685.     csnroffst = s->csnroffst;

  686.     while (csnroffst >= 0 && 

  687. 	   bit_alloc(s, bap, encoded_exp, exp_strategy, frame_bits, csnroffst, 0) < 0)

  688. 	csnroffst -= SNR_INC1;

  689.     if (csnroffst < 0) {

  690. 	fprintf(stderr, "Yack, Error !!!\n");

  691. 	return -1;

  692.     }

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

  694.            bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits, 

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

  696.         csnroffst += SNR_INC1;

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

  698.     }

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

  700.            bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits, csnroffst + 1, 0) >= 0) {

  701.         csnroffst++;

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

  703.     }

  704. 

  705.     fsnroffst = 0;

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

  707.            bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits, 

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

  709.         fsnroffst += SNR_INC1;

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

  711.     }

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

  713.            bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits, 

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

  715.         fsnroffst++;

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

  717.     }

  718.     

  719.     s->csnroffst = csnroffst;

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

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

  722. #if defined(DEBUG_BITALLOC)

  723.     {

  724.         int j;

  725. 

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

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

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

  729.                 printf("bap=");

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

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

  732.                 }

  733.                 printf("\n");

  734.             }

  735.         }

  736.     }

  737. #endif

  738.     return 0;

  739. }

  740. 

  741. static int AC3_encode_init(AVCodecContext *avctx)

  742. {

  743.     int freq = avctx->sample_rate;

  744.     int bitrate = avctx->bit_rate;

  745.     int channels = avctx->channels;

  746.     AC3EncodeContext *s = avctx->priv_data;

  747.     int i, j, k, l, ch, v;

  748.     float alpha;

  749.     static unsigned short freqs[3] = { 48000, 44100, 32000 };

  750.     static int acmod_defs[6] = {

  751. 	0x01, /* C */

  752. 	0x02, /* L R */

  753. 	0x03, /* L C R */

  754. 	0x06, /* L R SL SR */

  755. 	0x07, /* L C R SL SR */

  756. 	0x07, /* L C R SL SR (+LFE) */

  757.     };

  758. 

  759.     avctx->frame_size = AC3_FRAME_SIZE;

  760.     avctx->key_frame = 1; /* always key frame */

  761.     

  762.     /* number of channels */

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

  764. 	return -1;

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

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

  767.     s->nb_all_channels = channels;

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

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

  770. 

  771.     /* frequency */

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

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

  774.             if ((freqs[j] >> i) == freq)

  775.                 goto found;

  776.     }

  777.     return -1;

  778.  found:    

  779.     s->sample_rate = freq;

  780.     s->halfratecod = i;

  781.     s->fscod = j;

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

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

  784. 

  785.     /* bitrate & frame size */

  786.     bitrate /= 1000;

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

  788.         if ((bitratetab[i] >> s->halfratecod) == bitrate)

  789.             break;

  790.     }

  791.     if (i == 19)

  792.         return -1;

  793.     s->bit_rate = bitrate;

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

  795.     s->frame_size_min = (bitrate * 1000 * AC3_FRAME_SIZE) / (freq * 16);

  796.     /* for now we do not handle fractional sizes */

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

  798.     

  799.     /* bit allocation init */

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

  801.         /* bandwidth for each channel */

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

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

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

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

  806.     }

  807.     if (s->lfe) {

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

  809.     }

  810.     /* initial snr offset */

  811.     s->csnroffst = 40;

  812. 

  813.     /* compute bndtab and masktab from bandsz */

  814.     k = 0;

  815.     l = 0;

  816.     for(i=0;i<50;i++) {

  817.         bndtab[i] = l;

  818.         v = bndsz[i];

  819.         for(j=0;j<v;j++) masktab[k++]=i;

  820.         l += v;

  821.     }

  822.     bndtab[50] = 0;

  823. 

  824.     /* mdct init */

  825.     fft_init(MDCT_NBITS - 2);

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

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

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

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

  830.     }

  831. 

  832.     ac3_crc_init();

  833. 

  834.     return 0;

  835. }

  836. 

  837. /* output the AC3 frame header */

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

  839. {

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

  841. 

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

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

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

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

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

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

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

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

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

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

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

  853.     if (s->acmod == 0x02)

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

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

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

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

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

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

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

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

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

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

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

  865. }

  866. 

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

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

  869. {

  870.     int v;

  871. 

  872.     if (c >= 0) {

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

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

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

  876.     } else {

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

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

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

  880.     }

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

  882.     return v;

  883. }

  884. 

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

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

  887. {

  888.     int lshift, m, v;

  889. 

  890.     lshift = e + qbits - 24;

  891.     if (lshift >= 0)

  892.         v = c << lshift;

  893.     else

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

  895.     /* rounding */

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

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

  898.     if (v >= m)

  899.         v = m - 1;

  900.     assert(v >= -m);

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

  902. }

  903. 

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

  905.    frame */

  906. static void output_audio_block(AC3EncodeContext *s,

  907.                                UINT8 exp_strategy[AC3_MAX_CHANNELS],

  908.                                UINT8 encoded_exp[AC3_MAX_CHANNELS][N/2],

  909.                                UINT8 bap[AC3_MAX_CHANNELS][N/2],

  910.                                INT32 mdct_coefs[AC3_MAX_CHANNELS][N/2],

  911.                                INT8 global_exp[AC3_MAX_CHANNELS],

  912.                                int block_num)

  913. {

  914.     int ch, nb_groups, group_size, i, baie;

  915.     UINT8 *p;

  916.     UINT16 qmant[AC3_MAX_CHANNELS][N/2];

  917.     int exp0, exp1;

  918.     int mant1_cnt, mant2_cnt, mant4_cnt;

  919.     UINT16 *qmant1_ptr, *qmant2_ptr, *qmant4_ptr;

  920.     int delta0, delta1, delta2;

  921. 

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

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

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

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

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

  927.     if (block_num == 0) {

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

  929.            waste of bit :-) */

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

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

  932.     } else {

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

  934.     }

  935. 

  936.     if (s->acmod == 2) {

  937.         put_bits(&s->pb, 1, 0); /* no matrixing (but should be used in the future) */

  938.     }

  939. 

  940. #if defined(DEBUG) 

  941.     {

  942.         static int count = 0;

  943.         printf("Block #%d (%d)\n", block_num, count++);

  944.     }

  945. #endif

  946.     /* exponent strategy */

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

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

  949.     }

  950.     

  951.     if (s->lfe) {

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

  953.     }

  954. 

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

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

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

  958.     }

  959.     

  960.     /* exponents */

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

  962.         switch(exp_strategy[ch]) {

  963.         case EXP_REUSE:

  964.             continue;

  965.         case EXP_D15:

  966.             group_size = 1;

  967.             break;

  968.         case EXP_D25:

  969.             group_size = 2;

  970.             break;

  971.         default:

  972.         case EXP_D45:

  973.             group_size = 4;

  974.             break;

  975.         }

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

  977.         p = encoded_exp[ch];

  978. 

  979.         /* first exponent */

  980.         exp1 = *p++;

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

  982. 

  983.         /* next ones are delta encoded */

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

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

  986.             exp0 = exp1;

  987.             exp1 = p[0];

  988.             p += group_size;

  989.             delta0 = exp1 - exp0 + 2;

  990. 

  991.             exp0 = exp1;

  992.             exp1 = p[0];

  993.             p += group_size;

  994.             delta1 = exp1 - exp0 + 2;

  995. 

  996.             exp0 = exp1;

  997.             exp1 = p[0];

  998.             p += group_size;

  999.             delta2 = exp1 - exp0 + 2;

  1000. 

  1001.             put_bits(&s->pb, 7, ((delta0 * 5 + delta1) * 5) + delta2);

  1002.         }

  1003. 

  1004. 	if (ch != s->lfe_channel)

  1005. 	    put_bits(&s->pb, 2, 0); /* no gain range info */

  1006.     }

  1007. 

  1008.     /* bit allocation info */

  1009.     baie = (block_num == 0);

  1010.     put_bits(&s->pb, 1, baie);

  1011.     if (baie) {

  1012.         put_bits(&s->pb, 2, s->sdecaycod);

  1013.         put_bits(&s->pb, 2, s->fdecaycod);

  1014.         put_bits(&s->pb, 2, s->sgaincod);

  1015.         put_bits(&s->pb, 2, s->dbkneecod);

  1016.         put_bits(&s->pb, 3, s->floorcod);

  1017.     }

  1018. 

  1019.     /* snr offset */

  1020.     put_bits(&s->pb, 1, baie); /* always present with bai */

  1021.     if (baie) {

  1022.         put_bits(&s->pb, 6, s->csnroffst);

  1023.         for(ch=0;ch<s->nb_all_channels;ch++) {

  1024.             put_bits(&s->pb, 4, s->fsnroffst[ch]);

  1025.             put_bits(&s->pb, 3, s->fgaincod[ch]);

  1026.         }

  1027.     }

  1028.     

  1029.     put_bits(&s->pb, 1, 0); /* no delta bit allocation */

  1030.     put_bits(&s->pb, 1, 0); /* no data to skip */

  1031. 

  1032.     /* mantissa encoding : we use two passes to handle the grouping. A

  1033.        one pass method may be faster, but it would necessitate to

  1034.        modify the output stream. */

  1035. 

  1036.     /* first pass: quantize */

  1037.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  1038.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  1039. 

  1040.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1041.         int b, c, e, v;

  1042. 

  1043.         for(i=0;i<s->nb_coefs[ch];i++) {

  1044.             c = mdct_coefs[ch][i];

  1045.             e = encoded_exp[ch][i] - global_exp[ch];

  1046.             b = bap[ch][i];

  1047.             switch(b) {

  1048.             case 0:

  1049.                 v = 0;

  1050.                 break;

  1051.             case 1:

  1052.                 v = sym_quant(c, e, 3);

  1053.                 switch(mant1_cnt) {

  1054.                 case 0:

  1055.                     qmant1_ptr = &qmant[ch][i];

  1056.                     v = 9 * v;

  1057.                     mant1_cnt = 1;

  1058.                     break;

  1059.                 case 1:

  1060.                     *qmant1_ptr += 3 * v;

  1061.                     mant1_cnt = 2;

  1062.                     v = 128;

  1063.                     break;

  1064.                 default:

  1065.                     *qmant1_ptr += v;

  1066.                     mant1_cnt = 0;

  1067.                     v = 128;

  1068.                     break;

  1069.                 }

  1070.                 break;

  1071.             case 2:

  1072.                 v = sym_quant(c, e, 5);

  1073.                 switch(mant2_cnt) {

  1074.                 case 0:

  1075.                     qmant2_ptr = &qmant[ch][i];

  1076.                     v = 25 * v;

  1077.                     mant2_cnt = 1;

  1078.                     break;

  1079.                 case 1:

  1080.                     *qmant2_ptr += 5 * v;

  1081.                     mant2_cnt = 2;

  1082.                     v = 128;

  1083.                     break;

  1084.                 default:

  1085.                     *qmant2_ptr += v;

  1086.                     mant2_cnt = 0;

  1087.                     v = 128;

  1088.                     break;

  1089.                 }

  1090.                 break;

  1091.             case 3:

  1092.                 v = sym_quant(c, e, 7);

  1093.                 break;

  1094.             case 4:

  1095.                 v = sym_quant(c, e, 11);

  1096.                 switch(mant4_cnt) {

  1097.                 case 0:

  1098.                     qmant4_ptr = &qmant[ch][i];

  1099.                     v = 11 * v;

  1100.                     mant4_cnt = 1;

  1101.                     break;

  1102.                 default:

  1103.                     *qmant4_ptr += v;

  1104.                     mant4_cnt = 0;

  1105.                     v = 128;

  1106.                     break;

  1107.                 }

  1108.                 break;

  1109.             case 5:

  1110.                 v = sym_quant(c, e, 15);

  1111.                 break;

  1112.             case 14:

  1113.                 v = asym_quant(c, e, 14);

  1114.                 break;

  1115.             case 15:

  1116.                 v = asym_quant(c, e, 16);

  1117.                 break;

  1118.             default:

  1119.                 v = asym_quant(c, e, b - 1);

  1120.                 break;

  1121.             }

  1122.             qmant[ch][i] = v;

  1123.         }

  1124.     }

  1125. 

  1126.     /* second pass : output the values */

  1127.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1128.         int b, q;

  1129.         

  1130.         for(i=0;i<s->nb_coefs[ch];i++) {

  1131.             q = qmant[ch][i];

  1132.             b = bap[ch][i];

  1133.             switch(b) {

  1134.             case 0:

  1135.                 break;

  1136.             case 1:

  1137.                 if (q != 128) 

  1138.                     put_bits(&s->pb, 5, q);

  1139.                 break;

  1140.             case 2:

  1141.                 if (q != 128) 

  1142.                     put_bits(&s->pb, 7, q);

  1143.                 break;

  1144.             case 3:

  1145.                 put_bits(&s->pb, 3, q);

  1146.                 break;

  1147.             case 4:

  1148.                 if (q != 128)

  1149.                     put_bits(&s->pb, 7, q);

  1150.                 break;

  1151.             case 14:

  1152.                 put_bits(&s->pb, 14, q);

  1153.                 break;

  1154.             case 15:

  1155.                 put_bits(&s->pb, 16, q);

  1156.                 break;

  1157.             default:

  1158.                 put_bits(&s->pb, b - 1, q);

  1159.                 break;

  1160.             }

  1161.         }

  1162.     }

  1163. }

  1164. 

  1165. /* compute the ac3 crc */

  1166. 

  1167. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1168. 

  1169. static void ac3_crc_init(void)

  1170. {

  1171.     unsigned int c, n, k;

  1172. 

  1173.     for(n=0;n<256;n++) {

  1174.         c = n << 8;

  1175.         for (k = 0; k < 8; k++) {

  1176.             if (c & (1 << 15)) 

  1177.                 c = ((c << 1) & 0xffff) ^ (CRC16_POLY & 0xffff);

  1178.             else

  1179.                 c = c << 1;

  1180.         }

  1181.         crc_table[n] = c;

  1182.     }

  1183. }

  1184. 

  1185. static unsigned int ac3_crc(UINT8 *data, int n, unsigned int crc)

  1186. {

  1187.     int i;

  1188.     for(i=0;i<n;i++) {

  1189.         crc = (crc_table[data[i] ^ (crc >> 8)] ^ (crc << 8)) & 0xffff;

  1190.     }

  1191.     return crc;

  1192. }

  1193. 

  1194. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1195. {

  1196.     unsigned int c;

  1197. 

  1198.     c = 0;

  1199.     while (a) {

  1200.         if (a & 1)

  1201.             c ^= b;

  1202.         a = a >> 1;

  1203.         b = b << 1;

  1204.         if (b & (1 << 16))

  1205.             b ^= poly;

  1206.     }

  1207.     return c;

  1208. }

  1209. 

  1210. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1211. {

  1212.     unsigned int r;

  1213.     r = 1;

  1214.     while (n) {

  1215.         if (n & 1)

  1216.             r = mul_poly(r, a, poly);

  1217.         a = mul_poly(a, a, poly);

  1218.         n >>= 1;

  1219.     }

  1220.     return r;

  1221. }

  1222. 

  1223. 

  1224. /* compute log2(max(abs(tab[]))) */

  1225. static int log2_tab(INT16 *tab, int n)

  1226. {

  1227.     int i, v;

  1228. 

  1229.     v = 0;

  1230.     for(i=0;i<n;i++) {

  1231.         v |= abs(tab[i]);

  1232.     }

  1233.     return av_log2(v);

  1234. }

  1235. 

  1236. static void lshift_tab(INT16 *tab, int n, int lshift)

  1237. {

  1238.     int i;

  1239. 

  1240.     if (lshift > 0) {

  1241.         for(i=0;i<n;i++) {

  1242.             tab[i] <<= lshift;

  1243.         }

  1244.     } else if (lshift < 0) {

  1245.         lshift = -lshift;

  1246.         for(i=0;i<n;i++) {

  1247.             tab[i] >>= lshift;

  1248.         }

  1249.     }

  1250. }

  1251. 

  1252. /* fill the end of the frame and compute the two crcs */

  1253. static int output_frame_end(AC3EncodeContext *s)

  1254. {

  1255.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1256.     UINT8 *frame;

  1257. 

  1258.     frame_size = s->frame_size; /* frame size in words */

  1259.     /* align to 8 bits */

  1260.     flush_put_bits(&s->pb);

  1261.     /* add zero bytes to reach the frame size */

  1262.     frame = s->pb.buf;

  1263.     n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;

  1264.     assert(n >= 0);

  1265.     memset(pbBufPtr(&s->pb), 0, n);

  1266.     

  1267.     /* Now we must compute both crcs : this is not so easy for crc1

  1268.        because it is at the beginning of the data... */

  1269.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1270.     crc1 = ac3_crc(frame + 4, (2 * frame_size_58) - 4, 0);

  1271.     /* XXX: could precompute crc_inv */

  1272.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1273.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1274.     frame[2] = crc1 >> 8;

  1275.     frame[3] = crc1;

  1276.     

  1277.     crc2 = ac3_crc(frame + 2 * frame_size_58, (frame_size - frame_size_58) * 2 - 2, 0);

  1278.     frame[2*frame_size - 2] = crc2 >> 8;

  1279.     frame[2*frame_size - 1] = crc2;

  1280. 

  1281.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1282.     return frame_size * 2;

  1283. }

  1284. 

  1285. int AC3_encode_frame(AVCodecContext *avctx,

  1286.                      unsigned char *frame, int buf_size, void *data)

  1287. {

  1288.     AC3EncodeContext *s = avctx->priv_data;

  1289.     short *samples = data;

  1290.     int i, j, k, v, ch;

  1291.     INT16 input_samples[N];

  1292.     INT32 mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1293.     UINT8 exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1294.     UINT8 exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

  1295.     UINT8 encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1296.     UINT8 bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1297.     INT8 exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

  1298.     int frame_bits;

  1299. 

  1300.     frame_bits = 0;

  1301.     for(ch=0;ch<s->nb_all_channels;ch++) {

  1302.         /* fixed mdct to the six sub blocks & exponent computation */

  1303.         for(i=0;i<NB_BLOCKS;i++) {

  1304.             INT16 *sptr;

  1305.             int sinc;

  1306. 

  1307.             /* compute input samples */

  1308.             memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(INT16));

  1309.             sinc = s->nb_all_channels;

  1310.             sptr = samples + (sinc * (N/2) * i) + ch;

  1311.             for(j=0;j<N/2;j++) {

  1312.                 v = *sptr;

  1313.                 input_samples[j + N/2] = v;

  1314.                 s->last_samples[ch][j] = v; 

  1315.                 sptr += sinc;

  1316.             }

  1317. 

  1318.             /* apply the MDCT window */

  1319.             for(j=0;j<N/2;j++) {

  1320.                 input_samples[j] = MUL16(input_samples[j], 

  1321.                                          ac3_window[j]) >> 15;

  1322.                 input_samples[N-j-1] = MUL16(input_samples[N-j-1], 

  1323.                                              ac3_window[j]) >> 15;

  1324.             }

  1325.         

  1326.             /* Normalize the samples to use the maximum available

  1327.                precision */

  1328.             v = 14 - log2_tab(input_samples, N);

  1329.             if (v < 0)

  1330.                 v = 0;

  1331.             exp_samples[i][ch] = v - 8;

  1332.             lshift_tab(input_samples, N, v);

  1333. 

  1334.             /* do the MDCT */

  1335.             mdct512(mdct_coef[i][ch], input_samples);

  1336.             

  1337.             /* compute "exponents". We take into account the

  1338.                normalization there */

  1339.             for(j=0;j<N/2;j++) {

  1340.                 int e;

  1341.                 v = abs(mdct_coef[i][ch][j]);

  1342.                 if (v == 0)

  1343.                     e = 24;

  1344.                 else {

  1345.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1346.                     if (e >= 24) {

  1347.                         e = 24;

  1348.                         mdct_coef[i][ch][j] = 0;

  1349.                     }

  1350.                 }

  1351.                 exp[i][ch][j] = e;

  1352.             }

  1353.         }

  1354.         

  1355.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1356. 

  1357.         /* compute the exponents as the decoder will see them. The

  1358.            EXP_REUSE case must be handled carefully : we select the

  1359.            min of the exponents */

  1360.         i = 0;

  1361.         while (i < NB_BLOCKS) {

  1362.             j = i + 1;

  1363.             while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1364.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1365.                 j++;

  1366.             }

  1367.             frame_bits += encode_exp(encoded_exp[i][ch],

  1368.                                      exp[i][ch], s->nb_coefs[ch], 

  1369.                                      exp_strategy[i][ch]);

  1370.             /* copy encoded exponents for reuse case */

  1371.             for(k=i+1;k<j;k++) {

  1372.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch], 

  1373.                        s->nb_coefs[ch] * sizeof(UINT8));

  1374.             }

  1375.             i = j;

  1376.         }

  1377.     }

  1378. 

  1379.     compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

  1380.     /* everything is known... let's output the frame */

  1381.     output_frame_header(s, frame);

  1382.         

  1383.     for(i=0;i<NB_BLOCKS;i++) {

  1384.         output_audio_block(s, exp_strategy[i], encoded_exp[i], 

  1385.                            bap[i], mdct_coef[i], exp_samples[i], i);

  1386.     }

  1387.     return output_frame_end(s);

  1388. }

  1389. 

  1390. #if 0

  1391. /*************************************************************************/

  1392. /* TEST */

  1393. 

  1394. #define FN (N/4)

  1395. 

  1396. void fft_test(void)

  1397. {

  1398.     IComplex in[FN], in1[FN];

  1399.     int k, n, i;

  1400.     float sum_re, sum_im, a;

  1401. 

  1402.     /* FFT test */

  1403. 

  1404.     for(i=0;i<FN;i++) {

  1405.         in[i].re = random() % 65535 - 32767;

  1406.         in[i].im = random() % 65535 - 32767;

  1407.         in1[i] = in[i];

  1408.     }

  1409.     fft(in, 7);

  1410. 

  1411.     /* do it by hand */

  1412.     for(k=0;k<FN;k++) {

  1413.         sum_re = 0;

  1414.         sum_im = 0;

  1415.         for(n=0;n<FN;n++) {

  1416.             a = -2 * M_PI * (n * k) / FN;

  1417.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1418.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1419.         }

  1420.         printf("%3d: %6d,%6d %6.0f,%6.0f\n", 

  1421.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN); 

  1422.     }

  1423. }

  1424. 

  1425. void mdct_test(void)

  1426. {

  1427.     INT16 input[N];

  1428.     INT32 output[N/2];

  1429.     float input1[N];

  1430.     float output1[N/2];

  1431.     float s, a, err, e, emax;

  1432.     int i, k, n;

  1433. 

  1434.     for(i=0;i<N;i++) {

  1435.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1436.         input1[i] = input[i];

  1437.     }

  1438. 

  1439.     mdct512(output, input);

  1440.     

  1441.     /* do it by hand */

  1442.     for(k=0;k<N/2;k++) {

  1443.         s = 0;

  1444.         for(n=0;n<N;n++) {

  1445.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1446.             s += input1[n] * cos(a);

  1447.         }

  1448.         output1[k] = -2 * s / N;

  1449.     }

  1450.     

  1451.     err = 0;

  1452.     emax = 0;

  1453.     for(i=0;i<N/2;i++) {

  1454.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1455.         e = output[i] - output1[i];

  1456.         if (e > emax)

  1457.             emax = e;

  1458.         err += e * e;

  1459.     }

  1460.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1461. }

  1462. 

  1463. void test_ac3(void)

  1464. {

  1465.     AC3EncodeContext ctx;

  1466.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1467.     short samples[AC3_FRAME_SIZE];

  1468.     int ret, i;

  1469.     

  1470.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1471. 

  1472.     fft_test();

  1473.     mdct_test();

  1474. 

  1475.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1476.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1477.     ret = AC3_encode_frame(&ctx, frame, samples);

  1478.     printf("ret=%d\n", ret);

  1479. }

  1480. #endif

  1481. 

  1482. AVCodec ac3_encoder = {

  1483.     "ac3",

  1484.     CODEC_TYPE_AUDIO,

  1485.     CODEC_ID_AC3,

  1486.     sizeof(AC3EncodeContext),

  1487.     AC3_encode_init,

  1488.     AC3_encode_frame,

  1489.     NULL,

  1490. };