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

  709.         }

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

  711. 	if (s->lfe)

  712. 	    frame_bits++; /* lfeexpstr */

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

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

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

  716.         }

  717.         frame_bits++; /* baie */

  718.         frame_bits++; /* snr */

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

  720.     }

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

  722.     /* bit alloc info */

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

  724.     /* csnroffset[6] */

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

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

  727. 

  728.     /* auxdatae, crcrsv */

  729.     frame_bits += 2;

  730. 

  731.     /* CRC */

  732.     frame_bits += 16;

  733. 

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

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

  736. 

  737.     csnroffst = s->csnroffst;

  738.     while (csnroffst >= 0 && 

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

  740. 	csnroffst -= SNR_INC1;

  741.     if (csnroffst < 0) {

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

  743. 	return -1;

  744.     }

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

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

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

  748.         csnroffst += SNR_INC1;

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

  750.     }

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

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

  753.         csnroffst++;

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

  755.     }

  756. 

  757.     fsnroffst = 0;

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

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

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

  761.         fsnroffst += SNR_INC1;

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

  763.     }

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

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

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

  767.         fsnroffst++;

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

  769.     }

  770.     

  771.     s->csnroffst = csnroffst;

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

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

  774. #if defined(DEBUG_BITALLOC)

  775.     {

  776.         int j;

  777. 

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

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

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

  781.                 printf("bap=");

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

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

  784.                 }

  785.                 printf("\n");

  786.             }

  787.         }

  788.     }

  789. #endif

  790.     return 0;

  791. }

  792. 

  793. void ac3_common_init(void)

  794. {

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

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

  797.     k = 0;

  798.     l = 0;

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

  800.         bndtab[i] = l;

  801.         v = bndsz[i];

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

  803.         l += v;

  804.     }

  805.     bndtab[50] = 0;

  806. }

  807. 

  808. 

  809. static int AC3_encode_init(AVCodecContext *avctx)

  810. {

  811.     int freq = avctx->sample_rate;

  812.     int bitrate = avctx->bit_rate;

  813.     int channels = avctx->channels;

  814.     AC3EncodeContext *s = avctx->priv_data;

  815.     int i, j, ch;

  816.     float alpha;

  817.     static const uint8_t acmod_defs[6] = {

  818. 	0x01, /* C */

  819. 	0x02, /* L R */

  820. 	0x03, /* L C R */

  821. 	0x06, /* L R SL SR */

  822. 	0x07, /* L C R SL SR */

  823. 	0x07, /* L C R SL SR (+LFE) */

  824.     };

  825. 

  826.     avctx->frame_size = AC3_FRAME_SIZE;

  827.     

  828.     /* number of channels */

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

  830. 	return -1;

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

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

  833.     s->nb_all_channels = channels;

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

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

  836. 

  837.     /* frequency */

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

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

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

  841.                 goto found;

  842.     }

  843.     return -1;

  844.  found:    

  845.     s->sample_rate = freq;

  846.     s->halfratecod = i;

  847.     s->fscod = j;

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

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

  850. 

  851.     /* bitrate & frame size */

  852.     bitrate /= 1000;

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

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

  855.             break;

  856.     }

  857.     if (i == 19)

  858.         return -1;

  859.     s->bit_rate = bitrate;

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

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

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

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

  864.     

  865.     /* bit allocation init */

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

  867.         /* bandwidth for each channel */

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

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

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

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

  872.     }

  873.     if (s->lfe) {

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

  875.     }

  876.     /* initial snr offset */

  877.     s->csnroffst = 40;

  878. 

  879.     ac3_common_init();

  880. 

  881.     /* mdct init */

  882.     fft_init(MDCT_NBITS - 2);

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

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

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

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

  887.     }

  888. 

  889.     ac3_crc_init();

  890.     

  891.     avctx->coded_frame= avcodec_alloc_frame();

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

  893. 

  894.     return 0;

  895. }

  896. 

  897. /* output the AC3 frame header */

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

  899. {

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

  901. 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  925. }

  926. 

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

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

  929. {

  930.     int v;

  931. 

  932.     if (c >= 0) {

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

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

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

  936.     } else {

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

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

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

  940.     }

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

  942.     return v;

  943. }

  944. 

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

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

  947. {

  948.     int lshift, m, v;

  949. 

  950.     lshift = e + qbits - 24;

  951.     if (lshift >= 0)

  952.         v = c << lshift;

  953.     else

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

  955.     /* rounding */

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

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

  958.     if (v >= m)

  959.         v = m - 1;

  960.     assert(v >= -m);

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

  962. }

  963. 

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

  965.    frame */

  966. static void output_audio_block(AC3EncodeContext *s,

  967.                                uint8_t exp_strategy[AC3_MAX_CHANNELS],

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

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

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

  971.                                int8_t global_exp[AC3_MAX_CHANNELS],

  972.                                int block_num)

  973. {

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

  975.     uint8_t *p;

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

  977.     int exp0, exp1;

  978.     int mant1_cnt, mant2_cnt, mant4_cnt;

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

  980.     int delta0, delta1, delta2;

  981. 

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

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

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

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

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

  987.     if (block_num == 0) {

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

  989.            waste of bit :-) */

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

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

  992.     } else {

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

  994.     }

  995. 

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

  997.       {

  998. 	if(block_num==0)

  999. 	  {

  1000. 	    /* first block must define rematrixing (rematstr)  */

  1001. 	    put_bits(&s->pb, 1, 1); 

  1002. 	    

  1003. 	    /* dummy rematrixing rematflg(1:4)=0 */

  1004. 	    for (rbnd=0;rbnd<4;rbnd++)

  1005. 	      put_bits(&s->pb, 1, 0); 

  1006. 	  }

  1007. 	else 

  1008. 	  {

  1009. 	    /* no matrixing (but should be used in the future) */

  1010. 	    put_bits(&s->pb, 1, 0);

  1011. 	  } 

  1012.       }

  1013. 

  1014. #if defined(DEBUG) 

  1015.     {

  1016.       static int count = 0;

  1017.       av_log(NULL, AV_LOG_DEBUG, "Block #%d (%d)\n", block_num, count++);

  1018.     }

  1019. #endif

  1020.     /* exponent strategy */

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

  1022.         put_bits(&s->pb, 2, exp_strategy[ch]);

  1023.     }

  1024.     

  1025.     if (s->lfe) {

  1026. 	put_bits(&s->pb, 1, exp_strategy[s->lfe_channel]);

  1027.     }

  1028. 

  1029.     for(ch=0;ch<s->nb_channels;ch++) {

  1030.         if (exp_strategy[ch] != EXP_REUSE)

  1031.             put_bits(&s->pb, 6, s->chbwcod[ch]);

  1032.     }

  1033.     

  1034.     /* exponents */

  1035.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1036.         switch(exp_strategy[ch]) {

  1037.         case EXP_REUSE:

  1038.             continue;

  1039.         case EXP_D15:

  1040.             group_size = 1;

  1041.             break;

  1042.         case EXP_D25:

  1043.             group_size = 2;

  1044.             break;

  1045.         default:

  1046.         case EXP_D45:

  1047.             group_size = 4;

  1048.             break;

  1049.         }

  1050. 	nb_groups = (s->nb_coefs[ch] + (group_size * 3) - 4) / (3 * group_size);

  1051.         p = encoded_exp[ch];

  1052. 

  1053.         /* first exponent */

  1054.         exp1 = *p++;

  1055.         put_bits(&s->pb, 4, exp1);

  1056. 

  1057.         /* next ones are delta encoded */

  1058.         for(i=0;i<nb_groups;i++) {

  1059.             /* merge three delta in one code */

  1060.             exp0 = exp1;

  1061.             exp1 = p[0];

  1062.             p += group_size;

  1063.             delta0 = exp1 - exp0 + 2;

  1064. 

  1065.             exp0 = exp1;

  1066.             exp1 = p[0];

  1067.             p += group_size;

  1068.             delta1 = exp1 - exp0 + 2;

  1069. 

  1070.             exp0 = exp1;

  1071.             exp1 = p[0];

  1072.             p += group_size;

  1073.             delta2 = exp1 - exp0 + 2;

  1074. 

  1075.             put_bits(&s->pb, 7, ((delta0 * 5 + delta1) * 5) + delta2);

  1076.         }

  1077. 

  1078. 	if (ch != s->lfe_channel)

  1079. 	    put_bits(&s->pb, 2, 0); /* no gain range info */

  1080.     }

  1081. 

  1082.     /* bit allocation info */

  1083.     baie = (block_num == 0);

  1084.     put_bits(&s->pb, 1, baie);

  1085.     if (baie) {

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

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

  1088.         put_bits(&s->pb, 2, s->sgaincod);

  1089.         put_bits(&s->pb, 2, s->dbkneecod);

  1090.         put_bits(&s->pb, 3, s->floorcod);

  1091.     }

  1092. 

  1093.     /* snr offset */

  1094.     put_bits(&s->pb, 1, baie); /* always present with bai */

  1095.     if (baie) {

  1096.         put_bits(&s->pb, 6, s->csnroffst);

  1097.         for(ch=0;ch<s->nb_all_channels;ch++) {

  1098.             put_bits(&s->pb, 4, s->fsnroffst[ch]);

  1099.             put_bits(&s->pb, 3, s->fgaincod[ch]);

  1100.         }

  1101.     }

  1102.     

  1103.     put_bits(&s->pb, 1, 0); /* no delta bit allocation */

  1104.     put_bits(&s->pb, 1, 0); /* no data to skip */

  1105. 

  1106.     /* mantissa encoding : we use two passes to handle the grouping. A

  1107.        one pass method may be faster, but it would necessitate to

  1108.        modify the output stream. */

  1109. 

  1110.     /* first pass: quantize */

  1111.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  1112.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  1113. 

  1114.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1115.         int b, c, e, v;

  1116. 

  1117.         for(i=0;i<s->nb_coefs[ch];i++) {

  1118.             c = mdct_coefs[ch][i];

  1119.             e = encoded_exp[ch][i] - global_exp[ch];

  1120.             b = bap[ch][i];

  1121.             switch(b) {

  1122.             case 0:

  1123.                 v = 0;

  1124.                 break;

  1125.             case 1:

  1126.                 v = sym_quant(c, e, 3);

  1127.                 switch(mant1_cnt) {

  1128.                 case 0:

  1129.                     qmant1_ptr = &qmant[ch][i];

  1130.                     v = 9 * v;

  1131.                     mant1_cnt = 1;

  1132.                     break;

  1133.                 case 1:

  1134.                     *qmant1_ptr += 3 * v;

  1135.                     mant1_cnt = 2;

  1136.                     v = 128;

  1137.                     break;

  1138.                 default:

  1139.                     *qmant1_ptr += v;

  1140.                     mant1_cnt = 0;

  1141.                     v = 128;

  1142.                     break;

  1143.                 }

  1144.                 break;

  1145.             case 2:

  1146.                 v = sym_quant(c, e, 5);

  1147.                 switch(mant2_cnt) {

  1148.                 case 0:

  1149.                     qmant2_ptr = &qmant[ch][i];

  1150.                     v = 25 * v;

  1151.                     mant2_cnt = 1;

  1152.                     break;

  1153.                 case 1:

  1154.                     *qmant2_ptr += 5 * v;

  1155.                     mant2_cnt = 2;

  1156.                     v = 128;

  1157.                     break;

  1158.                 default:

  1159.                     *qmant2_ptr += v;

  1160.                     mant2_cnt = 0;

  1161.                     v = 128;

  1162.                     break;

  1163.                 }

  1164.                 break;

  1165.             case 3:

  1166.                 v = sym_quant(c, e, 7);

  1167.                 break;

  1168.             case 4:

  1169.                 v = sym_quant(c, e, 11);

  1170.                 switch(mant4_cnt) {

  1171.                 case 0:

  1172.                     qmant4_ptr = &qmant[ch][i];

  1173.                     v = 11 * v;

  1174.                     mant4_cnt = 1;

  1175.                     break;

  1176.                 default:

  1177.                     *qmant4_ptr += v;

  1178.                     mant4_cnt = 0;

  1179.                     v = 128;

  1180.                     break;

  1181.                 }

  1182.                 break;

  1183.             case 5:

  1184.                 v = sym_quant(c, e, 15);

  1185.                 break;

  1186.             case 14:

  1187.                 v = asym_quant(c, e, 14);

  1188.                 break;

  1189.             case 15:

  1190.                 v = asym_quant(c, e, 16);

  1191.                 break;

  1192.             default:

  1193.                 v = asym_quant(c, e, b - 1);

  1194.                 break;

  1195.             }

  1196.             qmant[ch][i] = v;

  1197.         }

  1198.     }

  1199. 

  1200.     /* second pass : output the values */

  1201.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1202.         int b, q;

  1203.         

  1204.         for(i=0;i<s->nb_coefs[ch];i++) {

  1205.             q = qmant[ch][i];

  1206.             b = bap[ch][i];

  1207.             switch(b) {

  1208.             case 0:

  1209.                 break;

  1210.             case 1:

  1211.                 if (q != 128) 

  1212.                     put_bits(&s->pb, 5, q);

  1213.                 break;

  1214.             case 2:

  1215.                 if (q != 128) 

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

  1217.                 break;

  1218.             case 3:

  1219.                 put_bits(&s->pb, 3, q);

  1220.                 break;

  1221.             case 4:

  1222.                 if (q != 128)

  1223.                     put_bits(&s->pb, 7, q);

  1224.                 break;

  1225.             case 14:

  1226.                 put_bits(&s->pb, 14, q);

  1227.                 break;

  1228.             case 15:

  1229.                 put_bits(&s->pb, 16, q);

  1230.                 break;

  1231.             default:

  1232.                 put_bits(&s->pb, b - 1, q);

  1233.                 break;

  1234.             }

  1235.         }

  1236.     }

  1237. }

  1238. 

  1239. /* compute the ac3 crc */

  1240. 

  1241. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1242. 

  1243. static void ac3_crc_init(void)

  1244. {

  1245.     unsigned int c, n, k;

  1246. 

  1247.     for(n=0;n<256;n++) {

  1248.         c = n << 8;

  1249.         for (k = 0; k < 8; k++) {

  1250.             if (c & (1 << 15)) 

  1251.                 c = ((c << 1) & 0xffff) ^ (CRC16_POLY & 0xffff);

  1252.             else

  1253.                 c = c << 1;

  1254.         }

  1255.         crc_table[n] = c;

  1256.     }

  1257. }

  1258. 

  1259. static unsigned int ac3_crc(uint8_t *data, int n, unsigned int crc)

  1260. {

  1261.     int i;

  1262.     for(i=0;i<n;i++) {

  1263.         crc = (crc_table[data[i] ^ (crc >> 8)] ^ (crc << 8)) & 0xffff;

  1264.     }

  1265.     return crc;

  1266. }

  1267. 

  1268. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1269. {

  1270.     unsigned int c;

  1271. 

  1272.     c = 0;

  1273.     while (a) {

  1274.         if (a & 1)

  1275.             c ^= b;

  1276.         a = a >> 1;

  1277.         b = b << 1;

  1278.         if (b & (1 << 16))

  1279.             b ^= poly;

  1280.     }

  1281.     return c;

  1282. }

  1283. 

  1284. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1285. {

  1286.     unsigned int r;

  1287.     r = 1;

  1288.     while (n) {

  1289.         if (n & 1)

  1290.             r = mul_poly(r, a, poly);

  1291.         a = mul_poly(a, a, poly);

  1292.         n >>= 1;

  1293.     }

  1294.     return r;

  1295. }

  1296. 

  1297. 

  1298. /* compute log2(max(abs(tab[]))) */

  1299. static int log2_tab(int16_t *tab, int n)

  1300. {

  1301.     int i, v;

  1302. 

  1303.     v = 0;

  1304.     for(i=0;i<n;i++) {

  1305.         v |= abs(tab[i]);

  1306.     }

  1307.     return av_log2(v);

  1308. }

  1309. 

  1310. static void lshift_tab(int16_t *tab, int n, int lshift)

  1311. {

  1312.     int i;

  1313. 

  1314.     if (lshift > 0) {

  1315.         for(i=0;i<n;i++) {

  1316.             tab[i] <<= lshift;

  1317.         }

  1318.     } else if (lshift < 0) {

  1319.         lshift = -lshift;

  1320.         for(i=0;i<n;i++) {

  1321.             tab[i] >>= lshift;

  1322.         }

  1323.     }

  1324. }

  1325. 

  1326. /* fill the end of the frame and compute the two crcs */

  1327. static int output_frame_end(AC3EncodeContext *s)

  1328. {

  1329.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1330.     uint8_t *frame;

  1331. 

  1332.     frame_size = s->frame_size; /* frame size in words */

  1333.     /* align to 8 bits */

  1334.     flush_put_bits(&s->pb);

  1335.     /* add zero bytes to reach the frame size */

  1336.     frame = s->pb.buf;

  1337.     n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;

  1338.     assert(n >= 0);

  1339.     if(n>0)

  1340.       memset(pbBufPtr(&s->pb), 0, n);

  1341.     

  1342.     /* Now we must compute both crcs : this is not so easy for crc1

  1343.        because it is at the beginning of the data... */

  1344.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1345.     crc1 = ac3_crc(frame + 4, (2 * frame_size_58) - 4, 0);

  1346.     /* XXX: could precompute crc_inv */

  1347.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1348.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1349.     frame[2] = crc1 >> 8;

  1350.     frame[3] = crc1;

  1351.     

  1352.     crc2 = ac3_crc(frame + 2 * frame_size_58, (frame_size - frame_size_58) * 2 - 2, 0);

  1353.     frame[2*frame_size - 2] = crc2 >> 8;

  1354.     frame[2*frame_size - 1] = crc2;

  1355. 

  1356.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1357.     return frame_size * 2;

  1358. }

  1359. 

  1360. static int AC3_encode_frame(AVCodecContext *avctx,

  1361.                             unsigned char *frame, int buf_size, void *data)

  1362. {

  1363.     AC3EncodeContext *s = avctx->priv_data;

  1364.     int16_t *samples = data;

  1365.     int i, j, k, v, ch;

  1366.     int16_t input_samples[N];

  1367.     int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

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

  1369.     uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

  1370.     uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1371.     uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1372.     int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

  1373.     int frame_bits;

  1374. 

  1375.     frame_bits = 0;

  1376.     for(ch=0;ch<s->nb_all_channels;ch++) {

  1377.         /* fixed mdct to the six sub blocks & exponent computation */

  1378.         for(i=0;i<NB_BLOCKS;i++) {

  1379.             int16_t *sptr;

  1380.             int sinc;

  1381. 

  1382.             /* compute input samples */

  1383.             memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(int16_t));

  1384.             sinc = s->nb_all_channels;

  1385.             sptr = samples + (sinc * (N/2) * i) + ch;

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

  1387.                 v = *sptr;

  1388.                 input_samples[j + N/2] = v;

  1389.                 s->last_samples[ch][j] = v; 

  1390.                 sptr += sinc;

  1391.             }

  1392. 

  1393.             /* apply the MDCT window */

  1394.             for(j=0;j<N/2;j++) {

  1395.                 input_samples[j] = MUL16(input_samples[j], 

  1396.                                          ac3_window[j]) >> 15;

  1397.                 input_samples[N-j-1] = MUL16(input_samples[N-j-1], 

  1398.                                              ac3_window[j]) >> 15;

  1399.             }

  1400.         

  1401.             /* Normalize the samples to use the maximum available

  1402.                precision */

  1403.             v = 14 - log2_tab(input_samples, N);

  1404.             if (v < 0)

  1405.                 v = 0;

  1406.             exp_samples[i][ch] = v - 8;

  1407.             lshift_tab(input_samples, N, v);

  1408. 

  1409.             /* do the MDCT */

  1410.             mdct512(mdct_coef[i][ch], input_samples);

  1411.             

  1412.             /* compute "exponents". We take into account the

  1413.                normalization there */

  1414.             for(j=0;j<N/2;j++) {

  1415.                 int e;

  1416.                 v = abs(mdct_coef[i][ch][j]);

  1417.                 if (v == 0)

  1418.                     e = 24;

  1419.                 else {

  1420.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1421.                     if (e >= 24) {

  1422.                         e = 24;

  1423.                         mdct_coef[i][ch][j] = 0;

  1424.                     }

  1425.                 }

  1426.                 exp[i][ch][j] = e;

  1427.             }

  1428.         }

  1429.         

  1430.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1431. 

  1432.         /* compute the exponents as the decoder will see them. The

  1433.            EXP_REUSE case must be handled carefully : we select the

  1434.            min of the exponents */

  1435.         i = 0;

  1436.         while (i < NB_BLOCKS) {

  1437.             j = i + 1;

  1438.             while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1439.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1440.                 j++;

  1441.             }

  1442.             frame_bits += encode_exp(encoded_exp[i][ch],

  1443.                                      exp[i][ch], s->nb_coefs[ch], 

  1444.                                      exp_strategy[i][ch]);

  1445.             /* copy encoded exponents for reuse case */

  1446.             for(k=i+1;k<j;k++) {

  1447.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch], 

  1448.                        s->nb_coefs[ch] * sizeof(uint8_t));

  1449.             }

  1450.             i = j;

  1451.         }

  1452.     }

  1453. 

  1454.     compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

  1455.     /* everything is known... let's output the frame */

  1456.     output_frame_header(s, frame);

  1457.         

  1458.     for(i=0;i<NB_BLOCKS;i++) {

  1459.         output_audio_block(s, exp_strategy[i], encoded_exp[i], 

  1460.                            bap[i], mdct_coef[i], exp_samples[i], i);

  1461.     }

  1462.     return output_frame_end(s);

  1463. }

  1464. 

  1465. static int AC3_encode_close(AVCodecContext *avctx)

  1466. {

  1467.     av_freep(&avctx->coded_frame);

  1468.     return 0;

  1469. }

  1470. 

  1471. #if 0

  1472. /*************************************************************************/

  1473. /* TEST */

  1474. 

  1475. #define FN (N/4)

  1476. 

  1477. void fft_test(void)

  1478. {

  1479.     IComplex in[FN], in1[FN];

  1480.     int k, n, i;

  1481.     float sum_re, sum_im, a;

  1482. 

  1483.     /* FFT test */

  1484. 

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

  1486.         in[i].re = random() % 65535 - 32767;

  1487.         in[i].im = random() % 65535 - 32767;

  1488.         in1[i] = in[i];

  1489.     }

  1490.     fft(in, 7);

  1491. 

  1492.     /* do it by hand */

  1493.     for(k=0;k<FN;k++) {

  1494.         sum_re = 0;

  1495.         sum_im = 0;

  1496.         for(n=0;n<FN;n++) {

  1497.             a = -2 * M_PI * (n * k) / FN;

  1498.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1499.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1500.         }

  1501.         printf("%3d: %6d,%6d %6.0f,%6.0f\n", 

  1502.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN); 

  1503.     }

  1504. }

  1505. 

  1506. void mdct_test(void)

  1507. {

  1508.     int16_t input[N];

  1509.     int32_t output[N/2];

  1510.     float input1[N];

  1511.     float output1[N/2];

  1512.     float s, a, err, e, emax;

  1513.     int i, k, n;

  1514. 

  1515.     for(i=0;i<N;i++) {

  1516.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1517.         input1[i] = input[i];

  1518.     }

  1519. 

  1520.     mdct512(output, input);

  1521.     

  1522.     /* do it by hand */

  1523.     for(k=0;k<N/2;k++) {

  1524.         s = 0;

  1525.         for(n=0;n<N;n++) {

  1526.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1527.             s += input1[n] * cos(a);

  1528.         }

  1529.         output1[k] = -2 * s / N;

  1530.     }

  1531.     

  1532.     err = 0;

  1533.     emax = 0;

  1534.     for(i=0;i<N/2;i++) {

  1535.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1536.         e = output[i] - output1[i];

  1537.         if (e > emax)

  1538.             emax = e;

  1539.         err += e * e;

  1540.     }

  1541.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1542. }

  1543. 

  1544. void test_ac3(void)

  1545. {

  1546.     AC3EncodeContext ctx;

  1547.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1548.     short samples[AC3_FRAME_SIZE];

  1549.     int ret, i;

  1550.     

  1551.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1552. 

  1553.     fft_test();

  1554.     mdct_test();

  1555. 

  1556.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1557.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1558.     ret = AC3_encode_frame(&ctx, frame, samples);

  1559.     printf("ret=%d\n", ret);

  1560. }

  1561. #endif

  1562. 

  1563. AVCodec ac3_encoder = {

  1564.     "ac3",

  1565.     CODEC_TYPE_AUDIO,

  1566.     CODEC_ID_AC3,

  1567.     sizeof(AC3EncodeContext),

  1568.     AC3_encode_init,

  1569.     AC3_encode_frame,

  1570.     AC3_encode_close,

  1571.     NULL,

  1572. };