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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 library is free software; you can redistribute it and/or

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

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

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

  9.  *

  10.  * This library 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 GNU

  13.  * Lesser General Public License for more details.

  14.  *

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

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

  17.  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

  18.  */

  19. //#define DEBUG

  20. //#define DEBUG_BITALLOC

  21. #include "avcodec.h"

  22. 

  23. #include "ac3.h"

  24. 

  25. typedef struct AC3EncodeContext {

  26.     PutBitContext pb;

  27.     int nb_channels;

  28.     int nb_all_channels;

  29.     int lfe_channel;

  30.     int bit_rate;

  31.     int sample_rate;

  32.     int bsid;

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

  34.     int frame_size; /* current frame size in words */

  35.     int halfratecod;

  36.     int frmsizecod;

  37.     int fscod; /* frequency */

  38.     int acmod;

  39.     int lfe;

  40.     int bsmod;

  41.     short last_samples[AC3_MAX_CHANNELS][256];

  42.     int chbwcod[AC3_MAX_CHANNELS];

  43.     int nb_coefs[AC3_MAX_CHANNELS];

  44.     

  45.     /* bitrate allocation control */

  46.     int sgaincod, sdecaycod, fdecaycod, dbkneecod, floorcod; 

  47.     AC3BitAllocParameters bit_alloc;

  48.     int csnroffst;

  49.     int fgaincod[AC3_MAX_CHANNELS];

  50.     int fsnroffst[AC3_MAX_CHANNELS];

  51.     /* mantissa encoding */

  52.     int mant1_cnt, mant2_cnt, mant4_cnt;

  53. } AC3EncodeContext;

  54. 

  55. #include "ac3tab.h"

  56. 

  57. #define MDCT_NBITS 9

  58. #define N         (1 << MDCT_NBITS)

  59. 

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

  61. #define EXP_DIFF_THRESHOLD 1000

  62. 

  63. static void fft_init(int ln);

  64. static void ac3_crc_init(void);

  65. 

  66. static inline INT16 fix15(float a)

  67. {

  68.     int v;

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

  70.     if (v < -32767)

  71.         v = -32767;

  72.     else if (v > 32767) 

  73.         v = 32767;

  74.     return v;

  75. }

  76. 

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

  78. {

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

  80.         a = 384 ;

  81.     } else if (b0 > b1) { 

  82.         a = a - 64;

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

  84.     }

  85.     return a;

  86. }

  87. 

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

  89. {

  90.     if (bin < 7) {

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

  92.             a = 384 ;

  93.         } else if (b0 > b1) { 

  94.             a = a - 64;

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

  96.         }

  97.     } else if (bin < 20) {

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

  99.             a = 320 ;

  100.         } else if (b0 > b1) {

  101.             a= a - 64;

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

  103.         }

  104.     } else {

  105.         a = a - 128;

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

  107.     }

  108.     return a;

  109. }

  110. 

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

  112.    spec. */

  113. void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, UINT8 *bap,

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

  115.                                    int snroffset, int fgain, int is_lfe,

  116.                                    int deltbae,int deltnseg, 

  117.                                    UINT8 *deltoffst, UINT8 *deltlen, UINT8 *deltba)

  118. {

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

  120.     int fastleak,slowleak,address,tmp;

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

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

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

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

  125. 

  126.     /* exponent mapping to PSD */

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

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

  129.     }

  130. 

  131.     /* PSD integration */

  132.     j=start;

  133.     k=masktab[start];

  134.     do {

  135.         v=psd[j];

  136.         j++;

  137.         end1=bndtab[k+1];

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

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

  140.             int c,adr;

  141.             /* logadd */

  142.             v1=psd[j];

  143.             c=v-v1;

  144.             if (c >= 0) {

  145.                 adr=c >> 1;

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

  147.                 v=v + latab[adr];

  148.             } else {

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

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

  151.                 v=v1 + latab[adr];

  152.             }

  153.             j++;

  154.         }

  155.         bndpsd[k]=v;

  156.         k++;

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

  158. 

  159.     /* excitation function */

  160.     bndstrt = masktab[start];

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

  162.     

  163.     if (bndstrt == 0) {

  164.         lowcomp = 0;

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

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

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

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

  169.         begin = 7 ;

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

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

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

  173.             fastleak = bndpsd[bin] - fgain ;

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

  175.             excite[bin] = fastleak - lowcomp ;

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

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

  178.                     begin = bin + 1 ;

  179.                     break ;

  180.                 }

  181.             }

  182.         }

  183.     

  184.         end1=bndend;

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

  186.     

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

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

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

  190.         

  191.             fastleak -= s->fdecay ;

  192.             v = bndpsd[bin] - fgain;

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

  194.         

  195.             slowleak -= s->sdecay ;

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

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

  198.         

  199.             v=fastleak - lowcomp;

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

  201.         

  202.             excite[bin] = v;

  203.         }

  204.         begin = 22;

  205.     } else {

  206.         /* coupling channel */

  207.         begin = bndstrt;

  208.         

  209.         fastleak = (s->cplfleak << 8) + 768;

  210.         slowleak = (s->cplsleak << 8) + 768;

  211.     }

  212. 

  213.     for (bin = begin; bin < bndend; bin++) {

  214.         fastleak -= s->fdecay ;

  215.         v = bndpsd[bin] - fgain;

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

  217.         slowleak -= s->sdecay ;

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

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

  220. 

  221.         v=fastleak;

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

  223.         excite[bin] = v;

  224.     }

  225. 

  226.     /* compute masking curve */

  227. 

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

  229.         v1 = excite[bin];

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

  231.         if (tmp > 0) {

  232.             v1 += tmp >> 2;

  233.         }

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

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

  236.         mask[bin] = v;

  237.     }

  238. 

  239.     /* delta bit allocation */

  240. 

  241.     if (deltbae == 0 || deltbae == 1) {

  242.         int band, seg, delta;

  243.         band = 0 ;

  244.         for (seg = 0; seg < deltnseg; seg++) {

  245.             band += deltoffst[seg] ;

  246.             if (deltba[seg] >= 4) {

  247.                 delta = (deltba[seg] - 3) << 7;

  248.             } else {

  249.                 delta = (deltba[seg] - 4) << 7;

  250.             }

  251.             for (k = 0; k < deltlen[seg]; k++) {

  252.                 mask[band] += delta ;

  253.                 band++ ;

  254.             }

  255.         }

  256.     }

  257. 

  258.     /* compute bit allocation */

  259.     

  260.     i = start ;

  261.     j = masktab[start] ;

  262.     do {

  263.         v=mask[j];

  264.         v -= snroffset ;

  265.         v -= s->floor ;

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

  267.         v &= 0x1fe0 ;

  268.         v += s->floor ;

  269. 

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

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

  272. 

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

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

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

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

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

  278.             i++;

  279.         }

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

  281. }

  282. 

  283. typedef struct IComplex {

  284.     short re,im;

  285. } IComplex;

  286. 

  287. static void fft_init(int ln)

  288. {

  289.     int i, j, m, n;

  290.     float alpha;

  291. 

  292.     n = 1 << ln;

  293. 

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

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

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

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

  298.     }

  299. 

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

  301.         m=0;

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

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

  304.         }

  305.         fft_rev[i]=m;

  306.     }

  307. }

  308. 

  309. /* butter fly op */

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

  311. {\

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

  313.   bx=pre1;\

  314.   by=pim1;\

  315.   ax=qre1;\

  316.   ay=qim1;\

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

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

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

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

  321. }

  322. 

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

  324. 

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

  326. {\

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

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

  329. }

  330. 

  331. 

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

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

  334. {

  335.     int	j, l, np, np2;

  336.     int	nblocks, nloops;

  337.     register IComplex *p,*q;

  338.     int tmp_re, tmp_im;

  339. 

  340.     np = 1 << ln;

  341. 

  342.     /* reverse */

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

  344.         int k;

  345.         IComplex tmp;

  346.         k = fft_rev[j];

  347.         if (k < j) {

  348.             tmp = z[k];

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

  350.             z[j] = tmp;

  351.         }

  352.     }

  353. 

  354.     /* pass 0 */

  355. 

  356.     p=&z[0];

  357.     j=(np >> 1);

  358.     do {

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

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

  361.         p+=2;

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

  363. 

  364.     /* pass 1 */

  365. 

  366.     p=&z[0];

  367.     j=np >> 2;

  368.     do {

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

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

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

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

  373.         p+=4;

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

  375. 

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

  377. 

  378.     nblocks = np >> 3;

  379.     nloops = 1 << 2;

  380.     np2 = np >> 1;

  381.     do {

  382.         p = z;

  383.         q = z + nloops;

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

  385. 

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

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

  388.             

  389.             p++;

  390.             q++;

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

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

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

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

  395.                 p++;

  396.                 q++;

  397.             }

  398.             p += nloops;

  399.             q += nloops;

  400.         }

  401.         nblocks = nblocks >> 1;

  402.         nloops = nloops << 1;

  403.     } while (nblocks != 0);

  404. }

  405. 

  406. /* do a 512 point mdct */

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

  408. {

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

  410.     INT16 rot[N]; 

  411.     IComplex x[N/4];

  412. 

  413.     /* shift to simplify computations */

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

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

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

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

  418.         

  419.     /* pre rotation */

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

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

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

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

  424.     }

  425. 

  426.     fft(x, MDCT_NBITS - 2);

  427.   

  428.     /* post rotation */

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

  430.         re = x[i].re;

  431.         im = x[i].im;

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

  433.         out[2*i] = im1;

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

  435.     }

  436. }

  437. 

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

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

  440. {

  441.     int sum, i;

  442.     sum = 0;

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

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

  445.     }

  446.     return sum;

  447. }

  448. 

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

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

  451.                                  int ch, int is_lfe)

  452. {

  453.     int i, j;

  454.     int exp_diff;

  455.     

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

  457.        reused in the next frame */

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

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

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

  461. #ifdef DEBUG            

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

  463. #endif

  464.         if (exp_diff > EXP_DIFF_THRESHOLD)

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

  466.         else

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

  468.     }

  469.     if (is_lfe)

  470. 	return;

  471. 

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

  473.        recoded, we use a coarse encoding */

  474.     i = 0;

  475.     while (i < NB_BLOCKS) {

  476.         j = i + 1;

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

  478.             j++;

  479.         switch(j - i) {

  480.         case 1:

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

  482.             break;

  483.         case 2:

  484.         case 3:

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

  486.             break;

  487.         default:

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

  489.             break;

  490.         }

  491. 	i = j;

  492.     }

  493. }

  494. 

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

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

  497. {

  498.     int i;

  499. 

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

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

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

  503.     }

  504. }

  505.                                  

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

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

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

  509.                       UINT8 exp[N/2], 

  510.                       int nb_exps,

  511.                       int exp_strategy)

  512. {

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

  514.     UINT8 exp1[N/2];

  515. 

  516.     switch(exp_strategy) {

  517.     case EXP_D15:

  518.         group_size = 1;

  519.         break;

  520.     case EXP_D25:

  521.         group_size = 2;

  522.         break;

  523.     default:

  524.     case EXP_D45:

  525.         group_size = 4;

  526.         break;

  527.     }

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

  529. 

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

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

  532.     k = 1;

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

  534.         exp_min = exp[k];

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

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

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

  538.                 exp_min = exp[k+j];

  539.         }

  540.         exp1[i] = exp_min;

  541.         k += group_size;

  542.     }

  543. 

  544.     /* constraint for DC exponent */

  545.     if (exp1[0] > 15)

  546.         exp1[0] = 15;

  547. 

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

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

  550.        but I am lazy */

  551.     do {

  552.         recurse = 0;

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

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

  555.             if (delta > 2) {

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

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

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

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

  560.                exponent, which means we must recurse */

  561.                 recurse = 1;

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

  563.             }

  564.         }

  565.     } while (recurse);

  566.     

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

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

  569.     k = 1;

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

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

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

  573.         }

  574.         k += group_size;

  575.     }

  576.     

  577. #if defined(DEBUG)

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

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

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

  581.     }

  582.     printf("\n");

  583. #endif

  584. 

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

  586. }

  587. 

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

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

  590. {

  591.     int bits, mant, i;

  592. 

  593.     bits = 0;

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

  595.         mant = m[i];

  596.         switch(mant) {

  597.         case 0:

  598.             /* nothing */

  599.             break;

  600.         case 1:

  601.             /* 3 mantissa in 5 bits */

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

  603.                 bits += 5;

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

  605.                 s->mant1_cnt = 0;

  606.             break;

  607.         case 2:

  608.             /* 3 mantissa in 7 bits */

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

  610.                 bits += 7;

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

  612.                 s->mant2_cnt = 0;

  613.             break;

  614.         case 3:

  615.             bits += 3;

  616.             break;

  617.         case 4:

  618.             /* 2 mantissa in 7 bits */

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

  620.                 bits += 7;

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

  622.                 s->mant4_cnt = 0;

  623.             break;

  624.         case 14:

  625.             bits += 14;

  626.             break;

  627.         case 15:

  628.             bits += 16;

  629.             break;

  630.         default:

  631.             bits += mant - 1;

  632.             break;

  633.         }

  634.     }

  635.     return bits;

  636. }

  637. 

  638. 

  639. static int bit_alloc(AC3EncodeContext *s,

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

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

  642.                      UINT8 exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  643.                      int frame_bits, int csnroffst, int fsnroffst)

  644. {

  645.     int i, ch;

  646. 

  647.     /* compute size */

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

  649.         s->mant1_cnt = 0;

  650.         s->mant2_cnt = 0;

  651.         s->mant4_cnt = 0;

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

  653.             ac3_parametric_bit_allocation(&s->bit_alloc, 

  654.                                           bap[i][ch], (INT8 *)encoded_exp[i][ch], 

  655.                                           0, s->nb_coefs[ch], 

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

  657.                                            fsnroffst) << 2, 

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

  659.                                           ch == s->lfe_channel,

  660.                                           2, 0, NULL, NULL, NULL);

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

  662.                                                  s->nb_coefs[ch]);

  663.         }

  664.     }

  665. #if 0

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

  667.            csnroffst, fsnroffst, frame_bits, 

  668.            16 * s->frame_size - ((frame_bits + 7) & ~7));

  669. #endif

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

  671. }

  672. 

  673. #define SNR_INC1 4

  674. 

  675. static int compute_bit_allocation(AC3EncodeContext *s,

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

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

  678.                                   UINT8 exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  679.                                   int frame_bits)

  680. {

  681.     int i, ch;

  682.     int csnroffst, fsnroffst;

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

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

  685. 

  686.     /* init default parameters */

  687.     s->sdecaycod = 2;

  688.     s->fdecaycod = 1;

  689.     s->sgaincod = 1;

  690.     s->dbkneecod = 2;

  691.     s->floorcod = 4;

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

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

  694.     

  695.     /* compute real values */

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

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

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

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

  700.     s->bit_alloc.sgain = sgaintab[s->sgaincod];

  701.     s->bit_alloc.dbknee = dbkneetab[s->dbkneecod];

  702.     s->bit_alloc.floor = floortab[s->floorcod];

  703.     

  704.     /* header size */

  705.     frame_bits += 65;

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

  707.     //    frame_bits += 2;

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

  709. 

  710.     /* audio blocks */

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

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

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

  714.             frame_bits++; /* rematstr */

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

  716. 	if (s->lfe)

  717. 	    frame_bits++; /* lfeexpstr */

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

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

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

  721.         }

  722.         frame_bits++; /* baie */

  723.         frame_bits++; /* snr */

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

  725.     }

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

  727.     /* bit alloc info */

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

  729.     /* csnroffset[6] */

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

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

  732. 

  733.     /* CRC */

  734.     frame_bits += 16;

  735. 

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

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

  738. 

  739.     csnroffst = s->csnroffst;

  740.     while (csnroffst >= 0 && 

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

  742. 	csnroffst -= SNR_INC1;

  743.     if (csnroffst < 0) {

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

  745. 	return -1;

  746.     }

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

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

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

  750.         csnroffst += SNR_INC1;

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

  752.     }

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

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

  755.         csnroffst++;

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

  757.     }

  758. 

  759.     fsnroffst = 0;

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

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

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

  763.         fsnroffst += SNR_INC1;

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

  765.     }

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

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

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

  769.         fsnroffst++;

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

  771.     }

  772.     

  773.     s->csnroffst = csnroffst;

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

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

  776. #if defined(DEBUG_BITALLOC)

  777.     {

  778.         int j;

  779. 

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

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

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

  783.                 printf("bap=");

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

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

  786.                 }

  787.                 printf("\n");

  788.             }

  789.         }

  790.     }

  791. #endif

  792.     return 0;

  793. }

  794. 

  795. void ac3_common_init(void)

  796. {

  797.     int i, j, k, l, v;

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

  799.     k = 0;

  800.     l = 0;

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

  802.         bndtab[i] = l;

  803.         v = bndsz[i];

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

  805.         l += v;

  806.     }

  807.     bndtab[50] = 0;

  808. }

  809. 

  810. 

  811. static int AC3_encode_init(AVCodecContext *avctx)

  812. {

  813.     int freq = avctx->sample_rate;

  814.     int bitrate = avctx->bit_rate;

  815.     int channels = avctx->channels;

  816.     AC3EncodeContext *s = avctx->priv_data;

  817.     int i, j, ch;

  818.     float alpha;

  819.     static const UINT8 acmod_defs[6] = {

  820. 	0x01, /* C */

  821. 	0x02, /* L R */

  822. 	0x03, /* L C R */

  823. 	0x06, /* L R SL SR */

  824. 	0x07, /* L C R SL SR */

  825. 	0x07, /* L C R SL SR (+LFE) */

  826.     };

  827. 

  828.     avctx->frame_size = AC3_FRAME_SIZE;

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

  830.     

  831.     /* number of channels */

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

  833. 	return -1;

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

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

  836.     s->nb_all_channels = channels;

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

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

  839. 

  840.     /* frequency */

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

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

  843.             if ((ac3_freqs[j] >> i) == freq)

  844.                 goto found;

  845.     }

  846.     return -1;

  847.  found:    

  848.     s->sample_rate = freq;

  849.     s->halfratecod = i;

  850.     s->fscod = j;

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

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

  853. 

  854.     /* bitrate & frame size */

  855.     bitrate /= 1000;

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

  857.         if ((ac3_bitratetab[i] >> s->halfratecod) == bitrate)

  858.             break;

  859.     }

  860.     if (i == 19)

  861.         return -1;

  862.     s->bit_rate = bitrate;

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

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

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

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

  867.     

  868.     /* bit allocation init */

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

  870.         /* bandwidth for each channel */

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

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

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

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

  875.     }

  876.     if (s->lfe) {

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

  878.     }

  879.     /* initial snr offset */

  880.     s->csnroffst = 40;

  881. 

  882.     ac3_common_init();

  883. 

  884.     /* mdct init */

  885.     fft_init(MDCT_NBITS - 2);

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

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

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

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

  890.     }

  891. 

  892.     ac3_crc_init();

  893. 

  894.     return 0;

  895. }

  896. 

  897. /* output the AC3 frame header */

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

  899. {

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

  901. 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  925. }

  926. 

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

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

  929. {

  930.     int v;

  931. 

  932.     if (c >= 0) {

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

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

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

  936.     } else {

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

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

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

  940.     }

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

  942.     return v;

  943. }

  944. 

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

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

  947. {

  948.     int lshift, m, v;

  949. 

  950.     lshift = e + qbits - 24;

  951.     if (lshift >= 0)

  952.         v = c << lshift;

  953.     else

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

  955.     /* rounding */

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

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

  958.     if (v >= m)

  959.         v = m - 1;

  960.     assert(v >= -m);

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

  962. }

  963. 

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

  965.    frame */

  966. static void output_audio_block(AC3EncodeContext *s,

  967.                                UINT8 exp_strategy[AC3_MAX_CHANNELS],

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

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

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

  971.                                INT8 global_exp[AC3_MAX_CHANNELS],

  972.                                int block_num)

  973. {

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

  975.     UINT8 *p;

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

  977.     int exp0, exp1;

  978.     int mant1_cnt, mant2_cnt, mant4_cnt;

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

  980.     int delta0, delta1, delta2;

  981. 

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

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

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

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

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

  987.     if (block_num == 0) {

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

  989.            waste of bit :-) */

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

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

  992.     } else {

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

  994.     }

  995. 

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

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

  998.     }

  999. 

  1000. #if defined(DEBUG) 

  1001.     {

  1002.         static int count = 0;

  1003.         printf("Block #%d (%d)\n", block_num, count++);

  1004.     }

  1005. #endif

  1006.     /* exponent strategy */

  1007.     for(ch=0;ch<s->nb_channels;ch++) {

  1008.         put_bits(&s->pb, 2, exp_strategy[ch]);

  1009.     }

  1010.     

  1011.     if (s->lfe) {

  1012. 	put_bits(&s->pb, 1, exp_strategy[s->lfe_channel]);

  1013.     }

  1014. 

  1015.     for(ch=0;ch<s->nb_channels;ch++) {

  1016.         if (exp_strategy[ch] != EXP_REUSE)

  1017.             put_bits(&s->pb, 6, s->chbwcod[ch]);

  1018.     }

  1019.     

  1020.     /* exponents */

  1021.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1022.         switch(exp_strategy[ch]) {

  1023.         case EXP_REUSE:

  1024.             continue;

  1025.         case EXP_D15:

  1026.             group_size = 1;

  1027.             break;

  1028.         case EXP_D25:

  1029.             group_size = 2;

  1030.             break;

  1031.         default:

  1032.         case EXP_D45:

  1033.             group_size = 4;

  1034.             break;

  1035.         }

  1036. 	nb_groups = (s->nb_coefs[ch] + (group_size * 3) - 4) / (3 * group_size);

  1037.         p = encoded_exp[ch];

  1038. 

  1039.         /* first exponent */

  1040.         exp1 = *p++;

  1041.         put_bits(&s->pb, 4, exp1);

  1042. 

  1043.         /* next ones are delta encoded */

  1044.         for(i=0;i<nb_groups;i++) {

  1045.             /* merge three delta in one code */

  1046.             exp0 = exp1;

  1047.             exp1 = p[0];

  1048.             p += group_size;

  1049.             delta0 = exp1 - exp0 + 2;

  1050. 

  1051.             exp0 = exp1;

  1052.             exp1 = p[0];

  1053.             p += group_size;

  1054.             delta1 = exp1 - exp0 + 2;

  1055. 

  1056.             exp0 = exp1;

  1057.             exp1 = p[0];

  1058.             p += group_size;

  1059.             delta2 = exp1 - exp0 + 2;

  1060. 

  1061.             put_bits(&s->pb, 7, ((delta0 * 5 + delta1) * 5) + delta2);

  1062.         }

  1063. 

  1064. 	if (ch != s->lfe_channel)

  1065. 	    put_bits(&s->pb, 2, 0); /* no gain range info */

  1066.     }

  1067. 

  1068.     /* bit allocation info */

  1069.     baie = (block_num == 0);

  1070.     put_bits(&s->pb, 1, baie);

  1071.     if (baie) {

  1072.         put_bits(&s->pb, 2, s->sdecaycod);

  1073.         put_bits(&s->pb, 2, s->fdecaycod);

  1074.         put_bits(&s->pb, 2, s->sgaincod);

  1075.         put_bits(&s->pb, 2, s->dbkneecod);

  1076.         put_bits(&s->pb, 3, s->floorcod);

  1077.     }

  1078. 

  1079.     /* snr offset */

  1080.     put_bits(&s->pb, 1, baie); /* always present with bai */

  1081.     if (baie) {

  1082.         put_bits(&s->pb, 6, s->csnroffst);

  1083.         for(ch=0;ch<s->nb_all_channels;ch++) {

  1084.             put_bits(&s->pb, 4, s->fsnroffst[ch]);

  1085.             put_bits(&s->pb, 3, s->fgaincod[ch]);

  1086.         }

  1087.     }

  1088.     

  1089.     put_bits(&s->pb, 1, 0); /* no delta bit allocation */

  1090.     put_bits(&s->pb, 1, 0); /* no data to skip */

  1091. 

  1092.     /* mantissa encoding : we use two passes to handle the grouping. A

  1093.        one pass method may be faster, but it would necessitate to

  1094.        modify the output stream. */

  1095. 

  1096.     /* first pass: quantize */

  1097.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  1098.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  1099. 

  1100.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1101.         int b, c, e, v;

  1102. 

  1103.         for(i=0;i<s->nb_coefs[ch];i++) {

  1104.             c = mdct_coefs[ch][i];

  1105.             e = encoded_exp[ch][i] - global_exp[ch];

  1106.             b = bap[ch][i];

  1107.             switch(b) {

  1108.             case 0:

  1109.                 v = 0;

  1110.                 break;

  1111.             case 1:

  1112.                 v = sym_quant(c, e, 3);

  1113.                 switch(mant1_cnt) {

  1114.                 case 0:

  1115.                     qmant1_ptr = &qmant[ch][i];

  1116.                     v = 9 * v;

  1117.                     mant1_cnt = 1;

  1118.                     break;

  1119.                 case 1:

  1120.                     *qmant1_ptr += 3 * v;

  1121.                     mant1_cnt = 2;

  1122.                     v = 128;

  1123.                     break;

  1124.                 default:

  1125.                     *qmant1_ptr += v;

  1126.                     mant1_cnt = 0;

  1127.                     v = 128;

  1128.                     break;

  1129.                 }

  1130.                 break;

  1131.             case 2:

  1132.                 v = sym_quant(c, e, 5);

  1133.                 switch(mant2_cnt) {

  1134.                 case 0:

  1135.                     qmant2_ptr = &qmant[ch][i];

  1136.                     v = 25 * v;

  1137.                     mant2_cnt = 1;

  1138.                     break;

  1139.                 case 1:

  1140.                     *qmant2_ptr += 5 * v;

  1141.                     mant2_cnt = 2;

  1142.                     v = 128;

  1143.                     break;

  1144.                 default:

  1145.                     *qmant2_ptr += v;

  1146.                     mant2_cnt = 0;

  1147.                     v = 128;

  1148.                     break;

  1149.                 }

  1150.                 break;

  1151.             case 3:

  1152.                 v = sym_quant(c, e, 7);

  1153.                 break;

  1154.             case 4:

  1155.                 v = sym_quant(c, e, 11);

  1156.                 switch(mant4_cnt) {

  1157.                 case 0:

  1158.                     qmant4_ptr = &qmant[ch][i];

  1159.                     v = 11 * v;

  1160.                     mant4_cnt = 1;

  1161.                     break;

  1162.                 default:

  1163.                     *qmant4_ptr += v;

  1164.                     mant4_cnt = 0;

  1165.                     v = 128;

  1166.                     break;

  1167.                 }

  1168.                 break;

  1169.             case 5:

  1170.                 v = sym_quant(c, e, 15);

  1171.                 break;

  1172.             case 14:

  1173.                 v = asym_quant(c, e, 14);

  1174.                 break;

  1175.             case 15:

  1176.                 v = asym_quant(c, e, 16);

  1177.                 break;

  1178.             default:

  1179.                 v = asym_quant(c, e, b - 1);

  1180.                 break;

  1181.             }

  1182.             qmant[ch][i] = v;

  1183.         }

  1184.     }

  1185. 

  1186.     /* second pass : output the values */

  1187.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1188.         int b, q;

  1189.         

  1190.         for(i=0;i<s->nb_coefs[ch];i++) {

  1191.             q = qmant[ch][i];

  1192.             b = bap[ch][i];

  1193.             switch(b) {

  1194.             case 0:

  1195.                 break;

  1196.             case 1:

  1197.                 if (q != 128) 

  1198.                     put_bits(&s->pb, 5, q);

  1199.                 break;

  1200.             case 2:

  1201.                 if (q != 128) 

  1202.                     put_bits(&s->pb, 7, q);

  1203.                 break;

  1204.             case 3:

  1205.                 put_bits(&s->pb, 3, q);

  1206.                 break;

  1207.             case 4:

  1208.                 if (q != 128)

  1209.                     put_bits(&s->pb, 7, q);

  1210.                 break;

  1211.             case 14:

  1212.                 put_bits(&s->pb, 14, q);

  1213.                 break;

  1214.             case 15:

  1215.                 put_bits(&s->pb, 16, q);

  1216.                 break;

  1217.             default:

  1218.                 put_bits(&s->pb, b - 1, q);

  1219.                 break;

  1220.             }

  1221.         }

  1222.     }

  1223. }

  1224. 

  1225. /* compute the ac3 crc */

  1226. 

  1227. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1228. 

  1229. static void ac3_crc_init(void)

  1230. {

  1231.     unsigned int c, n, k;

  1232. 

  1233.     for(n=0;n<256;n++) {

  1234.         c = n << 8;

  1235.         for (k = 0; k < 8; k++) {

  1236.             if (c & (1 << 15)) 

  1237.                 c = ((c << 1) & 0xffff) ^ (CRC16_POLY & 0xffff);

  1238.             else

  1239.                 c = c << 1;

  1240.         }

  1241.         crc_table[n] = c;

  1242.     }

  1243. }

  1244. 

  1245. static unsigned int ac3_crc(UINT8 *data, int n, unsigned int crc)

  1246. {

  1247.     int i;

  1248.     for(i=0;i<n;i++) {

  1249.         crc = (crc_table[data[i] ^ (crc >> 8)] ^ (crc << 8)) & 0xffff;

  1250.     }

  1251.     return crc;

  1252. }

  1253. 

  1254. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1255. {

  1256.     unsigned int c;

  1257. 

  1258.     c = 0;

  1259.     while (a) {

  1260.         if (a & 1)

  1261.             c ^= b;

  1262.         a = a >> 1;

  1263.         b = b << 1;

  1264.         if (b & (1 << 16))

  1265.             b ^= poly;

  1266.     }

  1267.     return c;

  1268. }

  1269. 

  1270. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1271. {

  1272.     unsigned int r;

  1273.     r = 1;

  1274.     while (n) {

  1275.         if (n & 1)

  1276.             r = mul_poly(r, a, poly);

  1277.         a = mul_poly(a, a, poly);

  1278.         n >>= 1;

  1279.     }

  1280.     return r;

  1281. }

  1282. 

  1283. 

  1284. /* compute log2(max(abs(tab[]))) */

  1285. static int log2_tab(INT16 *tab, int n)

  1286. {

  1287.     int i, v;

  1288. 

  1289.     v = 0;

  1290.     for(i=0;i<n;i++) {

  1291.         v |= abs(tab[i]);

  1292.     }

  1293.     return av_log2(v);

  1294. }

  1295. 

  1296. static void lshift_tab(INT16 *tab, int n, int lshift)

  1297. {

  1298.     int i;

  1299. 

  1300.     if (lshift > 0) {

  1301.         for(i=0;i<n;i++) {

  1302.             tab[i] <<= lshift;

  1303.         }

  1304.     } else if (lshift < 0) {

  1305.         lshift = -lshift;

  1306.         for(i=0;i<n;i++) {

  1307.             tab[i] >>= lshift;

  1308.         }

  1309.     }

  1310. }

  1311. 

  1312. /* fill the end of the frame and compute the two crcs */

  1313. static int output_frame_end(AC3EncodeContext *s)

  1314. {

  1315.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1316.     UINT8 *frame;

  1317. 

  1318.     frame_size = s->frame_size; /* frame size in words */

  1319.     /* align to 8 bits */

  1320.     flush_put_bits(&s->pb);

  1321.     /* add zero bytes to reach the frame size */

  1322.     frame = s->pb.buf;

  1323.     n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;

  1324.     assert(n >= 0);

  1325.     memset(pbBufPtr(&s->pb), 0, n);

  1326.     

  1327.     /* Now we must compute both crcs : this is not so easy for crc1

  1328.        because it is at the beginning of the data... */

  1329.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1330.     crc1 = ac3_crc(frame + 4, (2 * frame_size_58) - 4, 0);

  1331.     /* XXX: could precompute crc_inv */

  1332.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1333.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1334.     frame[2] = crc1 >> 8;

  1335.     frame[3] = crc1;

  1336.     

  1337.     crc2 = ac3_crc(frame + 2 * frame_size_58, (frame_size - frame_size_58) * 2 - 2, 0);

  1338.     frame[2*frame_size - 2] = crc2 >> 8;

  1339.     frame[2*frame_size - 1] = crc2;

  1340. 

  1341.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1342.     return frame_size * 2;

  1343. }

  1344. 

  1345. static int AC3_encode_frame(AVCodecContext *avctx,

  1346.                             unsigned char *frame, int buf_size, void *data)

  1347. {

  1348.     AC3EncodeContext *s = avctx->priv_data;

  1349.     short *samples = data;

  1350.     int i, j, k, v, ch;

  1351.     INT16 input_samples[N];

  1352.     INT32 mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1353.     UINT8 exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1354.     UINT8 exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

  1355.     UINT8 encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1356.     UINT8 bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1357.     INT8 exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

  1358.     int frame_bits;

  1359. 

  1360.     frame_bits = 0;

  1361.     for(ch=0;ch<s->nb_all_channels;ch++) {

  1362.         /* fixed mdct to the six sub blocks & exponent computation */

  1363.         for(i=0;i<NB_BLOCKS;i++) {

  1364.             INT16 *sptr;

  1365.             int sinc;

  1366. 

  1367.             /* compute input samples */

  1368.             memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(INT16));

  1369.             sinc = s->nb_all_channels;

  1370.             sptr = samples + (sinc * (N/2) * i) + ch;

  1371.             for(j=0;j<N/2;j++) {

  1372.                 v = *sptr;

  1373.                 input_samples[j + N/2] = v;

  1374.                 s->last_samples[ch][j] = v; 

  1375.                 sptr += sinc;

  1376.             }

  1377. 

  1378.             /* apply the MDCT window */

  1379.             for(j=0;j<N/2;j++) {

  1380.                 input_samples[j] = MUL16(input_samples[j], 

  1381.                                          ac3_window[j]) >> 15;

  1382.                 input_samples[N-j-1] = MUL16(input_samples[N-j-1], 

  1383.                                              ac3_window[j]) >> 15;

  1384.             }

  1385.         

  1386.             /* Normalize the samples to use the maximum available

  1387.                precision */

  1388.             v = 14 - log2_tab(input_samples, N);

  1389.             if (v < 0)

  1390.                 v = 0;

  1391.             exp_samples[i][ch] = v - 8;

  1392.             lshift_tab(input_samples, N, v);

  1393. 

  1394.             /* do the MDCT */

  1395.             mdct512(mdct_coef[i][ch], input_samples);

  1396.             

  1397.             /* compute "exponents". We take into account the

  1398.                normalization there */

  1399.             for(j=0;j<N/2;j++) {

  1400.                 int e;

  1401.                 v = abs(mdct_coef[i][ch][j]);

  1402.                 if (v == 0)

  1403.                     e = 24;

  1404.                 else {

  1405.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1406.                     if (e >= 24) {

  1407.                         e = 24;

  1408.                         mdct_coef[i][ch][j] = 0;

  1409.                     }

  1410.                 }

  1411.                 exp[i][ch][j] = e;

  1412.             }

  1413.         }

  1414.         

  1415.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1416. 

  1417.         /* compute the exponents as the decoder will see them. The

  1418.            EXP_REUSE case must be handled carefully : we select the

  1419.            min of the exponents */

  1420.         i = 0;

  1421.         while (i < NB_BLOCKS) {

  1422.             j = i + 1;

  1423.             while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1424.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1425.                 j++;

  1426.             }

  1427.             frame_bits += encode_exp(encoded_exp[i][ch],

  1428.                                      exp[i][ch], s->nb_coefs[ch], 

  1429.                                      exp_strategy[i][ch]);

  1430.             /* copy encoded exponents for reuse case */

  1431.             for(k=i+1;k<j;k++) {

  1432.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch], 

  1433.                        s->nb_coefs[ch] * sizeof(UINT8));

  1434.             }

  1435.             i = j;

  1436.         }

  1437.     }

  1438. 

  1439.     compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

  1440.     /* everything is known... let's output the frame */

  1441.     output_frame_header(s, frame);

  1442.         

  1443.     for(i=0;i<NB_BLOCKS;i++) {

  1444.         output_audio_block(s, exp_strategy[i], encoded_exp[i], 

  1445.                            bap[i], mdct_coef[i], exp_samples[i], i);

  1446.     }

  1447.     return output_frame_end(s);

  1448. }

  1449. 

  1450. #if 0

  1451. /*************************************************************************/

  1452. /* TEST */

  1453. 

  1454. #define FN (N/4)

  1455. 

  1456. void fft_test(void)

  1457. {

  1458.     IComplex in[FN], in1[FN];

  1459.     int k, n, i;

  1460.     float sum_re, sum_im, a;

  1461. 

  1462.     /* FFT test */

  1463. 

  1464.     for(i=0;i<FN;i++) {

  1465.         in[i].re = random() % 65535 - 32767;

  1466.         in[i].im = random() % 65535 - 32767;

  1467.         in1[i] = in[i];

  1468.     }

  1469.     fft(in, 7);

  1470. 

  1471.     /* do it by hand */

  1472.     for(k=0;k<FN;k++) {

  1473.         sum_re = 0;

  1474.         sum_im = 0;

  1475.         for(n=0;n<FN;n++) {

  1476.             a = -2 * M_PI * (n * k) / FN;

  1477.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1478.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1479.         }

  1480.         printf("%3d: %6d,%6d %6.0f,%6.0f\n", 

  1481.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN); 

  1482.     }

  1483. }

  1484. 

  1485. void mdct_test(void)

  1486. {

  1487.     INT16 input[N];

  1488.     INT32 output[N/2];

  1489.     float input1[N];

  1490.     float output1[N/2];

  1491.     float s, a, err, e, emax;

  1492.     int i, k, n;

  1493. 

  1494.     for(i=0;i<N;i++) {

  1495.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1496.         input1[i] = input[i];

  1497.     }

  1498. 

  1499.     mdct512(output, input);

  1500.     

  1501.     /* do it by hand */

  1502.     for(k=0;k<N/2;k++) {

  1503.         s = 0;

  1504.         for(n=0;n<N;n++) {

  1505.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1506.             s += input1[n] * cos(a);

  1507.         }

  1508.         output1[k] = -2 * s / N;

  1509.     }

  1510.     

  1511.     err = 0;

  1512.     emax = 0;

  1513.     for(i=0;i<N/2;i++) {

  1514.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1515.         e = output[i] - output1[i];

  1516.         if (e > emax)

  1517.             emax = e;

  1518.         err += e * e;

  1519.     }

  1520.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1521. }

  1522. 

  1523. void test_ac3(void)

  1524. {

  1525.     AC3EncodeContext ctx;

  1526.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1527.     short samples[AC3_FRAME_SIZE];

  1528.     int ret, i;

  1529.     

  1530.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1531. 

  1532.     fft_test();

  1533.     mdct_test();

  1534. 

  1535.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1536.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1537.     ret = AC3_encode_frame(&ctx, frame, samples);

  1538.     printf("ret=%d\n", ret);

  1539. }

  1540. #endif

  1541. 

  1542. AVCodec ac3_encoder = {

  1543.     "ac3",

  1544.     CODEC_TYPE_AUDIO,

  1545.     CODEC_ID_AC3,

  1546.     sizeof(AC3EncodeContext),

  1547.     AC3_encode_init,

  1548.     AC3_encode_frame,

  1549.     NULL,

  1550. };