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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. #include "bitstream.h"

  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.         av_log(NULL, AV_LOG_DEBUG, "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, exp_min;

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

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

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

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

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

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

  559. 

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

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

  562.     k = 1;

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

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

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

  566.         }

  567.         k += group_size;

  568.     }

  569.     

  570. #if defined(DEBUG)

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

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

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

  574.     }

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

  576. #endif

  577. 

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

  579. }

  580. 

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

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

  583. {

  584.     int bits, mant, i;

  585. 

  586.     bits = 0;

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

  588.         mant = m[i];

  589.         switch(mant) {

  590.         case 0:

  591.             /* nothing */

  592.             break;

  593.         case 1:

  594.             /* 3 mantissa in 5 bits */

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

  596.                 bits += 5;

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

  598.                 s->mant1_cnt = 0;

  599.             break;

  600.         case 2:

  601.             /* 3 mantissa in 7 bits */

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

  603.                 bits += 7;

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

  605.                 s->mant2_cnt = 0;

  606.             break;

  607.         case 3:

  608.             bits += 3;

  609.             break;

  610.         case 4:

  611.             /* 2 mantissa in 7 bits */

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

  613.                 bits += 7;

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

  615.                 s->mant4_cnt = 0;

  616.             break;

  617.         case 14:

  618.             bits += 14;

  619.             break;

  620.         case 15:

  621.             bits += 16;

  622.             break;

  623.         default:

  624.             bits += mant - 1;

  625.             break;

  626.         }

  627.     }

  628.     return bits;

  629. }

  630. 

  631. 

  632. static int bit_alloc(AC3EncodeContext *s,

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

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

  635.                      uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  636.                      int frame_bits, int csnroffst, int fsnroffst)

  637. {

  638.     int i, ch;

  639. 

  640.     /* compute size */

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

  642.         s->mant1_cnt = 0;

  643.         s->mant2_cnt = 0;

  644.         s->mant4_cnt = 0;

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

  646.             ac3_parametric_bit_allocation(&s->bit_alloc, 

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

  648.                                           0, s->nb_coefs[ch], 

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

  650.                                            fsnroffst) << 2, 

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

  652.                                           ch == s->lfe_channel,

  653.                                           2, 0, NULL, NULL, NULL);

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

  655.                                                  s->nb_coefs[ch]);

  656.         }

  657.     }

  658. #if 0

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

  660.            csnroffst, fsnroffst, frame_bits, 

  661.            16 * s->frame_size - ((frame_bits + 7) & ~7));

  662. #endif

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

  664. }

  665. 

  666. #define SNR_INC1 4

  667. 

  668. static int compute_bit_allocation(AC3EncodeContext *s,

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

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

  671.                                   uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  672.                                   int frame_bits)

  673. {

  674.     int i, ch;

  675.     int csnroffst, fsnroffst;

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

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

  678. 

  679.     /* init default parameters */

  680.     s->sdecaycod = 2;

  681.     s->fdecaycod = 1;

  682.     s->sgaincod = 1;

  683.     s->dbkneecod = 2;

  684.     s->floorcod = 4;

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

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

  687.     

  688.     /* compute real values */

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

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

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

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

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

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

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

  696.     

  697.     /* header size */

  698.     frame_bits += 65;

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

  700.     //    frame_bits += 2;

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

  702. 

  703.     /* audio blocks */

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

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

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

  707.             frame_bits++; /* rematstr */

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

  709. 	if (s->lfe)

  710. 	    frame_bits++; /* lfeexpstr */

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

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

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

  714.         }

  715.         frame_bits++; /* baie */

  716.         frame_bits++; /* snr */

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

  718.     }

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

  720.     /* bit alloc info */

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

  722.     /* csnroffset[6] */

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

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

  725. 

  726.     /* auxdatae, crcrsv */

  727.     frame_bits += 2;

  728. 

  729.     /* CRC */

  730.     frame_bits += 16;

  731. 

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

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

  734. 

  735.     csnroffst = s->csnroffst;

  736.     while (csnroffst >= 0 && 

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

  738. 	csnroffst -= SNR_INC1;

  739.     if (csnroffst < 0) {

  740. 	av_log(NULL, AV_LOG_ERROR, "Yack, Error !!!\n");

  741. 	return -1;

  742.     }

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

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

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

  746.         csnroffst += SNR_INC1;

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

  748.     }

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

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

  751.         csnroffst++;

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

  753.     }

  754. 

  755.     fsnroffst = 0;

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

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

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

  759.         fsnroffst += SNR_INC1;

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

  761.     }

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

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

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

  765.         fsnroffst++;

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

  767.     }

  768.     

  769.     s->csnroffst = csnroffst;

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

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

  772. #if defined(DEBUG_BITALLOC)

  773.     {

  774.         int j;

  775. 

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

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

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

  779.                 printf("bap=");

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

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

  782.                 }

  783.                 printf("\n");

  784.             }

  785.         }

  786.     }

  787. #endif

  788.     return 0;

  789. }

  790. 

  791. void ac3_common_init(void)

  792. {

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

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

  795.     k = 0;

  796.     l = 0;

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

  798.         bndtab[i] = l;

  799.         v = bndsz[i];

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

  801.         l += v;

  802.     }

  803.     bndtab[50] = 0;

  804. }

  805. 

  806. 

  807. static int AC3_encode_init(AVCodecContext *avctx)

  808. {

  809.     int freq = avctx->sample_rate;

  810.     int bitrate = avctx->bit_rate;

  811.     int channels = avctx->channels;

  812.     AC3EncodeContext *s = avctx->priv_data;

  813.     int i, j, ch;

  814.     float alpha;

  815.     static const uint8_t acmod_defs[6] = {

  816. 	0x01, /* C */

  817. 	0x02, /* L R */

  818. 	0x03, /* L C R */

  819. 	0x06, /* L R SL SR */

  820. 	0x07, /* L C R SL SR */

  821. 	0x07, /* L C R SL SR (+LFE) */

  822.     };

  823. 

  824.     avctx->frame_size = AC3_FRAME_SIZE;

  825.     

  826.     /* number of channels */

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

  828. 	return -1;

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

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

  831.     s->nb_all_channels = channels;

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

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

  834. 

  835.     /* frequency */

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

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

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

  839.                 goto found;

  840.     }

  841.     return -1;

  842.  found:    

  843.     s->sample_rate = freq;

  844.     s->halfratecod = i;

  845.     s->fscod = j;

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

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

  848. 

  849.     /* bitrate & frame size */

  850.     bitrate /= 1000;

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

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

  853.             break;

  854.     }

  855.     if (i == 19)

  856.         return -1;

  857.     s->bit_rate = bitrate;

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

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

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

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

  862.     

  863.     /* bit allocation init */

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

  865.         /* bandwidth for each channel */

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

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

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

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

  870.     }

  871.     if (s->lfe) {

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

  873.     }

  874.     /* initial snr offset */

  875.     s->csnroffst = 40;

  876. 

  877.     ac3_common_init();

  878. 

  879.     /* mdct init */

  880.     fft_init(MDCT_NBITS - 2);

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

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

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

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

  885.     }

  886. 

  887.     ac3_crc_init();

  888.     

  889.     avctx->coded_frame= avcodec_alloc_frame();

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

  891. 

  892.     return 0;

  893. }

  894. 

  895. /* output the AC3 frame header */

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

  897. {

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

  899. 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  923. }

  924. 

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

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

  927. {

  928.     int v;

  929. 

  930.     if (c >= 0) {

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

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

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

  934.     } else {

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

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

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

  938.     }

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

  940.     return v;

  941. }

  942. 

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

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

  945. {

  946.     int lshift, m, v;

  947. 

  948.     lshift = e + qbits - 24;

  949.     if (lshift >= 0)

  950.         v = c << lshift;

  951.     else

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

  953.     /* rounding */

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

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

  956.     if (v >= m)

  957.         v = m - 1;

  958.     assert(v >= -m);

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

  960. }

  961. 

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

  963.    frame */

  964. static void output_audio_block(AC3EncodeContext *s,

  965.                                uint8_t exp_strategy[AC3_MAX_CHANNELS],

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

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

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

  969.                                int8_t global_exp[AC3_MAX_CHANNELS],

  970.                                int block_num)

  971. {

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

  973.     uint8_t *p;

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

  975.     int exp0, exp1;

  976.     int mant1_cnt, mant2_cnt, mant4_cnt;

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

  978.     int delta0, delta1, delta2;

  979. 

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

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

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

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

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

  985.     if (block_num == 0) {

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

  987.            waste of bit :-) */

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

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

  990.     } else {

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

  992.     }

  993. 

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

  995.       {

  996. 	if(block_num==0)

  997. 	  {

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

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

  1000. 	    

  1001. 	    /* dummy rematrixing rematflg(1:4)=0 */

  1002. 	    for (rbnd=0;rbnd<4;rbnd++)

  1003. 	      put_bits(&s->pb, 1, 0); 

  1004. 	  }

  1005. 	else 

  1006. 	  {

  1007. 	    /* no matrixing (but should be used in the future) */

  1008. 	    put_bits(&s->pb, 1, 0);

  1009. 	  } 

  1010.       }

  1011. 

  1012. #if defined(DEBUG) 

  1013.     {

  1014.       static int count = 0;

  1015.       av_log(NULL, AV_LOG_DEBUG, "Block #%d (%d)\n", block_num, count++);

  1016.     }

  1017. #endif

  1018.     /* exponent strategy */

  1019.     for(ch=0;ch<s->nb_channels;ch++) {

  1020.         put_bits(&s->pb, 2, exp_strategy[ch]);

  1021.     }

  1022.     

  1023.     if (s->lfe) {

  1024. 	put_bits(&s->pb, 1, exp_strategy[s->lfe_channel]);

  1025.     }

  1026. 

  1027.     for(ch=0;ch<s->nb_channels;ch++) {

  1028.         if (exp_strategy[ch] != EXP_REUSE)

  1029.             put_bits(&s->pb, 6, s->chbwcod[ch]);

  1030.     }

  1031.     

  1032.     /* exponents */

  1033.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1034.         switch(exp_strategy[ch]) {

  1035.         case EXP_REUSE:

  1036.             continue;

  1037.         case EXP_D15:

  1038.             group_size = 1;

  1039.             break;

  1040.         case EXP_D25:

  1041.             group_size = 2;

  1042.             break;

  1043.         default:

  1044.         case EXP_D45:

  1045.             group_size = 4;

  1046.             break;

  1047.         }

  1048. 	nb_groups = (s->nb_coefs[ch] + (group_size * 3) - 4) / (3 * group_size);

  1049.         p = encoded_exp[ch];

  1050. 

  1051.         /* first exponent */

  1052.         exp1 = *p++;

  1053.         put_bits(&s->pb, 4, exp1);

  1054. 

  1055.         /* next ones are delta encoded */

  1056.         for(i=0;i<nb_groups;i++) {

  1057.             /* merge three delta in one code */

  1058.             exp0 = exp1;

  1059.             exp1 = p[0];

  1060.             p += group_size;

  1061.             delta0 = exp1 - exp0 + 2;

  1062. 

  1063.             exp0 = exp1;

  1064.             exp1 = p[0];

  1065.             p += group_size;

  1066.             delta1 = exp1 - exp0 + 2;

  1067. 

  1068.             exp0 = exp1;

  1069.             exp1 = p[0];

  1070.             p += group_size;

  1071.             delta2 = exp1 - exp0 + 2;

  1072. 

  1073.             put_bits(&s->pb, 7, ((delta0 * 5 + delta1) * 5) + delta2);

  1074.         }

  1075. 

  1076. 	if (ch != s->lfe_channel)

  1077. 	    put_bits(&s->pb, 2, 0); /* no gain range info */

  1078.     }

  1079. 

  1080.     /* bit allocation info */

  1081.     baie = (block_num == 0);

  1082.     put_bits(&s->pb, 1, baie);

  1083.     if (baie) {

  1084.         put_bits(&s->pb, 2, s->sdecaycod);

  1085.         put_bits(&s->pb, 2, s->fdecaycod);

  1086.         put_bits(&s->pb, 2, s->sgaincod);

  1087.         put_bits(&s->pb, 2, s->dbkneecod);

  1088.         put_bits(&s->pb, 3, s->floorcod);

  1089.     }

  1090. 

  1091.     /* snr offset */

  1092.     put_bits(&s->pb, 1, baie); /* always present with bai */

  1093.     if (baie) {

  1094.         put_bits(&s->pb, 6, s->csnroffst);

  1095.         for(ch=0;ch<s->nb_all_channels;ch++) {

  1096.             put_bits(&s->pb, 4, s->fsnroffst[ch]);

  1097.             put_bits(&s->pb, 3, s->fgaincod[ch]);

  1098.         }

  1099.     }

  1100.     

  1101.     put_bits(&s->pb, 1, 0); /* no delta bit allocation */

  1102.     put_bits(&s->pb, 1, 0); /* no data to skip */

  1103. 

  1104.     /* mantissa encoding : we use two passes to handle the grouping. A

  1105.        one pass method may be faster, but it would necessitate to

  1106.        modify the output stream. */

  1107. 

  1108.     /* first pass: quantize */

  1109.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  1110.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  1111. 

  1112.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1113.         int b, c, e, v;

  1114. 

  1115.         for(i=0;i<s->nb_coefs[ch];i++) {

  1116.             c = mdct_coefs[ch][i];

  1117.             e = encoded_exp[ch][i] - global_exp[ch];

  1118.             b = bap[ch][i];

  1119.             switch(b) {

  1120.             case 0:

  1121.                 v = 0;

  1122.                 break;

  1123.             case 1:

  1124.                 v = sym_quant(c, e, 3);

  1125.                 switch(mant1_cnt) {

  1126.                 case 0:

  1127.                     qmant1_ptr = &qmant[ch][i];

  1128.                     v = 9 * v;

  1129.                     mant1_cnt = 1;

  1130.                     break;

  1131.                 case 1:

  1132.                     *qmant1_ptr += 3 * v;

  1133.                     mant1_cnt = 2;

  1134.                     v = 128;

  1135.                     break;

  1136.                 default:

  1137.                     *qmant1_ptr += v;

  1138.                     mant1_cnt = 0;

  1139.                     v = 128;

  1140.                     break;

  1141.                 }

  1142.                 break;

  1143.             case 2:

  1144.                 v = sym_quant(c, e, 5);

  1145.                 switch(mant2_cnt) {

  1146.                 case 0:

  1147.                     qmant2_ptr = &qmant[ch][i];

  1148.                     v = 25 * v;

  1149.                     mant2_cnt = 1;

  1150.                     break;

  1151.                 case 1:

  1152.                     *qmant2_ptr += 5 * v;

  1153.                     mant2_cnt = 2;

  1154.                     v = 128;

  1155.                     break;

  1156.                 default:

  1157.                     *qmant2_ptr += v;

  1158.                     mant2_cnt = 0;

  1159.                     v = 128;

  1160.                     break;

  1161.                 }

  1162.                 break;

  1163.             case 3:

  1164.                 v = sym_quant(c, e, 7);

  1165.                 break;

  1166.             case 4:

  1167.                 v = sym_quant(c, e, 11);

  1168.                 switch(mant4_cnt) {

  1169.                 case 0:

  1170.                     qmant4_ptr = &qmant[ch][i];

  1171.                     v = 11 * v;

  1172.                     mant4_cnt = 1;

  1173.                     break;

  1174.                 default:

  1175.                     *qmant4_ptr += v;

  1176.                     mant4_cnt = 0;

  1177.                     v = 128;

  1178.                     break;

  1179.                 }

  1180.                 break;

  1181.             case 5:

  1182.                 v = sym_quant(c, e, 15);

  1183.                 break;

  1184.             case 14:

  1185.                 v = asym_quant(c, e, 14);

  1186.                 break;

  1187.             case 15:

  1188.                 v = asym_quant(c, e, 16);

  1189.                 break;

  1190.             default:

  1191.                 v = asym_quant(c, e, b - 1);

  1192.                 break;

  1193.             }

  1194.             qmant[ch][i] = v;

  1195.         }

  1196.     }

  1197. 

  1198.     /* second pass : output the values */

  1199.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1200.         int b, q;

  1201.         

  1202.         for(i=0;i<s->nb_coefs[ch];i++) {

  1203.             q = qmant[ch][i];

  1204.             b = bap[ch][i];

  1205.             switch(b) {

  1206.             case 0:

  1207.                 break;

  1208.             case 1:

  1209.                 if (q != 128) 

  1210.                     put_bits(&s->pb, 5, q);

  1211.                 break;

  1212.             case 2:

  1213.                 if (q != 128) 

  1214.                     put_bits(&s->pb, 7, q);

  1215.                 break;

  1216.             case 3:

  1217.                 put_bits(&s->pb, 3, q);

  1218.                 break;

  1219.             case 4:

  1220.                 if (q != 128)

  1221.                     put_bits(&s->pb, 7, q);

  1222.                 break;

  1223.             case 14:

  1224.                 put_bits(&s->pb, 14, q);

  1225.                 break;

  1226.             case 15:

  1227.                 put_bits(&s->pb, 16, q);

  1228.                 break;

  1229.             default:

  1230.                 put_bits(&s->pb, b - 1, q);

  1231.                 break;

  1232.             }

  1233.         }

  1234.     }

  1235. }

  1236. 

  1237. /* compute the ac3 crc */

  1238. 

  1239. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1240. 

  1241. static void ac3_crc_init(void)

  1242. {

  1243.     unsigned int c, n, k;

  1244. 

  1245.     for(n=0;n<256;n++) {

  1246.         c = n << 8;

  1247.         for (k = 0; k < 8; k++) {

  1248.             if (c & (1 << 15)) 

  1249.                 c = ((c << 1) & 0xffff) ^ (CRC16_POLY & 0xffff);

  1250.             else

  1251.                 c = c << 1;

  1252.         }

  1253.         crc_table[n] = c;

  1254.     }

  1255. }

  1256. 

  1257. static unsigned int ac3_crc(uint8_t *data, int n, unsigned int crc)

  1258. {

  1259.     int i;

  1260.     for(i=0;i<n;i++) {

  1261.         crc = (crc_table[data[i] ^ (crc >> 8)] ^ (crc << 8)) & 0xffff;

  1262.     }

  1263.     return crc;

  1264. }

  1265. 

  1266. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1267. {

  1268.     unsigned int c;

  1269. 

  1270.     c = 0;

  1271.     while (a) {

  1272.         if (a & 1)

  1273.             c ^= b;

  1274.         a = a >> 1;

  1275.         b = b << 1;

  1276.         if (b & (1 << 16))

  1277.             b ^= poly;

  1278.     }

  1279.     return c;

  1280. }

  1281. 

  1282. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1283. {

  1284.     unsigned int r;

  1285.     r = 1;

  1286.     while (n) {

  1287.         if (n & 1)

  1288.             r = mul_poly(r, a, poly);

  1289.         a = mul_poly(a, a, poly);

  1290.         n >>= 1;

  1291.     }

  1292.     return r;

  1293. }

  1294. 

  1295. 

  1296. /* compute log2(max(abs(tab[]))) */

  1297. static int log2_tab(int16_t *tab, int n)

  1298. {

  1299.     int i, v;

  1300. 

  1301.     v = 0;

  1302.     for(i=0;i<n;i++) {

  1303.         v |= abs(tab[i]);

  1304.     }

  1305.     return av_log2(v);

  1306. }

  1307. 

  1308. static void lshift_tab(int16_t *tab, int n, int lshift)

  1309. {

  1310.     int i;

  1311. 

  1312.     if (lshift > 0) {

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

  1314.             tab[i] <<= lshift;

  1315.         }

  1316.     } else if (lshift < 0) {

  1317.         lshift = -lshift;

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

  1319.             tab[i] >>= lshift;

  1320.         }

  1321.     }

  1322. }

  1323. 

  1324. /* fill the end of the frame and compute the two crcs */

  1325. static int output_frame_end(AC3EncodeContext *s)

  1326. {

  1327.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1328.     uint8_t *frame;

  1329. 

  1330.     frame_size = s->frame_size; /* frame size in words */

  1331.     /* align to 8 bits */

  1332.     flush_put_bits(&s->pb);

  1333.     /* add zero bytes to reach the frame size */

  1334.     frame = s->pb.buf;

  1335.     n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;

  1336.     assert(n >= 0);

  1337.     if(n>0)

  1338.       memset(pbBufPtr(&s->pb), 0, n);

  1339.     

  1340.     /* Now we must compute both crcs : this is not so easy for crc1

  1341.        because it is at the beginning of the data... */

  1342.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1343.     crc1 = ac3_crc(frame + 4, (2 * frame_size_58) - 4, 0);

  1344.     /* XXX: could precompute crc_inv */

  1345.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1346.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1347.     frame[2] = crc1 >> 8;

  1348.     frame[3] = crc1;

  1349.     

  1350.     crc2 = ac3_crc(frame + 2 * frame_size_58, (frame_size - frame_size_58) * 2 - 2, 0);

  1351.     frame[2*frame_size - 2] = crc2 >> 8;

  1352.     frame[2*frame_size - 1] = crc2;

  1353. 

  1354.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1355.     return frame_size * 2;

  1356. }

  1357. 

  1358. static int AC3_encode_frame(AVCodecContext *avctx,

  1359.                             unsigned char *frame, int buf_size, void *data)

  1360. {

  1361.     AC3EncodeContext *s = avctx->priv_data;

  1362.     int16_t *samples = data;

  1363.     int i, j, k, v, ch;

  1364.     int16_t input_samples[N];

  1365.     int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1366.     uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1367.     uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

  1368.     uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1369.     uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1370.     int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

  1371.     int frame_bits;

  1372. 

  1373.     frame_bits = 0;

  1374.     for(ch=0;ch<s->nb_all_channels;ch++) {

  1375.         /* fixed mdct to the six sub blocks & exponent computation */

  1376.         for(i=0;i<NB_BLOCKS;i++) {

  1377.             int16_t *sptr;

  1378.             int sinc;

  1379. 

  1380.             /* compute input samples */

  1381.             memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(int16_t));

  1382.             sinc = s->nb_all_channels;

  1383.             sptr = samples + (sinc * (N/2) * i) + ch;

  1384.             for(j=0;j<N/2;j++) {

  1385.                 v = *sptr;

  1386.                 input_samples[j + N/2] = v;

  1387.                 s->last_samples[ch][j] = v; 

  1388.                 sptr += sinc;

  1389.             }

  1390. 

  1391.             /* apply the MDCT window */

  1392.             for(j=0;j<N/2;j++) {

  1393.                 input_samples[j] = MUL16(input_samples[j], 

  1394.                                          ac3_window[j]) >> 15;

  1395.                 input_samples[N-j-1] = MUL16(input_samples[N-j-1], 

  1396.                                              ac3_window[j]) >> 15;

  1397.             }

  1398.         

  1399.             /* Normalize the samples to use the maximum available

  1400.                precision */

  1401.             v = 14 - log2_tab(input_samples, N);

  1402.             if (v < 0)

  1403.                 v = 0;

  1404.             exp_samples[i][ch] = v - 8;

  1405.             lshift_tab(input_samples, N, v);

  1406. 

  1407.             /* do the MDCT */

  1408.             mdct512(mdct_coef[i][ch], input_samples);

  1409.             

  1410.             /* compute "exponents". We take into account the

  1411.                normalization there */

  1412.             for(j=0;j<N/2;j++) {

  1413.                 int e;

  1414.                 v = abs(mdct_coef[i][ch][j]);

  1415.                 if (v == 0)

  1416.                     e = 24;

  1417.                 else {

  1418.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1419.                     if (e >= 24) {

  1420.                         e = 24;

  1421.                         mdct_coef[i][ch][j] = 0;

  1422.                     }

  1423.                 }

  1424.                 exp[i][ch][j] = e;

  1425.             }

  1426.         }

  1427.         

  1428.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1429. 

  1430.         /* compute the exponents as the decoder will see them. The

  1431.            EXP_REUSE case must be handled carefully : we select the

  1432.            min of the exponents */

  1433.         i = 0;

  1434.         while (i < NB_BLOCKS) {

  1435.             j = i + 1;

  1436.             while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1437.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1438.                 j++;

  1439.             }

  1440.             frame_bits += encode_exp(encoded_exp[i][ch],

  1441.                                      exp[i][ch], s->nb_coefs[ch], 

  1442.                                      exp_strategy[i][ch]);

  1443.             /* copy encoded exponents for reuse case */

  1444.             for(k=i+1;k<j;k++) {

  1445.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch], 

  1446.                        s->nb_coefs[ch] * sizeof(uint8_t));

  1447.             }

  1448.             i = j;

  1449.         }

  1450.     }

  1451. 

  1452.     compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

  1453.     /* everything is known... let's output the frame */

  1454.     output_frame_header(s, frame);

  1455.         

  1456.     for(i=0;i<NB_BLOCKS;i++) {

  1457.         output_audio_block(s, exp_strategy[i], encoded_exp[i], 

  1458.                            bap[i], mdct_coef[i], exp_samples[i], i);

  1459.     }

  1460.     return output_frame_end(s);

  1461. }

  1462. 

  1463. static int AC3_encode_close(AVCodecContext *avctx)

  1464. {

  1465.     av_freep(&avctx->coded_frame);

  1466.     return 0;

  1467. }

  1468. 

  1469. #if 0

  1470. /*************************************************************************/

  1471. /* TEST */

  1472. 

  1473. #define FN (N/4)

  1474. 

  1475. void fft_test(void)

  1476. {

  1477.     IComplex in[FN], in1[FN];

  1478.     int k, n, i;

  1479.     float sum_re, sum_im, a;

  1480. 

  1481.     /* FFT test */

  1482. 

  1483.     for(i=0;i<FN;i++) {

  1484.         in[i].re = random() % 65535 - 32767;

  1485.         in[i].im = random() % 65535 - 32767;

  1486.         in1[i] = in[i];

  1487.     }

  1488.     fft(in, 7);

  1489. 

  1490.     /* do it by hand */

  1491.     for(k=0;k<FN;k++) {

  1492.         sum_re = 0;

  1493.         sum_im = 0;

  1494.         for(n=0;n<FN;n++) {

  1495.             a = -2 * M_PI * (n * k) / FN;

  1496.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1497.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1498.         }

  1499.         printf("%3d: %6d,%6d %6.0f,%6.0f\n", 

  1500.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN); 

  1501.     }

  1502. }

  1503. 

  1504. void mdct_test(void)

  1505. {

  1506.     int16_t input[N];

  1507.     int32_t output[N/2];

  1508.     float input1[N];

  1509.     float output1[N/2];

  1510.     float s, a, err, e, emax;

  1511.     int i, k, n;

  1512. 

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

  1514.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1515.         input1[i] = input[i];

  1516.     }

  1517. 

  1518.     mdct512(output, input);

  1519.     

  1520.     /* do it by hand */

  1521.     for(k=0;k<N/2;k++) {

  1522.         s = 0;

  1523.         for(n=0;n<N;n++) {

  1524.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1525.             s += input1[n] * cos(a);

  1526.         }

  1527.         output1[k] = -2 * s / N;

  1528.     }

  1529.     

  1530.     err = 0;

  1531.     emax = 0;

  1532.     for(i=0;i<N/2;i++) {

  1533.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1534.         e = output[i] - output1[i];

  1535.         if (e > emax)

  1536.             emax = e;

  1537.         err += e * e;

  1538.     }

  1539.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1540. }

  1541. 

  1542. void test_ac3(void)

  1543. {

  1544.     AC3EncodeContext ctx;

  1545.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1546.     short samples[AC3_FRAME_SIZE];

  1547.     int ret, i;

  1548.     

  1549.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1550. 

  1551.     fft_test();

  1552.     mdct_test();

  1553. 

  1554.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1555.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1556.     ret = AC3_encode_frame(&ctx, frame, samples);

  1557.     printf("ret=%d\n", ret);

  1558. }

  1559. #endif

  1560. 

  1561. AVCodec ac3_encoder = {

  1562.     "ac3",

  1563.     CODEC_TYPE_AUDIO,

  1564.     CODEC_ID_AC3,

  1565.     sizeof(AC3EncodeContext),

  1566.     AC3_encode_init,

  1567.     AC3_encode_frame,

  1568.     AC3_encode_close,

  1569.     NULL,

  1570. };