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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. 

  34. typedef struct AC3EncodeContext {

  35.     PutBitContext pb;

  36.     int nb_channels;

  37.     int nb_all_channels;

  38.     int lfe_channel;

  39.     const uint8_t *channel_map;

  40.     int bit_rate;

  41.     unsigned int sample_rate;

  42.     unsigned int bitstream_id;

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

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

  45.     unsigned int bits_written;

  46.     unsigned int samples_written;

  47.     int sr_shift;

  48.     unsigned int frame_size_code;

  49.     unsigned int sr_code; /* frequency */

  50.     unsigned int channel_mode;

  51.     int lfe;

  52.     unsigned int bitstream_mode;

  53.     short last_samples[AC3_MAX_CHANNELS][256];

  54.     unsigned int chbwcod[AC3_MAX_CHANNELS];

  55.     int nb_coefs[AC3_MAX_CHANNELS];

  56. 

  57.     /* bitrate allocation control */

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

  59.     AC3BitAllocParameters bit_alloc;

  60.     int coarse_snr_offset;

  61.     int fast_gain_code[AC3_MAX_CHANNELS];

  62.     int fine_snr_offset[AC3_MAX_CHANNELS];

  63.     /* mantissa encoding */

  64.     int mant1_cnt, mant2_cnt, mant4_cnt;

  65. } AC3EncodeContext;

  66. 

  67. static int16_t costab[64];

  68. static int16_t sintab[64];

  69. static int16_t xcos1[128];

  70. static int16_t xsin1[128];

  71. 

  72. #define MDCT_NBITS 9

  73. #define N         (1 << MDCT_NBITS)

  74. 

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

  76. #define EXP_DIFF_THRESHOLD 1000

  77. 

  78. static inline int16_t fix15(float a)

  79. {

  80.     int v;

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

  82.     if (v < -32767)

  83.         v = -32767;

  84.     else if (v > 32767)

  85.         v = 32767;

  86.     return v;

  87. }

  88. 

  89. typedef struct IComplex {

  90.     short re,im;

  91. } IComplex;

  92. 

  93. static av_cold void fft_init(int ln)

  94. {

  95.     int i, n;

  96.     float alpha;

  97. 

  98.     n = 1 << ln;

  99. 

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

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

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

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

  104.     }

  105. }

  106. 

  107. /* butter fly op */

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

  109. {\

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

  111.   bx=pre1;\

  112.   by=pim1;\

  113.   ax=qre1;\

  114.   ay=qim1;\

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

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

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

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

  119. }

  120. 

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

  122. {\

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

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

  125. }

  126. 

  127. 

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

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

  130. {

  131.     int        j, l, np, np2;

  132.     int        nblocks, nloops;

  133.     register IComplex *p,*q;

  134.     int tmp_re, tmp_im;

  135. 

  136.     np = 1 << ln;

  137. 

  138.     /* reverse */

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

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

  141.         if (k < j)

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

  143.     }

  144. 

  145.     /* pass 0 */

  146. 

  147.     p=&z[0];

  148.     j=(np >> 1);

  149.     do {

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

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

  152.         p+=2;

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

  154. 

  155.     /* pass 1 */

  156. 

  157.     p=&z[0];

  158.     j=np >> 2;

  159.     do {

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

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

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

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

  164.         p+=4;

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

  166. 

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

  168. 

  169.     nblocks = np >> 3;

  170.     nloops = 1 << 2;

  171.     np2 = np >> 1;

  172.     do {

  173.         p = z;

  174.         q = z + nloops;

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

  176. 

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

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

  179. 

  180.             p++;

  181.             q++;

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

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

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

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

  186.                 p++;

  187.                 q++;

  188.             }

  189.             p += nloops;

  190.             q += nloops;

  191.         }

  192.         nblocks = nblocks >> 1;

  193.         nloops = nloops << 1;

  194.     } while (nblocks != 0);

  195. }

  196. 

  197. /* do a 512 point mdct */

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

  199. {

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

  201.     int16_t rot[N];

  202.     IComplex x[N/4];

  203. 

  204.     /* shift to simplify computations */

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

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

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

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

  209. 

  210.     /* pre rotation */

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

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

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

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

  215.     }

  216. 

  217.     fft(x, MDCT_NBITS - 2);

  218. 

  219.     /* post rotation */

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

  221.         re = x[i].re;

  222.         im = x[i].im;

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

  224.         out[2*i] = im1;

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

  226.     }

  227. }

  228. 

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

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

  231. {

  232.     int sum, i;

  233.     sum = 0;

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

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

  236.     }

  237.     return sum;

  238. }

  239. 

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

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

  242.                                  int ch, int is_lfe)

  243. {

  244.     int i, j;

  245.     int exp_diff;

  246. 

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

  248.        reused in the next frame */

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

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

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

  252. #ifdef DEBUG

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

  254. #endif

  255.         if (exp_diff > EXP_DIFF_THRESHOLD)

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

  257.         else

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

  259.     }

  260.     if (is_lfe)

  261.         return;

  262. 

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

  264.        recoded, we use a coarse encoding */

  265.     i = 0;

  266.     while (i < NB_BLOCKS) {

  267.         j = i + 1;

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

  269.             j++;

  270.         switch(j - i) {

  271.         case 1:

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

  273.             break;

  274.         case 2:

  275.         case 3:

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

  277.             break;

  278.         default:

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

  280.             break;

  281.         }

  282.         i = j;

  283.     }

  284. }

  285. 

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

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

  288. {

  289.     int i;

  290. 

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

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

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

  294.     }

  295. }

  296. 

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

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

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

  300.                       uint8_t exp[N/2],

  301.                       int nb_exps,

  302.                       int exp_strategy)

  303. {

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

  305.     uint8_t exp1[N/2];

  306. 

  307.     switch(exp_strategy) {

  308.     case EXP_D15:

  309.         group_size = 1;

  310.         break;

  311.     case EXP_D25:

  312.         group_size = 2;

  313.         break;

  314.     default:

  315.     case EXP_D45:

  316.         group_size = 4;

  317.         break;

  318.     }

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

  320. 

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

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

  323.     k = 1;

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

  325.         exp_min = exp[k];

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

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

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

  329.                 exp_min = exp[k+j];

  330.         }

  331.         exp1[i] = exp_min;

  332.         k += group_size;

  333.     }

  334. 

  335.     /* constraint for DC exponent */

  336.     if (exp1[0] > 15)

  337.         exp1[0] = 15;

  338. 

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

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

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

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

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

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

  345. 

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

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

  348.     k = 1;

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

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

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

  352.         }

  353.         k += group_size;

  354.     }

  355. 

  356. #if defined(DEBUG)

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

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

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

  360.     }

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

  362. #endif

  363. 

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

  365. }

  366. 

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

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

  369. {

  370.     int bits, mant, i;

  371. 

  372.     bits = 0;

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

  374.         mant = m[i];

  375.         switch(mant) {

  376.         case 0:

  377.             /* nothing */

  378.             break;

  379.         case 1:

  380.             /* 3 mantissa in 5 bits */

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

  382.                 bits += 5;

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

  384.                 s->mant1_cnt = 0;

  385.             break;

  386.         case 2:

  387.             /* 3 mantissa in 7 bits */

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

  389.                 bits += 7;

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

  391.                 s->mant2_cnt = 0;

  392.             break;

  393.         case 3:

  394.             bits += 3;

  395.             break;

  396.         case 4:

  397.             /* 2 mantissa in 7 bits */

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

  399.                 bits += 7;

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

  401.                 s->mant4_cnt = 0;

  402.             break;

  403.         case 14:

  404.             bits += 14;

  405.             break;

  406.         case 15:

  407.             bits += 16;

  408.             break;

  409.         default:

  410.             bits += mant - 1;

  411.             break;

  412.         }

  413.     }

  414.     return bits;

  415. }

  416. 

  417. 

  418. static void bit_alloc_masking(AC3EncodeContext *s,

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

  420.                               uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

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

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

  423. {

  424.     int blk, ch;

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

  426. 

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

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

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

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

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

  432.             } else {

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

  434.                                           s->nb_coefs[ch],

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

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

  437.                                            0, s->nb_coefs[ch],

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

  439.                                            ch == s->lfe_channel,

  440.                                            DBA_NONE, 0, NULL, NULL, NULL,

  441.                                            mask[blk][ch]);

  442.             }

  443.         }

  444.     }

  445. }

  446. 

  447. static int bit_alloc(AC3EncodeContext *s,

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

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

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

  451.                      int frame_bits, int coarse_snr_offset, int fine_snr_offset)

  452. {

  453.     int i, ch;

  454.     int snr_offset;

  455. 

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

  457. 

  458.     /* compute size */

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

  460.         s->mant1_cnt = 0;

  461.         s->mant2_cnt = 0;

  462.         s->mant4_cnt = 0;

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

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

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

  466.                                       s->bit_alloc.floor, ff_ac3_bap_tab,

  467.                                       bap[i][ch]);

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

  469.                                                  s->nb_coefs[ch]);

  470.         }

  471.     }

  472. #if 0

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

  474.            coarse_snr_offset, fine_snr_offset, frame_bits,

  475.            16 * s->frame_size - ((frame_bits + 7) & ~7));

  476. #endif

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

  478. }

  479. 

  480. #define SNR_INC1 4

  481. 

  482. static int compute_bit_allocation(AC3EncodeContext *s,

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

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

  485.                                   uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

  486.                                   int frame_bits)

  487. {

  488.     int i, ch;

  489.     int coarse_snr_offset, fine_snr_offset;

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

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

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

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

  494. 

  495.     /* init default parameters */

  496.     s->slow_decay_code = 2;

  497.     s->fast_decay_code = 1;

  498.     s->slow_gain_code = 1;

  499.     s->db_per_bit_code = 2;

  500.     s->floor_code = 4;

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

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

  503. 

  504.     /* compute real values */

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

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

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

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

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

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

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

  512. 

  513.     /* header size */

  514.     frame_bits += 65;

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

  516.     //    frame_bits += 2;

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

  518. 

  519.     /* audio blocks */

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

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

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

  523.             frame_bits++; /* rematstr */

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

  525.         }

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

  527.         if (s->lfe)

  528.             frame_bits++; /* lfeexpstr */

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

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

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

  532.         }

  533.         frame_bits++; /* baie */

  534.         frame_bits++; /* snr */

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

  536.     }

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

  538.     /* bit alloc info */

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

  540.     /* csnroffset[6] */

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

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

  543. 

  544.     /* auxdatae, crcrsv */

  545.     frame_bits += 2;

  546. 

  547.     /* CRC */

  548.     frame_bits += 16;

  549. 

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

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

  552. 

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

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

  555. 

  556.     coarse_snr_offset = s->coarse_snr_offset;

  557.     while (coarse_snr_offset >= 0 &&

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

  559.         coarse_snr_offset -= SNR_INC1;

  560.     if (coarse_snr_offset < 0) {

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

  562.         return -1;

  563.     }

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

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

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

  567.         coarse_snr_offset += SNR_INC1;

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

  569.     }

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

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

  572.         coarse_snr_offset++;

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

  574.     }

  575. 

  576.     fine_snr_offset = 0;

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

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

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

  580.         fine_snr_offset += SNR_INC1;

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

  582.     }

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

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

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

  586.         fine_snr_offset++;

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

  588.     }

  589. 

  590.     s->coarse_snr_offset = coarse_snr_offset;

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

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

  593. #if defined(DEBUG_BITALLOC)

  594.     {

  595.         int j;

  596. 

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

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

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

  600.                 printf("bap=");

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

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

  603.                 }

  604.                 printf("\n");

  605.             }

  606.         }

  607.     }

  608. #endif

  609.     return 0;

  610. }

  611. 

  612. static av_cold int AC3_encode_init(AVCodecContext *avctx)

  613. {

  614.     int freq = avctx->sample_rate;

  615.     int bitrate = avctx->bit_rate;

  616.     int channels = avctx->channels;

  617.     AC3EncodeContext *s = avctx->priv_data;

  618.     int i, j, ch;

  619.     float alpha;

  620.     int bw_code;

  621.     static const uint8_t channel_mode_defs[6] = {

  622.         0x01, /* C */

  623.         0x02, /* L R */

  624.         0x03, /* L C R */

  625.         0x06, /* L R SL SR */

  626.         0x07, /* L C R SL SR */

  627.         0x07, /* L C R SL SR (+LFE) */

  628.     };

  629. 

  630.     avctx->frame_size = AC3_FRAME_SIZE;

  631. 

  632.     ac3_common_init();

  633. 

  634.     /* number of channels */

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

  636.         return -1;

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

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

  639.     s->nb_all_channels = channels;

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

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

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

  643. 

  644.     /* frequency */

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

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

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

  648.                 goto found;

  649.     }

  650.     return -1;

  651.  found:

  652.     s->sample_rate = freq;

  653.     s->sr_shift = i;

  654.     s->sr_code = j;

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

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

  657. 

  658.     /* bitrate & frame size */

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

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

  661.             break;

  662.     }

  663.     if (i == 19)

  664.         return -1;

  665.     s->bit_rate = bitrate;

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

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

  668.     s->bits_written = 0;

  669.     s->samples_written = 0;

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

  671. 

  672.     /* bit allocation init */

  673.     if(avctx->cutoff) {

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

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

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

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

  678.     } else {

  679.         /* use default bandwidth setting */

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

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

  682.         bw_code = 50;

  683.     }

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

  685.         /* bandwidth for each channel */

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

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

  688.     }

  689.     if (s->lfe) {

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

  691.     }

  692.     /* initial snr offset */

  693.     s->coarse_snr_offset = 40;

  694. 

  695.     /* mdct init */

  696.     fft_init(MDCT_NBITS - 2);

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

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

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

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

  701.     }

  702. 

  703.     avctx->coded_frame= avcodec_alloc_frame();

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

  705. 

  706.     return 0;

  707. }

  708. 

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

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

  711. {

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

  713. 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  737. }

  738. 

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

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

  741. {

  742.     int v;

  743. 

  744.     if (c >= 0) {

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

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

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

  748.     } else {

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

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

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

  752.     }

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

  754.     return v;

  755. }

  756. 

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

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

  759. {

  760.     int lshift, m, v;

  761. 

  762.     lshift = e + qbits - 24;

  763.     if (lshift >= 0)

  764.         v = c << lshift;

  765.     else

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

  767.     /* rounding */

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

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

  770.     if (v >= m)

  771.         v = m - 1;

  772.     assert(v >= -m);

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

  774. }

  775. 

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

  777.    frame */

  778. static void output_audio_block(AC3EncodeContext *s,

  779.                                uint8_t exp_strategy[AC3_MAX_CHANNELS],

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

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

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

  783.                                int8_t global_exp[AC3_MAX_CHANNELS],

  784.                                int block_num)

  785. {

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

  787.     uint8_t *p;

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

  789.     int exp0, exp1;

  790.     int mant1_cnt, mant2_cnt, mant4_cnt;

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

  792.     int delta0, delta1, delta2;

  793. 

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

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

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

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

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

  799.     if (block_num == 0) {

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

  801.            waste of bit :-) */

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

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

  804.     } else {

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

  806.     }

  807. 

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

  809.       {

  810.         if(block_num==0)

  811.           {

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

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

  814. 

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

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

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

  818.           }

  819.         else

  820.           {

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

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

  823.           }

  824.       }

  825. 

  826. #if defined(DEBUG)

  827.     {

  828.       static int count = 0;

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

  830.     }

  831. #endif

  832.     /* exponent strategy */

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

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

  835.     }

  836. 

  837.     if (s->lfe) {

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

  839.     }

  840. 

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

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

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

  844.     }

  845. 

  846.     /* exponents */

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

  848.         switch(exp_strategy[ch]) {

  849.         case EXP_REUSE:

  850.             continue;

  851.         case EXP_D15:

  852.             group_size = 1;

  853.             break;

  854.         case EXP_D25:

  855.             group_size = 2;

  856.             break;

  857.         default:

  858.         case EXP_D45:

  859.             group_size = 4;

  860.             break;

  861.         }

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

  863.         p = encoded_exp[ch];

  864. 

  865.         /* first exponent */

  866.         exp1 = *p++;

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

  868. 

  869.         /* next ones are delta encoded */

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

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

  872.             exp0 = exp1;

  873.             exp1 = p[0];

  874.             p += group_size;

  875.             delta0 = exp1 - exp0 + 2;

  876. 

  877.             exp0 = exp1;

  878.             exp1 = p[0];

  879.             p += group_size;

  880.             delta1 = exp1 - exp0 + 2;

  881. 

  882.             exp0 = exp1;

  883.             exp1 = p[0];

  884.             p += group_size;

  885.             delta2 = exp1 - exp0 + 2;

  886. 

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

  888.         }

  889. 

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

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

  892.     }

  893. 

  894.     /* bit allocation info */

  895.     baie = (block_num == 0);

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

  897.     if (baie) {

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

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

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

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

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

  903.     }

  904. 

  905.     /* snr offset */

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

  907.     if (baie) {

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

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

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

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

  912.         }

  913.     }

  914. 

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

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

  917. 

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

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

  920.        modify the output stream. */

  921. 

  922.     /* first pass: quantize */

  923.     mant1_cnt = mant2_cnt = mant4_cnt = 0;

  924.     qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

  925. 

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

  927.         int b, c, e, v;

  928. 

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

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

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

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

  933.             switch(b) {

  934.             case 0:

  935.                 v = 0;

  936.                 break;

  937.             case 1:

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

  939.                 switch(mant1_cnt) {

  940.                 case 0:

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

  942.                     v = 9 * v;

  943.                     mant1_cnt = 1;

  944.                     break;

  945.                 case 1:

  946.                     *qmant1_ptr += 3 * v;

  947.                     mant1_cnt = 2;

  948.                     v = 128;

  949.                     break;

  950.                 default:

  951.                     *qmant1_ptr += v;

  952.                     mant1_cnt = 0;

  953.                     v = 128;

  954.                     break;

  955.                 }

  956.                 break;

  957.             case 2:

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

  959.                 switch(mant2_cnt) {

  960.                 case 0:

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

  962.                     v = 25 * v;

  963.                     mant2_cnt = 1;

  964.                     break;

  965.                 case 1:

  966.                     *qmant2_ptr += 5 * v;

  967.                     mant2_cnt = 2;

  968.                     v = 128;

  969.                     break;

  970.                 default:

  971.                     *qmant2_ptr += v;

  972.                     mant2_cnt = 0;

  973.                     v = 128;

  974.                     break;

  975.                 }

  976.                 break;

  977.             case 3:

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

  979.                 break;

  980.             case 4:

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

  982.                 switch(mant4_cnt) {

  983.                 case 0:

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

  985.                     v = 11 * v;

  986.                     mant4_cnt = 1;

  987.                     break;

  988.                 default:

  989.                     *qmant4_ptr += v;

  990.                     mant4_cnt = 0;

  991.                     v = 128;

  992.                     break;

  993.                 }

  994.                 break;

  995.             case 5:

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

  997.                 break;

  998.             case 14:

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

  1000.                 break;

  1001.             case 15:

  1002.                 v = asym_quant(c, e, 16);

  1003.                 break;

  1004.             default:

  1005.                 v = asym_quant(c, e, b - 1);

  1006.                 break;

  1007.             }

  1008.             qmant[ch][i] = v;

  1009.         }

  1010.     }

  1011. 

  1012.     /* second pass : output the values */

  1013.     for (ch = 0; ch < s->nb_all_channels; ch++) {

  1014.         int b, q;

  1015. 

  1016.         for(i=0;i<s->nb_coefs[ch];i++) {

  1017.             q = qmant[ch][i];

  1018.             b = bap[ch][i];

  1019.             switch(b) {

  1020.             case 0:

  1021.                 break;

  1022.             case 1:

  1023.                 if (q != 128)

  1024.                     put_bits(&s->pb, 5, q);

  1025.                 break;

  1026.             case 2:

  1027.                 if (q != 128)

  1028.                     put_bits(&s->pb, 7, q);

  1029.                 break;

  1030.             case 3:

  1031.                 put_bits(&s->pb, 3, q);

  1032.                 break;

  1033.             case 4:

  1034.                 if (q != 128)

  1035.                     put_bits(&s->pb, 7, q);

  1036.                 break;

  1037.             case 14:

  1038.                 put_bits(&s->pb, 14, q);

  1039.                 break;

  1040.             case 15:

  1041.                 put_bits(&s->pb, 16, q);

  1042.                 break;

  1043.             default:

  1044.                 put_bits(&s->pb, b - 1, q);

  1045.                 break;

  1046.             }

  1047.         }

  1048.     }

  1049. }

  1050. 

  1051. #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

  1052. 

  1053. static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

  1054. {

  1055.     unsigned int c;

  1056. 

  1057.     c = 0;

  1058.     while (a) {

  1059.         if (a & 1)

  1060.             c ^= b;

  1061.         a = a >> 1;

  1062.         b = b << 1;

  1063.         if (b & (1 << 16))

  1064.             b ^= poly;

  1065.     }

  1066.     return c;

  1067. }

  1068. 

  1069. static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

  1070. {

  1071.     unsigned int r;

  1072.     r = 1;

  1073.     while (n) {

  1074.         if (n & 1)

  1075.             r = mul_poly(r, a, poly);

  1076.         a = mul_poly(a, a, poly);

  1077.         n >>= 1;

  1078.     }

  1079.     return r;

  1080. }

  1081. 

  1082. 

  1083. /* compute log2(max(abs(tab[]))) */

  1084. static int log2_tab(int16_t *tab, int n)

  1085. {

  1086.     int i, v;

  1087. 

  1088.     v = 0;

  1089.     for(i=0;i<n;i++) {

  1090.         v |= abs(tab[i]);

  1091.     }

  1092.     return av_log2(v);

  1093. }

  1094. 

  1095. static void lshift_tab(int16_t *tab, int n, int lshift)

  1096. {

  1097.     int i;

  1098. 

  1099.     if (lshift > 0) {

  1100.         for(i=0;i<n;i++) {

  1101.             tab[i] <<= lshift;

  1102.         }

  1103.     } else if (lshift < 0) {

  1104.         lshift = -lshift;

  1105.         for(i=0;i<n;i++) {

  1106.             tab[i] >>= lshift;

  1107.         }

  1108.     }

  1109. }

  1110. 

  1111. /* fill the end of the frame and compute the two crcs */

  1112. static int output_frame_end(AC3EncodeContext *s)

  1113. {

  1114.     int frame_size, frame_size_58, n, crc1, crc2, crc_inv;

  1115.     uint8_t *frame;

  1116. 

  1117.     frame_size = s->frame_size; /* frame size in words */

  1118.     /* align to 8 bits */

  1119.     flush_put_bits(&s->pb);

  1120.     /* add zero bytes to reach the frame size */

  1121.     frame = s->pb.buf;

  1122.     n = 2 * s->frame_size - (put_bits_ptr(&s->pb) - frame) - 2;

  1123.     assert(n >= 0);

  1124.     if(n>0)

  1125.       memset(put_bits_ptr(&s->pb), 0, n);

  1126. 

  1127.     /* Now we must compute both crcs : this is not so easy for crc1

  1128.        because it is at the beginning of the data... */

  1129.     frame_size_58 = (frame_size >> 1) + (frame_size >> 3);

  1130.     crc1 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

  1131.                            frame + 4, 2 * frame_size_58 - 4));

  1132.     /* XXX: could precompute crc_inv */

  1133.     crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);

  1134.     crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);

  1135.     AV_WB16(frame+2,crc1);

  1136. 

  1137.     crc2 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,

  1138.                            frame + 2 * frame_size_58,

  1139.                            (frame_size - frame_size_58) * 2 - 2));

  1140.     AV_WB16(frame+2*frame_size-2,crc2);

  1141. 

  1142.     //    printf("n=%d frame_size=%d\n", n, frame_size);

  1143.     return frame_size * 2;

  1144. }

  1145. 

  1146. static int AC3_encode_frame(AVCodecContext *avctx,

  1147.                             unsigned char *frame, int buf_size, void *data)

  1148. {

  1149.     AC3EncodeContext *s = avctx->priv_data;

  1150.     int16_t *samples = data;

  1151.     int i, j, k, v, ch;

  1152.     int16_t input_samples[N];

  1153.     int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1154.     uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1155.     uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];

  1156.     uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1157.     uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

  1158.     int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];

  1159.     int frame_bits;

  1160. 

  1161.     frame_bits = 0;

  1162.     for(ch=0;ch<s->nb_all_channels;ch++) {

  1163.         int ich = s->channel_map[ch];

  1164.         /* fixed mdct to the six sub blocks & exponent computation */

  1165.         for(i=0;i<NB_BLOCKS;i++) {

  1166.             int16_t *sptr;

  1167.             int sinc;

  1168. 

  1169.             /* compute input samples */

  1170.             memcpy(input_samples, s->last_samples[ich], N/2 * sizeof(int16_t));

  1171.             sinc = s->nb_all_channels;

  1172.             sptr = samples + (sinc * (N/2) * i) + ich;

  1173.             for(j=0;j<N/2;j++) {

  1174.                 v = *sptr;

  1175.                 input_samples[j + N/2] = v;

  1176.                 s->last_samples[ich][j] = v;

  1177.                 sptr += sinc;

  1178.             }

  1179. 

  1180.             /* apply the MDCT window */

  1181.             for(j=0;j<N/2;j++) {

  1182.                 input_samples[j] = MUL16(input_samples[j],

  1183.                                          ff_ac3_window[j]) >> 15;

  1184.                 input_samples[N-j-1] = MUL16(input_samples[N-j-1],

  1185.                                              ff_ac3_window[j]) >> 15;

  1186.             }

  1187. 

  1188.             /* Normalize the samples to use the maximum available

  1189.                precision */

  1190.             v = 14 - log2_tab(input_samples, N);

  1191.             if (v < 0)

  1192.                 v = 0;

  1193.             exp_samples[i][ch] = v - 9;

  1194.             lshift_tab(input_samples, N, v);

  1195. 

  1196.             /* do the MDCT */

  1197.             mdct512(mdct_coef[i][ch], input_samples);

  1198. 

  1199.             /* compute "exponents". We take into account the

  1200.                normalization there */

  1201.             for(j=0;j<N/2;j++) {

  1202.                 int e;

  1203.                 v = abs(mdct_coef[i][ch][j]);

  1204.                 if (v == 0)

  1205.                     e = 24;

  1206.                 else {

  1207.                     e = 23 - av_log2(v) + exp_samples[i][ch];

  1208.                     if (e >= 24) {

  1209.                         e = 24;

  1210.                         mdct_coef[i][ch][j] = 0;

  1211.                     }

  1212.                 }

  1213.                 exp[i][ch][j] = e;

  1214.             }

  1215.         }

  1216. 

  1217.         compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

  1218. 

  1219.         /* compute the exponents as the decoder will see them. The

  1220.            EXP_REUSE case must be handled carefully : we select the

  1221.            min of the exponents */

  1222.         i = 0;

  1223.         while (i < NB_BLOCKS) {

  1224.             j = i + 1;

  1225.             while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {

  1226.                 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);

  1227.                 j++;

  1228.             }

  1229.             frame_bits += encode_exp(encoded_exp[i][ch],

  1230.                                      exp[i][ch], s->nb_coefs[ch],

  1231.                                      exp_strategy[i][ch]);

  1232.             /* copy encoded exponents for reuse case */

  1233.             for(k=i+1;k<j;k++) {

  1234.                 memcpy(encoded_exp[k][ch], encoded_exp[i][ch],

  1235.                        s->nb_coefs[ch] * sizeof(uint8_t));

  1236.             }

  1237.             i = j;

  1238.         }

  1239.     }

  1240. 

  1241.     /* adjust for fractional frame sizes */

  1242.     while(s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {

  1243.         s->bits_written -= s->bit_rate;

  1244.         s->samples_written -= s->sample_rate;

  1245.     }

  1246.     s->frame_size = s->frame_size_min + (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);

  1247.     s->bits_written += s->frame_size * 16;

  1248.     s->samples_written += AC3_FRAME_SIZE;

  1249. 

  1250.     compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);

  1251.     /* everything is known... let's output the frame */

  1252.     output_frame_header(s, frame);

  1253. 

  1254.     for(i=0;i<NB_BLOCKS;i++) {

  1255.         output_audio_block(s, exp_strategy[i], encoded_exp[i],

  1256.                            bap[i], mdct_coef[i], exp_samples[i], i);

  1257.     }

  1258.     return output_frame_end(s);

  1259. }

  1260. 

  1261. static av_cold int AC3_encode_close(AVCodecContext *avctx)

  1262. {

  1263.     av_freep(&avctx->coded_frame);

  1264.     return 0;

  1265. }

  1266. 

  1267. #if 0

  1268. /*************************************************************************/

  1269. /* TEST */

  1270. 

  1271. #undef random

  1272. #define FN (N/4)

  1273. 

  1274. void fft_test(void)

  1275. {

  1276.     IComplex in[FN], in1[FN];

  1277.     int k, n, i;

  1278.     float sum_re, sum_im, a;

  1279. 

  1280.     /* FFT test */

  1281. 

  1282.     for(i=0;i<FN;i++) {

  1283.         in[i].re = random() % 65535 - 32767;

  1284.         in[i].im = random() % 65535 - 32767;

  1285.         in1[i] = in[i];

  1286.     }

  1287.     fft(in, 7);

  1288. 

  1289.     /* do it by hand */

  1290.     for(k=0;k<FN;k++) {

  1291.         sum_re = 0;

  1292.         sum_im = 0;

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

  1294.             a = -2 * M_PI * (n * k) / FN;

  1295.             sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);

  1296.             sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);

  1297.         }

  1298.         printf("%3d: %6d,%6d %6.0f,%6.0f\n",

  1299.                k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);

  1300.     }

  1301. }

  1302. 

  1303. void mdct_test(void)

  1304. {

  1305.     int16_t input[N];

  1306.     int32_t output[N/2];

  1307.     float input1[N];

  1308.     float output1[N/2];

  1309.     float s, a, err, e, emax;

  1310.     int i, k, n;

  1311. 

  1312.     for(i=0;i<N;i++) {

  1313.         input[i] = (random() % 65535 - 32767) * 9 / 10;

  1314.         input1[i] = input[i];

  1315.     }

  1316. 

  1317.     mdct512(output, input);

  1318. 

  1319.     /* do it by hand */

  1320.     for(k=0;k<N/2;k++) {

  1321.         s = 0;

  1322.         for(n=0;n<N;n++) {

  1323.             a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));

  1324.             s += input1[n] * cos(a);

  1325.         }

  1326.         output1[k] = -2 * s / N;

  1327.     }

  1328. 

  1329.     err = 0;

  1330.     emax = 0;

  1331.     for(i=0;i<N/2;i++) {

  1332.         printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);

  1333.         e = output[i] - output1[i];

  1334.         if (e > emax)

  1335.             emax = e;

  1336.         err += e * e;

  1337.     }

  1338.     printf("err2=%f emax=%f\n", err / (N/2), emax);

  1339. }

  1340. 

  1341. void test_ac3(void)

  1342. {

  1343.     AC3EncodeContext ctx;

  1344.     unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];

  1345.     short samples[AC3_FRAME_SIZE];

  1346.     int ret, i;

  1347. 

  1348.     AC3_encode_init(&ctx, 44100, 64000, 1);

  1349. 

  1350.     fft_test();

  1351.     mdct_test();

  1352. 

  1353.     for(i=0;i<AC3_FRAME_SIZE;i++)

  1354.         samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);

  1355.     ret = AC3_encode_frame(&ctx, frame, samples);

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

  1357. }

  1358. #endif

  1359. 

  1360. AVCodec ac3_encoder = {

  1361.     "ac3",

  1362.     CODEC_TYPE_AUDIO,

  1363.     CODEC_ID_AC3,

  1364.     sizeof(AC3EncodeContext),

  1365.     AC3_encode_init,

  1366.     AC3_encode_frame,

  1367.     AC3_encode_close,

  1368.     NULL,

  1369.     .sample_fmts = (enum SampleFormat[]){SAMPLE_FMT_S16,SAMPLE_FMT_NONE},

  1370.     .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),

  1371. };