libavcodec/mpegaudio.c

   1 /*
   2  * The simplest mpeg audio layer 2 encoder
   3  * Copyright (c) 2000, 2001 Fabrice Bellard.
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; either
   8  * version 2 of the License, or (at your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public
  16  * License along with this library; if not, write to the Free Software
  17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  18  */
  19 #include "avcodec.h"
  20 #include "mpegaudio.h"
  21
  22 /* currently, cannot change these constants (need to modify
  23    quantization stage) */
  24 #define FRAC_BITS 15
  25 #define WFRAC_BITS  14
  26 #define MUL(a,b) (((INT64)(a) * (INT64)(b)) >> FRAC_BITS)
  27 #define FIX(a)   ((int)((a) * (1 << FRAC_BITS)))
  28
  29 #define SAMPLES_BUF_SIZE 4096
  30
  31 typedef struct MpegAudioContext {
  32     PutBitContext pb;
  33     int nb_channels;
  34     int freq, bit_rate;
  35     int lsf;           /* 1 if mpeg2 low bitrate selected */
  36     int bitrate_index; /* bit rate */
  37     int freq_index;
  38     int frame_size; /* frame size, in bits, without padding */
  39     INT64 nb_samples; /* total number of samples encoded */
  40     /* padding computation */
  41     int frame_frac, frame_frac_incr, do_padding;
  42     short samples_buf[MPA_MAX_CHANNELS][SAMPLES_BUF_SIZE]; /* buffer for filter */
  43     int samples_offset[MPA_MAX_CHANNELS];       /* offset in samples_buf */
  44     int sb_samples[MPA_MAX_CHANNELS][3][12][SBLIMIT];
  45     unsigned char scale_factors[MPA_MAX_CHANNELS][SBLIMIT][3]; /* scale factors */
  46     /* code to group 3 scale factors */
  47     unsigned char scale_code[MPA_MAX_CHANNELS][SBLIMIT];
  48     int sblimit; /* number of used subbands */
  49     const unsigned char *alloc_table;
  50 } MpegAudioContext;
  51
  52 /* define it to use floats in quantization (I don't like floats !) */
  53 //#define USE_FLOATS
  54
  55 #include "mpegaudiotab.h"
  56
  57 int MPA_encode_init(AVCodecContext *avctx)
  58 {
  59     MpegAudioContext *s = avctx->priv_data;
  60     int freq = avctx->sample_rate;
  61     int bitrate = avctx->bit_rate;
  62     int channels = avctx->channels;
  63     int i, v, table;
  64     float a;
  65
  66     if (channels > 2)
  67         return -1;
  68     bitrate = bitrate / 1000;
  69     s->nb_channels = channels;
  70     s->freq = freq;
  71     s->bit_rate = bitrate * 1000;
  72     avctx->frame_size = MPA_FRAME_SIZE;
  73     avctx->key_frame = 1; /* always key frame */
  74
  75     /* encoding freq */
  76     s->lsf = 0;
  77     for(i=0;i<3;i++) {
  78         if (mpa_freq_tab[i] == freq)
  79             break;
  80         if ((mpa_freq_tab[i] / 2) == freq) {
  81             s->lsf = 1;
  82             break;
  83         }
  84     }
  85     if (i == 3)
  86         return -1;
  87     s->freq_index = i;
  88
  89     /* encoding bitrate & frequency */
  90     for(i=0;i<15;i++) {
  91         if (mpa_bitrate_tab[s->lsf][1][i] == bitrate)
  92             break;
  93     }
  94     if (i == 15)
  95         return -1;
  96     s->bitrate_index = i;
  97
  98     /* compute total header size & pad bit */
  99
 100     a = (float)(bitrate * 1000 * MPA_FRAME_SIZE) / (freq * 8.0);
 101     s->frame_size = ((int)a) * 8;
 102
 103     /* frame fractional size to compute padding */
 104     s->frame_frac = 0;
 105     s->frame_frac_incr = (int)((a - floor(a)) * 65536.0);
 106
 107     /* select the right allocation table */
 108     table = l2_select_table(bitrate, s->nb_channels, freq, s->lsf);
 109
 110     /* number of used subbands */
 111     s->sblimit = sblimit_table[table];
 112     s->alloc_table = alloc_tables[table];
 113
 114 #ifdef DEBUG
 115     printf("%d kb/s, %d Hz, frame_size=%d bits, table=%d, padincr=%x\n",
 116            bitrate, freq, s->frame_size, table, s->frame_frac_incr);
 117 #endif
 118
 119     for(i=0;i<s->nb_channels;i++)
 120         s->samples_offset[i] = 0;
 121
 122     for(i=0;i<257;i++) {
 123         int v;
 124         v = mpa_enwindow[i];
 125 #if WFRAC_BITS != 16
 126         v = (v + (1 << (16 - WFRAC_BITS - 1))) >> (16 - WFRAC_BITS);
 127 #endif
 128         filter_bank[i] = v;
 129         if ((i & 63) != 0)
 130             v = -v;
 131         if (i != 0)
 132             filter_bank[512 - i] = v;
 133     }
 134
 135     for(i=0;i<64;i++) {
 136         v = (int)(pow(2.0, (3 - i) / 3.0) * (1 << 20));
 137         if (v <= 0)
 138             v = 1;
 139         scale_factor_table[i] = v;
 140 #ifdef USE_FLOATS
 141         scale_factor_inv_table[i] = pow(2.0, -(3 - i) / 3.0) / (float)(1 << 20);
 142 #else
 143 #define P 15
 144         scale_factor_shift[i] = 21 - P - (i / 3);
 145         scale_factor_mult[i] = (1 << P) * pow(2.0, (i % 3) / 3.0);
 146 #endif
 147     }
 148     for(i=0;i<128;i++) {
 149         v = i - 64;
 150         if (v <= -3)
 151             v = 0;
 152         else if (v < 0)
 153             v = 1;
 154         else if (v == 0)
 155             v = 2;
 156         else if (v < 3)
 157             v = 3;
 158         else
 159             v = 4;
 160         scale_diff_table[i] = v;
 161     }
 162
 163     for(i=0;i<17;i++) {
 164         v = quant_bits[i];
 165         if (v < 0)
 166             v = -v;
 167         else
 168             v = v * 3;
 169         total_quant_bits[i] = 12 * v;
 170     }
 171
 172     return 0;
 173 }
 174
 175 /* 32 point floating point IDCT without 1/sqrt(2) coef zero scaling */
 176 static void idct32(int *out, int *tab)
 177 {
 178     int i, j;
 179     int *t, *t1, xr;
 180     const int *xp = costab32;
 181
 182     for(j=31;j>=3;j-=2) tab[j] += tab[j - 2];
 183
 184     t = tab + 30;
 185     t1 = tab + 2;
 186     do {
 187         t[0] += t[-4];
 188         t[1] += t[1 - 4];
 189         t -= 4;
 190     } while (t != t1);
 191
 192     t = tab + 28;
 193     t1 = tab + 4;
 194     do {
 195         t[0] += t[-8];
 196         t[1] += t[1-8];
 197         t[2] += t[2-8];
 198         t[3] += t[3-8];
 199         t -= 8;
 200     } while (t != t1);
 201
 202     t = tab;
 203     t1 = tab + 32;
 204     do {
 205         t[ 3] = -t[ 3];
 206         t[ 6] = -t[ 6];
 207
 208         t[11] = -t[11];
 209         t[12] = -t[12];
 210         t[13] = -t[13];
 211         t[15] = -t[15];
 212         t += 16;
 213     } while (t != t1);
 214
 215
 216     t = tab;
 217     t1 = tab + 8;
 218     do {
 219         int x1, x2, x3, x4;
 220
 221         x3 = MUL(t[16], FIX(SQRT2*0.5));
 222         x4 = t[0] - x3;
 223         x3 = t[0] + x3;
 224
 225         x2 = MUL(-(t[24] + t[8]), FIX(SQRT2*0.5));
 226         x1 = MUL((t[8] - x2), xp[0]);
 227         x2 = MUL((t[8] + x2), xp[1]);
 228
 229         t[ 0] = x3 + x1;
 230         t[ 8] = x4 - x2;
 231         t[16] = x4 + x2;
 232         t[24] = x3 - x1;
 233         t++;
 234     } while (t != t1);
 235
 236     xp += 2;
 237     t = tab;
 238     t1 = tab + 4;
 239     do {
 240         xr = MUL(t[28],xp[0]);
 241         t[28] = (t[0] - xr);
 242         t[0] = (t[0] + xr);
 243
 244         xr = MUL(t[4],xp[1]);
 245         t[ 4] = (t[24] - xr);
 246         t[24] = (t[24] + xr);
 247
 248         xr = MUL(t[20],xp[2]);
 249         t[20] = (t[8] - xr);
 250         t[ 8] = (t[8] + xr);
 251
 252         xr = MUL(t[12],xp[3]);
 253         t[12] = (t[16] - xr);
 254         t[16] = (t[16] + xr);
 255         t++;
 256     } while (t != t1);
 257     xp += 4;
 258
 259     for (i = 0; i < 4; i++) {
 260         xr = MUL(tab[30-i*4],xp[0]);
 261         tab[30-i*4] = (tab[i*4] - xr);
 262         tab[   i*4] = (tab[i*4] + xr);
 263
 264         xr = MUL(tab[ 2+i*4],xp[1]);
 265         tab[ 2+i*4] = (tab[28-i*4] - xr);
 266         tab[28-i*4] = (tab[28-i*4] + xr);
 267
 268         xr = MUL(tab[31-i*4],xp[0]);
 269         tab[31-i*4] = (tab[1+i*4] - xr);
 270         tab[ 1+i*4] = (tab[1+i*4] + xr);
 271
 272         xr = MUL(tab[ 3+i*4],xp[1]);
 273         tab[ 3+i*4] = (tab[29-i*4] - xr);
 274         tab[29-i*4] = (tab[29-i*4] + xr);
 275
 276         xp += 2;
 277     }
 278
 279     t = tab + 30;
 280     t1 = tab + 1;
 281     do {
 282         xr = MUL(t1[0], *xp);
 283         t1[0] = (t[0] - xr);
 284         t[0] = (t[0] + xr);
 285         t -= 2;
 286         t1 += 2;
 287         xp++;
 288     } while (t >= tab);
 289
 290     for(i=0;i<32;i++) {
 291         out[i] = tab[bitinv32[i]];
 292     }
 293 }
 294
 295 #define WSHIFT (WFRAC_BITS + 15 - FRAC_BITS)
 296
 297 static void filter(MpegAudioContext *s, int ch, short *samples, int incr)
 298 {
 299     short *p, *q;
 300     int sum, offset, i, j;
 301     int tmp[64];
 302     int tmp1[32];
 303     int *out;
 304
 305     //    print_pow1(samples, 1152);
 306
 307     offset = s->samples_offset[ch];
 308     out = &s->sb_samples[ch][0][0][0];
 309     for(j=0;j<36;j++) {
 310         /* 32 samples at once */
 311         for(i=0;i<32;i++) {
 312             s->samples_buf[ch][offset + (31 - i)] = samples[0];
 313             samples += incr;
 314         }
 315
 316         /* filter */
 317         p = s->samples_buf[ch] + offset;
 318         q = filter_bank;
 319         /* maxsum = 23169 */
 320         for(i=0;i<64;i++) {
 321             sum = p[0*64] * q[0*64];
 322             sum += p[1*64] * q[1*64];
 323             sum += p[2*64] * q[2*64];
 324             sum += p[3*64] * q[3*64];
 325             sum += p[4*64] * q[4*64];
 326             sum += p[5*64] * q[5*64];
 327             sum += p[6*64] * q[6*64];
 328             sum += p[7*64] * q[7*64];
 329             tmp[i] = sum;
 330             p++;
 331             q++;
 332         }
 333         tmp1[0] = tmp[16] >> WSHIFT;
 334         for( i=1; i<=16; i++ ) tmp1[i] = (tmp[i+16]+tmp[16-i]) >> WSHIFT;
 335         for( i=17; i<=31; i++ ) tmp1[i] = (tmp[i+16]-tmp[80-i]) >> WSHIFT;
 336
 337         idct32(out, tmp1);
 338
 339         /* advance of 32 samples */
 340         offset -= 32;
 341         out += 32;
 342         /* handle the wrap around */
 343         if (offset < 0) {
 344             memmove(s->samples_buf[ch] + SAMPLES_BUF_SIZE - (512 - 32),
 345                     s->samples_buf[ch], (512 - 32) * 2);
 346             offset = SAMPLES_BUF_SIZE - 512;
 347         }
 348     }
 349     s->samples_offset[ch] = offset;
 350
 351     //    print_pow(s->sb_samples, 1152);
 352 }
 353
 354 static void compute_scale_factors(unsigned char scale_code[SBLIMIT],
 355                                   unsigned char scale_factors[SBLIMIT][3],
 356                                   int sb_samples[3][12][SBLIMIT],
 357                                   int sblimit)
 358 {
 359     int *p, vmax, v, n, i, j, k, code;
 360     int index, d1, d2;
 361     unsigned char *sf = &scale_factors[0][0];
 362
 363     for(j=0;j<sblimit;j++) {
 364         for(i=0;i<3;i++) {
 365             /* find the max absolute value */
 366             p = &sb_samples[i][0][j];
 367             vmax = abs(*p);
 368             for(k=1;k<12;k++) {
 369                 p += SBLIMIT;
 370                 v = abs(*p);
 371                 if (v > vmax)
 372                     vmax = v;
 373             }
 374             /* compute the scale factor index using log 2 computations */
 375             if (vmax > 0) {
 376                 n = av_log2(vmax);
 377                 /* n is the position of the MSB of vmax. now
 378                    use at most 2 compares to find the index */
 379                 index = (21 - n) * 3 - 3;
 380                 if (index >= 0) {
 381                     while (vmax <= scale_factor_table[index+1])
 382                         index++;
 383                 } else {
 384                     index = 0; /* very unlikely case of overflow */
 385                 }
 386             } else {
 387                 index = 62; /* value 63 is not allowed */
 388             }
 389
 390 #if 0
 391             printf("%2d:%d in=%x %x %d\n",
 392                    j, i, vmax, scale_factor_table[index], index);
 393 #endif
 394             /* store the scale factor */
 395             assert(index >=0 && index <= 63);
 396             sf[i] = index;
 397         }
 398
 399         /* compute the transmission factor : look if the scale factors
 400            are close enough to each other */
 401         d1 = scale_diff_table[sf[0] - sf[1] + 64];
 402         d2 = scale_diff_table[sf[1] - sf[2] + 64];
 403
 404         /* handle the 25 cases */
 405         switch(d1 * 5 + d2) {
 406         case 0*5+0:
 407         case 0*5+4:
 408         case 3*5+4:
 409         case 4*5+0:
 410         case 4*5+4:
 411             code = 0;
 412             break;
 413         case 0*5+1:
 414         case 0*5+2:
 415         case 4*5+1:
 416         case 4*5+2:
 417             code = 3;
 418             sf[2] = sf[1];
 419             break;
 420         case 0*5+3:
 421         case 4*5+3:
 422             code = 3;
 423             sf[1] = sf[2];
 424             break;
 425         case 1*5+0:
 426         case 1*5+4:
 427         case 2*5+4:
 428             code = 1;
 429             sf[1] = sf[0];
 430             break;
 431         case 1*5+1:
 432         case 1*5+2:
 433         case 2*5+0:
 434         case 2*5+1:
 435         case 2*5+2:
 436             code = 2;
 437             sf[1] = sf[2] = sf[0];
 438             break;
 439         case 2*5+3:
 440         case 3*5+3:
 441             code = 2;
 442             sf[0] = sf[1] = sf[2];
 443             break;
 444         case 3*5+0:
 445         case 3*5+1:
 446         case 3*5+2:
 447             code = 2;
 448             sf[0] = sf[2] = sf[1];
 449             break;
 450         case 1*5+3:
 451             code = 2;
 452             if (sf[0] > sf[2])
 453               sf[0] = sf[2];
 454             sf[1] = sf[2] = sf[0];
 455             break;
 456         default:
 457             abort();
 458         }
 459
 460 #if 0
 461         printf("%d: %2d %2d %2d %d %d -> %d\n", j,
 462                sf[0], sf[1], sf[2], d1, d2, code);
 463 #endif
 464         scale_code[j] = code;
 465         sf += 3;
 466     }
 467 }
 468
 469 /* The most important function : psycho acoustic module. In this
 470    encoder there is basically none, so this is the worst you can do,
 471    but also this is the simpler. */
 472 static void psycho_acoustic_model(MpegAudioContext *s, short smr[SBLIMIT])
 473 {
 474     int i;
 475
 476     for(i=0;i<s->sblimit;i++) {
 477         smr[i] = (int)(fixed_smr[i] * 10);
 478     }
 479 }
 480
 481
 482 #define SB_NOTALLOCATED  0
 483 #define SB_ALLOCATED     1
 484 #define SB_NOMORE        2
 485
 486 /* Try to maximize the smr while using a number of bits inferior to
 487    the frame size. I tried to make the code simpler, faster and
 488    smaller than other encoders :-) */
 489 static void compute_bit_allocation(MpegAudioContext *s,
 490                                    short smr1[MPA_MAX_CHANNELS][SBLIMIT],
 491                                    unsigned char bit_alloc[MPA_MAX_CHANNELS][SBLIMIT],
 492                                    int *padding)
 493 {
 494     int i, ch, b, max_smr, max_ch, max_sb, current_frame_size, max_frame_size;
 495     int incr;
 496     short smr[MPA_MAX_CHANNELS][SBLIMIT];
 497     unsigned char subband_status[MPA_MAX_CHANNELS][SBLIMIT];
 498     const unsigned char *alloc;
 499
 500     memcpy(smr, smr1, s->nb_channels * sizeof(short) * SBLIMIT);
 501     memset(subband_status, SB_NOTALLOCATED, s->nb_channels * SBLIMIT);
 502     memset(bit_alloc, 0, s->nb_channels * SBLIMIT);
 503
 504     /* compute frame size and padding */
 505     max_frame_size = s->frame_size;
 506     s->frame_frac += s->frame_frac_incr;
 507     if (s->frame_frac >= 65536) {
 508         s->frame_frac -= 65536;
 509         s->do_padding = 1;
 510         max_frame_size += 8;
 511     } else {
 512         s->do_padding = 0;
 513     }
 514
 515     /* compute the header + bit alloc size */
 516     current_frame_size = 32;
 517     alloc = s->alloc_table;
 518     for(i=0;i<s->sblimit;i++) {
 519         incr = alloc[0];
 520         current_frame_size += incr * s->nb_channels;
 521         alloc += 1 << incr;
 522     }
 523     for(;;) {
 524         /* look for the subband with the largest signal to mask ratio */
 525         max_sb = -1;
 526         max_ch = -1;
 527         max_smr = 0x80000000;
 528         for(ch=0;ch<s->nb_channels;ch++) {
 529             for(i=0;i<s->sblimit;i++) {
 530                 if (smr[ch][i] > max_smr && subband_status[ch][i] != SB_NOMORE) {
 531                     max_smr = smr[ch][i];
 532                     max_sb = i;
 533                     max_ch = ch;
 534                 }
 535             }
 536         }
 537 #if 0
 538         printf("current=%d max=%d max_sb=%d alloc=%d\n",
 539                current_frame_size, max_frame_size, max_sb,
 540                bit_alloc[max_sb]);
 541 #endif
 542         if (max_sb < 0)
 543             break;
 544
 545         /* find alloc table entry (XXX: not optimal, should use
 546            pointer table) */
 547         alloc = s->alloc_table;
 548         for(i=0;i<max_sb;i++) {
 549             alloc += 1 << alloc[0];
 550         }
 551
 552         if (subband_status[max_ch][max_sb] == SB_NOTALLOCATED) {
 553             /* nothing was coded for this band: add the necessary bits */
 554             incr = 2 + nb_scale_factors[s->scale_code[max_ch][max_sb]] * 6;
 555             incr += total_quant_bits[alloc[1]];
 556         } else {
 557             /* increments bit allocation */
 558             b = bit_alloc[max_ch][max_sb];
 559             incr = total_quant_bits[alloc[b + 1]] -
 560                 total_quant_bits[alloc[b]];
 561         }
 562
 563         if (current_frame_size + incr <= max_frame_size) {
 564             /* can increase size */
 565             b = ++bit_alloc[max_ch][max_sb];
 566             current_frame_size += incr;
 567             /* decrease smr by the resolution we added */
 568             smr[max_ch][max_sb] = smr1[max_ch][max_sb] - quant_snr[alloc[b]];
 569             /* max allocation size reached ? */
 570             if (b == ((1 << alloc[0]) - 1))
 571                 subband_status[max_ch][max_sb] = SB_NOMORE;
 572             else
 573                 subband_status[max_ch][max_sb] = SB_ALLOCATED;
 574         } else {
 575             /* cannot increase the size of this subband */
 576             subband_status[max_ch][max_sb] = SB_NOMORE;
 577         }
 578     }
 579     *padding = max_frame_size - current_frame_size;
 580     assert(*padding >= 0);
 581
 582 #if 0
 583     for(i=0;i<s->sblimit;i++) {
 584         printf("%d ", bit_alloc[i]);
 585     }
 586     printf("\n");
 587 #endif
 588 }
 589
 590 /*
 591  * Output the mpeg audio layer 2 frame. Note how the code is small
 592  * compared to other encoders :-)
 593  */
 594 static void encode_frame(MpegAudioContext *s,
 595                          unsigned char bit_alloc[MPA_MAX_CHANNELS][SBLIMIT],
 596                          int padding)
 597 {
 598     int i, j, k, l, bit_alloc_bits, b, ch;
 599     unsigned char *sf;
 600     int q[3];
 601     PutBitContext *p = &s->pb;
 602
 603     /* header */
 604
 605     put_bits(p, 12, 0xfff);
 606     put_bits(p, 1, 1 - s->lsf); /* 1 = mpeg1 ID, 0 = mpeg2 lsf ID */
 607     put_bits(p, 2, 4-2);  /* layer 2 */
 608     put_bits(p, 1, 1); /* no error protection */
 609     put_bits(p, 4, s->bitrate_index);
 610     put_bits(p, 2, s->freq_index);
 611     put_bits(p, 1, s->do_padding); /* use padding */
 612     put_bits(p, 1, 0);             /* private_bit */
 613     put_bits(p, 2, s->nb_channels == 2 ? MPA_STEREO : MPA_MONO);
 614     put_bits(p, 2, 0); /* mode_ext */
 615     put_bits(p, 1, 0); /* no copyright */
 616     put_bits(p, 1, 1); /* original */
 617     put_bits(p, 2, 0); /* no emphasis */
 618
 619     /* bit allocation */
 620     j = 0;
 621     for(i=0;i<s->sblimit;i++) {
 622         bit_alloc_bits = s->alloc_table[j];
 623         for(ch=0;ch<s->nb_channels;ch++) {
 624             put_bits(p, bit_alloc_bits, bit_alloc[ch][i]);
 625         }
 626         j += 1 << bit_alloc_bits;
 627     }
 628
 629     /* scale codes */
 630     for(i=0;i<s->sblimit;i++) {
 631         for(ch=0;ch<s->nb_channels;ch++) {
 632             if (bit_alloc[ch][i])
 633                 put_bits(p, 2, s->scale_code[ch][i]);
 634         }
 635     }
 636
 637     /* scale factors */
 638     for(i=0;i<s->sblimit;i++) {
 639         for(ch=0;ch<s->nb_channels;ch++) {
 640             if (bit_alloc[ch][i]) {
 641                 sf = &s->scale_factors[ch][i][0];
 642                 switch(s->scale_code[ch][i]) {
 643                 case 0:
 644                     put_bits(p, 6, sf[0]);
 645                     put_bits(p, 6, sf[1]);
 646                     put_bits(p, 6, sf[2]);
 647                     break;
 648                 case 3:
 649                 case 1:
 650                     put_bits(p, 6, sf[0]);
 651                     put_bits(p, 6, sf[2]);
 652                     break;
 653                 case 2:
 654                     put_bits(p, 6, sf[0]);
 655                     break;
 656                 }
 657             }
 658         }
 659     }
 660
 661     /* quantization & write sub band samples */
 662
 663     for(k=0;k<3;k++) {
 664         for(l=0;l<12;l+=3) {
 665             j = 0;
 666             for(i=0;i<s->sblimit;i++) {
 667                 bit_alloc_bits = s->alloc_table[j];
 668                 for(ch=0;ch<s->nb_channels;ch++) {
 669                     b = bit_alloc[ch][i];
 670                     if (b) {
 671                         int qindex, steps, m, sample, bits;
 672                         /* we encode 3 sub band samples of the same sub band at a time */
 673                         qindex = s->alloc_table[j+b];
 674                         steps = quant_steps[qindex];
 675                         for(m=0;m<3;m++) {
 676                             sample = s->sb_samples[ch][k][l + m][i];
 677                             /* divide by scale factor */
 678 #ifdef USE_FLOATS
 679                             {
 680                                 float a;
 681                                 a = (float)sample * scale_factor_inv_table[s->scale_factors[ch][i][k]];
 682                                 q[m] = (int)((a + 1.0) * steps * 0.5);
 683                             }
 684 #else
 685                             {
 686                                 int q1, e, shift, mult;
 687                                 e = s->scale_factors[ch][i][k];
 688                                 shift = scale_factor_shift[e];
 689                                 mult = scale_factor_mult[e];
 690
 691                                 /* normalize to P bits */
 692                                 if (shift < 0)
 693                                     q1 = sample << (-shift);
 694                                 else
 695                                     q1 = sample >> shift;
 696                                 q1 = (q1 * mult) >> P;
 697                                 q[m] = ((q1 + (1 << P)) * steps) >> (P + 1);
 698                             }
 699 #endif
 700                             if (q[m] >= steps)
 701                                 q[m] = steps - 1;
 702                             assert(q[m] >= 0 && q[m] < steps);
 703                         }
 704                         bits = quant_bits[qindex];
 705                         if (bits < 0) {
 706                             /* group the 3 values to save bits */
 707                             put_bits(p, -bits,
 708                                      q[0] + steps * (q[1] + steps * q[2]));
 709 #if 0
 710                             printf("%d: gr1 %d\n",
 711                                    i, q[0] + steps * (q[1] + steps * q[2]));
 712 #endif
 713                         } else {
 714 #if 0
 715                             printf("%d: gr3 %d %d %d\n",
 716                                    i, q[0], q[1], q[2]);
 717 #endif
 718                             put_bits(p, bits, q[0]);
 719                             put_bits(p, bits, q[1]);
 720                             put_bits(p, bits, q[2]);
 721                         }
 722                     }
 723                 }
 724                 /* next subband in alloc table */
 725                 j += 1 << bit_alloc_bits;
 726             }
 727         }
 728     }
 729
 730     /* padding */
 731     for(i=0;i<padding;i++)
 732         put_bits(p, 1, 0);
 733
 734     /* flush */
 735     flush_put_bits(p);
 736 }
 737
 738 int MPA_encode_frame(AVCodecContext *avctx,
 739                      unsigned char *frame, int buf_size, void *data)
 740 {
 741     MpegAudioContext *s = avctx->priv_data;
 742     short *samples = data;
 743     short smr[MPA_MAX_CHANNELS][SBLIMIT];
 744     unsigned char bit_alloc[MPA_MAX_CHANNELS][SBLIMIT];
 745     int padding, i;
 746
 747     for(i=0;i<s->nb_channels;i++) {
 748         filter(s, i, samples + i, s->nb_channels);
 749     }
 750
 751     for(i=0;i<s->nb_channels;i++) {
 752         compute_scale_factors(s->scale_code[i], s->scale_factors[i],
 753                               s->sb_samples[i], s->sblimit);
 754     }
 755     for(i=0;i<s->nb_channels;i++) {
 756         psycho_acoustic_model(s, smr[i]);
 757     }
 758     compute_bit_allocation(s, smr, bit_alloc, &padding);
 759
 760     init_put_bits(&s->pb, frame, MPA_MAX_CODED_FRAME_SIZE, NULL, NULL);
 761
 762     encode_frame(s, bit_alloc, padding);
 763
 764     s->nb_samples += MPA_FRAME_SIZE;
 765     return pbBufPtr(&s->pb) - s->pb.buf;
 766 }
 767
 768
 769 AVCodec mp2_encoder = {
 770     "mp2",
 771     CODEC_TYPE_AUDIO,
 772     CODEC_ID_MP2,
 773     sizeof(MpegAudioContext),
 774     MPA_encode_init,
 775     MPA_encode_frame,
 776     NULL,
 777 };
 778
 779 #undef FIX