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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 file is part of FFmpeg.

  6.  *

  7.  * FFmpeg is free software; you can redistribute it and/or

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

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

  10.  * version 2.1 of the License, or (at your option) any later version.

  11.  *

  12.  * FFmpeg is distributed in the hope that it will be useful,

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

  14.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

  15.  * Lesser General Public License for more details.

  16.  *

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

  18.  * License along with FFmpeg; if not, write to the Free Software

  19.  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

  20.  */

  21. 

  22. /**

  23.  * @file ac3enc.c

  24.  * The simplest AC3 encoder.

  25.  */

  26. //#define DEBUG

  27. //#define DEBUG_BITALLOC

  28. #include "avcodec.h"

  29. #include "bitstream.h"

  30. #include "crc.h"

  31. #include "ac3.h"

  32. 

  33. typedef struct AC3EncodeContext {

  34.     PutBitContext pb;

  35.     int nb_channels;

  36.     int nb_all_channels;

  37.     int lfe_channel;

  38.     int bit_rate;

  39.     unsigned int sample_rate;

  40.     unsigned int bsid;

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

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

  43.     unsigned int bits_written;

  44.     unsigned int samples_written;

  45.     int halfratecod;

  46.     unsigned int frmsizecod;

  47.     unsigned int fscod; /* frequency */

  48.     unsigned int acmod;

  49.     int lfe;

  50.     unsigned int bsmod;

  51.     short last_samples[AC3_MAX_CHANNELS][256];

  52.     unsigned int chbwcod[AC3_MAX_CHANNELS];

  53.     int nb_coefs[AC3_MAX_CHANNELS];

  54. 

  55.     /* bitrate allocation control */

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

  57.     AC3BitAllocParameters bit_alloc;

  58.     int csnroffst;

  59.     int fgaincod[AC3_MAX_CHANNELS];

  60.     int fsnroffst[AC3_MAX_CHANNELS];

  61.     /* mantissa encoding */

  62.     int mant1_cnt, mant2_cnt, mant4_cnt;

  63. } AC3EncodeContext;

  64. 

  65. #include "ac3tab.h"

  66. 

  67. #define MDCT_NBITS 9

  68. #define N         (1 << MDCT_NBITS)

  69. 

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

  71. #define EXP_DIFF_THRESHOLD 1000

  72. 

  73. static void fft_init(int ln);

  74. 

  75. static inline int16_t fix15(float a)

  76. {

  77.     int v;

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

  79.     if (v < -32767)

  80.         v = -32767;

  81.     else if (v > 32767)

  82.         v = 32767;

  83.     return v;

  84. }

  85. 

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

  87. {

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

  89.         a = 384 ;

  90.     } else if (b0 > b1) {

  91.         a = a - 64;

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

  93.     }

  94.     return a;

  95. }

  96. 

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

  98. {

  99.     if (bin < 7) {

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

  101.             a = 384 ;

  102.         } else if (b0 > b1) {

  103.             a = a - 64;

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

  105.         }

  106.     } else if (bin < 20) {

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

  108.             a = 320 ;

  109.         } else if (b0 > b1) {

  110.             a= a - 64;

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

  112.         }

  113.     } else {

  114.         a = a - 128;

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

  116.     }

  117.     return a;

  118. }

  119. 

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

  121.    spec. */

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

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

  124.                                    int snroffset, int fgain, int is_lfe,

  125.                                    int deltbae,int deltnseg,

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

  127. {

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

  129.     int fastleak,slowleak,address,tmp;

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

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

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

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

  134. 

  135.     /* exponent mapping to PSD */

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

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

  138.     }

  139. 

  140.     /* PSD integration */

  141.     j=start;

  142.     k=masktab[start];

  143.     do {

  144.         v=psd[j];

  145.         j++;

  146.         end1=bndtab[k+1];

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

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

  149.             int c,adr;

  150.             /* logadd */

  151.             v1=psd[j];

  152.             c=v-v1;

  153.             if (c >= 0) {

  154.                 adr=c >> 1;

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

  156.                 v=v + latab[adr];

  157.             } else {

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

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

  160.                 v=v1 + latab[adr];

  161.             }

  162.             j++;

  163.         }

  164.         bndpsd[k]=v;

  165.         k++;

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

  167. 

  168.     /* excitation function */

  169.     bndstrt = masktab[start];

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

  171. 

  172.     if (bndstrt == 0) {

  173.         lowcomp = 0;

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

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

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

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

  178.         begin = 7 ;

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

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

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

  182.             fastleak = bndpsd[bin] - fgain ;

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

  184.             excite[bin] = fastleak - lowcomp ;

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

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

  187.                     begin = bin + 1 ;

  188.                     break ;

  189.                 }

  190.             }

  191.         }

  192. 

  193.         end1=bndend;

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

  195. 

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

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

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

  199. 

  200.             fastleak -= s->fdecay ;

  201.             v = bndpsd[bin] - fgain;

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

  203. 

  204.             slowleak -= s->sdecay ;

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

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

  207. 

  208.             v=fastleak - lowcomp;

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

  210. 

  211.             excite[bin] = v;

  212.         }

  213.         begin = 22;

  214.     } else {

  215.         /* coupling channel */

  216.         begin = bndstrt;

  217. 

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

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

  220.     }

  221. 

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

  223.         fastleak -= s->fdecay ;

  224.         v = bndpsd[bin] - fgain;

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

  226.         slowleak -= s->sdecay ;

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

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

  229. 

  230.         v=fastleak;

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

  232.         excite[bin] = v;

  233.     }

  234. 

  235.     /* compute masking curve */

  236. 

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

  238.         v1 = excite[bin];

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

  240.         if (tmp > 0) {

  241.             v1 += tmp >> 2;

  242.         }

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

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

  245.         mask[bin] = v;

  246.     }

  247. 

  248.     /* delta bit allocation */

  249. 

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

  251.         int band, seg, delta;

  252.         band = 0 ;

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

  254.             band += deltoffst[seg] ;

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

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

  257.             } else {

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

  259.             }

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

  261.                 mask[band] += delta ;

  262.                 band++ ;

  263.             }

  264.         }

  265.     }

  266. 

  267.     /* compute bit allocation */

  268. 

  269.     i = start ;

  270.     j = masktab[start] ;

  271.     do {

  272.         v=mask[j];

  273.         v -= snroffset ;

  274.         v -= s->floor ;

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

  276.         v &= 0x1fe0 ;

  277.         v += s->floor ;

  278. 

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

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

  281. 

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

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

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

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

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

  287.             i++;

  288.         }

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

  290. }

  291. 

  292. typedef struct IComplex {

  293.     short re,im;

  294. } IComplex;

  295. 

  296. static void fft_init(int ln)

  297. {

  298.     int i, j, m, n;

  299.     float alpha;

  300. 

  301.     n = 1 << ln;

  302. 

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

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

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

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

  307.     }

  308. 

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

  310.         m=0;

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

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

  313.         }

  314.         fft_rev[i]=m;

  315.     }

  316. }

  317. 

  318. /* butter fly op */

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

  320. {\

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

  322.   bx=pre1;\

  323.   by=pim1;\

  324.   ax=qre1;\

  325.   ay=qim1;\

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

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

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

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

  330. }

  331. 

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

  333. 

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

  335. {\

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

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

  338. }

  339. 

  340. 

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

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

  343. {

  344.     int        j, l, np, np2;

  345.     int        nblocks, nloops;

  346.     register IComplex *p,*q;

  347.     int tmp_re, tmp_im;

  348. 

  349.     np = 1 << ln;

  350. 

  351.     /* reverse */

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

  353.         int k;

  354.         IComplex tmp;

  355.         k = fft_rev[j];

  356.         if (k < j) {

  357.             tmp = z[k];

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

  359.             z[j] = tmp;

  360.         }

  361.     }

  362. 

  363.     /* pass 0 */

  364. 

  365.     p=&z[0];

  366.     j=(np >> 1);

  367.     do {

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

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

  370.         p+=2;

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

  372. 

  373.     /* pass 1 */

  374. 

  375.     p=&z[0];

  376.     j=np >> 2;

  377.     do {

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

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

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

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

  382.         p+=4;

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

  384. 

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

  386. 

  387.     nblocks = np >> 3;

  388.     nloops = 1 << 2;

  389.     np2 = np >> 1;

  390.     do {

  391.         p = z;

  392.         q = z + nloops;

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

  394. 

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

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

  397. 

  398.             p++;

  399.             q++;

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

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

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

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

  404.                 p++;

  405.                 q++;

  406.             }

  407.             p += nloops;

  408.             q += nloops;

  409.         }

  410.         nblocks = nblocks >> 1;

  411.         nloops = nloops << 1;

  412.     } while (nblocks != 0);

  413. }

  414. 

  415. /* do a 512 point mdct */

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

  417. {

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

  419.     int16_t rot[N];

  420.     IComplex x[N/4];

  421. 

  422.     /* shift to simplify computations */

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

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

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

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

  427. 

  428.     /* pre rotation */

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

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

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

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

  433.     }

  434. 

  435.     fft(x, MDCT_NBITS - 2);

  436. 

  437.     /* post rotation */

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

  439.         re = x[i].re;

  440.         im = x[i].im;

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

  442.         out[2*i] = im1;

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

  444.     }

  445. }

  446. 

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

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

  449. {

  450.     int sum, i;

  451.     sum = 0;

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

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

  454.     }

  455.     return sum;

  456. }

  457. 

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

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

  460.                                  int ch, int is_lfe)

  461. {

  462.     int i, j;

  463.     int exp_diff;

  464. 

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

  466.        reused in the next frame */

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

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

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

  470. #ifdef DEBUG

  471.         av_log(NULL, AV_LOG_DEBUG, "exp_diff=%d\n", exp_diff);

  472. #endif

  473.         if (exp_diff > EXP_DIFF_THRESHOLD)

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

  475.         else

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

  477.     }

  478.     if (is_lfe)

  479.         return;

  480. 

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

  482.        recoded, we use a coarse encoding */

  483.     i = 0;

  484.     while (i < NB_BLOCKS) {

  485.         j = i + 1;

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

  487.             j++;

  488.         switch(j - i) {

  489.         case 1:

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

  491.             break;

  492.         case 2:

  493.         case 3:

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

  495.             break;

  496.         default:

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

  498.             break;

  499.         }

  500.         i = j;

  501.     }

  502. }

  503. 

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

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

  506. {

  507.     int i;

  508. 

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

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

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

  512.     }

  513. }

  514. 

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

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

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

  518.                       uint8_t exp[N/2],

  519.                       int nb_exps,

  520.                       int exp_strategy)

  521. {

  522.     int group_size, nb_groups, i, j, k, exp_min;

  523.     uint8_t exp1[N/2];

  524. 

  525.     switch(exp_strategy) {

  526.     case EXP_D15:

  527.         group_size = 1;

  528.         break;

  529.     case EXP_D25:

  530.         group_size = 2;

  531.         break;

  532.     default:

  533.     case EXP_D45:

  534.         group_size = 4;

  535.         break;

  536.     }

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

  538. 

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

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

  541.     k = 1;

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

  543.         exp_min = exp[k];

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

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

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

  547.                 exp_min = exp[k+j];

  548.         }

  549.         exp1[i] = exp_min;

  550.         k += group_size;

  551.     }

  552. 

  553.     /* constraint for DC exponent */

  554.     if (exp1[0] > 15)

  555.         exp1[0] = 15;

  556. 

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

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

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

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

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

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

  563. 

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

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

  566.     k = 1;

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

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

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

  570.         }

  571.         k += group_size;

  572.     }

  573. 

  574. #if defined(DEBUG)

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

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

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

  578.     }

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

  580. #endif

  581. 

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

  583. }

  584. 

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

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

  587. {

  588.     int bits, mant, i;

  589. 

  590.     bits = 0;

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

  592.         mant = m[i];

  593.         switch(mant) {

  594.         case 0:

  595.             /* nothing */

  596.             break;

  597.         case 1:

  598.             /* 3 mantissa in 5 bits */

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

  600.                 bits += 5;

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

  602.                 s->mant1_cnt = 0;

  603.             break;

  604.         case 2:

  605.             /* 3 mantissa in 7 bits */

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

  607.                 bits += 7;

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

  609.                 s->mant2_cnt = 0;

  610.             break;

  611.         case 3:

  612.             bits += 3;

  613.             break;

  614.         case 4:

  615.             /* 2 mantissa in 7 bits */

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

  617.                 bits += 7;

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

  619.                 s->mant4_cnt = 0;

  620.             break;

  621.         case 14:

  622.             bits += 14;

  623.             break;

  624.         case 15:

  625.             bits += 16;

  626.             break;

  627.         default:

  628.             bits += mant - 1;

  629.             break;

  630.         }

  631.     }

  632.     return bits;

  633. }

  634. 

  635. 

  636. static int bit_alloc(AC3EncodeContext *s,

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

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

  639.                      uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  640.                      int frame_bits, int csnroffst, int fsnroffst)

  641. {

  642.     int i, ch;

  643. 

  644.     /* compute size */

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

  646.         s->mant1_cnt = 0;

  647.         s->mant2_cnt = 0;

  648.         s->mant4_cnt = 0;

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

  650.             ac3_parametric_bit_allocation(&s->bit_alloc,

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

  652.                                           0, s->nb_coefs[ch],

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

  654.                                            fsnroffst) << 2,

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

  656.                                           ch == s->lfe_channel,

  657.                                           2, 0, NULL, NULL, NULL);

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

  659.                                                  s->nb_coefs[ch]);

  660.         }

  661.     }

  662. #if 0

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

  664.            csnroffst, fsnroffst, frame_bits,

  665.            16 * s->frame_size - ((frame_bits + 7) & ~7));

  666. #endif

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

  668. }

  669. 

  670. #define SNR_INC1 4

  671. 

  672. static int compute_bit_allocation(AC3EncodeContext *s,

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

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

  675.                                   uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  676.                                   int frame_bits)

  677. {

  678.     int i, ch;

  679.     int csnroffst, fsnroffst;

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

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

  682. 

  683.     /* init default parameters */

  684.     s->sdecaycod = 2;

  685.     s->fdecaycod = 1;

  686.     s->sgaincod = 1;

  687.     s->dbkneecod = 2;

  688.     s->floorcod = 4;

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

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

  691. 

  692.     /* compute real values */

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

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

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

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

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

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

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

  700. 

  701.     /* header size */

  702.     frame_bits += 65;

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

  704.     //    frame_bits += 2;

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

  706. 

  707.     /* audio blocks */

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

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

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

  711.             frame_bits++; /* rematstr */

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

  713.         }

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

  715.         if (s->lfe)

  716.             frame_bits++; /* lfeexpstr */

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

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

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

  720.         }

  721.         frame_bits++; /* baie */

  722.         frame_bits++; /* snr */

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

  724.     }

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

  726.     /* bit alloc info */

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

  728.     /* csnroffset[6] */

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

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

  731. 

  732.     /* auxdatae, crcrsv */

  733.     frame_bits += 2;

  734. 

  735.     /* CRC */

  736.     frame_bits += 16;

  737. 

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

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

  740. 

  741.     csnroffst = s->csnroffst;

  742.     while (csnroffst >= 0 &&

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

  744.         csnroffst -= SNR_INC1;

  745.     if (csnroffst < 0) {

  746.         av_log(NULL, AV_LOG_ERROR, "Bit allocation failed, try increasing the bitrate, -ab 384 for example!\n");

  747.         return -1;

  748.     }

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

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

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

  752.         csnroffst += SNR_INC1;

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

  754.     }

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

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

  757.         csnroffst++;

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

  759.     }

  760. 

  761.     fsnroffst = 0;

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

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

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

  765.         fsnroffst += SNR_INC1;

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

  767.     }

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

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

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

  771.         fsnroffst++;

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

  773.     }

  774. 

  775.     s->csnroffst = csnroffst;

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

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

  778. #if defined(DEBUG_BITALLOC)

  779.     {

  780.         int j;

  781. 

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

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

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

  785.                 printf("bap=");

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

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

  788.                 }

  789.                 printf("\n");

  790.             }

  791.         }

  792.     }

  793. #endif

  794.     return 0;

  795. }

  796. 

  797. void ac3_common_init(void)

  798. {

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

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

  801.     k = 0;

  802.     l = 0;

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

  804.         bndtab[i] = l;

  805.         v = bndsz[i];

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

  807.         l += v;

  808.     }

  809.     bndtab[50] = l;

  810. }

  811. 

  812. 

  813. static int AC3_encode_init(AVCodecContext *avctx)

  814. {

  815.     int freq = avctx->sample_rate;

  816.     int bitrate = avctx->bit_rate;

  817.     int channels = avctx->channels;

  818.     AC3EncodeContext *s = avctx->priv_data;

  819.     int i, j, ch;

  820.     float alpha;

  821.     static const uint8_t acmod_defs[6] = {

  822.         0x01, /* C */

  823.         0x02, /* L R */

  824.         0x03, /* L C R */

  825.         0x06, /* L R SL SR */

  826.         0x07, /* L C R SL SR */

  827.         0x07, /* L C R SL SR (+LFE) */

  828.     };

  829. 

  830.     avctx->frame_size = AC3_FRAME_SIZE;

  831. 

  832.     /* number of channels */

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

  834.         return -1;

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

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

  837.     s->nb_all_channels = channels;

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

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

  840. 

  841.     /* frequency */

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

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

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

  845.                 goto found;

  846.     }

  847.     return -1;

  848.  found:

  849.     s->sample_rate = freq;

  850.     s->halfratecod = i;

  851.     s->fscod = j;

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

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

  854. 

  855.     /* bitrate & frame size */

  856.     bitrate /= 1000;

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

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

  859.             break;

  860.     }

  861.     if (i == 19)

  862.         return -1;

  863.     s->bit_rate = bitrate;

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

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

  866.     s->bits_written = 0;

  867.     s->samples_written = 0;

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

  869. 

  870.     /* bit allocation init */

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

  872.         /* bandwidth for each channel */

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

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

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

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

  877.     }

  878.     if (s->lfe) {

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

  880.     }

  881.     /* initial snr offset */

  882.     s->csnroffst = 40;

  883. 

  884.     ac3_common_init();

  885. 

  886.     /* mdct init */

  887.     fft_init(MDCT_NBITS - 2);

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

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

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

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

  892.     }

  893. 

  894.     avctx->coded_frame= avcodec_alloc_frame();

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

  896. 

  897.     return 0;

  898. }

  899. 

  900. /* output the AC3 frame header */

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

  902. {

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

  904. 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  928. }

  929. 

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

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

  932. {

  933.     int v;

  934. 

  935.     if (c >= 0) {

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

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

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

  939.     } else {

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

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

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

  943.     }

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

  945.     return v;

  946. }

  947. 

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

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

  950. {

  951.     int lshift, m, v;

  952. 

  953.     lshift = e + qbits - 24;

  954.     if (lshift >= 0)

  955.         v = c << lshift;

  956.     else

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

  958.     /* rounding */

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

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

  961.     if (v >= m)

  962.         v = m - 1;

  963.     assert(v >= -m);

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

  965. }

  966. 

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

  968.    frame */

  969. static void output_audio_block(AC3EncodeContext *s,

  970.                                uint8_t exp_strategy[AC3_MAX_CHANNELS],

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

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

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

  974.                                int8_t global_exp[AC3_MAX_CHANNELS],

  975.                                int block_num)

  976. {

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

  978.     uint8_t *p;

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

  980.     int exp0, exp1;

  981.     int mant1_cnt, mant2_cnt, mant4_cnt;

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

  983.     int delta0, delta1, delta2;

  984. 

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

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

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

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

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

  990.     if (block_num == 0) {

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

  992.            waste of bit :-) */

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

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

  995.     } else {

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

  997.     }

  998. 

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

  1000.       {

  1001.         if(block_num==0)

  1002.           {

  1003.             /* first block must define rematrixing (rematstr)  */

  1004.             put_bits(&s->pb, 1, 1);

  1005. 

  1006.             /* dummy rematrixing rematflg(1:4)=0 */

  1007.             for (rbnd=0;rbnd<4;rbnd++)

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

  1009.           }

  1010.         else

  1011.           {

  1012.             /* no matrixing (but should be used in the future) */

  1013.             put_bits(&s->pb, 1, 0);

  1014.           }

  1015.       }

  1016. 

  1017. #if defined(DEBUG)

  1018.     {

  1019.       static int count = 0;

  1020.       av_log(NULL, AV_LOG_DEBUG, "Block #%d (%d)\n", block_num, count++);

  1021.     }

  1022. #endif

  1023.     /* exponent strategy */

  1024.     for(ch=0;ch<s->nb_channels;ch++) {

  1025.         put_bits(&s->pb, 2, exp_strategy[ch]);

  1026.     }

  1027. 

  1028.     if (s->lfe) {

  1029.         put_bits(&s->pb, 1, exp_strategy[s->lfe_channel]);

  1030.     }

  1031. 

  1032.     for(ch=0;ch<s->nb_channels;ch++) {

  1033.         if (exp_strategy[ch] != EXP_REUSE)

  1034.             put_bits(&s->pb, 6, s->chbwcod[ch]);

  1035.     }

  1036. 

  1037.     /* exponents */

  1038.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1039.         switch(exp_strategy[ch]) {

  1040.         case EXP_REUSE:

  1041.             continue;

  1042.         case EXP_D15:

  1043.             group_size = 1;

  1044.             break;

  1045.         case EXP_D25:

  1046.             group_size = 2;

  1047.             break;

  1048.         default:

  1049.         case EXP_D45:

  1050.             group_size = 4;

  1051.             break;

  1052.         }

  1053.         nb_groups = (s->nb_coefs[ch] + (group_size * 3) - 4) / (3 * group_size);

  1054.         p = encoded_exp[ch];

  1055. 

  1056.         /* first exponent */

  1057.         exp1 = *p++;

  1058.         put_bits(&s->pb, 4, exp1);

  1059. 

  1060.         /* next ones are delta encoded */

  1061.         for(i=0;i<nb_groups;i++) {

  1062.             /* merge three delta in one code */

  1063.             exp0 = exp1;

  1064.             exp1 = p[0];

  1065.             p += group_size;

  1066.             delta0 = exp1 - exp0 + 2;

  1067. 

  1068.             exp0 = exp1;

  1069.             exp1 = p[0];

  1070.             p += group_size;

  1071.             delta1 = exp1 - exp0 + 2;

  1072. 

  1073.             exp0 = exp1;

  1074.             exp1 = p[0];

  1075.             p += group_size;

  1076.             delta2 = exp1 - exp0 + 2;

  1077. 

  1078.             put_bits(&s->pb, 7, ((delta0 * 5 + delta1) * 5) + delta2);

  1079.         }

  1080. 

  1081.         if (ch != s->lfe_channel)

  1082.             put_bits(&s->pb, 2, 0); /* no gain range info */

  1083.     }

  1084. 

  1085.     /* bit allocation info */

  1086.     baie = (block_num == 0);

  1087.     put_bits(&s->pb, 1, baie);

  1088.     if (baie) {

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

  1090.         put_bits(&s->pb, 2, s->fdecaycod);

  1091.         put_bits(&s->pb, 2, s->sgaincod);

  1092.         put_bits(&s->pb, 2, s->dbkneecod);

  1093.         put_bits(&s->pb, 3, s->floorcod);

  1094.     }

  1095. 

  1096.     /* snr offset */

  1097.     put_bits(&s->pb, 1, baie); /* always present with bai */

  1098.     if (baie) {

  1099.         put_bits(&s->pb, 6, s->csnroffst);

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

  1101.             put_bits(&s->pb, 4, s->fsnroffst[ch]);

  1102.             put_bits(&s->pb, 3, s->fgaincod[ch]);

  1103.         }

  1104.     }

  1105. 

  1106.     put_bits(&s->pb, 1, 0); /* no delta bit allocation */

  1107.     put_bits(&s->pb, 1, 0); /* no data to skip */

  1108. 

  1109.     /* mantissa encoding : we use two passes to handle the grouping. A

  1110.        one pass method may be faster, but it would necessitate to

  1111.        modify the output stream. */

  1112. 

  1113.     /* first pass: quantize */

  1114.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  1115.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  1116. 

  1117.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1118.         int b, c, e, v;

  1119. 

  1120.         for(i=0;i<s->nb_coefs[ch];i++) {

  1121.             c = mdct_coefs[ch][i];

  1122.             e = encoded_exp[ch][i] - global_exp[ch];

  1123.             b = bap[ch][i];

  1124.             switch(b) {

  1125.             case 0:

  1126.                 v = 0;

  1127.                 break;

  1128.             case 1:

  1129.                 v = sym_quant(c, e, 3);

  1130.                 switch(mant1_cnt) {

  1131.                 case 0:

  1132.                     qmant1_ptr = &qmant[ch][i];

  1133.                     v = 9 * v;

  1134.                     mant1_cnt = 1;

  1135.                     break;

  1136.                 case 1:

  1137.                     *qmant1_ptr += 3 * v;

  1138.                     mant1_cnt = 2;

  1139.                     v = 128;

  1140.                     break;

  1141.                 default:

  1142.                     *qmant1_ptr += v;

  1143.                     mant1_cnt = 0;

  1144.                     v = 128;

  1145.                     break;

  1146.                 }

  1147.                 break;

  1148.             case 2:

  1149.                 v = sym_quant(c, e, 5);

  1150.                 switch(mant2_cnt) {

  1151.                 case 0:

  1152.                     qmant2_ptr = &qmant[ch][i];

  1153.                     v = 25 * v;

  1154.                     mant2_cnt = 1;

  1155.                     break;

  1156.                 case 1:

  1157.                     *qmant2_ptr += 5 * v;

  1158.                     mant2_cnt = 2;

  1159.                     v = 128;

  1160.                     break;

  1161.                 default:

  1162.                     *qmant2_ptr += v;

  1163.                     mant2_cnt = 0;

  1164.                     v = 128;

  1165.                     break;

  1166.                 }

  1167.                 break;

  1168.             case 3:

  1169.                 v = sym_quant(c, e, 7);

  1170.                 break;

  1171.             case 4:

  1172.                 v = sym_quant(c, e, 11);

  1173.                 switch(mant4_cnt) {

  1174.                 case 0:

  1175.                     qmant4_ptr = &qmant[ch][i];

  1176.                     v = 11 * v;

  1177.                     mant4_cnt = 1;

  1178.                     break;

  1179.                 default:

  1180.                     *qmant4_ptr += v;

  1181.                     mant4_cnt = 0;

  1182.                     v = 128;

  1183.                     break;

  1184.                 }

  1185.                 break;

  1186.             case 5:

  1187.                 v = sym_quant(c, e, 15);

  1188.                 break;

  1189.             case 14:

  1190.                 v = asym_quant(c, e, 14);

  1191.                 break;

  1192.             case 15:

  1193.                 v = asym_quant(c, e, 16);

  1194.                 break;

  1195.             default:

  1196.                 v = asym_quant(c, e, b - 1);

  1197.                 break;

  1198.             }

  1199.             qmant[ch][i] = v;

  1200.         }

  1201.     }

  1202. 

  1203.     /* second pass : output the values */

  1204.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1205.         int b, q;

  1206. 

  1207.         for(i=0;i<s->nb_coefs[ch];i++) {

  1208.             q = qmant[ch][i];

  1209.             b = bap[ch][i];

  1210.             switch(b) {

  1211.             case 0:

  1212.                 break;

  1213.             case 1:

  1214.                 if (q != 128)

  1215.                     put_bits(&s->pb, 5, q);

  1216.                 break;

  1217.             case 2:

  1218.                 if (q != 128)

  1219.                     put_bits(&s->pb, 7, q);

  1220.                 break;

  1221.             case 3:

  1222.                 put_bits(&s->pb, 3, q);

  1223.                 break;

  1224.             case 4:

  1225.                 if (q != 128)

  1226.                     put_bits(&s->pb, 7, q);

  1227.                 break;

  1228.             case 14:

  1229.                 put_bits(&s->pb, 14, q);

  1230.                 break;

  1231.             case 15:

  1232.                 put_bits(&s->pb, 16, q);

  1233.                 break;

  1234.             default:

  1235.                 put_bits(&s->pb, b - 1, q);

  1236.                 break;

  1237.             }

  1238.         }

  1239.     }

  1240. }

  1241. 

  1242. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1243. 

  1244. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1245. {

  1246.     unsigned int c;

  1247. 

  1248.     c = 0;

  1249.     while (a) {

  1250.         if (a & 1)

  1251.             c ^= b;

  1252.         a = a >> 1;

  1253.         b = b << 1;

  1254.         if (b & (1 << 16))

  1255.             b ^= poly;

  1256.     }

  1257.     return c;

  1258. }

  1259. 

  1260. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1261. {

  1262.     unsigned int r;

  1263.     r = 1;

  1264.     while (n) {

  1265.         if (n & 1)

  1266.             r = mul_poly(r, a, poly);

  1267.         a = mul_poly(a, a, poly);

  1268.         n >>= 1;

  1269.     }

  1270.     return r;

  1271. }

  1272. 

  1273. 

  1274. /* compute log2(max(abs(tab[]))) */

  1275. static int log2_tab(int16_t *tab, int n)

  1276. {

  1277.     int i, v;

  1278. 

  1279.     v = 0;

  1280.     for(i=0;i<n;i++) {

  1281.         v |= abs(tab[i]);

  1282.     }

  1283.     return av_log2(v);

  1284. }

  1285. 

  1286. static void lshift_tab(int16_t *tab, int n, int lshift)

  1287. {

  1288.     int i;

  1289. 

  1290.     if (lshift > 0) {

  1291.         for(i=0;i<n;i++) {

  1292.             tab[i] <<= lshift;

  1293.         }

  1294.     } else if (lshift < 0) {

  1295.         lshift = -lshift;

  1296.         for(i=0;i<n;i++) {

  1297.             tab[i] >>= lshift;

  1298.         }

  1299.     }

  1300. }

  1301. 

  1302. /* fill the end of the frame and compute the two crcs */

  1303. static int output_frame_end(AC3EncodeContext *s)

  1304. {

  1305.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1306.     uint8_t *frame;

  1307. 

  1308.     frame_size = s->frame_size; /* frame size in words */

  1309.     /* align to 8 bits */

  1310.     flush_put_bits(&s->pb);

  1311.     /* add zero bytes to reach the frame size */

  1312.     frame = s->pb.buf;

  1313.     n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;

  1314.     assert(n >= 0);

  1315.     if(n>0)

  1316.       memset(pbBufPtr(&s->pb), 0, n);

  1317. 

  1318.     /* Now we must compute both crcs : this is not so easy for crc1

  1319.        because it is at the beginning of the data... */

  1320.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1321.     crc1 = bswap_16(av_crc(av_crc8005, 0, frame + 4, 2 * frame_size_58 - 4));

  1322.     /* XXX: could precompute crc_inv */

  1323.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1324.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1325.     frame[2] = crc1 >> 8;

  1326.     frame[3] = crc1;

  1327. 

  1328.     crc2 = bswap_16(av_crc(av_crc8005, 0, frame + 2 * frame_size_58, (frame_size - frame_size_58) * 2 - 2));

  1329.     frame[2*frame_size - 2] = crc2 >> 8;

  1330.     frame[2*frame_size - 1] = crc2;

  1331. 

  1332.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1333.     return frame_size * 2;

  1334. }

  1335. 

  1336. static int AC3_encode_frame(AVCodecContext *avctx,

  1337.                             unsigned char *frame, int buf_size, void *data)

  1338. {

  1339.     AC3EncodeContext *s = avctx->priv_data;

  1340.     int16_t *samples = data;

  1341.     int i, j, k, v, ch;

  1342.     int16_t input_samples[N];

  1343.     int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1344.     uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1345.     uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

  1346.     uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1347.     uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1348.     int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

  1349.     int frame_bits;

  1350. 

  1351.     frame_bits = 0;

  1352.     for(ch=0;ch<s->nb_all_channels;ch++) {

  1353.         /* fixed mdct to the six sub blocks & exponent computation */

  1354.         for(i=0;i<NB_BLOCKS;i++) {

  1355.             int16_t *sptr;

  1356.             int sinc;

  1357. 

  1358.             /* compute input samples */

  1359.             memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(int16_t));

  1360.             sinc = s->nb_all_channels;

  1361.             sptr = samples + (sinc * (N/2) * i) + ch;

  1362.             for(j=0;j<N/2;j++) {

  1363.                 v = *sptr;

  1364.                 input_samples[j + N/2] = v;

  1365.                 s->last_samples[ch][j] = v;

  1366.                 sptr += sinc;

  1367.             }

  1368. 

  1369.             /* apply the MDCT window */

  1370.             for(j=0;j<N/2;j++) {

  1371.                 input_samples[j] = MUL16(input_samples[j],

  1372.                                          ac3_window[j]) >> 15;

  1373.                 input_samples[N-j-1] = MUL16(input_samples[N-j-1],

  1374.                                              ac3_window[j]) >> 15;

  1375.             }

  1376. 

  1377.             /* Normalize the samples to use the maximum available

  1378.                precision */

  1379.             v = 14 - log2_tab(input_samples, N);

  1380.             if (v < 0)

  1381.                 v = 0;

  1382.             exp_samples[i][ch] = v - 9;

  1383.             lshift_tab(input_samples, N, v);

  1384. 

  1385.             /* do the MDCT */

  1386.             mdct512(mdct_coef[i][ch], input_samples);

  1387. 

  1388.             /* compute "exponents". We take into account the

  1389.                normalization there */

  1390.             for(j=0;j<N/2;j++) {

  1391.                 int e;

  1392.                 v = abs(mdct_coef[i][ch][j]);

  1393.                 if (v == 0)

  1394.                     e = 24;

  1395.                 else {

  1396.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1397.                     if (e >= 24) {

  1398.                         e = 24;

  1399.                         mdct_coef[i][ch][j] = 0;

  1400.                     }

  1401.                 }

  1402.                 exp[i][ch][j] = e;

  1403.             }

  1404.         }

  1405. 

  1406.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1407. 

  1408.         /* compute the exponents as the decoder will see them. The

  1409.            EXP_REUSE case must be handled carefully : we select the

  1410.            min of the exponents */

  1411.         i = 0;

  1412.         while (i < NB_BLOCKS) {

  1413.             j = i + 1;

  1414.             while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1415.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1416.                 j++;

  1417.             }

  1418.             frame_bits += encode_exp(encoded_exp[i][ch],

  1419.                                      exp[i][ch], s->nb_coefs[ch],

  1420.                                      exp_strategy[i][ch]);

  1421.             /* copy encoded exponents for reuse case */

  1422.             for(k=i+1;k<j;k++) {

  1423.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch],

  1424.                        s->nb_coefs[ch] * sizeof(uint8_t));

  1425.             }

  1426.             i = j;

  1427.         }

  1428.     }

  1429. 

  1430.     /* adjust for fractional frame sizes */

  1431.     while(s->bits_written >= s->bit_rate*1000 && s->samples_written >= s->sample_rate) {

  1432.         s->bits_written -= s->bit_rate*1000;

  1433.         s->samples_written -= s->sample_rate;

  1434.     }

  1435.     s->frame_size = s->frame_size_min + (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate*1000);

  1436.     s->bits_written += s->frame_size * 16;

  1437.     s->samples_written += AC3_FRAME_SIZE;

  1438. 

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

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

  1441.     output_frame_header(s, frame);

  1442. 

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

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

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

  1446.     }

  1447.     return output_frame_end(s);

  1448. }

  1449. 

  1450. static int AC3_encode_close(AVCodecContext *avctx)

  1451. {

  1452.     av_freep(&avctx->coded_frame);

  1453.     return 0;

  1454. }

  1455. 

  1456. #if 0

  1457. /*************************************************************************/

  1458. /* TEST */

  1459. 

  1460. #define FN (N/4)

  1461. 

  1462. void fft_test(void)

  1463. {

  1464.     IComplex in[FN], in1[FN];

  1465.     int k, n, i;

  1466.     float sum_re, sum_im, a;

  1467. 

  1468.     /* FFT test */

  1469. 

  1470.     for(i=0;i<FN;i++) {

  1471.         in[i].re = random() % 65535 - 32767;

  1472.         in[i].im = random() % 65535 - 32767;

  1473.         in1[i] = in[i];

  1474.     }

  1475.     fft(in, 7);

  1476. 

  1477.     /* do it by hand */

  1478.     for(k=0;k<FN;k++) {

  1479.         sum_re = 0;

  1480.         sum_im = 0;

  1481.         for(n=0;n<FN;n++) {

  1482.             a = -2 * M_PI * (n * k) / FN;

  1483.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1484.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1485.         }

  1486.         printf("%3d: %6d,%6d %6.0f,%6.0f\n",

  1487.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);

  1488.     }

  1489. }

  1490. 

  1491. void mdct_test(void)

  1492. {

  1493.     int16_t input[N];

  1494.     int32_t output[N/2];

  1495.     float input1[N];

  1496.     float output1[N/2];

  1497.     float s, a, err, e, emax;

  1498.     int i, k, n;

  1499. 

  1500.     for(i=0;i<N;i++) {

  1501.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1502.         input1[i] = input[i];

  1503.     }

  1504. 

  1505.     mdct512(output, input);

  1506. 

  1507.     /* do it by hand */

  1508.     for(k=0;k<N/2;k++) {

  1509.         s = 0;

  1510.         for(n=0;n<N;n++) {

  1511.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1512.             s += input1[n] * cos(a);

  1513.         }

  1514.         output1[k] = -2 * s / N;

  1515.     }

  1516. 

  1517.     err = 0;

  1518.     emax = 0;

  1519.     for(i=0;i<N/2;i++) {

  1520.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1521.         e = output[i] - output1[i];

  1522.         if (e > emax)

  1523.             emax = e;

  1524.         err += e * e;

  1525.     }

  1526.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1527. }

  1528. 

  1529. void test_ac3(void)

  1530. {

  1531.     AC3EncodeContext ctx;

  1532.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1533.     short samples[AC3_FRAME_SIZE];

  1534.     int ret, i;

  1535. 

  1536.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1537. 

  1538.     fft_test();

  1539.     mdct_test();

  1540. 

  1541.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1542.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1543.     ret = AC3_encode_frame(&ctx, frame, samples);

  1544.     printf("ret=%d\n", ret);

  1545. }

  1546. #endif

  1547. 

  1548. AVCodec ac3_encoder = {

  1549.     "ac3",

  1550.     CODEC_TYPE_AUDIO,

  1551.     CODEC_ID_AC3,

  1552.     sizeof(AC3EncodeContext),

  1553.     AC3_encode_init,

  1554.     AC3_encode_frame,

  1555.     AC3_encode_close,

  1556.     NULL,

  1557. };