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FFmpeg/libavcodec/ac3enc.c

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  1. /*

  2.  * The simplest AC-3 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 libavcodec/ac3enc.c

  24.  * The simplest AC-3 encoder.

  25.  */

  26. //#define DEBUG

  27. //#define DEBUG_BITALLOC

  28. #include "libavutil/crc.h"

  29. #include "avcodec.h"

  30. #include "get_bits.h" // for ff_reverse

  31. #include "put_bits.h"

  32. #include "ac3.h"

  33. #include "audioconvert.h"

  34. 

  35. typedef struct AC3EncodeContext {

  36.     PutBitContext pb;

  37.     int nb_channels;

  38.     int nb_all_channels;

  39.     int lfe_channel;

  40.     const uint8_t *channel_map;

  41.     int bit_rate;

  42.     unsigned int sample_rate;

  43.     unsigned int bitstream_id;

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

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

  46.     unsigned int bits_written;

  47.     unsigned int samples_written;

  48.     int sr_shift;

  49.     unsigned int frame_size_code;

  50.     unsigned int sr_code; /* frequency */

  51.     unsigned int channel_mode;

  52.     int lfe;

  53.     unsigned int bitstream_mode;

  54.     short last_samples[AC3_MAX_CHANNELS][256];

  55.     unsigned int chbwcod[AC3_MAX_CHANNELS];

  56.     int nb_coefs[AC3_MAX_CHANNELS];

  57. 

  58.     /* bitrate allocation control */

  59.     int slow_gain_code, slow_decay_code, fast_decay_code, db_per_bit_code, floor_code;

  60.     AC3BitAllocParameters bit_alloc;

  61.     int coarse_snr_offset;

  62.     int fast_gain_code[AC3_MAX_CHANNELS];

  63.     int fine_snr_offset[AC3_MAX_CHANNELS];

  64.     /* mantissa encoding */

  65.     int mant1_cnt, mant2_cnt, mant4_cnt;

  66. } AC3EncodeContext;

  67. 

  68. static int16_t costab[64];

  69. static int16_t sintab[64];

  70. static int16_t xcos1[128];

  71. static int16_t xsin1[128];

  72. 

  73. #define MDCT_NBITS 9

  74. #define N         (1 << MDCT_NBITS)

  75. 

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

  77. #define EXP_DIFF_THRESHOLD 1000

  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 av_cold void fft_init(int ln)

  95. {

  96.     int i, 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. 

  108. /* butter fly op */

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

  110. {\

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

  112.   bx=pre1;\

  113.   by=pim1;\

  114.   ax=qre1;\

  115.   ay=qim1;\

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

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

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

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

  120. }

  121. 

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

  123. {\

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

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

  126. }

  127. 

  128. 

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

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

  131. {

  132.     int        j, l, np, np2;

  133.     int        nblocks, nloops;

  134.     register IComplex *p,*q;

  135.     int tmp_re, tmp_im;

  136. 

  137.     np = 1 << ln;

  138. 

  139.     /* reverse */

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

  141.         int k = ff_reverse[j] >> (8 - ln);

  142.         if (k < j)

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

  144.     }

  145. 

  146.     /* pass 0 */

  147. 

  148.     p=&z[0];

  149.     j=(np >> 1);

  150.     do {

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

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

  153.         p+=2;

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

  155. 

  156.     /* pass 1 */

  157. 

  158.     p=&z[0];

  159.     j=np >> 2;

  160.     do {

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

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

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

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

  165.         p+=4;

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

  167. 

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

  169. 

  170.     nblocks = np >> 3;

  171.     nloops = 1 << 2;

  172.     np2 = np >> 1;

  173.     do {

  174.         p = z;

  175.         q = z + nloops;

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

  177. 

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

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

  180. 

  181.             p++;

  182.             q++;

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

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

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

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

  187.                 p++;

  188.                 q++;

  189.             }

  190.             p += nloops;

  191.             q += nloops;

  192.         }

  193.         nblocks = nblocks >> 1;

  194.         nloops = nloops << 1;

  195.     } while (nblocks != 0);

  196. }

  197. 

  198. /* do a 512 point mdct */

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

  200. {

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

  202.     int16_t rot[N];

  203.     IComplex x[N/4];

  204. 

  205.     /* shift to simplify computations */

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

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

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

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

  210. 

  211.     /* pre rotation */

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

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

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

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

  216.     }

  217. 

  218.     fft(x, MDCT_NBITS - 2);

  219. 

  220.     /* post rotation */

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

  222.         re = x[i].re;

  223.         im = x[i].im;

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

  225.         out[2*i] = im1;

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

  227.     }

  228. }

  229. 

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

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

  232. {

  233.     int sum, i;

  234.     sum = 0;

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

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

  237.     }

  238.     return sum;

  239. }

  240. 

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

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

  243.                                  int ch, int is_lfe)

  244. {

  245.     int i, j;

  246.     int exp_diff;

  247. 

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

  249.        reused in the next frame */

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

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

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

  253. #ifdef DEBUG

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

  255. #endif

  256.         if (exp_diff > EXP_DIFF_THRESHOLD)

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

  258.         else

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

  260.     }

  261.     if (is_lfe)

  262.         return;

  263. 

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

  265.        recoded, we use a coarse encoding */

  266.     i = 0;

  267.     while (i < NB_BLOCKS) {

  268.         j = i + 1;

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

  270.             j++;

  271.         switch(j - i) {

  272.         case 1:

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

  274.             break;

  275.         case 2:

  276.         case 3:

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

  278.             break;

  279.         default:

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

  281.             break;

  282.         }

  283.         i = j;

  284.     }

  285. }

  286. 

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

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

  289. {

  290.     int i;

  291. 

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

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

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

  295.     }

  296. }

  297. 

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

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

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

  301.                       uint8_t exp[N/2],

  302.                       int nb_exps,

  303.                       int exp_strategy)

  304. {

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

  306.     uint8_t exp1[N/2];

  307. 

  308.     switch(exp_strategy) {

  309.     case EXP_D15:

  310.         group_size = 1;

  311.         break;

  312.     case EXP_D25:

  313.         group_size = 2;

  314.         break;

  315.     default:

  316.     case EXP_D45:

  317.         group_size = 4;

  318.         break;

  319.     }

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

  321. 

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

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

  324.     k = 1;

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

  326.         exp_min = exp[k];

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

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

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

  330.                 exp_min = exp[k+j];

  331.         }

  332.         exp1[i] = exp_min;

  333.         k += group_size;

  334.     }

  335. 

  336.     /* constraint for DC exponent */

  337.     if (exp1[0] > 15)

  338.         exp1[0] = 15;

  339. 

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

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

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

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

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

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

  346. 

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

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

  349.     k = 1;

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

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

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

  353.         }

  354.         k += group_size;

  355.     }

  356. 

  357. #if defined(DEBUG)

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

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

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

  361.     }

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

  363. #endif

  364. 

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

  366. }

  367. 

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

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

  370. {

  371.     int bits, mant, i;

  372. 

  373.     bits = 0;

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

  375.         mant = m[i];

  376.         switch(mant) {

  377.         case 0:

  378.             /* nothing */

  379.             break;

  380.         case 1:

  381.             /* 3 mantissa in 5 bits */

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

  383.                 bits += 5;

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

  385.                 s->mant1_cnt = 0;

  386.             break;

  387.         case 2:

  388.             /* 3 mantissa in 7 bits */

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

  390.                 bits += 7;

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

  392.                 s->mant2_cnt = 0;

  393.             break;

  394.         case 3:

  395.             bits += 3;

  396.             break;

  397.         case 4:

  398.             /* 2 mantissa in 7 bits */

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

  400.                 bits += 7;

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

  402.                 s->mant4_cnt = 0;

  403.             break;

  404.         case 14:

  405.             bits += 14;

  406.             break;

  407.         case 15:

  408.             bits += 16;

  409.             break;

  410.         default:

  411.             bits += mant - 1;

  412.             break;

  413.         }

  414.     }

  415.     return bits;

  416. }

  417. 

  418. 

  419. static void bit_alloc_masking(AC3EncodeContext *s,

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

  421.                               uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

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

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

  424. {

  425.     int blk, ch;

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

  427. 

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

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

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

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

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

  433.             } else {

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

  435.                                           s->nb_coefs[ch],

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

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

  438.                                            0, s->nb_coefs[ch],

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

  440.                                            ch == s->lfe_channel,

  441.                                            DBA_NONE, 0, NULL, NULL, NULL,

  442.                                            mask[blk][ch]);

  443.             }

  444.         }

  445.     }

  446. }

  447. 

  448. static int bit_alloc(AC3EncodeContext *s,

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

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

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

  452.                      int frame_bits, int coarse_snr_offset, int fine_snr_offset)

  453. {

  454.     int i, ch;

  455.     int snr_offset;

  456. 

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

  458. 

  459.     /* compute size */

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

  461.         s->mant1_cnt = 0;

  462.         s->mant2_cnt = 0;

  463.         s->mant4_cnt = 0;

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

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

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

  467.                                       s->bit_alloc.floor, ff_ac3_bap_tab,

  468.                                       bap[i][ch]);

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

  470.                                                  s->nb_coefs[ch]);

  471.         }

  472.     }

  473. #if 0

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

  475.            coarse_snr_offset, fine_snr_offset, frame_bits,

  476.            16 * s->frame_size - ((frame_bits + 7) & ~7));

  477. #endif

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

  479. }

  480. 

  481. #define SNR_INC1 4

  482. 

  483. static int compute_bit_allocation(AC3EncodeContext *s,

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

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

  486.                                   uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  487.                                   int frame_bits)

  488. {

  489.     int i, ch;

  490.     int coarse_snr_offset, fine_snr_offset;

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

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

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

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

  495. 

  496.     /* init default parameters */

  497.     s->slow_decay_code = 2;

  498.     s->fast_decay_code = 1;

  499.     s->slow_gain_code = 1;

  500.     s->db_per_bit_code = 2;

  501.     s->floor_code = 4;

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

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

  504. 

  505.     /* compute real values */

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

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

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

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

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

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

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

  513. 

  514.     /* header size */

  515.     frame_bits += 65;

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

  517.     //    frame_bits += 2;

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

  519. 

  520.     /* audio blocks */

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

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

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

  524.             frame_bits++; /* rematstr */

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

  526.         }

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

  528.         if (s->lfe)

  529.             frame_bits++; /* lfeexpstr */

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

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

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

  533.         }

  534.         frame_bits++; /* baie */

  535.         frame_bits++; /* snr */

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

  537.     }

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

  539.     /* bit alloc info */

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

  541.     /* csnroffset[6] */

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

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

  544. 

  545.     /* auxdatae, crcrsv */

  546.     frame_bits += 2;

  547. 

  548.     /* CRC */

  549.     frame_bits += 16;

  550. 

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

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

  553. 

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

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

  556. 

  557.     coarse_snr_offset = s->coarse_snr_offset;

  558.     while (coarse_snr_offset >= 0 &&

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

  560.         coarse_snr_offset -= SNR_INC1;

  561.     if (coarse_snr_offset < 0) {

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

  563.         return -1;

  564.     }

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

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

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

  568.         coarse_snr_offset += SNR_INC1;

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

  570.     }

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

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

  573.         coarse_snr_offset++;

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

  575.     }

  576. 

  577.     fine_snr_offset = 0;

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

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

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

  581.         fine_snr_offset += SNR_INC1;

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

  583.     }

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

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

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

  587.         fine_snr_offset++;

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

  589.     }

  590. 

  591.     s->coarse_snr_offset = coarse_snr_offset;

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

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

  594. #if defined(DEBUG_BITALLOC)

  595.     {

  596.         int j;

  597. 

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

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

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

  601.                 printf("bap=");

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

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

  604.                 }

  605.                 printf("\n");

  606.             }

  607.         }

  608.     }

  609. #endif

  610.     return 0;

  611. }

  612. 

  613. static av_cold int set_channel_info(AC3EncodeContext *s, int channels,

  614.                                     int64_t *channel_layout)

  615. {

  616.     int ch_layout;

  617. 

  618.     if (channels < 1 || channels > AC3_MAX_CHANNELS)

  619.         return -1;

  620.     if ((uint64_t)*channel_layout > 0x7FF)

  621.         return -1;

  622.     ch_layout = *channel_layout;

  623.     if (!ch_layout)

  624.         ch_layout = avcodec_guess_channel_layout(channels, CODEC_ID_AC3, NULL);

  625.     if (avcodec_channel_layout_num_channels(ch_layout) != channels)

  626.         return -1;

  627. 

  628.     s->lfe = !!(ch_layout & CH_LOW_FREQUENCY);

  629.     s->nb_all_channels = channels;

  630.     s->nb_channels = channels - s->lfe;

  631.     s->lfe_channel = s->lfe ? s->nb_channels : -1;

  632.     if (s->lfe)

  633.         ch_layout -= CH_LOW_FREQUENCY;

  634. 

  635.     switch (ch_layout) {

  636.     case CH_LAYOUT_MONO:           s->channel_mode = AC3_CHMODE_MONO;   break;

  637.     case CH_LAYOUT_STEREO:         s->channel_mode = AC3_CHMODE_STEREO; break;

  638.     case CH_LAYOUT_SURROUND:       s->channel_mode = AC3_CHMODE_3F;     break;

  639.     case CH_LAYOUT_2_1:            s->channel_mode = AC3_CHMODE_2F1R;   break;

  640.     case CH_LAYOUT_4POINT0:        s->channel_mode = AC3_CHMODE_3F1R;   break;

  641.     case CH_LAYOUT_QUAD:

  642.     case CH_LAYOUT_2_2:            s->channel_mode = AC3_CHMODE_2F2R;   break;

  643.     case CH_LAYOUT_5POINT0:

  644.     case CH_LAYOUT_5POINT0_BACK:   s->channel_mode = AC3_CHMODE_3F2R;   break;

  645.     default:

  646.         return -1;

  647.     }

  648. 

  649.     s->channel_map = ff_ac3_enc_channel_map[s->channel_mode][s->lfe];

  650.     *channel_layout = ch_layout;

  651.     if (s->lfe)

  652.         *channel_layout |= CH_LOW_FREQUENCY;

  653. 

  654.     return 0;

  655. }

  656. 

  657. static av_cold int AC3_encode_init(AVCodecContext *avctx)

  658. {

  659.     int freq = avctx->sample_rate;

  660.     int bitrate = avctx->bit_rate;

  661.     AC3EncodeContext *s = avctx->priv_data;

  662.     int i, j, ch;

  663.     float alpha;

  664.     int bw_code;

  665. 

  666.     avctx->frame_size = AC3_FRAME_SIZE;

  667. 

  668.     ac3_common_init();

  669. 

  670.     if (!avctx->channel_layout) {

  671.         av_log(avctx, AV_LOG_WARNING, "No channel layout specified. The "

  672.                                       "encoder will guess the layout, but it "

  673.                                       "might be incorrect.\n");

  674.     }

  675.     if (set_channel_info(s, avctx->channels, &avctx->channel_layout)) {

  676.         av_log(avctx, AV_LOG_ERROR, "invalid channel layout\n");

  677.         return -1;

  678.     }

  679. 

  680.     /* frequency */

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

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

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

  684.                 goto found;

  685.     }

  686.     return -1;

  687.  found:

  688.     s->sample_rate = freq;

  689.     s->sr_shift = i;

  690.     s->sr_code = j;

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

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

  693. 

  694.     /* bitrate & frame size */

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

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

  697.             break;

  698.     }

  699.     if (i == 19)

  700.         return -1;

  701.     s->bit_rate = bitrate;

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

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

  704.     s->bits_written = 0;

  705.     s->samples_written = 0;

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

  707. 

  708.     /* bit allocation init */

  709.     if(avctx->cutoff) {

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

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

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

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

  714.     } else {

  715.         /* use default bandwidth setting */

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

  717.            size, so that we avoid annoying high frequency artifacts */

  718.         bw_code = 50;

  719.     }

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

  721.         /* bandwidth for each channel */

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

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

  724.     }

  725.     if (s->lfe) {

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

  727.     }

  728.     /* initial snr offset */

  729.     s->coarse_snr_offset = 40;

  730. 

  731.     /* mdct init */

  732.     fft_init(MDCT_NBITS - 2);

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

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

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

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

  737.     }

  738. 

  739.     avctx->coded_frame= avcodec_alloc_frame();

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

  741. 

  742.     return 0;

  743. }

  744. 

  745. /* output the AC-3 frame header */

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

  747. {

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

  749. 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  773. }

  774. 

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

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

  777. {

  778.     int v;

  779. 

  780.     if (c >= 0) {

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

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

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

  784.     } else {

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

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

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

  788.     }

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

  790.     return v;

  791. }

  792. 

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

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

  795. {

  796.     int lshift, m, v;

  797. 

  798.     lshift = e + qbits - 24;

  799.     if (lshift >= 0)

  800.         v = c << lshift;

  801.     else

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

  803.     /* rounding */

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

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

  806.     if (v >= m)

  807.         v = m - 1;

  808.     assert(v >= -m);

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

  810. }

  811. 

  812. /* Output one audio block. There are NB_BLOCKS audio blocks in one AC-3

  813.    frame */

  814. static void output_audio_block(AC3EncodeContext *s,

  815.                                uint8_t exp_strategy[AC3_MAX_CHANNELS],

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

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

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

  819.                                int8_t global_exp[AC3_MAX_CHANNELS],

  820.                                int block_num)

  821. {

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

  823.     uint8_t *p;

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

  825.     int exp0, exp1;

  826.     int mant1_cnt, mant2_cnt, mant4_cnt;

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

  828.     int delta0, delta1, delta2;

  829. 

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

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

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

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

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

  835.     if (block_num == 0) {

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

  837.            waste of bit :-) */

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

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

  840.     } else {

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

  842.     }

  843. 

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

  845.       {

  846.         if(block_num==0)

  847.           {

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

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

  850. 

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

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

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

  854.           }

  855.         else

  856.           {

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

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

  859.           }

  860.       }

  861. 

  862. #if defined(DEBUG)

  863.     {

  864.       static int count = 0;

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

  866.     }

  867. #endif

  868.     /* exponent strategy */

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

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

  871.     }

  872. 

  873.     if (s->lfe) {

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

  875.     }

  876. 

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

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

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

  880.     }

  881. 

  882.     /* exponents */

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

  884.         switch(exp_strategy[ch]) {

  885.         case EXP_REUSE:

  886.             continue;

  887.         case EXP_D15:

  888.             group_size = 1;

  889.             break;

  890.         case EXP_D25:

  891.             group_size = 2;

  892.             break;

  893.         default:

  894.         case EXP_D45:

  895.             group_size = 4;

  896.             break;

  897.         }

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

  899.         p = encoded_exp[ch];

  900. 

  901.         /* first exponent */

  902.         exp1 = *p++;

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

  904. 

  905.         /* next ones are delta encoded */

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

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

  908.             exp0 = exp1;

  909.             exp1 = p[0];

  910.             p += group_size;

  911.             delta0 = exp1 - exp0 + 2;

  912. 

  913.             exp0 = exp1;

  914.             exp1 = p[0];

  915.             p += group_size;

  916.             delta1 = exp1 - exp0 + 2;

  917. 

  918.             exp0 = exp1;

  919.             exp1 = p[0];

  920.             p += group_size;

  921.             delta2 = exp1 - exp0 + 2;

  922. 

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

  924.         }

  925. 

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

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

  928.     }

  929. 

  930.     /* bit allocation info */

  931.     baie = (block_num == 0);

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

  933.     if (baie) {

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

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

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

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

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

  939.     }

  940. 

  941.     /* snr offset */

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

  943.     if (baie) {

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

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

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

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

  948.         }

  949.     }

  950. 

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

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

  953. 

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

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

  956.        modify the output stream. */

  957. 

  958.     /* first pass: quantize */

  959.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  960.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  961. 

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

  963.         int b, c, e, v;

  964. 

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

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

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

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

  969.             switch(b) {

  970.             case 0:

  971.                 v = 0;

  972.                 break;

  973.             case 1:

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

  975.                 switch(mant1_cnt) {

  976.                 case 0:

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

  978.                     v = 9 * v;

  979.                     mant1_cnt = 1;

  980.                     break;

  981.                 case 1:

  982.                     *qmant1_ptr += 3 * v;

  983.                     mant1_cnt = 2;

  984.                     v = 128;

  985.                     break;

  986.                 default:

  987.                     *qmant1_ptr += v;

  988.                     mant1_cnt = 0;

  989.                     v = 128;

  990.                     break;

  991.                 }

  992.                 break;

  993.             case 2:

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

  995.                 switch(mant2_cnt) {

  996.                 case 0:

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

  998.                     v = 25 * v;

  999.                     mant2_cnt = 1;

  1000.                     break;

  1001.                 case 1:

  1002.                     *qmant2_ptr += 5 * v;

  1003.                     mant2_cnt = 2;

  1004.                     v = 128;

  1005.                     break;

  1006.                 default:

  1007.                     *qmant2_ptr += v;

  1008.                     mant2_cnt = 0;

  1009.                     v = 128;

  1010.                     break;

  1011.                 }

  1012.                 break;

  1013.             case 3:

  1014.                 v = sym_quant(c, e, 7);

  1015.                 break;

  1016.             case 4:

  1017.                 v = sym_quant(c, e, 11);

  1018.                 switch(mant4_cnt) {

  1019.                 case 0:

  1020.                     qmant4_ptr = &qmant[ch][i];

  1021.                     v = 11 * v;

  1022.                     mant4_cnt = 1;

  1023.                     break;

  1024.                 default:

  1025.                     *qmant4_ptr += v;

  1026.                     mant4_cnt = 0;

  1027.                     v = 128;

  1028.                     break;

  1029.                 }

  1030.                 break;

  1031.             case 5:

  1032.                 v = sym_quant(c, e, 15);

  1033.                 break;

  1034.             case 14:

  1035.                 v = asym_quant(c, e, 14);

  1036.                 break;

  1037.             case 15:

  1038.                 v = asym_quant(c, e, 16);

  1039.                 break;

  1040.             default:

  1041.                 v = asym_quant(c, e, b - 1);

  1042.                 break;

  1043.             }

  1044.             qmant[ch][i] = v;

  1045.         }

  1046.     }

  1047. 

  1048.     /* second pass : output the values */

  1049.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1050.         int b, q;

  1051. 

  1052.         for(i=0;i<s->nb_coefs[ch];i++) {

  1053.             q = qmant[ch][i];

  1054.             b = bap[ch][i];

  1055.             switch(b) {

  1056.             case 0:

  1057.                 break;

  1058.             case 1:

  1059.                 if (q != 128)

  1060.                     put_bits(&s->pb, 5, q);

  1061.                 break;

  1062.             case 2:

  1063.                 if (q != 128)

  1064.                     put_bits(&s->pb, 7, q);

  1065.                 break;

  1066.             case 3:

  1067.                 put_bits(&s->pb, 3, q);

  1068.                 break;

  1069.             case 4:

  1070.                 if (q != 128)

  1071.                     put_bits(&s->pb, 7, q);

  1072.                 break;

  1073.             case 14:

  1074.                 put_bits(&s->pb, 14, q);

  1075.                 break;

  1076.             case 15:

  1077.                 put_bits(&s->pb, 16, q);

  1078.                 break;

  1079.             default:

  1080.                 put_bits(&s->pb, b - 1, q);

  1081.                 break;

  1082.             }

  1083.         }

  1084.     }

  1085. }

  1086. 

  1087. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1088. 

  1089. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1090. {

  1091.     unsigned int c;

  1092. 

  1093.     c = 0;

  1094.     while (a) {

  1095.         if (a & 1)

  1096.             c ^= b;

  1097.         a = a >> 1;

  1098.         b = b << 1;

  1099.         if (b & (1 << 16))

  1100.             b ^= poly;

  1101.     }

  1102.     return c;

  1103. }

  1104. 

  1105. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1106. {

  1107.     unsigned int r;

  1108.     r = 1;

  1109.     while (n) {

  1110.         if (n & 1)

  1111.             r = mul_poly(r, a, poly);

  1112.         a = mul_poly(a, a, poly);

  1113.         n >>= 1;

  1114.     }

  1115.     return r;

  1116. }

  1117. 

  1118. 

  1119. /* compute log2(max(abs(tab[]))) */

  1120. static int log2_tab(int16_t *tab, int n)

  1121. {

  1122.     int i, v;

  1123. 

  1124.     v = 0;

  1125.     for(i=0;i<n;i++) {

  1126.         v |= abs(tab[i]);

  1127.     }

  1128.     return av_log2(v);

  1129. }

  1130. 

  1131. static void lshift_tab(int16_t *tab, int n, int lshift)

  1132. {

  1133.     int i;

  1134. 

  1135.     if (lshift > 0) {

  1136.         for(i=0;i<n;i++) {

  1137.             tab[i] <<= lshift;

  1138.         }

  1139.     } else if (lshift < 0) {

  1140.         lshift = -lshift;

  1141.         for(i=0;i<n;i++) {

  1142.             tab[i] >>= lshift;

  1143.         }

  1144.     }

  1145. }

  1146. 

  1147. /* fill the end of the frame and compute the two crcs */

  1148. static int output_frame_end(AC3EncodeContext *s)

  1149. {

  1150.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1151.     uint8_t *frame;

  1152. 

  1153.     frame_size = s->frame_size; /* frame size in words */

  1154.     /* align to 8 bits */

  1155.     flush_put_bits(&s->pb);

  1156.     /* add zero bytes to reach the frame size */

  1157.     frame = s->pb.buf;

  1158.     n = 2 * s->frame_size - (put_bits_ptr(&s->pb) - frame) - 2;

  1159.     assert(n >= 0);

  1160.     if(n>0)

  1161.       memset(put_bits_ptr(&s->pb), 0, n);

  1162. 

  1163.     /* Now we must compute both crcs : this is not so easy for crc1

  1164.        because it is at the beginning of the data... */

  1165.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1166.     crc1 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

  1167.                            frame + 4, 2 * frame_size_58 - 4));

  1168.     /* XXX: could precompute crc_inv */

  1169.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1170.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1171.     AV_WB16(frame+2,crc1);

  1172. 

  1173.     crc2 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

  1174.                            frame + 2 * frame_size_58,

  1175.                            (frame_size - frame_size_58) * 2 - 2));

  1176.     AV_WB16(frame+2*frame_size-2,crc2);

  1177. 

  1178.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1179.     return frame_size * 2;

  1180. }

  1181. 

  1182. static int AC3_encode_frame(AVCodecContext *avctx,

  1183.                             unsigned char *frame, int buf_size, void *data)

  1184. {

  1185.     AC3EncodeContext *s = avctx->priv_data;

  1186.     int16_t *samples = data;

  1187.     int i, j, k, v, ch;

  1188.     int16_t input_samples[N];

  1189.     int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1190.     uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1191.     uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

  1192.     uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1193.     uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1194.     int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

  1195.     int frame_bits;

  1196. 

  1197.     frame_bits = 0;

  1198.     for(ch=0;ch<s->nb_all_channels;ch++) {

  1199.         int ich = s->channel_map[ch];

  1200.         /* fixed mdct to the six sub blocks & exponent computation */

  1201.         for(i=0;i<NB_BLOCKS;i++) {

  1202.             int16_t *sptr;

  1203.             int sinc;

  1204. 

  1205.             /* compute input samples */

  1206.             memcpy(input_samples, s->last_samples[ich], N/2 * sizeof(int16_t));

  1207.             sinc = s->nb_all_channels;

  1208.             sptr = samples + (sinc * (N/2) * i) + ich;

  1209.             for(j=0;j<N/2;j++) {

  1210.                 v = *sptr;

  1211.                 input_samples[j + N/2] = v;

  1212.                 s->last_samples[ich][j] = v;

  1213.                 sptr += sinc;

  1214.             }

  1215. 

  1216.             /* apply the MDCT window */

  1217.             for(j=0;j<N/2;j++) {

  1218.                 input_samples[j] = MUL16(input_samples[j],

  1219.                                          ff_ac3_window[j]) >> 15;

  1220.                 input_samples[N-j-1] = MUL16(input_samples[N-j-1],

  1221.                                              ff_ac3_window[j]) >> 15;

  1222.             }

  1223. 

  1224.             /* Normalize the samples to use the maximum available

  1225.                precision */

  1226.             v = 14 - log2_tab(input_samples, N);

  1227.             if (v < 0)

  1228.                 v = 0;

  1229.             exp_samples[i][ch] = v - 9;

  1230.             lshift_tab(input_samples, N, v);

  1231. 

  1232.             /* do the MDCT */

  1233.             mdct512(mdct_coef[i][ch], input_samples);

  1234. 

  1235.             /* compute "exponents". We take into account the

  1236.                normalization there */

  1237.             for(j=0;j<N/2;j++) {

  1238.                 int e;

  1239.                 v = abs(mdct_coef[i][ch][j]);

  1240.                 if (v == 0)

  1241.                     e = 24;

  1242.                 else {

  1243.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1244.                     if (e >= 24) {

  1245.                         e = 24;

  1246.                         mdct_coef[i][ch][j] = 0;

  1247.                     }

  1248.                 }

  1249.                 exp[i][ch][j] = e;

  1250.             }

  1251.         }

  1252. 

  1253.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1254. 

  1255.         /* compute the exponents as the decoder will see them. The

  1256.            EXP_REUSE case must be handled carefully : we select the

  1257.            min of the exponents */

  1258.         i = 0;

  1259.         while (i < NB_BLOCKS) {

  1260.             j = i + 1;

  1261.             while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1262.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1263.                 j++;

  1264.             }

  1265.             frame_bits += encode_exp(encoded_exp[i][ch],

  1266.                                      exp[i][ch], s->nb_coefs[ch],

  1267.                                      exp_strategy[i][ch]);

  1268.             /* copy encoded exponents for reuse case */

  1269.             for(k=i+1;k<j;k++) {

  1270.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch],

  1271.                        s->nb_coefs[ch] * sizeof(uint8_t));

  1272.             }

  1273.             i = j;

  1274.         }

  1275.     }

  1276. 

  1277.     /* adjust for fractional frame sizes */

  1278.     while(s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {

  1279.         s->bits_written -= s->bit_rate;

  1280.         s->samples_written -= s->sample_rate;

  1281.     }

  1282.     s->frame_size = s->frame_size_min + (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);

  1283.     s->bits_written += s->frame_size * 16;

  1284.     s->samples_written += AC3_FRAME_SIZE;

  1285. 

  1286.     compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

  1287.     /* everything is known... let's output the frame */

  1288.     output_frame_header(s, frame);

  1289. 

  1290.     for(i=0;i<NB_BLOCKS;i++) {

  1291.         output_audio_block(s, exp_strategy[i], encoded_exp[i],

  1292.                            bap[i], mdct_coef[i], exp_samples[i], i);

  1293.     }

  1294.     return output_frame_end(s);

  1295. }

  1296. 

  1297. static av_cold int AC3_encode_close(AVCodecContext *avctx)

  1298. {

  1299.     av_freep(&avctx->coded_frame);

  1300.     return 0;

  1301. }

  1302. 

  1303. #if 0

  1304. /*************************************************************************/

  1305. /* TEST */

  1306. 

  1307. #undef random

  1308. #define FN (N/4)

  1309. 

  1310. void fft_test(void)

  1311. {

  1312.     IComplex in[FN], in1[FN];

  1313.     int k, n, i;

  1314.     float sum_re, sum_im, a;

  1315. 

  1316.     /* FFT test */

  1317. 

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

  1319.         in[i].re = random() % 65535 - 32767;

  1320.         in[i].im = random() % 65535 - 32767;

  1321.         in1[i] = in[i];

  1322.     }

  1323.     fft(in, 7);

  1324. 

  1325.     /* do it by hand */

  1326.     for(k=0;k<FN;k++) {

  1327.         sum_re = 0;

  1328.         sum_im = 0;

  1329.         for(n=0;n<FN;n++) {

  1330.             a = -2 * M_PI * (n * k) / FN;

  1331.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1332.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1333.         }

  1334.         printf("%3d: %6d,%6d %6.0f,%6.0f\n",

  1335.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);

  1336.     }

  1337. }

  1338. 

  1339. void mdct_test(void)

  1340. {

  1341.     int16_t input[N];

  1342.     int32_t output[N/2];

  1343.     float input1[N];

  1344.     float output1[N/2];

  1345.     float s, a, err, e, emax;

  1346.     int i, k, n;

  1347. 

  1348.     for(i=0;i<N;i++) {

  1349.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1350.         input1[i] = input[i];

  1351.     }

  1352. 

  1353.     mdct512(output, input);

  1354. 

  1355.     /* do it by hand */

  1356.     for(k=0;k<N/2;k++) {

  1357.         s = 0;

  1358.         for(n=0;n<N;n++) {

  1359.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1360.             s += input1[n] * cos(a);

  1361.         }

  1362.         output1[k] = -2 * s / N;

  1363.     }

  1364. 

  1365.     err = 0;

  1366.     emax = 0;

  1367.     for(i=0;i<N/2;i++) {

  1368.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1369.         e = output[i] - output1[i];

  1370.         if (e > emax)

  1371.             emax = e;

  1372.         err += e * e;

  1373.     }

  1374.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1375. }

  1376. 

  1377. void test_ac3(void)

  1378. {

  1379.     AC3EncodeContext ctx;

  1380.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1381.     short samples[AC3_FRAME_SIZE];

  1382.     int ret, i;

  1383. 

  1384.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1385. 

  1386.     fft_test();

  1387.     mdct_test();

  1388. 

  1389.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1390.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1391.     ret = AC3_encode_frame(&ctx, frame, samples);

  1392.     printf("ret=%d\n", ret);

  1393. }

  1394. #endif

  1395. 

  1396. AVCodec ac3_encoder = {

  1397.     "ac3",

  1398.     CODEC_TYPE_AUDIO,

  1399.     CODEC_ID_AC3,

  1400.     sizeof(AC3EncodeContext),

  1401.     AC3_encode_init,

  1402.     AC3_encode_frame,

  1403.     AC3_encode_close,

  1404.     NULL,

  1405.     .sample_fmts = (enum SampleFormat[]){SAMPLE_FMT_S16,SAMPLE_FMT_NONE},

  1406.     .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),

  1407.     .channel_layouts = (int64_t[]){

  1408.         CH_LAYOUT_MONO,

  1409.         CH_LAYOUT_STEREO,

  1410.         CH_LAYOUT_2_1,

  1411.         CH_LAYOUT_SURROUND,

  1412.         CH_LAYOUT_2_2,

  1413.         CH_LAYOUT_QUAD,

  1414.         CH_LAYOUT_4POINT0,

  1415.         CH_LAYOUT_5POINT0,

  1416.         CH_LAYOUT_5POINT0_BACK,

  1417.        (CH_LAYOUT_MONO     | CH_LOW_FREQUENCY),

  1418.        (CH_LAYOUT_STEREO   | CH_LOW_FREQUENCY),

  1419.        (CH_LAYOUT_2_1      | CH_LOW_FREQUENCY),

  1420.        (CH_LAYOUT_SURROUND | CH_LOW_FREQUENCY),

  1421.        (CH_LAYOUT_2_2      | CH_LOW_FREQUENCY),

  1422.        (CH_LAYOUT_QUAD     | CH_LOW_FREQUENCY),

  1423.        (CH_LAYOUT_4POINT0  | CH_LOW_FREQUENCY),

  1424.         CH_LAYOUT_5POINT1,

  1425.         CH_LAYOUT_5POINT1_BACK,

  1426.         0 },

  1427. };