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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

  24.  * The simplest AC-3 encoder.

  25.  */

  26. //#define DEBUG

  27. 

  28. #include "libavcore/audioconvert.h"

  29. #include "libavutil/crc.h"

  30. #include "avcodec.h"

  31. #include "libavutil/common.h" /* for av_reverse */

  32. #include "put_bits.h"

  33. #include "ac3.h"

  34. #include "audioconvert.h"

  35. 

  36. typedef struct AC3EncodeContext {

  37.     PutBitContext pb;

  38. 

  39.     int bitstream_id;

  40.     int bitstream_mode;

  41. 

  42.     int bit_rate;

  43.     int sample_rate;

  44. 

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

  46.     int frame_size; /* current frame size in words */

  47.     int frame_size_code;

  48.     int bits_written;

  49.     int samples_written;

  50. 

  51.     int fbw_channels;

  52.     int channels;

  53.     int lfe_on;

  54.     int lfe_channel;

  55.     int channel_mode;

  56.     const uint8_t *channel_map;

  57. 

  58.     int bandwidth_code[AC3_MAX_CHANNELS];

  59.     int nb_coefs[AC3_MAX_CHANNELS];

  60. 

  61.     /* bitrate allocation control */

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

  63.     AC3BitAllocParameters bit_alloc;

  64.     int coarse_snr_offset;

  65.     int fast_gain_code[AC3_MAX_CHANNELS];

  66.     int fine_snr_offset[AC3_MAX_CHANNELS];

  67. 

  68.     /* mantissa encoding */

  69.     int mant1_cnt, mant2_cnt, mant4_cnt;

  70. 

  71.     int16_t last_samples[AC3_MAX_CHANNELS][AC3_BLOCK_SIZE];

  72. } AC3EncodeContext;

  73. 

  74. static int16_t costab[64];

  75. static int16_t sintab[64];

  76. static int16_t xcos1[128];

  77. static int16_t xsin1[128];

  78. 

  79. #define MDCT_NBITS 9

  80. #define MDCT_SAMPLES (1 << MDCT_NBITS)

  81. 

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

  83. #define EXP_DIFF_THRESHOLD 1000

  84. 

  85. static inline int16_t fix15(float a)

  86. {

  87.     int v;

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

  89.     if (v < -32767)

  90.         v = -32767;

  91.     else if (v > 32767)

  92.         v = 32767;

  93.     return v;

  94. }

  95. 

  96. typedef struct IComplex {

  97.     int16_t re,im;

  98. } IComplex;

  99. 

  100. static av_cold void fft_init(int ln)

  101. {

  102.     int i, n;

  103.     float alpha;

  104. 

  105.     n = 1 << ln;

  106. 

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

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

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

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

  111.     }

  112. }

  113. 

  114. /* butter fly op */

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

  116. {\

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

  118.   bx=pre1;\

  119.   by=pim1;\

  120.   ax=qre1;\

  121.   ay=qim1;\

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

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

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

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

  126. }

  127. 

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

  129. {\

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

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

  132. }

  133. 

  134. 

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

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

  137. {

  138.     int        j, l, np, np2;

  139.     int        nblocks, nloops;

  140.     register IComplex *p,*q;

  141.     int tmp_re, tmp_im;

  142. 

  143.     np = 1 << ln;

  144. 

  145.     /* reverse */

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

  147.         int k = av_reverse[j] >> (8 - ln);

  148.         if (k < j)

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

  150.     }

  151. 

  152.     /* pass 0 */

  153. 

  154.     p=&z[0];

  155.     j=(np >> 1);

  156.     do {

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

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

  159.         p+=2;

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

  161. 

  162.     /* pass 1 */

  163. 

  164.     p=&z[0];

  165.     j=np >> 2;

  166.     do {

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

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

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

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

  171.         p+=4;

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

  173. 

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

  175. 

  176.     nblocks = np >> 3;

  177.     nloops = 1 << 2;

  178.     np2 = np >> 1;

  179.     do {

  180.         p = z;

  181.         q = z + nloops;

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

  183. 

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

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

  186. 

  187.             p++;

  188.             q++;

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

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

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

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

  193.                 p++;

  194.                 q++;

  195.             }

  196.             p += nloops;

  197.             q += nloops;

  198.         }

  199.         nblocks = nblocks >> 1;

  200.         nloops = nloops << 1;

  201.     } while (nblocks != 0);

  202. }

  203. 

  204. /* do a 512 point mdct */

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

  206. {

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

  208.     int16_t rot[MDCT_SAMPLES];

  209.     IComplex x[MDCT_SAMPLES/4];

  210. 

  211.     /* shift to simplify computations */

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

  213.         rot[i] = -in[i + 3*MDCT_SAMPLES/4];

  214.     for(i=MDCT_SAMPLES/4;i<MDCT_SAMPLES;i++)

  215.         rot[i] = in[i - MDCT_SAMPLES/4];

  216. 

  217.     /* pre rotation */

  218.     for(i=0;i<MDCT_SAMPLES/4;i++) {

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

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

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

  222.     }

  223. 

  224.     fft(x, MDCT_NBITS - 2);

  225. 

  226.     /* post rotation */

  227.     for(i=0;i<MDCT_SAMPLES/4;i++) {

  228.         re = x[i].re;

  229.         im = x[i].im;

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

  231.         out[2*i] = im1;

  232.         out[MDCT_SAMPLES/2-1-2*i] = re1;

  233.     }

  234. }

  235. 

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

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

  238. {

  239.     int sum, i;

  240.     sum = 0;

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

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

  243.     }

  244.     return sum;

  245. }

  246. 

  247. static void compute_exp_strategy(uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS],

  248.                                  uint8_t exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],

  249.                                  int ch, int is_lfe)

  250. {

  251.     int i, j;

  252.     int exp_diff;

  253. 

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

  255.        reused in the next frame */

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

  257.     for(i=1;i<AC3_MAX_BLOCKS;i++) {

  258.         exp_diff = calc_exp_diff(exp[i][ch], exp[i-1][ch], AC3_MAX_COEFS);

  259.         if (exp_diff > EXP_DIFF_THRESHOLD)

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

  261.         else

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

  263.     }

  264.     if (is_lfe)

  265.         return;

  266. 

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

  268.        recoded, we use a coarse encoding */

  269.     i = 0;

  270.     while (i < AC3_MAX_BLOCKS) {

  271.         j = i + 1;

  272.         while (j < AC3_MAX_BLOCKS && exp_strategy[j][ch] == EXP_REUSE)

  273.             j++;

  274.         switch(j - i) {

  275.         case 1:

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

  277.             break;

  278.         case 2:

  279.         case 3:

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

  281.             break;

  282.         default:

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

  284.             break;

  285.         }

  286.         i = j;

  287.     }

  288. }

  289. 

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

  291. static void exponent_min(uint8_t exp[AC3_MAX_COEFS], uint8_t exp1[AC3_MAX_COEFS], int n)

  292. {

  293.     int i;

  294. 

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

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

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

  298.     }

  299. }

  300. 

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

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

  303. static int encode_exp(uint8_t encoded_exp[AC3_MAX_COEFS],

  304.                       uint8_t exp[AC3_MAX_COEFS],

  305.                       int nb_exps,

  306.                       int exp_strategy)

  307. {

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

  309.     uint8_t exp1[AC3_MAX_COEFS];

  310. 

  311.     switch(exp_strategy) {

  312.     case EXP_D15:

  313.         group_size = 1;

  314.         break;

  315.     case EXP_D25:

  316.         group_size = 2;

  317.         break;

  318.     default:

  319.     case EXP_D45:

  320.         group_size = 4;

  321.         break;

  322.     }

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

  324. 

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

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

  327.     k = 1;

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

  329.         exp_min = exp[k];

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

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

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

  333.                 exp_min = exp[k+j];

  334.         }

  335.         exp1[i] = exp_min;

  336.         k += group_size;

  337.     }

  338. 

  339.     /* constraint for DC exponent */

  340.     if (exp1[0] > 15)

  341.         exp1[0] = 15;

  342. 

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

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

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

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

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

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

  349. 

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

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

  352.     k = 1;

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

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

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

  356.         }

  357.         k += group_size;

  358.     }

  359. 

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

  361. }

  362. 

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

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

  365. {

  366.     int bits, mant, i;

  367. 

  368.     bits = 0;

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

  370.         mant = m[i];

  371.         switch(mant) {

  372.         case 0:

  373.             /* nothing */

  374.             break;

  375.         case 1:

  376.             /* 3 mantissa in 5 bits */

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

  378.                 bits += 5;

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

  380.                 s->mant1_cnt = 0;

  381.             break;

  382.         case 2:

  383.             /* 3 mantissa in 7 bits */

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

  385.                 bits += 7;

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

  387.                 s->mant2_cnt = 0;

  388.             break;

  389.         case 3:

  390.             bits += 3;

  391.             break;

  392.         case 4:

  393.             /* 2 mantissa in 7 bits */

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

  395.                 bits += 7;

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

  397.                 s->mant4_cnt = 0;

  398.             break;

  399.         case 14:

  400.             bits += 14;

  401.             break;

  402.         case 15:

  403.             bits += 16;

  404.             break;

  405.         default:

  406.             bits += mant - 1;

  407.             break;

  408.         }

  409.     }

  410.     return bits;

  411. }

  412. 

  413. 

  414. static void bit_alloc_masking(AC3EncodeContext *s,

  415.                               uint8_t encoded_exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],

  416.                               uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS],

  417.                               int16_t psd[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],

  418.                               int16_t mask[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][50])

  419. {

  420.     int blk, ch;

  421.     int16_t band_psd[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][50];

  422. 

  423.     for(blk=0; blk<AC3_MAX_BLOCKS; blk++) {

  424.         for(ch=0;ch<s->channels;ch++) {

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

  426.                 memcpy(psd[blk][ch], psd[blk-1][ch], AC3_MAX_COEFS*sizeof(int16_t));

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

  428.             } else {

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

  430.                                           s->nb_coefs[ch],

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

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

  433.                                            0, s->nb_coefs[ch],

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

  435.                                            ch == s->lfe_channel,

  436.                                            DBA_NONE, 0, NULL, NULL, NULL,

  437.                                            mask[blk][ch]);

  438.             }

  439.         }

  440.     }

  441. }

  442. 

  443. static int bit_alloc(AC3EncodeContext *s,

  444.                      int16_t mask[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][50],

  445.                      int16_t psd[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],

  446.                      uint8_t bap[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],

  447.                      int frame_bits, int coarse_snr_offset, int fine_snr_offset)

  448. {

  449.     int i, ch;

  450.     int snr_offset;

  451. 

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

  453. 

  454.     /* compute size */

  455.     for(i=0;i<AC3_MAX_BLOCKS;i++) {

  456.         s->mant1_cnt = 0;

  457.         s->mant2_cnt = 0;

  458.         s->mant4_cnt = 0;

  459.         for(ch=0;ch<s->channels;ch++) {

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

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

  462.                                       s->bit_alloc.floor, ff_ac3_bap_tab,

  463.                                       bap[i][ch]);

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

  465.                                                  s->nb_coefs[ch]);

  466.         }

  467.     }

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

  469. }

  470. 

  471. #define SNR_INC1 4

  472. 

  473. static int compute_bit_allocation(AC3EncodeContext *s,

  474.                                   uint8_t bap[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],

  475.                                   uint8_t encoded_exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],

  476.                                   uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS],

  477.                                   int frame_bits)

  478. {

  479.     int i, ch;

  480.     int coarse_snr_offset, fine_snr_offset;

  481.     uint8_t bap1[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];

  482.     int16_t psd[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];

  483.     int16_t mask[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][50];

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

  485. 

  486.     /* init default parameters */

  487.     s->slow_decay_code = 2;

  488.     s->fast_decay_code = 1;

  489.     s->slow_gain_code = 1;

  490.     s->db_per_bit_code = 2;

  491.     s->floor_code = 4;

  492.     for(ch=0;ch<s->channels;ch++)

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

  494. 

  495.     /* compute real values */

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

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

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

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

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

  501. 

  502.     /* header size */

  503.     frame_bits += 65;

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

  505.     //    frame_bits += 2;

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

  507. 

  508.     /* audio blocks */

  509.     for(i=0;i<AC3_MAX_BLOCKS;i++) {

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

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

  512.             frame_bits++; /* rematstr */

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

  514.         }

  515.         frame_bits += 2 * s->fbw_channels; /* chexpstr[2] * c */

  516.         if (s->lfe_on)

  517.             frame_bits++; /* lfeexpstr */

  518.         for(ch=0;ch<s->fbw_channels;ch++) {

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

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

  521.         }

  522.         frame_bits++; /* baie */

  523.         frame_bits++; /* snr */

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

  525.     }

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

  527.     /* bit alloc info */

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

  529.     /* csnroffset[6] */

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

  531.     frame_bits += 2*4 + 3 + 6 + s->channels * (4 + 3);

  532. 

  533.     /* auxdatae, crcrsv */

  534.     frame_bits += 2;

  535. 

  536.     /* CRC */

  537.     frame_bits += 16;

  538. 

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

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

  541. 

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

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

  544. 

  545.     coarse_snr_offset = s->coarse_snr_offset;

  546.     while (coarse_snr_offset >= 0 &&

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

  548.         coarse_snr_offset -= SNR_INC1;

  549.     if (coarse_snr_offset < 0) {

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

  551.         return -1;

  552.     }

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

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

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

  556.         coarse_snr_offset += SNR_INC1;

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

  558.     }

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

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

  561.         coarse_snr_offset++;

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

  563.     }

  564. 

  565.     fine_snr_offset = 0;

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

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

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

  569.         fine_snr_offset += SNR_INC1;

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

  571.     }

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

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

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

  575.         fine_snr_offset++;

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

  577.     }

  578. 

  579.     s->coarse_snr_offset = coarse_snr_offset;

  580.     for(ch=0;ch<s->channels;ch++)

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

  582. 

  583.     return 0;

  584. }

  585. 

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

  587.                                     int64_t *channel_layout)

  588. {

  589.     int ch_layout;

  590. 

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

  592.         return -1;

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

  594.         return -1;

  595.     ch_layout = *channel_layout;

  596.     if (!ch_layout)

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

  598.     if (av_get_channel_layout_nb_channels(ch_layout) != channels)

  599.         return -1;

  600. 

  601.     s->lfe_on       = !!(ch_layout & AV_CH_LOW_FREQUENCY);

  602.     s->channels     = channels;

  603.     s->fbw_channels = channels - s->lfe_on;

  604.     s->lfe_channel  = s->lfe_on ? s->fbw_channels : -1;

  605.     if (s->lfe_on)

  606.         ch_layout -= AV_CH_LOW_FREQUENCY;

  607. 

  608.     switch (ch_layout) {

  609.     case AV_CH_LAYOUT_MONO:           s->channel_mode = AC3_CHMODE_MONO;   break;

  610.     case AV_CH_LAYOUT_STEREO:         s->channel_mode = AC3_CHMODE_STEREO; break;

  611.     case AV_CH_LAYOUT_SURROUND:       s->channel_mode = AC3_CHMODE_3F;     break;

  612.     case AV_CH_LAYOUT_2_1:            s->channel_mode = AC3_CHMODE_2F1R;   break;

  613.     case AV_CH_LAYOUT_4POINT0:        s->channel_mode = AC3_CHMODE_3F1R;   break;

  614.     case AV_CH_LAYOUT_QUAD:

  615.     case AV_CH_LAYOUT_2_2:            s->channel_mode = AC3_CHMODE_2F2R;   break;

  616.     case AV_CH_LAYOUT_5POINT0:

  617.     case AV_CH_LAYOUT_5POINT0_BACK:   s->channel_mode = AC3_CHMODE_3F2R;   break;

  618.     default:

  619.         return -1;

  620.     }

  621. 

  622.     s->channel_map = ff_ac3_enc_channel_map[s->channel_mode][s->lfe_on];

  623.     *channel_layout = ch_layout;

  624.     if (s->lfe_on)

  625.         *channel_layout |= AV_CH_LOW_FREQUENCY;

  626. 

  627.     return 0;

  628. }

  629. 

  630. static av_cold int AC3_encode_init(AVCodecContext *avctx)

  631. {

  632.     int freq = avctx->sample_rate;

  633.     int bitrate = avctx->bit_rate;

  634.     AC3EncodeContext *s = avctx->priv_data;

  635.     int i, j, ch;

  636.     float alpha;

  637.     int bw_code;

  638. 

  639.     avctx->frame_size = AC3_FRAME_SIZE;

  640. 

  641.     ac3_common_init();

  642. 

  643.     if (!avctx->channel_layout) {

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

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

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

  647.     }

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

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

  650.         return -1;

  651.     }

  652. 

  653.     /* frequency */

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

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

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

  657.                 goto found;

  658.     }

  659.     return -1;

  660.  found:

  661.     s->sample_rate = freq;

  662.     s->bit_alloc.sr_shift = i;

  663.     s->bit_alloc.sr_code = j;

  664.     s->bitstream_id = 8 + s->bit_alloc.sr_shift;

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

  666. 

  667.     /* bitrate & frame size */

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

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

  670.             break;

  671.     }

  672.     if (i == 19)

  673.         return -1;

  674.     s->bit_rate = bitrate;

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

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

  677.     s->bits_written = 0;

  678.     s->samples_written = 0;

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

  680. 

  681.     /* bit allocation init */

  682.     if(avctx->cutoff) {

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

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

  685.         int fbw_coeffs = cutoff * 2 * AC3_MAX_COEFS / s->sample_rate;

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

  687.     } else {

  688.         /* use default bandwidth setting */

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

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

  691.         bw_code = 50;

  692.     }

  693.     for(ch=0;ch<s->fbw_channels;ch++) {

  694.         /* bandwidth for each channel */

  695.         s->bandwidth_code[ch] = bw_code;

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

  697.     }

  698.     if (s->lfe_on) {

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

  700.     }

  701.     /* initial snr offset */

  702.     s->coarse_snr_offset = 40;

  703. 

  704.     /* mdct init */

  705.     fft_init(MDCT_NBITS - 2);

  706.     for(i=0;i<MDCT_SAMPLES/4;i++) {

  707.         alpha = 2 * M_PI * (i + 1.0 / 8.0) / (float)MDCT_SAMPLES;

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

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

  710.     }

  711. 

  712.     avctx->coded_frame= avcodec_alloc_frame();

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

  714. 

  715.     return 0;

  716. }

  717. 

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

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

  720. {

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

  722. 

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

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

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

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

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

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

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

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

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

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

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

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

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

  736.     put_bits(&s->pb, 1, s->lfe_on); /* LFE */

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

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

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

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

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

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

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

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

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

  746. }

  747. 

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

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

  750. {

  751.     int v;

  752. 

  753.     if (c >= 0) {

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

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

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

  757.     } else {

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

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

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

  761.     }

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

  763.     return v;

  764. }

  765. 

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

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

  768. {

  769.     int lshift, m, v;

  770. 

  771.     lshift = e + qbits - 24;

  772.     if (lshift >= 0)

  773.         v = c << lshift;

  774.     else

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

  776.     /* rounding */

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

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

  779.     if (v >= m)

  780.         v = m - 1;

  781.     assert(v >= -m);

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

  783. }

  784. 

  785. /* Output one audio block. There are AC3_MAX_BLOCKS audio blocks in one AC-3

  786.    frame */

  787. static void output_audio_block(AC3EncodeContext *s,

  788.                                uint8_t exp_strategy[AC3_MAX_CHANNELS],

  789.                                uint8_t encoded_exp[AC3_MAX_CHANNELS][AC3_MAX_COEFS],

  790.                                uint8_t bap[AC3_MAX_CHANNELS][AC3_MAX_COEFS],

  791.                                int32_t mdct_coefs[AC3_MAX_CHANNELS][AC3_MAX_COEFS],

  792.                                int8_t global_exp[AC3_MAX_CHANNELS],

  793.                                int block_num)

  794. {

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

  796.     uint8_t *p;

  797.     uint16_t qmant[AC3_MAX_CHANNELS][AC3_MAX_COEFS];

  798.     int exp0, exp1;

  799.     int mant1_cnt, mant2_cnt, mant4_cnt;

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

  801.     int delta0, delta1, delta2;

  802. 

  803.     for(ch=0;ch<s->fbw_channels;ch++)

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

  805.     for(ch=0;ch<s->fbw_channels;ch++)

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

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

  808.     if (block_num == 0) {

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

  810.            waste of bit :-) */

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

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

  813.     } else {

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

  815.     }

  816. 

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

  818.       {

  819.         if(block_num==0)

  820.           {

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

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

  823. 

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

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

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

  827.           }

  828.         else

  829.           {

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

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

  832.           }

  833.       }

  834. 

  835.     /* exponent strategy */

  836.     for(ch=0;ch<s->fbw_channels;ch++) {

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

  838.     }

  839. 

  840.     if (s->lfe_on) {

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

  842.     }

  843. 

  844.     for(ch=0;ch<s->fbw_channels;ch++) {

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

  846.             put_bits(&s->pb, 6, s->bandwidth_code[ch]);

  847.     }

  848. 

  849.     /* exponents */

  850.     for (ch = 0; ch < s->channels; ch++) {

  851.         switch(exp_strategy[ch]) {

  852.         case EXP_REUSE:

  853.             continue;

  854.         case EXP_D15:

  855.             group_size = 1;

  856.             break;

  857.         case EXP_D25:

  858.             group_size = 2;

  859.             break;

  860.         default:

  861.         case EXP_D45:

  862.             group_size = 4;

  863.             break;

  864.         }

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

  866.         p = encoded_exp[ch];

  867. 

  868.         /* first exponent */

  869.         exp1 = *p++;

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

  871. 

  872.         /* next ones are delta encoded */

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

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

  875.             exp0 = exp1;

  876.             exp1 = p[0];

  877.             p += group_size;

  878.             delta0 = exp1 - exp0 + 2;

  879. 

  880.             exp0 = exp1;

  881.             exp1 = p[0];

  882.             p += group_size;

  883.             delta1 = exp1 - exp0 + 2;

  884. 

  885.             exp0 = exp1;

  886.             exp1 = p[0];

  887.             p += group_size;

  888.             delta2 = exp1 - exp0 + 2;

  889. 

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

  891.         }

  892. 

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

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

  895.     }

  896. 

  897.     /* bit allocation info */

  898.     baie = (block_num == 0);

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

  900.     if (baie) {

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

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

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

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

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

  906.     }

  907. 

  908.     /* snr offset */

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

  910.     if (baie) {

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

  912.         for(ch=0;ch<s->channels;ch++) {

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

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

  915.         }

  916.     }

  917. 

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

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

  920. 

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

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

  923.        modify the output stream. */

  924. 

  925.     /* first pass: quantize */

  926.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  927.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  928. 

  929.     for (ch = 0; ch < s->channels; ch++) {

  930.         int b, c, e, v;

  931. 

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

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

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

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

  936.             switch(b) {

  937.             case 0:

  938.                 v = 0;

  939.                 break;

  940.             case 1:

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

  942.                 switch(mant1_cnt) {

  943.                 case 0:

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

  945.                     v = 9 * v;

  946.                     mant1_cnt = 1;

  947.                     break;

  948.                 case 1:

  949.                     *qmant1_ptr += 3 * v;

  950.                     mant1_cnt = 2;

  951.                     v = 128;

  952.                     break;

  953.                 default:

  954.                     *qmant1_ptr += v;

  955.                     mant1_cnt = 0;

  956.                     v = 128;

  957.                     break;

  958.                 }

  959.                 break;

  960.             case 2:

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

  962.                 switch(mant2_cnt) {

  963.                 case 0:

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

  965.                     v = 25 * v;

  966.                     mant2_cnt = 1;

  967.                     break;

  968.                 case 1:

  969.                     *qmant2_ptr += 5 * v;

  970.                     mant2_cnt = 2;

  971.                     v = 128;

  972.                     break;

  973.                 default:

  974.                     *qmant2_ptr += v;

  975.                     mant2_cnt = 0;

  976.                     v = 128;

  977.                     break;

  978.                 }

  979.                 break;

  980.             case 3:

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

  982.                 break;

  983.             case 4:

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

  985.                 switch(mant4_cnt) {

  986.                 case 0:

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

  988.                     v = 11 * v;

  989.                     mant4_cnt = 1;

  990.                     break;

  991.                 default:

  992.                     *qmant4_ptr += v;

  993.                     mant4_cnt = 0;

  994.                     v = 128;

  995.                     break;

  996.                 }

  997.                 break;

  998.             case 5:

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

  1000.                 break;

  1001.             case 14:

  1002.                 v = asym_quant(c, e, 14);

  1003.                 break;

  1004.             case 15:

  1005.                 v = asym_quant(c, e, 16);

  1006.                 break;

  1007.             default:

  1008.                 v = asym_quant(c, e, b - 1);

  1009.                 break;

  1010.             }

  1011.             qmant[ch][i] = v;

  1012.         }

  1013.     }

  1014. 

  1015.     /* second pass : output the values */

  1016.     for (ch = 0; ch < s->channels; ch++) {

  1017.         int b, q;

  1018. 

  1019.         for(i=0;i<s->nb_coefs[ch];i++) {

  1020.             q = qmant[ch][i];

  1021.             b = bap[ch][i];

  1022.             switch(b) {

  1023.             case 0:

  1024.                 break;

  1025.             case 1:

  1026.                 if (q != 128)

  1027.                     put_bits(&s->pb, 5, q);

  1028.                 break;

  1029.             case 2:

  1030.                 if (q != 128)

  1031.                     put_bits(&s->pb, 7, q);

  1032.                 break;

  1033.             case 3:

  1034.                 put_bits(&s->pb, 3, q);

  1035.                 break;

  1036.             case 4:

  1037.                 if (q != 128)

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

  1039.                 break;

  1040.             case 14:

  1041.                 put_bits(&s->pb, 14, q);

  1042.                 break;

  1043.             case 15:

  1044.                 put_bits(&s->pb, 16, q);

  1045.                 break;

  1046.             default:

  1047.                 put_bits(&s->pb, b - 1, q);

  1048.                 break;

  1049.             }

  1050.         }

  1051.     }

  1052. }

  1053. 

  1054. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1055. 

  1056. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1057. {

  1058.     unsigned int c;

  1059. 

  1060.     c = 0;

  1061.     while (a) {

  1062.         if (a & 1)

  1063.             c ^= b;

  1064.         a = a >> 1;

  1065.         b = b << 1;

  1066.         if (b & (1 << 16))

  1067.             b ^= poly;

  1068.     }

  1069.     return c;

  1070. }

  1071. 

  1072. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1073. {

  1074.     unsigned int r;

  1075.     r = 1;

  1076.     while (n) {

  1077.         if (n & 1)

  1078.             r = mul_poly(r, a, poly);

  1079.         a = mul_poly(a, a, poly);

  1080.         n >>= 1;

  1081.     }

  1082.     return r;

  1083. }

  1084. 

  1085. 

  1086. /* compute log2(max(abs(tab[]))) */

  1087. static int log2_tab(int16_t *tab, int n)

  1088. {

  1089.     int i, v;

  1090. 

  1091.     v = 0;

  1092.     for(i=0;i<n;i++) {

  1093.         v |= abs(tab[i]);

  1094.     }

  1095.     return av_log2(v);

  1096. }

  1097. 

  1098. static void lshift_tab(int16_t *tab, int n, int lshift)

  1099. {

  1100.     int i;

  1101. 

  1102.     if (lshift > 0) {

  1103.         for(i=0;i<n;i++) {

  1104.             tab[i] <<= lshift;

  1105.         }

  1106.     } else if (lshift < 0) {

  1107.         lshift = -lshift;

  1108.         for(i=0;i<n;i++) {

  1109.             tab[i] >>= lshift;

  1110.         }

  1111.     }

  1112. }

  1113. 

  1114. /* fill the end of the frame and compute the two crcs */

  1115. static int output_frame_end(AC3EncodeContext *s)

  1116. {

  1117.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1118.     uint8_t *frame;

  1119. 

  1120.     frame_size = s->frame_size; /* frame size in words */

  1121.     /* align to 8 bits */

  1122.     flush_put_bits(&s->pb);

  1123.     /* add zero bytes to reach the frame size */

  1124.     frame = s->pb.buf;

  1125.     n = 2 * s->frame_size - (put_bits_ptr(&s->pb) - frame) - 2;

  1126.     assert(n >= 0);

  1127.     if(n>0)

  1128.       memset(put_bits_ptr(&s->pb), 0, n);

  1129. 

  1130.     /* Now we must compute both crcs : this is not so easy for crc1

  1131.        because it is at the beginning of the data... */

  1132.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1133.     crc1 = av_bswap16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

  1134.                            frame + 4, 2 * frame_size_58 - 4));

  1135.     /* XXX: could precompute crc_inv */

  1136.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1137.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1138.     AV_WB16(frame+2,crc1);

  1139. 

  1140.     crc2 = av_bswap16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

  1141.                            frame + 2 * frame_size_58,

  1142.                            (frame_size - frame_size_58) * 2 - 2));

  1143.     AV_WB16(frame+2*frame_size-2,crc2);

  1144. 

  1145.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1146.     return frame_size * 2;

  1147. }

  1148. 

  1149. static int AC3_encode_frame(AVCodecContext *avctx,

  1150.                             unsigned char *frame, int buf_size, void *data)

  1151. {

  1152.     AC3EncodeContext *s = avctx->priv_data;

  1153.     const int16_t *samples = data;

  1154.     int i, j, k, v, ch;

  1155.     int16_t input_samples[AC3_WINDOW_SIZE];

  1156.     int32_t mdct_coef[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];

  1157.     uint8_t exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];

  1158.     uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS];

  1159.     uint8_t encoded_exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];

  1160.     uint8_t bap[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];

  1161.     int8_t exp_samples[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS];

  1162.     int frame_bits;

  1163. 

  1164.     frame_bits = 0;

  1165.     for(ch=0;ch<s->channels;ch++) {

  1166.         int ich = s->channel_map[ch];

  1167.         /* fixed mdct to the six sub blocks & exponent computation */

  1168.         for(i=0;i<AC3_MAX_BLOCKS;i++) {

  1169.             const int16_t *sptr;

  1170.             int sinc;

  1171. 

  1172.             /* compute input samples */

  1173.             memcpy(input_samples, s->last_samples[ich], AC3_BLOCK_SIZE * sizeof(int16_t));

  1174.             sinc = s->channels;

  1175.             sptr = samples + (sinc * AC3_BLOCK_SIZE * i) + ich;

  1176.             for(j=0;j<AC3_BLOCK_SIZE;j++) {

  1177.                 v = *sptr;

  1178.                 input_samples[j + AC3_BLOCK_SIZE] = v;

  1179.                 s->last_samples[ich][j] = v;

  1180.                 sptr += sinc;

  1181.             }

  1182. 

  1183.             /* apply the MDCT window */

  1184.             for(j=0;j<AC3_BLOCK_SIZE;j++) {

  1185.                 input_samples[j] = MUL16(input_samples[j],

  1186.                                          ff_ac3_window[j]) >> 15;

  1187.                 input_samples[AC3_WINDOW_SIZE-j-1] = MUL16(input_samples[AC3_WINDOW_SIZE-j-1],

  1188.                                              ff_ac3_window[j]) >> 15;

  1189.             }

  1190. 

  1191.             /* Normalize the samples to use the maximum available

  1192.                precision */

  1193.             v = 14 - log2_tab(input_samples, AC3_WINDOW_SIZE);

  1194.             if (v < 0)

  1195.                 v = 0;

  1196.             exp_samples[i][ch] = v - 9;

  1197.             lshift_tab(input_samples, AC3_WINDOW_SIZE, v);

  1198. 

  1199.             /* do the MDCT */

  1200.             mdct512(mdct_coef[i][ch], input_samples);

  1201. 

  1202.             /* compute "exponents". We take into account the

  1203.                normalization there */

  1204.             for(j=0;j<AC3_MAX_COEFS;j++) {

  1205.                 int e;

  1206.                 v = abs(mdct_coef[i][ch][j]);

  1207.                 if (v == 0)

  1208.                     e = 24;

  1209.                 else {

  1210.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1211.                     if (e >= 24) {

  1212.                         e = 24;

  1213.                         mdct_coef[i][ch][j] = 0;

  1214.                     }

  1215.                 }

  1216.                 exp[i][ch][j] = e;

  1217.             }

  1218.         }

  1219. 

  1220.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1221. 

  1222.         /* compute the exponents as the decoder will see them. The

  1223.            EXP_REUSE case must be handled carefully : we select the

  1224.            min of the exponents */

  1225.         i = 0;

  1226.         while (i < AC3_MAX_BLOCKS) {

  1227.             j = i + 1;

  1228.             while (j < AC3_MAX_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1229.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1230.                 j++;

  1231.             }

  1232.             frame_bits += encode_exp(encoded_exp[i][ch],

  1233.                                      exp[i][ch], s->nb_coefs[ch],

  1234.                                      exp_strategy[i][ch]);

  1235.             /* copy encoded exponents for reuse case */

  1236.             for(k=i+1;k<j;k++) {

  1237.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch],

  1238.                        s->nb_coefs[ch] * sizeof(uint8_t));

  1239.             }

  1240.             i = j;

  1241.         }

  1242.     }

  1243. 

  1244.     /* adjust for fractional frame sizes */

  1245.     while(s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {

  1246.         s->bits_written -= s->bit_rate;

  1247.         s->samples_written -= s->sample_rate;

  1248.     }

  1249.     s->frame_size = s->frame_size_min + (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);

  1250.     s->bits_written += s->frame_size * 16;

  1251.     s->samples_written += AC3_FRAME_SIZE;

  1252. 

  1253.     compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

  1254.     /* everything is known... let's output the frame */

  1255.     output_frame_header(s, frame);

  1256. 

  1257.     for(i=0;i<AC3_MAX_BLOCKS;i++) {

  1258.         output_audio_block(s, exp_strategy[i], encoded_exp[i],

  1259.                            bap[i], mdct_coef[i], exp_samples[i], i);

  1260.     }

  1261.     return output_frame_end(s);

  1262. }

  1263. 

  1264. static av_cold int AC3_encode_close(AVCodecContext *avctx)

  1265. {

  1266.     av_freep(&avctx->coded_frame);

  1267.     return 0;

  1268. }

  1269. 

  1270. #if 0

  1271. /*************************************************************************/

  1272. /* TEST */

  1273. 

  1274. #undef random

  1275. #define FN (N/4)

  1276. 

  1277. void fft_test(void)

  1278. {

  1279.     IComplex in[FN], in1[FN];

  1280.     int k, n, i;

  1281.     float sum_re, sum_im, a;

  1282. 

  1283.     /* FFT test */

  1284. 

  1285.     for(i=0;i<FN;i++) {

  1286.         in[i].re = random() % 65535 - 32767;

  1287.         in[i].im = random() % 65535 - 32767;

  1288.         in1[i] = in[i];

  1289.     }

  1290.     fft(in, 7);

  1291. 

  1292.     /* do it by hand */

  1293.     for(k=0;k<FN;k++) {

  1294.         sum_re = 0;

  1295.         sum_im = 0;

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

  1297.             a = -2 * M_PI * (n * k) / FN;

  1298.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1299.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1300.         }

  1301.         printf("%3d: %6d,%6d %6.0f,%6.0f\n",

  1302.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);

  1303.     }

  1304. }

  1305. 

  1306. void mdct_test(void)

  1307. {

  1308.     int16_t input[N];

  1309.     int32_t output[N/2];

  1310.     float input1[N];

  1311.     float output1[N/2];

  1312.     float s, a, err, e, emax;

  1313.     int i, k, n;

  1314. 

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

  1316.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1317.         input1[i] = input[i];

  1318.     }

  1319. 

  1320.     mdct512(output, input);

  1321. 

  1322.     /* do it by hand */

  1323.     for(k=0;k<N/2;k++) {

  1324.         s = 0;

  1325.         for(n=0;n<N;n++) {

  1326.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1327.             s += input1[n] * cos(a);

  1328.         }

  1329.         output1[k] = -2 * s / N;

  1330.     }

  1331. 

  1332.     err = 0;

  1333.     emax = 0;

  1334.     for(i=0;i<N/2;i++) {

  1335.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1336.         e = output[i] - output1[i];

  1337.         if (e > emax)

  1338.             emax = e;

  1339.         err += e * e;

  1340.     }

  1341.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1342. }

  1343. 

  1344. void test_ac3(void)

  1345. {

  1346.     AC3EncodeContext ctx;

  1347.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1348.     int16_t samples[AC3_FRAME_SIZE];

  1349.     int ret, i;

  1350. 

  1351.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1352. 

  1353.     fft_test();

  1354.     mdct_test();

  1355. 

  1356.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1357.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1358.     ret = AC3_encode_frame(&ctx, frame, samples);

  1359.     printf("ret=%d\n", ret);

  1360. }

  1361. #endif

  1362. 

  1363. AVCodec ac3_encoder = {

  1364.     "ac3",

  1365.     AVMEDIA_TYPE_AUDIO,

  1366.     CODEC_ID_AC3,

  1367.     sizeof(AC3EncodeContext),

  1368.     AC3_encode_init,

  1369.     AC3_encode_frame,

  1370.     AC3_encode_close,

  1371.     NULL,

  1372.     .sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_S16,AV_SAMPLE_FMT_NONE},

  1373.     .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),

  1374.     .channel_layouts = (const int64_t[]){

  1375.         AV_CH_LAYOUT_MONO,

  1376.         AV_CH_LAYOUT_STEREO,

  1377.         AV_CH_LAYOUT_2_1,

  1378.         AV_CH_LAYOUT_SURROUND,

  1379.         AV_CH_LAYOUT_2_2,

  1380.         AV_CH_LAYOUT_QUAD,

  1381.         AV_CH_LAYOUT_4POINT0,

  1382.         AV_CH_LAYOUT_5POINT0,

  1383.         AV_CH_LAYOUT_5POINT0_BACK,

  1384.        (AV_CH_LAYOUT_MONO     | AV_CH_LOW_FREQUENCY),

  1385.        (AV_CH_LAYOUT_STEREO   | AV_CH_LOW_FREQUENCY),

  1386.        (AV_CH_LAYOUT_2_1      | AV_CH_LOW_FREQUENCY),

  1387.        (AV_CH_LAYOUT_SURROUND | AV_CH_LOW_FREQUENCY),

  1388.        (AV_CH_LAYOUT_2_2      | AV_CH_LOW_FREQUENCY),

  1389.        (AV_CH_LAYOUT_QUAD     | AV_CH_LOW_FREQUENCY),

  1390.        (AV_CH_LAYOUT_4POINT0  | AV_CH_LOW_FREQUENCY),

  1391.         AV_CH_LAYOUT_5POINT1,

  1392.         AV_CH_LAYOUT_5POINT1_BACK,

  1393.         0 },

  1394. };