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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. 

  20. /**

  21.  * @file ac3enc.c

  22.  * The simplest AC3 encoder.

  23.  */

  24. //#define DEBUG

  25. //#define DEBUG_BITALLOC

  26. #include "avcodec.h"

  27. 

  28. #include "ac3.h"

  29. 

  30. typedef struct AC3EncodeContext {

  31.     PutBitContext pb;

  32.     int nb_channels;

  33.     int nb_all_channels;

  34.     int lfe_channel;

  35.     int bit_rate;

  36.     unsigned int sample_rate;

  37.     unsigned int bsid;

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

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

  40.     int halfratecod;

  41.     unsigned int frmsizecod;

  42.     unsigned int fscod; /* frequency */

  43.     unsigned int acmod;

  44.     int lfe;

  45.     unsigned int bsmod;

  46.     short last_samples[AC3_MAX_CHANNELS][256];

  47.     unsigned int chbwcod[AC3_MAX_CHANNELS];

  48.     int nb_coefs[AC3_MAX_CHANNELS];

  49.     

  50.     /* bitrate allocation control */

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

  52.     AC3BitAllocParameters bit_alloc;

  53.     int csnroffst;

  54.     int fgaincod[AC3_MAX_CHANNELS];

  55.     int fsnroffst[AC3_MAX_CHANNELS];

  56.     /* mantissa encoding */

  57.     int mant1_cnt, mant2_cnt, mant4_cnt;

  58. } AC3EncodeContext;

  59. 

  60. #include "ac3tab.h"

  61. 

  62. #define MDCT_NBITS 9

  63. #define N         (1 << MDCT_NBITS)

  64. 

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

  66. #define EXP_DIFF_THRESHOLD 1000

  67. 

  68. static void fft_init(int ln);

  69. static void ac3_crc_init(void);

  70. 

  71. static inline int16_t fix15(float a)

  72. {

  73.     int v;

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

  75.     if (v < -32767)

  76.         v = -32767;

  77.     else if (v > 32767) 

  78.         v = 32767;

  79.     return v;

  80. }

  81. 

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

  83. {

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

  85.         a = 384 ;

  86.     } else if (b0 > b1) { 

  87.         a = a - 64;

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

  89.     }

  90.     return a;

  91. }

  92. 

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

  94. {

  95.     if (bin < 7) {

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

  97.             a = 384 ;

  98.         } else if (b0 > b1) { 

  99.             a = a - 64;

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

  101.         }

  102.     } else if (bin < 20) {

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

  104.             a = 320 ;

  105.         } else if (b0 > b1) {

  106.             a= a - 64;

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

  108.         }

  109.     } else {

  110.         a = a - 128;

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

  112.     }

  113.     return a;

  114. }

  115. 

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

  117.    spec. */

  118. void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,

  119.                                    int8_t *exp, int start, int end,

  120.                                    int snroffset, int fgain, int is_lfe,

  121.                                    int deltbae,int deltnseg, 

  122.                                    uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba)

  123. {

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

  125.     int fastleak,slowleak,address,tmp;

  126.     int16_t psd[256]; /* scaled exponents */

  127.     int16_t bndpsd[50]; /* interpolated exponents */

  128.     int16_t excite[50]; /* excitation */

  129.     int16_t mask[50];   /* masking value */

  130. 

  131.     /* exponent mapping to PSD */

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

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

  134.     }

  135. 

  136.     /* PSD integration */

  137.     j=start;

  138.     k=masktab[start];

  139.     do {

  140.         v=psd[j];

  141.         j++;

  142.         end1=bndtab[k+1];

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

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

  145.             int c,adr;

  146.             /* logadd */

  147.             v1=psd[j];

  148.             c=v-v1;

  149.             if (c >= 0) {

  150.                 adr=c >> 1;

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

  152.                 v=v + latab[adr];

  153.             } else {

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

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

  156.                 v=v1 + latab[adr];

  157.             }

  158.             j++;

  159.         }

  160.         bndpsd[k]=v;

  161.         k++;

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

  163. 

  164.     /* excitation function */

  165.     bndstrt = masktab[start];

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

  167.     

  168.     if (bndstrt == 0) {

  169.         lowcomp = 0;

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

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

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

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

  174.         begin = 7 ;

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

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

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

  178.             fastleak = bndpsd[bin] - fgain ;

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

  180.             excite[bin] = fastleak - lowcomp ;

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

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

  183.                     begin = bin + 1 ;

  184.                     break ;

  185.                 }

  186.             }

  187.         }

  188.     

  189.         end1=bndend;

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

  191.     

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

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

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

  195.         

  196.             fastleak -= s->fdecay ;

  197.             v = bndpsd[bin] - fgain;

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

  199.         

  200.             slowleak -= s->sdecay ;

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

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

  203.         

  204.             v=fastleak - lowcomp;

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

  206.         

  207.             excite[bin] = v;

  208.         }

  209.         begin = 22;

  210.     } else {

  211.         /* coupling channel */

  212.         begin = bndstrt;

  213.         

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

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

  216.     }

  217. 

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

  219.         fastleak -= s->fdecay ;

  220.         v = bndpsd[bin] - fgain;

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

  222.         slowleak -= s->sdecay ;

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

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

  225. 

  226.         v=fastleak;

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

  228.         excite[bin] = v;

  229.     }

  230. 

  231.     /* compute masking curve */

  232. 

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

  234.         v1 = excite[bin];

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

  236.         if (tmp > 0) {

  237.             v1 += tmp >> 2;

  238.         }

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

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

  241.         mask[bin] = v;

  242.     }

  243. 

  244.     /* delta bit allocation */

  245. 

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

  247.         int band, seg, delta;

  248.         band = 0 ;

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

  250.             band += deltoffst[seg] ;

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

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

  253.             } else {

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

  255.             }

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

  257.                 mask[band] += delta ;

  258.                 band++ ;

  259.             }

  260.         }

  261.     }

  262. 

  263.     /* compute bit allocation */

  264.     

  265.     i = start ;

  266.     j = masktab[start] ;

  267.     do {

  268.         v=mask[j];

  269.         v -= snroffset ;

  270.         v -= s->floor ;

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

  272.         v &= 0x1fe0 ;

  273.         v += s->floor ;

  274. 

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

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

  277. 

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

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

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

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

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

  283.             i++;

  284.         }

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

  286. }

  287. 

  288. typedef struct IComplex {

  289.     short re,im;

  290. } IComplex;

  291. 

  292. static void fft_init(int ln)

  293. {

  294.     int i, j, m, n;

  295.     float alpha;

  296. 

  297.     n = 1 << ln;

  298. 

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

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

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

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

  303.     }

  304. 

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

  306.         m=0;

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

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

  309.         }

  310.         fft_rev[i]=m;

  311.     }

  312. }

  313. 

  314. /* butter fly op */

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

  316. {\

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

  318.   bx=pre1;\

  319.   by=pim1;\

  320.   ax=qre1;\

  321.   ay=qim1;\

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

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

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

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

  326. }

  327. 

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

  329. 

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

  331. {\

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

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

  334. }

  335. 

  336. 

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

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

  339. {

  340.     int	j, l, np, np2;

  341.     int	nblocks, nloops;

  342.     register IComplex *p,*q;

  343.     int tmp_re, tmp_im;

  344. 

  345.     np = 1 << ln;

  346. 

  347.     /* reverse */

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

  349.         int k;

  350.         IComplex tmp;

  351.         k = fft_rev[j];

  352.         if (k < j) {

  353.             tmp = z[k];

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

  355.             z[j] = tmp;

  356.         }

  357.     }

  358. 

  359.     /* pass 0 */

  360. 

  361.     p=&z[0];

  362.     j=(np >> 1);

  363.     do {

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

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

  366.         p+=2;

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

  368. 

  369.     /* pass 1 */

  370. 

  371.     p=&z[0];

  372.     j=np >> 2;

  373.     do {

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

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

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

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

  378.         p+=4;

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

  380. 

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

  382. 

  383.     nblocks = np >> 3;

  384.     nloops = 1 << 2;

  385.     np2 = np >> 1;

  386.     do {

  387.         p = z;

  388.         q = z + nloops;

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

  390. 

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

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

  393.             

  394.             p++;

  395.             q++;

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

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

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

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

  400.                 p++;

  401.                 q++;

  402.             }

  403.             p += nloops;

  404.             q += nloops;

  405.         }

  406.         nblocks = nblocks >> 1;

  407.         nloops = nloops << 1;

  408.     } while (nblocks != 0);

  409. }

  410. 

  411. /* do a 512 point mdct */

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

  413. {

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

  415.     int16_t rot[N]; 

  416.     IComplex x[N/4];

  417. 

  418.     /* shift to simplify computations */

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

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

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

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

  423.         

  424.     /* pre rotation */

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

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

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

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

  429.     }

  430. 

  431.     fft(x, MDCT_NBITS - 2);

  432.   

  433.     /* post rotation */

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

  435.         re = x[i].re;

  436.         im = x[i].im;

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

  438.         out[2*i] = im1;

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

  440.     }

  441. }

  442. 

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

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

  445. {

  446.     int sum, i;

  447.     sum = 0;

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

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

  450.     }

  451.     return sum;

  452. }

  453. 

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

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

  456.                                  int ch, int is_lfe)

  457. {

  458.     int i, j;

  459.     int exp_diff;

  460.     

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

  462.        reused in the next frame */

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

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

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

  466. #ifdef DEBUG            

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

  468. #endif

  469.         if (exp_diff > EXP_DIFF_THRESHOLD)

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

  471.         else

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

  473.     }

  474.     if (is_lfe)

  475. 	return;

  476. 

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

  478.        recoded, we use a coarse encoding */

  479.     i = 0;

  480.     while (i < NB_BLOCKS) {

  481.         j = i + 1;

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

  483.             j++;

  484.         switch(j - i) {

  485.         case 1:

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

  487.             break;

  488.         case 2:

  489.         case 3:

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

  491.             break;

  492.         default:

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

  494.             break;

  495.         }

  496. 	i = j;

  497.     }

  498. }

  499. 

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

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

  502. {

  503.     int i;

  504. 

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

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

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

  508.     }

  509. }

  510.                                  

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

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

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

  514.                       uint8_t exp[N/2], 

  515.                       int nb_exps,

  516.                       int exp_strategy)

  517. {

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

  519.     uint8_t exp1[N/2];

  520. 

  521.     switch(exp_strategy) {

  522.     case EXP_D15:

  523.         group_size = 1;

  524.         break;

  525.     case EXP_D25:

  526.         group_size = 2;

  527.         break;

  528.     default:

  529.     case EXP_D45:

  530.         group_size = 4;

  531.         break;

  532.     }

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

  534. 

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

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

  537.     k = 1;

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

  539.         exp_min = exp[k];

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

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

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

  543.                 exp_min = exp[k+j];

  544.         }

  545.         exp1[i] = exp_min;

  546.         k += group_size;

  547.     }

  548. 

  549.     /* constraint for DC exponent */

  550.     if (exp1[0] > 15)

  551.         exp1[0] = 15;

  552. 

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

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

  555.        but I am lazy */

  556.     do {

  557.         recurse = 0;

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

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

  560.             if (delta > 2) {

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

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

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

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

  565.                exponent, which means we must recurse */

  566.                 recurse = 1;

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

  568.             }

  569.         }

  570.     } while (recurse);

  571.     

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

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

  574.     k = 1;

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

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

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

  578.         }

  579.         k += group_size;

  580.     }

  581.     

  582. #if defined(DEBUG)

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

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

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

  586.     }

  587.     printf("\n");

  588. #endif

  589. 

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

  591. }

  592. 

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

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

  595. {

  596.     int bits, mant, i;

  597. 

  598.     bits = 0;

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

  600.         mant = m[i];

  601.         switch(mant) {

  602.         case 0:

  603.             /* nothing */

  604.             break;

  605.         case 1:

  606.             /* 3 mantissa in 5 bits */

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

  608.                 bits += 5;

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

  610.                 s->mant1_cnt = 0;

  611.             break;

  612.         case 2:

  613.             /* 3 mantissa in 7 bits */

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

  615.                 bits += 7;

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

  617.                 s->mant2_cnt = 0;

  618.             break;

  619.         case 3:

  620.             bits += 3;

  621.             break;

  622.         case 4:

  623.             /* 2 mantissa in 7 bits */

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

  625.                 bits += 7;

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

  627.                 s->mant4_cnt = 0;

  628.             break;

  629.         case 14:

  630.             bits += 14;

  631.             break;

  632.         case 15:

  633.             bits += 16;

  634.             break;

  635.         default:

  636.             bits += mant - 1;

  637.             break;

  638.         }

  639.     }

  640.     return bits;

  641. }

  642. 

  643. 

  644. static int bit_alloc(AC3EncodeContext *s,

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

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

  647.                      uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  648.                      int frame_bits, int csnroffst, int fsnroffst)

  649. {

  650.     int i, ch;

  651. 

  652.     /* compute size */

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

  654.         s->mant1_cnt = 0;

  655.         s->mant2_cnt = 0;

  656.         s->mant4_cnt = 0;

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

  658.             ac3_parametric_bit_allocation(&s->bit_alloc, 

  659.                                           bap[i][ch], (int8_t *)encoded_exp[i][ch], 

  660.                                           0, s->nb_coefs[ch], 

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

  662.                                            fsnroffst) << 2, 

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

  664.                                           ch == s->lfe_channel,

  665.                                           2, 0, NULL, NULL, NULL);

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

  667.                                                  s->nb_coefs[ch]);

  668.         }

  669.     }

  670. #if 0

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

  672.            csnroffst, fsnroffst, frame_bits, 

  673.            16 * s->frame_size - ((frame_bits + 7) & ~7));

  674. #endif

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

  676. }

  677. 

  678. #define SNR_INC1 4

  679. 

  680. static int compute_bit_allocation(AC3EncodeContext *s,

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

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

  683.                                   uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  684.                                   int frame_bits)

  685. {

  686.     int i, ch;

  687.     int csnroffst, fsnroffst;

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

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

  690. 

  691.     /* init default parameters */

  692.     s->sdecaycod = 2;

  693.     s->fdecaycod = 1;

  694.     s->sgaincod = 1;

  695.     s->dbkneecod = 2;

  696.     s->floorcod = 4;

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

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

  699.     

  700.     /* compute real values */

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

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

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

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

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

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

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

  708.     

  709.     /* header size */

  710.     frame_bits += 65;

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

  712.     //    frame_bits += 2;

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

  714. 

  715.     /* audio blocks */

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

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

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

  719.             frame_bits++; /* rematstr */

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

  721. 	if (s->lfe)

  722. 	    frame_bits++; /* lfeexpstr */

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

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

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

  726.         }

  727.         frame_bits++; /* baie */

  728.         frame_bits++; /* snr */

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

  730.     }

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

  732.     /* bit alloc info */

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

  734.     /* csnroffset[6] */

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

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

  737. 

  738.     /* CRC */

  739.     frame_bits += 16;

  740. 

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

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

  743. 

  744.     csnroffst = s->csnroffst;

  745.     while (csnroffst >= 0 && 

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

  747. 	csnroffst -= SNR_INC1;

  748.     if (csnroffst < 0) {

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

  750. 	return -1;

  751.     }

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

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

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

  755.         csnroffst += SNR_INC1;

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

  757.     }

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

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

  760.         csnroffst++;

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

  762.     }

  763. 

  764.     fsnroffst = 0;

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

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

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

  768.         fsnroffst += SNR_INC1;

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

  770.     }

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

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

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

  774.         fsnroffst++;

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

  776.     }

  777.     

  778.     s->csnroffst = csnroffst;

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

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

  781. #if defined(DEBUG_BITALLOC)

  782.     {

  783.         int j;

  784. 

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

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

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

  788.                 printf("bap=");

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

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

  791.                 }

  792.                 printf("\n");

  793.             }

  794.         }

  795.     }

  796. #endif

  797.     return 0;

  798. }

  799. 

  800. void ac3_common_init(void)

  801. {

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

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

  804.     k = 0;

  805.     l = 0;

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

  807.         bndtab[i] = l;

  808.         v = bndsz[i];

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

  810.         l += v;

  811.     }

  812.     bndtab[50] = 0;

  813. }

  814. 

  815. 

  816. static int AC3_encode_init(AVCodecContext *avctx)

  817. {

  818.     int freq = avctx->sample_rate;

  819.     int bitrate = avctx->bit_rate;

  820.     int channels = avctx->channels;

  821.     AC3EncodeContext *s = avctx->priv_data;

  822.     int i, j, ch;

  823.     float alpha;

  824.     static const uint8_t acmod_defs[6] = {

  825. 	0x01, /* C */

  826. 	0x02, /* L R */

  827. 	0x03, /* L C R */

  828. 	0x06, /* L R SL SR */

  829. 	0x07, /* L C R SL SR */

  830. 	0x07, /* L C R SL SR (+LFE) */

  831.     };

  832. 

  833.     avctx->frame_size = AC3_FRAME_SIZE;

  834.     

  835.     /* number of channels */

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

  837. 	return -1;

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

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

  840.     s->nb_all_channels = channels;

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

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

  843. 

  844.     /* frequency */

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

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

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

  848.                 goto found;

  849.     }

  850.     return -1;

  851.  found:    

  852.     s->sample_rate = freq;

  853.     s->halfratecod = i;

  854.     s->fscod = j;

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

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

  857. 

  858.     /* bitrate & frame size */

  859.     bitrate /= 1000;

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

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

  862.             break;

  863.     }

  864.     if (i == 19)

  865.         return -1;

  866.     s->bit_rate = bitrate;

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

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

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

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

  871.     

  872.     /* bit allocation init */

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

  874.         /* bandwidth for each channel */

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

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

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

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

  879.     }

  880.     if (s->lfe) {

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

  882.     }

  883.     /* initial snr offset */

  884.     s->csnroffst = 40;

  885. 

  886.     ac3_common_init();

  887. 

  888.     /* mdct init */

  889.     fft_init(MDCT_NBITS - 2);

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

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

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

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

  894.     }

  895. 

  896.     ac3_crc_init();

  897.     

  898.     avctx->coded_frame= avcodec_alloc_frame();

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

  900. 

  901.     return 0;

  902. }

  903. 

  904. /* output the AC3 frame header */

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

  906. {

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

  908. 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  932. }

  933. 

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

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

  936. {

  937.     int v;

  938. 

  939.     if (c >= 0) {

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

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

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

  943.     } else {

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

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

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

  947.     }

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

  949.     return v;

  950. }

  951. 

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

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

  954. {

  955.     int lshift, m, v;

  956. 

  957.     lshift = e + qbits - 24;

  958.     if (lshift >= 0)

  959.         v = c << lshift;

  960.     else

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

  962.     /* rounding */

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

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

  965.     if (v >= m)

  966.         v = m - 1;

  967.     assert(v >= -m);

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

  969. }

  970. 

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

  972.    frame */

  973. static void output_audio_block(AC3EncodeContext *s,

  974.                                uint8_t exp_strategy[AC3_MAX_CHANNELS],

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

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

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

  978.                                int8_t global_exp[AC3_MAX_CHANNELS],

  979.                                int block_num)

  980. {

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

  982.     uint8_t *p;

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

  984.     int exp0, exp1;

  985.     int mant1_cnt, mant2_cnt, mant4_cnt;

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

  987.     int delta0, delta1, delta2;

  988. 

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

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

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

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

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

  994.     if (block_num == 0) {

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

  996.            waste of bit :-) */

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

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

  999.     } else {

  1000.         put_bits(&s->pb, 1, 0); /* no new coupling strategy */

  1001.     }

  1002. 

  1003.     if (s->acmod == 2) {

  1004.         put_bits(&s->pb, 1, 0); /* no matrixing (but should be used in the future) */

  1005.     }

  1006. 

  1007. #if defined(DEBUG) 

  1008.     {

  1009.         static int count = 0;

  1010.         printf("Block #%d (%d)\n", block_num, count++);

  1011.     }

  1012. #endif

  1013.     /* exponent strategy */

  1014.     for(ch=0;ch<s->nb_channels;ch++) {

  1015.         put_bits(&s->pb, 2, exp_strategy[ch]);

  1016.     }

  1017.     

  1018.     if (s->lfe) {

  1019. 	put_bits(&s->pb, 1, exp_strategy[s->lfe_channel]);

  1020.     }

  1021. 

  1022.     for(ch=0;ch<s->nb_channels;ch++) {

  1023.         if (exp_strategy[ch] != EXP_REUSE)

  1024.             put_bits(&s->pb, 6, s->chbwcod[ch]);

  1025.     }

  1026.     

  1027.     /* exponents */

  1028.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1029.         switch(exp_strategy[ch]) {

  1030.         case EXP_REUSE:

  1031.             continue;

  1032.         case EXP_D15:

  1033.             group_size = 1;

  1034.             break;

  1035.         case EXP_D25:

  1036.             group_size = 2;

  1037.             break;

  1038.         default:

  1039.         case EXP_D45:

  1040.             group_size = 4;

  1041.             break;

  1042.         }

  1043. 	nb_groups = (s->nb_coefs[ch] + (group_size * 3) - 4) / (3 * group_size);

  1044.         p = encoded_exp[ch];

  1045. 

  1046.         /* first exponent */

  1047.         exp1 = *p++;

  1048.         put_bits(&s->pb, 4, exp1);

  1049. 

  1050.         /* next ones are delta encoded */

  1051.         for(i=0;i<nb_groups;i++) {

  1052.             /* merge three delta in one code */

  1053.             exp0 = exp1;

  1054.             exp1 = p[0];

  1055.             p += group_size;

  1056.             delta0 = exp1 - exp0 + 2;

  1057. 

  1058.             exp0 = exp1;

  1059.             exp1 = p[0];

  1060.             p += group_size;

  1061.             delta1 = exp1 - exp0 + 2;

  1062. 

  1063.             exp0 = exp1;

  1064.             exp1 = p[0];

  1065.             p += group_size;

  1066.             delta2 = exp1 - exp0 + 2;

  1067. 

  1068.             put_bits(&s->pb, 7, ((delta0 * 5 + delta1) * 5) + delta2);

  1069.         }

  1070. 

  1071. 	if (ch != s->lfe_channel)

  1072. 	    put_bits(&s->pb, 2, 0); /* no gain range info */

  1073.     }

  1074. 

  1075.     /* bit allocation info */

  1076.     baie = (block_num == 0);

  1077.     put_bits(&s->pb, 1, baie);

  1078.     if (baie) {

  1079.         put_bits(&s->pb, 2, s->sdecaycod);

  1080.         put_bits(&s->pb, 2, s->fdecaycod);

  1081.         put_bits(&s->pb, 2, s->sgaincod);

  1082.         put_bits(&s->pb, 2, s->dbkneecod);

  1083.         put_bits(&s->pb, 3, s->floorcod);

  1084.     }

  1085. 

  1086.     /* snr offset */

  1087.     put_bits(&s->pb, 1, baie); /* always present with bai */

  1088.     if (baie) {

  1089.         put_bits(&s->pb, 6, s->csnroffst);

  1090.         for(ch=0;ch<s->nb_all_channels;ch++) {

  1091.             put_bits(&s->pb, 4, s->fsnroffst[ch]);

  1092.             put_bits(&s->pb, 3, s->fgaincod[ch]);

  1093.         }

  1094.     }

  1095.     

  1096.     put_bits(&s->pb, 1, 0); /* no delta bit allocation */

  1097.     put_bits(&s->pb, 1, 0); /* no data to skip */

  1098. 

  1099.     /* mantissa encoding : we use two passes to handle the grouping. A

  1100.        one pass method may be faster, but it would necessitate to

  1101.        modify the output stream. */

  1102. 

  1103.     /* first pass: quantize */

  1104.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  1105.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  1106. 

  1107.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1108.         int b, c, e, v;

  1109. 

  1110.         for(i=0;i<s->nb_coefs[ch];i++) {

  1111.             c = mdct_coefs[ch][i];

  1112.             e = encoded_exp[ch][i] - global_exp[ch];

  1113.             b = bap[ch][i];

  1114.             switch(b) {

  1115.             case 0:

  1116.                 v = 0;

  1117.                 break;

  1118.             case 1:

  1119.                 v = sym_quant(c, e, 3);

  1120.                 switch(mant1_cnt) {

  1121.                 case 0:

  1122.                     qmant1_ptr = &qmant[ch][i];

  1123.                     v = 9 * v;

  1124.                     mant1_cnt = 1;

  1125.                     break;

  1126.                 case 1:

  1127.                     *qmant1_ptr += 3 * v;

  1128.                     mant1_cnt = 2;

  1129.                     v = 128;

  1130.                     break;

  1131.                 default:

  1132.                     *qmant1_ptr += v;

  1133.                     mant1_cnt = 0;

  1134.                     v = 128;

  1135.                     break;

  1136.                 }

  1137.                 break;

  1138.             case 2:

  1139.                 v = sym_quant(c, e, 5);

  1140.                 switch(mant2_cnt) {

  1141.                 case 0:

  1142.                     qmant2_ptr = &qmant[ch][i];

  1143.                     v = 25 * v;

  1144.                     mant2_cnt = 1;

  1145.                     break;

  1146.                 case 1:

  1147.                     *qmant2_ptr += 5 * v;

  1148.                     mant2_cnt = 2;

  1149.                     v = 128;

  1150.                     break;

  1151.                 default:

  1152.                     *qmant2_ptr += v;

  1153.                     mant2_cnt = 0;

  1154.                     v = 128;

  1155.                     break;

  1156.                 }

  1157.                 break;

  1158.             case 3:

  1159.                 v = sym_quant(c, e, 7);

  1160.                 break;

  1161.             case 4:

  1162.                 v = sym_quant(c, e, 11);

  1163.                 switch(mant4_cnt) {

  1164.                 case 0:

  1165.                     qmant4_ptr = &qmant[ch][i];

  1166.                     v = 11 * v;

  1167.                     mant4_cnt = 1;

  1168.                     break;

  1169.                 default:

  1170.                     *qmant4_ptr += v;

  1171.                     mant4_cnt = 0;

  1172.                     v = 128;

  1173.                     break;

  1174.                 }

  1175.                 break;

  1176.             case 5:

  1177.                 v = sym_quant(c, e, 15);

  1178.                 break;

  1179.             case 14:

  1180.                 v = asym_quant(c, e, 14);

  1181.                 break;

  1182.             case 15:

  1183.                 v = asym_quant(c, e, 16);

  1184.                 break;

  1185.             default:

  1186.                 v = asym_quant(c, e, b - 1);

  1187.                 break;

  1188.             }

  1189.             qmant[ch][i] = v;

  1190.         }

  1191.     }

  1192. 

  1193.     /* second pass : output the values */

  1194.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1195.         int b, q;

  1196.         

  1197.         for(i=0;i<s->nb_coefs[ch];i++) {

  1198.             q = qmant[ch][i];

  1199.             b = bap[ch][i];

  1200.             switch(b) {

  1201.             case 0:

  1202.                 break;

  1203.             case 1:

  1204.                 if (q != 128) 

  1205.                     put_bits(&s->pb, 5, q);

  1206.                 break;

  1207.             case 2:

  1208.                 if (q != 128) 

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

  1210.                 break;

  1211.             case 3:

  1212.                 put_bits(&s->pb, 3, q);

  1213.                 break;

  1214.             case 4:

  1215.                 if (q != 128)

  1216.                     put_bits(&s->pb, 7, q);

  1217.                 break;

  1218.             case 14:

  1219.                 put_bits(&s->pb, 14, q);

  1220.                 break;

  1221.             case 15:

  1222.                 put_bits(&s->pb, 16, q);

  1223.                 break;

  1224.             default:

  1225.                 put_bits(&s->pb, b - 1, q);

  1226.                 break;

  1227.             }

  1228.         }

  1229.     }

  1230. }

  1231. 

  1232. /* compute the ac3 crc */

  1233. 

  1234. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1235. 

  1236. static void ac3_crc_init(void)

  1237. {

  1238.     unsigned int c, n, k;

  1239. 

  1240.     for(n=0;n<256;n++) {

  1241.         c = n << 8;

  1242.         for (k = 0; k < 8; k++) {

  1243.             if (c & (1 << 15)) 

  1244.                 c = ((c << 1) & 0xffff) ^ (CRC16_POLY & 0xffff);

  1245.             else

  1246.                 c = c << 1;

  1247.         }

  1248.         crc_table[n] = c;

  1249.     }

  1250. }

  1251. 

  1252. static unsigned int ac3_crc(uint8_t *data, int n, unsigned int crc)

  1253. {

  1254.     int i;

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

  1256.         crc = (crc_table[data[i] ^ (crc >> 8)] ^ (crc << 8)) & 0xffff;

  1257.     }

  1258.     return crc;

  1259. }

  1260. 

  1261. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1262. {

  1263.     unsigned int c;

  1264. 

  1265.     c = 0;

  1266.     while (a) {

  1267.         if (a & 1)

  1268.             c ^= b;

  1269.         a = a >> 1;

  1270.         b = b << 1;

  1271.         if (b & (1 << 16))

  1272.             b ^= poly;

  1273.     }

  1274.     return c;

  1275. }

  1276. 

  1277. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1278. {

  1279.     unsigned int r;

  1280.     r = 1;

  1281.     while (n) {

  1282.         if (n & 1)

  1283.             r = mul_poly(r, a, poly);

  1284.         a = mul_poly(a, a, poly);

  1285.         n >>= 1;

  1286.     }

  1287.     return r;

  1288. }

  1289. 

  1290. 

  1291. /* compute log2(max(abs(tab[]))) */

  1292. static int log2_tab(int16_t *tab, int n)

  1293. {

  1294.     int i, v;

  1295. 

  1296.     v = 0;

  1297.     for(i=0;i<n;i++) {

  1298.         v |= abs(tab[i]);

  1299.     }

  1300.     return av_log2(v);

  1301. }

  1302. 

  1303. static void lshift_tab(int16_t *tab, int n, int lshift)

  1304. {

  1305.     int i;

  1306. 

  1307.     if (lshift > 0) {

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

  1309.             tab[i] <<= lshift;

  1310.         }

  1311.     } else if (lshift < 0) {

  1312.         lshift = -lshift;

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

  1314.             tab[i] >>= lshift;

  1315.         }

  1316.     }

  1317. }

  1318. 

  1319. /* fill the end of the frame and compute the two crcs */

  1320. static int output_frame_end(AC3EncodeContext *s)

  1321. {

  1322.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1323.     uint8_t *frame;

  1324. 

  1325.     frame_size = s->frame_size; /* frame size in words */

  1326.     /* align to 8 bits */

  1327.     flush_put_bits(&s->pb);

  1328.     /* add zero bytes to reach the frame size */

  1329.     frame = s->pb.buf;

  1330.     n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;

  1331.     assert(n >= 0);

  1332.     memset(pbBufPtr(&s->pb), 0, n);

  1333.     

  1334.     /* Now we must compute both crcs : this is not so easy for crc1

  1335.        because it is at the beginning of the data... */

  1336.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1337.     crc1 = ac3_crc(frame + 4, (2 * frame_size_58) - 4, 0);

  1338.     /* XXX: could precompute crc_inv */

  1339.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1340.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1341.     frame[2] = crc1 >> 8;

  1342.     frame[3] = crc1;

  1343.     

  1344.     crc2 = ac3_crc(frame + 2 * frame_size_58, (frame_size - frame_size_58) * 2 - 2, 0);

  1345.     frame[2*frame_size - 2] = crc2 >> 8;

  1346.     frame[2*frame_size - 1] = crc2;

  1347. 

  1348.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1349.     return frame_size * 2;

  1350. }

  1351. 

  1352. static int AC3_encode_frame(AVCodecContext *avctx,

  1353.                             unsigned char *frame, int buf_size, void *data)

  1354. {

  1355.     AC3EncodeContext *s = avctx->priv_data;

  1356.     short *samples = data;

  1357.     int i, j, k, v, ch;

  1358.     int16_t input_samples[N];

  1359.     int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1360.     uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1361.     uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

  1362.     uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1363.     uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1364.     int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

  1365.     int frame_bits;

  1366. 

  1367.     frame_bits = 0;

  1368.     for(ch=0;ch<s->nb_all_channels;ch++) {

  1369.         /* fixed mdct to the six sub blocks & exponent computation */

  1370.         for(i=0;i<NB_BLOCKS;i++) {

  1371.             int16_t *sptr;

  1372.             int sinc;

  1373. 

  1374.             /* compute input samples */

  1375.             memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(int16_t));

  1376.             sinc = s->nb_all_channels;

  1377.             sptr = samples + (sinc * (N/2) * i) + ch;

  1378.             for(j=0;j<N/2;j++) {

  1379.                 v = *sptr;

  1380.                 input_samples[j + N/2] = v;

  1381.                 s->last_samples[ch][j] = v; 

  1382.                 sptr += sinc;

  1383.             }

  1384. 

  1385.             /* apply the MDCT window */

  1386.             for(j=0;j<N/2;j++) {

  1387.                 input_samples[j] = MUL16(input_samples[j], 

  1388.                                          ac3_window[j]) >> 15;

  1389.                 input_samples[N-j-1] = MUL16(input_samples[N-j-1], 

  1390.                                              ac3_window[j]) >> 15;

  1391.             }

  1392.         

  1393.             /* Normalize the samples to use the maximum available

  1394.                precision */

  1395.             v = 14 - log2_tab(input_samples, N);

  1396.             if (v < 0)

  1397.                 v = 0;

  1398.             exp_samples[i][ch] = v - 8;

  1399.             lshift_tab(input_samples, N, v);

  1400. 

  1401.             /* do the MDCT */

  1402.             mdct512(mdct_coef[i][ch], input_samples);

  1403.             

  1404.             /* compute "exponents". We take into account the

  1405.                normalization there */

  1406.             for(j=0;j<N/2;j++) {

  1407.                 int e;

  1408.                 v = abs(mdct_coef[i][ch][j]);

  1409.                 if (v == 0)

  1410.                     e = 24;

  1411.                 else {

  1412.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1413.                     if (e >= 24) {

  1414.                         e = 24;

  1415.                         mdct_coef[i][ch][j] = 0;

  1416.                     }

  1417.                 }

  1418.                 exp[i][ch][j] = e;

  1419.             }

  1420.         }

  1421.         

  1422.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1423. 

  1424.         /* compute the exponents as the decoder will see them. The

  1425.            EXP_REUSE case must be handled carefully : we select the

  1426.            min of the exponents */

  1427.         i = 0;

  1428.         while (i < NB_BLOCKS) {

  1429.             j = i + 1;

  1430.             while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1431.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1432.                 j++;

  1433.             }

  1434.             frame_bits += encode_exp(encoded_exp[i][ch],

  1435.                                      exp[i][ch], s->nb_coefs[ch], 

  1436.                                      exp_strategy[i][ch]);

  1437.             /* copy encoded exponents for reuse case */

  1438.             for(k=i+1;k<j;k++) {

  1439.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch], 

  1440.                        s->nb_coefs[ch] * sizeof(uint8_t));

  1441.             }

  1442.             i = j;

  1443.         }

  1444.     }

  1445. 

  1446.     compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

  1447.     /* everything is known... let's output the frame */

  1448.     output_frame_header(s, frame);

  1449.         

  1450.     for(i=0;i<NB_BLOCKS;i++) {

  1451.         output_audio_block(s, exp_strategy[i], encoded_exp[i], 

  1452.                            bap[i], mdct_coef[i], exp_samples[i], i);

  1453.     }

  1454.     return output_frame_end(s);

  1455. }

  1456. 

  1457. static int AC3_encode_close(AVCodecContext *avctx)

  1458. {

  1459.     av_freep(&avctx->coded_frame);

  1460.     return 0;

  1461. }

  1462. 

  1463. #if 0

  1464. /*************************************************************************/

  1465. /* TEST */

  1466. 

  1467. #define FN (N/4)

  1468. 

  1469. void fft_test(void)

  1470. {

  1471.     IComplex in[FN], in1[FN];

  1472.     int k, n, i;

  1473.     float sum_re, sum_im, a;

  1474. 

  1475.     /* FFT test */

  1476. 

  1477.     for(i=0;i<FN;i++) {

  1478.         in[i].re = random() % 65535 - 32767;

  1479.         in[i].im = random() % 65535 - 32767;

  1480.         in1[i] = in[i];

  1481.     }

  1482.     fft(in, 7);

  1483. 

  1484.     /* do it by hand */

  1485.     for(k=0;k<FN;k++) {

  1486.         sum_re = 0;

  1487.         sum_im = 0;

  1488.         for(n=0;n<FN;n++) {

  1489.             a = -2 * M_PI * (n * k) / FN;

  1490.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1491.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1492.         }

  1493.         printf("%3d: %6d,%6d %6.0f,%6.0f\n", 

  1494.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN); 

  1495.     }

  1496. }

  1497. 

  1498. void mdct_test(void)

  1499. {

  1500.     int16_t input[N];

  1501.     int32_t output[N/2];

  1502.     float input1[N];

  1503.     float output1[N/2];

  1504.     float s, a, err, e, emax;

  1505.     int i, k, n;

  1506. 

  1507.     for(i=0;i<N;i++) {

  1508.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1509.         input1[i] = input[i];

  1510.     }

  1511. 

  1512.     mdct512(output, input);

  1513.     

  1514.     /* do it by hand */

  1515.     for(k=0;k<N/2;k++) {

  1516.         s = 0;

  1517.         for(n=0;n<N;n++) {

  1518.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1519.             s += input1[n] * cos(a);

  1520.         }

  1521.         output1[k] = -2 * s / N;

  1522.     }

  1523.     

  1524.     err = 0;

  1525.     emax = 0;

  1526.     for(i=0;i<N/2;i++) {

  1527.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1528.         e = output[i] - output1[i];

  1529.         if (e > emax)

  1530.             emax = e;

  1531.         err += e * e;

  1532.     }

  1533.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1534. }

  1535. 

  1536. void test_ac3(void)

  1537. {

  1538.     AC3EncodeContext ctx;

  1539.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1540.     short samples[AC3_FRAME_SIZE];

  1541.     int ret, i;

  1542.     

  1543.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1544. 

  1545.     fft_test();

  1546.     mdct_test();

  1547. 

  1548.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1549.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1550.     ret = AC3_encode_frame(&ctx, frame, samples);

  1551.     printf("ret=%d\n", ret);

  1552. }

  1553. #endif

  1554. 

  1555. AVCodec ac3_encoder = {

  1556.     "ac3",

  1557.     CODEC_TYPE_AUDIO,

  1558.     CODEC_ID_AC3,

  1559.     sizeof(AC3EncodeContext),

  1560.     AC3_encode_init,

  1561.     AC3_encode_frame,

  1562.     AC3_encode_close,

  1563.     NULL,

  1564. };