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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 bitstream_id;

  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 sr_shift;

  46.     unsigned int frame_size_code;

  47.     unsigned int sr_code; /* frequency */

  48.     unsigned int channel_mode;

  49.     int lfe;

  50.     unsigned int bitstream_mode;

  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 slow_gain_code, slow_decay_code, fast_decay_code, db_per_bit_code, floor_code;

  57.     AC3BitAllocParameters bit_alloc;

  58.     int coarse_snr_offset;

  59.     int fast_gain_code[AC3_MAX_CHANNELS];

  60.     int fine_snr_offset[AC3_MAX_CHANNELS];

  61.     /* mantissa encoding */

  62.     int mant1_cnt, mant2_cnt, mant4_cnt;

  63. } AC3EncodeContext;

  64. 

  65. static int16_t costab[64];

  66. static int16_t sintab[64];

  67. static int16_t fft_rev[512];

  68. static int16_t xcos1[128];

  69. static int16_t xsin1[128];

  70. 

  71. #define MDCT_NBITS 9

  72. #define N         (1 << MDCT_NBITS)

  73. 

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

  75. #define EXP_DIFF_THRESHOLD 1000

  76. 

  77. static void fft_init(int ln);

  78. 

  79. static inline int16_t fix15(float a)

  80. {

  81.     int v;

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

  83.     if (v < -32767)

  84.         v = -32767;

  85.     else if (v > 32767)

  86.         v = 32767;

  87.     return v;

  88. }

  89. 

  90. typedef struct IComplex {

  91.     short re,im;

  92. } IComplex;

  93. 

  94. static void fft_init(int ln)

  95. {

  96.     int i, j, m, n;

  97.     float alpha;

  98. 

  99.     n = 1 << ln;

  100. 

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

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

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

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

  105.     }

  106. 

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

  108.         m=0;

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

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

  111.         }

  112.         fft_rev[i]=m;

  113.     }

  114. }

  115. 

  116. /* butter fly op */

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

  118. {\

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

  120.   bx=pre1;\

  121.   by=pim1;\

  122.   ax=qre1;\

  123.   ay=qim1;\

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

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

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

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

  128. }

  129. 

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

  131. 

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

  133. {\

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

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

  136. }

  137. 

  138. 

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

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

  141. {

  142.     int        j, l, np, np2;

  143.     int        nblocks, nloops;

  144.     register IComplex *p,*q;

  145.     int tmp_re, tmp_im;

  146. 

  147.     np = 1 << ln;

  148. 

  149.     /* reverse */

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

  151.         int k;

  152.         k = fft_rev[j];

  153.         if (k < j)

  154.             FFSWAP(IComplex, z[k], z[j]);

  155.     }

  156. 

  157.     /* pass 0 */

  158. 

  159.     p=&z[0];

  160.     j=(np >> 1);

  161.     do {

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

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

  164.         p+=2;

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

  166. 

  167.     /* pass 1 */

  168. 

  169.     p=&z[0];

  170.     j=np >> 2;

  171.     do {

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

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

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

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

  176.         p+=4;

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

  178. 

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

  180. 

  181.     nblocks = np >> 3;

  182.     nloops = 1 << 2;

  183.     np2 = np >> 1;

  184.     do {

  185.         p = z;

  186.         q = z + nloops;

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

  188. 

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

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

  191. 

  192.             p++;

  193.             q++;

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

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

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

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

  198.                 p++;

  199.                 q++;

  200.             }

  201.             p += nloops;

  202.             q += nloops;

  203.         }

  204.         nblocks = nblocks >> 1;

  205.         nloops = nloops << 1;

  206.     } while (nblocks != 0);

  207. }

  208. 

  209. /* do a 512 point mdct */

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

  211. {

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

  213.     int16_t rot[N];

  214.     IComplex x[N/4];

  215. 

  216.     /* shift to simplify computations */

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

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

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

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

  221. 

  222.     /* pre rotation */

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

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

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

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

  227.     }

  228. 

  229.     fft(x, MDCT_NBITS - 2);

  230. 

  231.     /* post rotation */

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

  233.         re = x[i].re;

  234.         im = x[i].im;

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

  236.         out[2*i] = im1;

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

  238.     }

  239. }

  240. 

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

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

  243. {

  244.     int sum, i;

  245.     sum = 0;

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

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

  248.     }

  249.     return sum;

  250. }

  251. 

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

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

  254.                                  int ch, int is_lfe)

  255. {

  256.     int i, j;

  257.     int exp_diff;

  258. 

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

  260.        reused in the next frame */

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

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

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

  264. #ifdef DEBUG

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

  266. #endif

  267.         if (exp_diff > EXP_DIFF_THRESHOLD)

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

  269.         else

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

  271.     }

  272.     if (is_lfe)

  273.         return;

  274. 

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

  276.        recoded, we use a coarse encoding */

  277.     i = 0;

  278.     while (i < NB_BLOCKS) {

  279.         j = i + 1;

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

  281.             j++;

  282.         switch(j - i) {

  283.         case 1:

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

  285.             break;

  286.         case 2:

  287.         case 3:

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

  289.             break;

  290.         default:

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

  292.             break;

  293.         }

  294.         i = j;

  295.     }

  296. }

  297. 

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

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

  300. {

  301.     int i;

  302. 

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

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

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

  306.     }

  307. }

  308. 

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

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

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

  312.                       uint8_t exp[N/2],

  313.                       int nb_exps,

  314.                       int exp_strategy)

  315. {

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

  317.     uint8_t exp1[N/2];

  318. 

  319.     switch(exp_strategy) {

  320.     case EXP_D15:

  321.         group_size = 1;

  322.         break;

  323.     case EXP_D25:

  324.         group_size = 2;

  325.         break;

  326.     default:

  327.     case EXP_D45:

  328.         group_size = 4;

  329.         break;

  330.     }

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

  332. 

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

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

  335.     k = 1;

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

  337.         exp_min = exp[k];

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

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

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

  341.                 exp_min = exp[k+j];

  342.         }

  343.         exp1[i] = exp_min;

  344.         k += group_size;

  345.     }

  346. 

  347.     /* constraint for DC exponent */

  348.     if (exp1[0] > 15)

  349.         exp1[0] = 15;

  350. 

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

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

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

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

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

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

  357. 

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

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

  360.     k = 1;

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

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

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

  364.         }

  365.         k += group_size;

  366.     }

  367. 

  368. #if defined(DEBUG)

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

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

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

  372.     }

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

  374. #endif

  375. 

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

  377. }

  378. 

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

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

  381. {

  382.     int bits, mant, i;

  383. 

  384.     bits = 0;

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

  386.         mant = m[i];

  387.         switch(mant) {

  388.         case 0:

  389.             /* nothing */

  390.             break;

  391.         case 1:

  392.             /* 3 mantissa in 5 bits */

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

  394.                 bits += 5;

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

  396.                 s->mant1_cnt = 0;

  397.             break;

  398.         case 2:

  399.             /* 3 mantissa in 7 bits */

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

  401.                 bits += 7;

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

  403.                 s->mant2_cnt = 0;

  404.             break;

  405.         case 3:

  406.             bits += 3;

  407.             break;

  408.         case 4:

  409.             /* 2 mantissa in 7 bits */

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

  411.                 bits += 7;

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

  413.                 s->mant4_cnt = 0;

  414.             break;

  415.         case 14:

  416.             bits += 14;

  417.             break;

  418.         case 15:

  419.             bits += 16;

  420.             break;

  421.         default:

  422.             bits += mant - 1;

  423.             break;

  424.         }

  425.     }

  426.     return bits;

  427. }

  428. 

  429. 

  430. static void bit_alloc_masking(AC3EncodeContext *s,

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

  432.                               uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  433.                               int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

  434.                               int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50])

  435. {

  436.     int blk, ch;

  437.     int16_t band_psd[NB_BLOCKS][AC3_MAX_CHANNELS][50];

  438. 

  439.     for(blk=0; blk<NB_BLOCKS; blk++) {

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

  441.             if(exp_strategy[blk][ch] == EXP_REUSE) {

  442.                 memcpy(psd[blk][ch], psd[blk-1][ch], (N/2)*sizeof(int16_t));

  443.                 memcpy(mask[blk][ch], mask[blk-1][ch], 50*sizeof(int16_t));

  444.             } else {

  445.                 ff_ac3_bit_alloc_calc_psd(encoded_exp[blk][ch], 0,

  446.                                           s->nb_coefs[ch],

  447.                                           psd[blk][ch], band_psd[blk][ch]);

  448.                 ff_ac3_bit_alloc_calc_mask(&s->bit_alloc, band_psd[blk][ch],

  449.                                            0, s->nb_coefs[ch],

  450.                                            ff_ac3_fast_gain_tab[s->fast_gain_code[ch]],

  451.                                            ch == s->lfe_channel,

  452.                                            DBA_NONE, 0, NULL, NULL, NULL,

  453.                                            mask[blk][ch]);

  454.             }

  455.         }

  456.     }

  457. }

  458. 

  459. static int bit_alloc(AC3EncodeContext *s,

  460.                      int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50],

  461.                      int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

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

  463.                      int frame_bits, int coarse_snr_offset, int fine_snr_offset)

  464. {

  465.     int i, ch;

  466.     int snr_offset;

  467. 

  468.     snr_offset = (((coarse_snr_offset - 15) << 4) + fine_snr_offset) << 2;

  469. 

  470.     /* compute size */

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

  472.         s->mant1_cnt = 0;

  473.         s->mant2_cnt = 0;

  474.         s->mant4_cnt = 0;

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

  476.             ff_ac3_bit_alloc_calc_bap(mask[i][ch], psd[i][ch], 0,

  477.                                       s->nb_coefs[ch], snr_offset,

  478.                                       s->bit_alloc.floor, bap[i][ch]);

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

  480.                                                  s->nb_coefs[ch]);

  481.         }

  482.     }

  483. #if 0

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

  485.            coarse_snr_offset, fine_snr_offset, frame_bits,

  486.            16 * s->frame_size - ((frame_bits + 7) & ~7));

  487. #endif

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

  489. }

  490. 

  491. #define SNR_INC1 4

  492. 

  493. static int compute_bit_allocation(AC3EncodeContext *s,

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

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

  496.                                   uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  497.                                   int frame_bits)

  498. {

  499.     int i, ch;

  500.     int coarse_snr_offset, fine_snr_offset;

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

  502.     int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  503.     int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50];

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

  505. 

  506.     /* init default parameters */

  507.     s->slow_decay_code = 2;

  508.     s->fast_decay_code = 1;

  509.     s->slow_gain_code = 1;

  510.     s->db_per_bit_code = 2;

  511.     s->floor_code = 4;

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

  513.         s->fast_gain_code[ch] = 4;

  514. 

  515.     /* compute real values */

  516.     s->bit_alloc.sr_code = s->sr_code;

  517.     s->bit_alloc.sr_shift = s->sr_shift;

  518.     s->bit_alloc.slow_decay = ff_ac3_slow_decay_tab[s->slow_decay_code] >> s->sr_shift;

  519.     s->bit_alloc.fast_decay = ff_ac3_fast_decay_tab[s->fast_decay_code] >> s->sr_shift;

  520.     s->bit_alloc.slow_gain = ff_ac3_slow_gain_tab[s->slow_gain_code];

  521.     s->bit_alloc.db_per_bit = ff_ac3_db_per_bit_tab[s->db_per_bit_code];

  522.     s->bit_alloc.floor = ff_ac3_floor_tab[s->floor_code];

  523. 

  524.     /* header size */

  525.     frame_bits += 65;

  526.     // if (s->channel_mode == 2)

  527.     //    frame_bits += 2;

  528.     frame_bits += frame_bits_inc[s->channel_mode];

  529. 

  530.     /* audio blocks */

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

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

  533.         if (s->channel_mode == AC3_CHMODE_STEREO) {

  534.             frame_bits++; /* rematstr */

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

  536.         }

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

  538.         if (s->lfe)

  539.             frame_bits++; /* lfeexpstr */

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

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

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

  543.         }

  544.         frame_bits++; /* baie */

  545.         frame_bits++; /* snr */

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

  547.     }

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

  549.     /* bit alloc info */

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

  551.     /* csnroffset[6] */

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

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

  554. 

  555.     /* auxdatae, crcrsv */

  556.     frame_bits += 2;

  557. 

  558.     /* CRC */

  559.     frame_bits += 16;

  560. 

  561.     /* calculate psd and masking curve before doing bit allocation */

  562.     bit_alloc_masking(s, encoded_exp, exp_strategy, psd, mask);

  563. 

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

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

  566. 

  567.     coarse_snr_offset = s->coarse_snr_offset;

  568.     while (coarse_snr_offset >= 0 &&

  569.            bit_alloc(s, mask, psd, bap, frame_bits, coarse_snr_offset, 0) < 0)

  570.         coarse_snr_offset -= SNR_INC1;

  571.     if (coarse_snr_offset < 0) {

  572.         av_log(NULL, AV_LOG_ERROR, "Bit allocation failed. Try increasing the bitrate.\n");

  573.         return -1;

  574.     }

  575.     while ((coarse_snr_offset + SNR_INC1) <= 63 &&

  576.            bit_alloc(s, mask, psd, bap1, frame_bits,

  577.                      coarse_snr_offset + SNR_INC1, 0) >= 0) {

  578.         coarse_snr_offset += SNR_INC1;

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

  580.     }

  581.     while ((coarse_snr_offset + 1) <= 63 &&

  582.            bit_alloc(s, mask, psd, bap1, frame_bits, coarse_snr_offset + 1, 0) >= 0) {

  583.         coarse_snr_offset++;

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

  585.     }

  586. 

  587.     fine_snr_offset = 0;

  588.     while ((fine_snr_offset + SNR_INC1) <= 15 &&

  589.            bit_alloc(s, mask, psd, bap1, frame_bits,

  590.                      coarse_snr_offset, fine_snr_offset + SNR_INC1) >= 0) {

  591.         fine_snr_offset += SNR_INC1;

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

  593.     }

  594.     while ((fine_snr_offset + 1) <= 15 &&

  595.            bit_alloc(s, mask, psd, bap1, frame_bits,

  596.                      coarse_snr_offset, fine_snr_offset + 1) >= 0) {

  597.         fine_snr_offset++;

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

  599.     }

  600. 

  601.     s->coarse_snr_offset = coarse_snr_offset;

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

  603.         s->fine_snr_offset[ch] = fine_snr_offset;

  604. #if defined(DEBUG_BITALLOC)

  605.     {

  606.         int j;

  607. 

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

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

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

  611.                 printf("bap=");

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

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

  614.                 }

  615.                 printf("\n");

  616.             }

  617.         }

  618.     }

  619. #endif

  620.     return 0;

  621. }

  622. 

  623. static int AC3_encode_init(AVCodecContext *avctx)

  624. {

  625.     int freq = avctx->sample_rate;

  626.     int bitrate = avctx->bit_rate;

  627.     int channels = avctx->channels;

  628.     AC3EncodeContext *s = avctx->priv_data;

  629.     int i, j, ch;

  630.     float alpha;

  631.     int bw_code;

  632.     static const uint8_t channel_mode_defs[6] = {

  633.         0x01, /* C */

  634.         0x02, /* L R */

  635.         0x03, /* L C R */

  636.         0x06, /* L R SL SR */

  637.         0x07, /* L C R SL SR */

  638.         0x07, /* L C R SL SR (+LFE) */

  639.     };

  640. 

  641.     avctx->frame_size = AC3_FRAME_SIZE;

  642. 

  643.     ac3_common_init();

  644. 

  645.     /* number of channels */

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

  647.         return -1;

  648.     s->channel_mode = channel_mode_defs[channels - 1];

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

  650.     s->nb_all_channels = channels;

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

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

  653. 

  654.     /* frequency */

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

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

  657.             if ((ff_ac3_sample_rate_tab[j] >> i) == freq)

  658.                 goto found;

  659.     }

  660.     return -1;

  661.  found:

  662.     s->sample_rate = freq;

  663.     s->sr_shift = i;

  664.     s->sr_code = j;

  665.     s->bitstream_id = 8 + s->sr_shift;

  666.     s->bitstream_mode = 0; /* complete main audio service */

  667. 

  668.     /* bitrate & frame size */

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

  670.         if ((ff_ac3_bitrate_tab[i] >> s->sr_shift)*1000 == bitrate)

  671.             break;

  672.     }

  673.     if (i == 19)

  674.         return -1;

  675.     s->bit_rate = bitrate;

  676.     s->frame_size_code = i << 1;

  677.     s->frame_size_min = ff_ac3_frame_size_tab[s->frame_size_code][s->sr_code];

  678.     s->bits_written = 0;

  679.     s->samples_written = 0;

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

  681. 

  682.     /* bit allocation init */

  683.     if(avctx->cutoff) {

  684.         /* calculate bandwidth based on user-specified cutoff frequency */

  685.         int cutoff = av_clip(avctx->cutoff, 1, s->sample_rate >> 1);

  686.         int fbw_coeffs = cutoff * 512 / s->sample_rate;

  687.         bw_code = av_clip((fbw_coeffs - 73) / 3, 0, 60);

  688.     } else {

  689.         /* use default bandwidth setting */

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

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

  692.         bw_code = 50;

  693.     }

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

  695.         /* bandwidth for each channel */

  696.         s->chbwcod[ch] = bw_code;

  697.         s->nb_coefs[ch] = bw_code * 3 + 73;

  698.     }

  699.     if (s->lfe) {

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

  701.     }

  702.     /* initial snr offset */

  703.     s->coarse_snr_offset = 40;

  704. 

  705.     /* mdct init */

  706.     fft_init(MDCT_NBITS - 2);

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

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

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

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

  711.     }

  712. 

  713.     avctx->coded_frame= avcodec_alloc_frame();

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

  715. 

  716.     return 0;

  717. }

  718. 

  719. /* output the AC3 frame header */

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

  721. {

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

  723. 

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

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

  726.     put_bits(&s->pb, 2, s->sr_code);

  727.     put_bits(&s->pb, 6, s->frame_size_code + (s->frame_size - s->frame_size_min));

  728.     put_bits(&s->pb, 5, s->bitstream_id);

  729.     put_bits(&s->pb, 3, s->bitstream_mode);

  730.     put_bits(&s->pb, 3, s->channel_mode);

  731.     if ((s->channel_mode & 0x01) && s->channel_mode != AC3_CHMODE_MONO)

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

  733.     if (s->channel_mode & 0x04)

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

  735.     if (s->channel_mode == AC3_CHMODE_STEREO)

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

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

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

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

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

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

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

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

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

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

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

  747. }

  748. 

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

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

  751. {

  752.     int v;

  753. 

  754.     if (c >= 0) {

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

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

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

  758.     } else {

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

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

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

  762.     }

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

  764.     return v;

  765. }

  766. 

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

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

  769. {

  770.     int lshift, m, v;

  771. 

  772.     lshift = e + qbits - 24;

  773.     if (lshift >= 0)

  774.         v = c << lshift;

  775.     else

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

  777.     /* rounding */

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

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

  780.     if (v >= m)

  781.         v = m - 1;

  782.     assert(v >= -m);

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

  784. }

  785. 

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

  787.    frame */

  788. static void output_audio_block(AC3EncodeContext *s,

  789.                                uint8_t exp_strategy[AC3_MAX_CHANNELS],

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

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

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

  793.                                int8_t global_exp[AC3_MAX_CHANNELS],

  794.                                int block_num)

  795. {

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

  797.     uint8_t *p;

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

  799.     int exp0, exp1;

  800.     int mant1_cnt, mant2_cnt, mant4_cnt;

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

  802.     int delta0, delta1, delta2;

  803. 

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

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

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

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

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

  809.     if (block_num == 0) {

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

  811.            waste of bit :-) */

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

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

  814.     } else {

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

  816.     }

  817. 

  818.     if (s->channel_mode == AC3_CHMODE_STEREO)

  819.       {

  820.         if(block_num==0)

  821.           {

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

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

  824. 

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

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

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

  828.           }

  829.         else

  830.           {

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

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

  833.           }

  834.       }

  835. 

  836. #if defined(DEBUG)

  837.     {

  838.       static int count = 0;

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

  840.     }

  841. #endif

  842.     /* exponent strategy */

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

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

  845.     }

  846. 

  847.     if (s->lfe) {

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

  849.     }

  850. 

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

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

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

  854.     }

  855. 

  856.     /* exponents */

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

  858.         switch(exp_strategy[ch]) {

  859.         case EXP_REUSE:

  860.             continue;

  861.         case EXP_D15:

  862.             group_size = 1;

  863.             break;

  864.         case EXP_D25:

  865.             group_size = 2;

  866.             break;

  867.         default:

  868.         case EXP_D45:

  869.             group_size = 4;

  870.             break;

  871.         }

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

  873.         p = encoded_exp[ch];

  874. 

  875.         /* first exponent */

  876.         exp1 = *p++;

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

  878. 

  879.         /* next ones are delta encoded */

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

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

  882.             exp0 = exp1;

  883.             exp1 = p[0];

  884.             p += group_size;

  885.             delta0 = exp1 - exp0 + 2;

  886. 

  887.             exp0 = exp1;

  888.             exp1 = p[0];

  889.             p += group_size;

  890.             delta1 = exp1 - exp0 + 2;

  891. 

  892.             exp0 = exp1;

  893.             exp1 = p[0];

  894.             p += group_size;

  895.             delta2 = exp1 - exp0 + 2;

  896. 

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

  898.         }

  899. 

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

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

  902.     }

  903. 

  904.     /* bit allocation info */

  905.     baie = (block_num == 0);

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

  907.     if (baie) {

  908.         put_bits(&s->pb, 2, s->slow_decay_code);

  909.         put_bits(&s->pb, 2, s->fast_decay_code);

  910.         put_bits(&s->pb, 2, s->slow_gain_code);

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

  912.         put_bits(&s->pb, 3, s->floor_code);

  913.     }

  914. 

  915.     /* snr offset */

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

  917.     if (baie) {

  918.         put_bits(&s->pb, 6, s->coarse_snr_offset);

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

  920.             put_bits(&s->pb, 4, s->fine_snr_offset[ch]);

  921.             put_bits(&s->pb, 3, s->fast_gain_code[ch]);

  922.         }

  923.     }

  924. 

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

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

  927. 

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

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

  930.        modify the output stream. */

  931. 

  932.     /* first pass: quantize */

  933.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  934.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  935. 

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

  937.         int b, c, e, v;

  938. 

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

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

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

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

  943.             switch(b) {

  944.             case 0:

  945.                 v = 0;

  946.                 break;

  947.             case 1:

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

  949.                 switch(mant1_cnt) {

  950.                 case 0:

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

  952.                     v = 9 * v;

  953.                     mant1_cnt = 1;

  954.                     break;

  955.                 case 1:

  956.                     *qmant1_ptr += 3 * v;

  957.                     mant1_cnt = 2;

  958.                     v = 128;

  959.                     break;

  960.                 default:

  961.                     *qmant1_ptr += v;

  962.                     mant1_cnt = 0;

  963.                     v = 128;

  964.                     break;

  965.                 }

  966.                 break;

  967.             case 2:

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

  969.                 switch(mant2_cnt) {

  970.                 case 0:

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

  972.                     v = 25 * v;

  973.                     mant2_cnt = 1;

  974.                     break;

  975.                 case 1:

  976.                     *qmant2_ptr += 5 * v;

  977.                     mant2_cnt = 2;

  978.                     v = 128;

  979.                     break;

  980.                 default:

  981.                     *qmant2_ptr += v;

  982.                     mant2_cnt = 0;

  983.                     v = 128;

  984.                     break;

  985.                 }

  986.                 break;

  987.             case 3:

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

  989.                 break;

  990.             case 4:

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

  992.                 switch(mant4_cnt) {

  993.                 case 0:

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

  995.                     v = 11 * v;

  996.                     mant4_cnt = 1;

  997.                     break;

  998.                 default:

  999.                     *qmant4_ptr += v;

  1000.                     mant4_cnt = 0;

  1001.                     v = 128;

  1002.                     break;

  1003.                 }

  1004.                 break;

  1005.             case 5:

  1006.                 v = sym_quant(c, e, 15);

  1007.                 break;

  1008.             case 14:

  1009.                 v = asym_quant(c, e, 14);

  1010.                 break;

  1011.             case 15:

  1012.                 v = asym_quant(c, e, 16);

  1013.                 break;

  1014.             default:

  1015.                 v = asym_quant(c, e, b - 1);

  1016.                 break;

  1017.             }

  1018.             qmant[ch][i] = v;

  1019.         }

  1020.     }

  1021. 

  1022.     /* second pass : output the values */

  1023.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1024.         int b, q;

  1025. 

  1026.         for(i=0;i<s->nb_coefs[ch];i++) {

  1027.             q = qmant[ch][i];

  1028.             b = bap[ch][i];

  1029.             switch(b) {

  1030.             case 0:

  1031.                 break;

  1032.             case 1:

  1033.                 if (q != 128)

  1034.                     put_bits(&s->pb, 5, q);

  1035.                 break;

  1036.             case 2:

  1037.                 if (q != 128)

  1038.                     put_bits(&s->pb, 7, q);

  1039.                 break;

  1040.             case 3:

  1041.                 put_bits(&s->pb, 3, q);

  1042.                 break;

  1043.             case 4:

  1044.                 if (q != 128)

  1045.                     put_bits(&s->pb, 7, q);

  1046.                 break;

  1047.             case 14:

  1048.                 put_bits(&s->pb, 14, q);

  1049.                 break;

  1050.             case 15:

  1051.                 put_bits(&s->pb, 16, q);

  1052.                 break;

  1053.             default:

  1054.                 put_bits(&s->pb, b - 1, q);

  1055.                 break;

  1056.             }

  1057.         }

  1058.     }

  1059. }

  1060. 

  1061. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1062. 

  1063. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1064. {

  1065.     unsigned int c;

  1066. 

  1067.     c = 0;

  1068.     while (a) {

  1069.         if (a & 1)

  1070.             c ^= b;

  1071.         a = a >> 1;

  1072.         b = b << 1;

  1073.         if (b & (1 << 16))

  1074.             b ^= poly;

  1075.     }

  1076.     return c;

  1077. }

  1078. 

  1079. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1080. {

  1081.     unsigned int r;

  1082.     r = 1;

  1083.     while (n) {

  1084.         if (n & 1)

  1085.             r = mul_poly(r, a, poly);

  1086.         a = mul_poly(a, a, poly);

  1087.         n >>= 1;

  1088.     }

  1089.     return r;

  1090. }

  1091. 

  1092. 

  1093. /* compute log2(max(abs(tab[]))) */

  1094. static int log2_tab(int16_t *tab, int n)

  1095. {

  1096.     int i, v;

  1097. 

  1098.     v = 0;

  1099.     for(i=0;i<n;i++) {

  1100.         v |= abs(tab[i]);

  1101.     }

  1102.     return av_log2(v);

  1103. }

  1104. 

  1105. static void lshift_tab(int16_t *tab, int n, int lshift)

  1106. {

  1107.     int i;

  1108. 

  1109.     if (lshift > 0) {

  1110.         for(i=0;i<n;i++) {

  1111.             tab[i] <<= lshift;

  1112.         }

  1113.     } else if (lshift < 0) {

  1114.         lshift = -lshift;

  1115.         for(i=0;i<n;i++) {

  1116.             tab[i] >>= lshift;

  1117.         }

  1118.     }

  1119. }

  1120. 

  1121. /* fill the end of the frame and compute the two crcs */

  1122. static int output_frame_end(AC3EncodeContext *s)

  1123. {

  1124.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1125.     uint8_t *frame;

  1126. 

  1127.     frame_size = s->frame_size; /* frame size in words */

  1128.     /* align to 8 bits */

  1129.     flush_put_bits(&s->pb);

  1130.     /* add zero bytes to reach the frame size */

  1131.     frame = s->pb.buf;

  1132.     n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;

  1133.     assert(n >= 0);

  1134.     if(n>0)

  1135.       memset(pbBufPtr(&s->pb), 0, n);

  1136. 

  1137.     /* Now we must compute both crcs : this is not so easy for crc1

  1138.        because it is at the beginning of the data... */

  1139.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1140.     crc1 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

  1141.                            frame + 4, 2 * frame_size_58 - 4));

  1142.     /* XXX: could precompute crc_inv */

  1143.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1144.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1145.     AV_WB16(frame+2,crc1);

  1146. 

  1147.     crc2 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

  1148.                            frame + 2 * frame_size_58,

  1149.                            (frame_size - frame_size_58) * 2 - 2));

  1150.     AV_WB16(frame+2*frame_size-2,crc2);

  1151. 

  1152.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1153.     return frame_size * 2;

  1154. }

  1155. 

  1156. static int AC3_encode_frame(AVCodecContext *avctx,

  1157.                             unsigned char *frame, int buf_size, void *data)

  1158. {

  1159.     AC3EncodeContext *s = avctx->priv_data;

  1160.     int16_t *samples = data;

  1161.     int i, j, k, v, ch;

  1162.     int16_t input_samples[N];

  1163.     int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1164.     uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1165.     uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

  1166.     uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1167.     uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1168.     int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

  1169.     int frame_bits;

  1170. 

  1171.     frame_bits = 0;

  1172.     for(ch=0;ch<s->nb_all_channels;ch++) {

  1173.         /* fixed mdct to the six sub blocks & exponent computation */

  1174.         for(i=0;i<NB_BLOCKS;i++) {

  1175.             int16_t *sptr;

  1176.             int sinc;

  1177. 

  1178.             /* compute input samples */

  1179.             memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(int16_t));

  1180.             sinc = s->nb_all_channels;

  1181.             sptr = samples + (sinc * (N/2) * i) + ch;

  1182.             for(j=0;j<N/2;j++) {

  1183.                 v = *sptr;

  1184.                 input_samples[j + N/2] = v;

  1185.                 s->last_samples[ch][j] = v;

  1186.                 sptr += sinc;

  1187.             }

  1188. 

  1189.             /* apply the MDCT window */

  1190.             for(j=0;j<N/2;j++) {

  1191.                 input_samples[j] = MUL16(input_samples[j],

  1192.                                          ff_ac3_window[j]) >> 15;

  1193.                 input_samples[N-j-1] = MUL16(input_samples[N-j-1],

  1194.                                              ff_ac3_window[j]) >> 15;

  1195.             }

  1196. 

  1197.             /* Normalize the samples to use the maximum available

  1198.                precision */

  1199.             v = 14 - log2_tab(input_samples, N);

  1200.             if (v < 0)

  1201.                 v = 0;

  1202.             exp_samples[i][ch] = v - 9;

  1203.             lshift_tab(input_samples, N, v);

  1204. 

  1205.             /* do the MDCT */

  1206.             mdct512(mdct_coef[i][ch], input_samples);

  1207. 

  1208.             /* compute "exponents". We take into account the

  1209.                normalization there */

  1210.             for(j=0;j<N/2;j++) {

  1211.                 int e;

  1212.                 v = abs(mdct_coef[i][ch][j]);

  1213.                 if (v == 0)

  1214.                     e = 24;

  1215.                 else {

  1216.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1217.                     if (e >= 24) {

  1218.                         e = 24;

  1219.                         mdct_coef[i][ch][j] = 0;

  1220.                     }

  1221.                 }

  1222.                 exp[i][ch][j] = e;

  1223.             }

  1224.         }

  1225. 

  1226.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1227. 

  1228.         /* compute the exponents as the decoder will see them. The

  1229.            EXP_REUSE case must be handled carefully : we select the

  1230.            min of the exponents */

  1231.         i = 0;

  1232.         while (i < NB_BLOCKS) {

  1233.             j = i + 1;

  1234.             while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1235.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1236.                 j++;

  1237.             }

  1238.             frame_bits += encode_exp(encoded_exp[i][ch],

  1239.                                      exp[i][ch], s->nb_coefs[ch],

  1240.                                      exp_strategy[i][ch]);

  1241.             /* copy encoded exponents for reuse case */

  1242.             for(k=i+1;k<j;k++) {

  1243.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch],

  1244.                        s->nb_coefs[ch] * sizeof(uint8_t));

  1245.             }

  1246.             i = j;

  1247.         }

  1248.     }

  1249. 

  1250.     /* adjust for fractional frame sizes */

  1251.     while(s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {

  1252.         s->bits_written -= s->bit_rate;

  1253.         s->samples_written -= s->sample_rate;

  1254.     }

  1255.     s->frame_size = s->frame_size_min + (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);

  1256.     s->bits_written += s->frame_size * 16;

  1257.     s->samples_written += AC3_FRAME_SIZE;

  1258. 

  1259.     compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

  1260.     /* everything is known... let's output the frame */

  1261.     output_frame_header(s, frame);

  1262. 

  1263.     for(i=0;i<NB_BLOCKS;i++) {

  1264.         output_audio_block(s, exp_strategy[i], encoded_exp[i],

  1265.                            bap[i], mdct_coef[i], exp_samples[i], i);

  1266.     }

  1267.     return output_frame_end(s);

  1268. }

  1269. 

  1270. static int AC3_encode_close(AVCodecContext *avctx)

  1271. {

  1272.     av_freep(&avctx->coded_frame);

  1273.     return 0;

  1274. }

  1275. 

  1276. #if 0

  1277. /*************************************************************************/

  1278. /* TEST */

  1279. 

  1280. #undef random

  1281. #define FN (N/4)

  1282. 

  1283. void fft_test(void)

  1284. {

  1285.     IComplex in[FN], in1[FN];

  1286.     int k, n, i;

  1287.     float sum_re, sum_im, a;

  1288. 

  1289.     /* FFT test */

  1290. 

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

  1292.         in[i].re = random() % 65535 - 32767;

  1293.         in[i].im = random() % 65535 - 32767;

  1294.         in1[i] = in[i];

  1295.     }

  1296.     fft(in, 7);

  1297. 

  1298.     /* do it by hand */

  1299.     for(k=0;k<FN;k++) {

  1300.         sum_re = 0;

  1301.         sum_im = 0;

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

  1303.             a = -2 * M_PI * (n * k) / FN;

  1304.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1305.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1306.         }

  1307.         printf("%3d: %6d,%6d %6.0f,%6.0f\n",

  1308.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);

  1309.     }

  1310. }

  1311. 

  1312. void mdct_test(void)

  1313. {

  1314.     int16_t input[N];

  1315.     int32_t output[N/2];

  1316.     float input1[N];

  1317.     float output1[N/2];

  1318.     float s, a, err, e, emax;

  1319.     int i, k, n;

  1320. 

  1321.     for(i=0;i<N;i++) {

  1322.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1323.         input1[i] = input[i];

  1324.     }

  1325. 

  1326.     mdct512(output, input);

  1327. 

  1328.     /* do it by hand */

  1329.     for(k=0;k<N/2;k++) {

  1330.         s = 0;

  1331.         for(n=0;n<N;n++) {

  1332.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1333.             s += input1[n] * cos(a);

  1334.         }

  1335.         output1[k] = -2 * s / N;

  1336.     }

  1337. 

  1338.     err = 0;

  1339.     emax = 0;

  1340.     for(i=0;i<N/2;i++) {

  1341.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1342.         e = output[i] - output1[i];

  1343.         if (e > emax)

  1344.             emax = e;

  1345.         err += e * e;

  1346.     }

  1347.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1348. }

  1349. 

  1350. void test_ac3(void)

  1351. {

  1352.     AC3EncodeContext ctx;

  1353.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1354.     short samples[AC3_FRAME_SIZE];

  1355.     int ret, i;

  1356. 

  1357.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1358. 

  1359.     fft_test();

  1360.     mdct_test();

  1361. 

  1362.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1363.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1364.     ret = AC3_encode_frame(&ctx, frame, samples);

  1365.     printf("ret=%d\n", ret);

  1366. }

  1367. #endif

  1368. 

  1369. AVCodec ac3_encoder = {

  1370.     "ac3",

  1371.     CODEC_TYPE_AUDIO,

  1372.     CODEC_ID_AC3,

  1373.     sizeof(AC3EncodeContext),

  1374.     AC3_encode_init,

  1375.     AC3_encode_frame,

  1376.     AC3_encode_close,

  1377.     NULL,

  1378. };