libavcodec/mpegaudio.c

   1 /*
   2  * The simplest mpeg audio layer 2 encoder
   3  * Copyright (c) 2000, 2001 Gerard Lantau.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program 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
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  18  */
  19 #include "avcodec.h"
  20 #include <math.h>
  21 #include "mpegaudio.h"
  22
  23 /* currently, cannot change these constants (need to modify
  24    quantization stage) */
  25 #define FRAC_BITS 15
  26 #define WFRAC_BITS  14
  27 #define MUL(a,b) (((INT64)(a) * (INT64)(b)) >> FRAC_BITS)
  28 #define FIX(a)   ((int)((a) * (1 << FRAC_BITS)))
  29
  30 #define SAMPLES_BUF_SIZE 4096
  31
  32 typedef struct MpegAudioContext {
  33     PutBitContext pb;
  34     int nb_channels;
  35     int freq, bit_rate;
  36     int lsf;           /* 1 if mpeg2 low bitrate selected */
  37     int bitrate_index; /* bit rate */
  38     int freq_index;
  39     int frame_size; /* frame size, in bits, without padding */
  40     INT64 nb_samples; /* total number of samples encoded */
  41     /* padding computation */
  42     int frame_frac, frame_frac_incr, do_padding;
  43     short samples_buf[MPA_MAX_CHANNELS][SAMPLES_BUF_SIZE]; /* buffer for filter */
  44     int samples_offset[MPA_MAX_CHANNELS];       /* offset in samples_buf */
  45     int sb_samples[MPA_MAX_CHANNELS][3][12][SBLIMIT];
  46     unsigned char scale_factors[MPA_MAX_CHANNELS][SBLIMIT][3]; /* scale factors */
  47     /* code to group 3 scale factors */
  48     unsigned char scale_code[MPA_MAX_CHANNELS][SBLIMIT];
  49     int sblimit; /* number of used subbands */
  50     const unsigned char *alloc_table;
  51 } MpegAudioContext;
  52
  53 /* define it to use floats in quantization (I don't like floats !) */
  54 //#define USE_FLOATS
  55
  56 #include "mpegaudiotab.h"
  57
  58 int MPA_encode_init(AVCodecContext *avctx)
  59 {
  60     MpegAudioContext *s = avctx->priv_data;
  61     int freq = avctx->sample_rate;
  62     int bitrate = avctx->bit_rate;
  63     int channels = avctx->channels;
  64     int i, v, table;
  65     float a;
  66
  67     if (channels > 2)
  68         return -1;
  69     bitrate = bitrate / 1000;
  70     s->nb_channels = channels;
  71     s->freq = freq;
  72     s->bit_rate = bitrate * 1000;
  73     avctx->frame_size = MPA_FRAME_SIZE;
  74     avctx->key_frame = 1; /* always key frame */
  75
  76     /* encoding freq */
  77     s->lsf = 0;
  78     for(i=0;i<3;i++) {
  79         if (mpa_freq_tab[i] == freq)
  80             break;
  81         if ((mpa_freq_tab[i] / 2) == freq) {
  82             s->lsf = 1;
  83             break;
  84         }
  85     }
  86     if (i == 3)
  87         return -1;
  88     s->freq_index = i;
  89
  90     /* encoding bitrate & frequency */
  91     for(i=0;i<15;i++) {
  92         if (mpa_bitrate_tab[s->lsf][1][i] == bitrate)
  93             break;
  94     }
  95     if (i == 15)
  96         return -1;
  97     s->bitrate_index = i;
  98
  99     /* compute total header size & pad bit */
 100
 101     a = (float)(bitrate * 1000 * MPA_FRAME_SIZE) / (freq * 8.0);
 102     s->frame_size = ((int)a) * 8;
 103
 104     /* frame fractional size to compute padding */
 105     s->frame_frac = 0;
 106     s->frame_frac_incr = (int)((a - floor(a)) * 65536.0);
 107
 108     /* select the right allocation table */
 109     table = l2_select_table(bitrate, s->nb_channels, freq, s->lsf);
 110
 111     /* number of used subbands */
 112     s->sblimit = sblimit_table[table];
 113     s->alloc_table = alloc_tables[table];
 114
 115 #ifdef DEBUG
 116     printf("%d kb/s, %d Hz, frame_size=%d bits, table=%d, padincr=%x\n",
 117            bitrate, freq, s->frame_size, table, s->frame_frac_incr);
 118 #endif
 119
 120     for(i=0;i<s->nb_channels;i++)
 121         s->samples_offset[i] = 0;
 122
 123     for(i=0;i<257;i++) {
 124         int v;
 125         v = mpa_enwindow[i];
 126 #if WFRAC_BITS != 16
 127         v = (v + (1 << (16 - WFRAC_BITS - 1))) >> (16 - WFRAC_BITS);
 128 #endif
 129         filter_bank[i] = v;
 130         if ((i & 63) != 0)
 131             v = -v;
 132         if (i != 0)
 133             filter_bank[512 - i] = v;
 134     }
 135
 136     for(i=0;i<64;i++) {
 137         v = (int)(pow(2.0, (3 - i) / 3.0) * (1 << 20));
 138         if (v <= 0)
 139             v = 1;
 140         scale_factor_table[i] = v;
 141 #ifdef USE_FLOATS
 142         scale_factor_inv_table[i] = pow(2.0, -(3 - i) / 3.0) / (float)(1 << 20);
 143 #else
 144 #define P 15
 145         scale_factor_shift[i] = 21 - P - (i / 3);
 146         scale_factor_mult[i] = (1 << P) * pow(2.0, (i % 3) / 3.0);
 147 #endif
 148     }
 149     for(i=0;i<128;i++) {
 150         v = i - 64;
 151         if (v <= -3)
 152             v = 0;
 153         else if (v < 0)
 154             v = 1;
 155         else if (v == 0)
 156             v = 2;
 157         else if (v < 3)
 158             v = 3;
 159         else
 160             v = 4;
 161         scale_diff_table[i] = v;
 162     }
 163
 164     for(i=0;i<17;i++) {
 165         v = quant_bits[i];
 166         if (v < 0)
 167             v = -v;
 168         else
 169             v = v * 3;
 170         total_quant_bits[i] = 12 * v;
 171     }
 172
 173     return 0;
 174 }
 175
 176 /* 32 point floating point IDCT without 1/sqrt(2) coef zero scaling */
 177 static void idct32(int *out, int *tab)
 178 {
 179     int i, j;
 180     int *t, *t1, xr;
 181     const int *xp = costab32;
 182
 183     for(j=31;j>=3;j-=2) tab[j] += tab[j - 2];
 184
 185     t = tab + 30;
 186     t1 = tab + 2;
 187     do {
 188         t[0] += t[-4];
 189         t[1] += t[1 - 4];
 190         t -= 4;
 191     } while (t != t1);
 192
 193     t = tab + 28;
 194     t1 = tab + 4;
 195     do {
 196         t[0] += t[-8];
 197         t[1] += t[1-8];
 198         t[2] += t[2-8];
 199         t[3] += t[3-8];
 200         t -= 8;
 201     } while (t != t1);
 202
 203     t = tab;
 204     t1 = tab + 32;
 205     do {
 206         t[ 3] = -t[ 3];
 207         t[ 6] = -t[ 6];
 208
 209         t[11] = -t[11];
 210         t[12] = -t[12];
 211         t[13] = -t[13];
 212         t[15] = -t[15];
 213         t += 16;
 214     } while (t != t1);
 215
 216
 217     t = tab;
 218     t1 = tab + 8;
 219     do {
 220         int x1, x2, x3, x4;
 221
 222         x3 = MUL(t[16], FIX(SQRT2*0.5));
 223         x4 = t[0] - x3;
 224         x3 = t[0] + x3;
 225
 226         x2 = MUL(-(t[24] + t[8]), FIX(SQRT2*0.5));
 227         x1 = MUL((t[8] - x2), xp[0]);
 228         x2 = MUL((t[8] + x2), xp[1]);
 229
 230         t[ 0] = x3 + x1;
 231         t[ 8] = x4 - x2;
 232         t[16] = x4 + x2;
 233         t[24] = x3 - x1;
 234         t++;
 235     } while (t != t1);
 236
 237     xp += 2;
 238     t = tab;
 239     t1 = tab + 4;
 240     do {
 241         xr = MUL(t[28],xp[0]);
 242         t[28] = (t[0] - xr);
 243         t[0] = (t[0] + xr);
 244
 245         xr = MUL(t[4],xp[1]);
 246         t[ 4] = (t[24] - xr);
 247         t[24] = (t[24] + xr);
 248
 249         xr = MUL(t[20],xp[2]);
 250         t[20] = (t[8] - xr);
 251         t[ 8] = (t[8] + xr);
 252
 253         xr = MUL(t[12],xp[3]);
 254         t[12] = (t[16] - xr);
 255         t[16] = (t[16] + xr);
 256         t++;
 257     } while (t != t1);
 258     xp += 4;
 259
 260     for (i = 0; i < 4; i++) {
 261         xr = MUL(tab[30-i*4],xp[0]);
 262         tab[30-i*4] = (tab[i*4] - xr);
 263         tab[   i*4] = (tab[i*4] + xr);
 264
 265         xr = MUL(tab[ 2+i*4],xp[1]);
 266         tab[ 2+i*4] = (tab[28-i*4] - xr);
 267         tab[28-i*4] = (tab[28-i*4] + xr);
 268
 269         xr = MUL(tab[31-i*4],xp[0]);
 270         tab[31-i*4] = (tab[1+i*4] - xr);
 271         tab[ 1+i*4] = (tab[1+i*4] + xr);
 272
 273         xr = MUL(tab[ 3+i*4],xp[1]);
 274         tab[ 3+i*4] = (tab[29-i*4] - xr);
 275         tab[29-i*4] = (tab[29-i*4] + xr);
 276
 277         xp += 2;
 278     }
 279
 280     t = tab + 30;
 281     t1 = tab + 1;
 282     do {
 283         xr = MUL(t1[0], *xp);
 284         t1[0] = (t[0] - xr);
 285         t[0] = (t[0] + xr);
 286         t -= 2;
 287         t1 += 2;
 288         xp++;
 289     } while (t >= tab);
 290
 291     for(i=0;i<32;i++) {
 292         out[i] = tab[bitinv32[i]];
 293     }
 294 }
 295
 296 #define WSHIFT (WFRAC_BITS + 15 - FRAC_BITS)
 297
 298 static void filter(MpegAudioContext *s, int ch, short *samples, int incr)
 299 {
 300     short *p, *q;
 301     int sum, offset, i, j;
 302     int tmp[64];
 303     int tmp1[32];
 304     int *out;
 305
 306     //    print_pow1(samples, 1152);
 307
 308     offset = s->samples_offset[ch];
 309     out = &s->sb_samples[ch][0][0][0];
 310     for(j=0;j<36;j++) {
 311         /* 32 samples at once */
 312         for(i=0;i<32;i++) {
 313             s->samples_buf[ch][offset + (31 - i)] = samples[0];
 314             samples += incr;
 315         }
 316
 317         /* filter */
 318         p = s->samples_buf[ch] + offset;
 319         q = filter_bank;
 320         /* maxsum = 23169 */
 321         for(i=0;i<64;i++) {
 322             sum = p[0*64] * q[0*64];
 323             sum += p[1*64] * q[1*64];
 324             sum += p[2*64] * q[2*64];
 325             sum += p[3*64] * q[3*64];
 326             sum += p[4*64] * q[4*64];
 327             sum += p[5*64] * q[5*64];
 328             sum += p[6*64] * q[6*64];
 329             sum += p[7*64] * q[7*64];
 330             tmp[i] = sum;
 331             p++;
 332             q++;
 333         }
 334         tmp1[0] = tmp[16] >> WSHIFT;
 335         for( i=1; i<=16; i++ ) tmp1[i] = (tmp[i+16]+tmp[16-i]) >> WSHIFT;
 336         for( i=17; i<=31; i++ ) tmp1[i] = (tmp[i+16]-tmp[80-i]) >> WSHIFT;
 337
 338         idct32(out, tmp1);
 339
 340         /* advance of 32 samples */
 341         offset -= 32;
 342         out += 32;
 343         /* handle the wrap around */
 344         if (offset < 0) {
 345             memmove(s->samples_buf[ch] + SAMPLES_BUF_SIZE - (512 - 32),
 346                     s->samples_buf[ch], (512 - 32) * 2);
 347             offset = SAMPLES_BUF_SIZE - 512;
 348         }
 349     }
 350     s->samples_offset[ch] = offset;
 351
 352     //    print_pow(s->sb_samples, 1152);
 353 }
 354
 355 static void compute_scale_factors(unsigned char scale_code[SBLIMIT],
 356                                   unsigned char scale_factors[SBLIMIT][3],
 357                                   int sb_samples[3][12][SBLIMIT],
 358                                   int sblimit)
 359 {
 360     int *p, vmax, v, n, i, j, k, code;
 361     int index, d1, d2;
 362     unsigned char *sf = &scale_factors[0][0];
 363
 364     for(j=0;j<sblimit;j++) {
 365         for(i=0;i<3;i++) {
 366             /* find the max absolute value */
 367             p = &sb_samples[i][0][j];
 368             vmax = abs(*p);
 369             for(k=1;k<12;k++) {
 370                 p += SBLIMIT;
 371                 v = abs(*p);
 372                 if (v > vmax)
 373                     vmax = v;
 374             }
 375             /* compute the scale factor index using log 2 computations */
 376             if (vmax > 0) {
 377                 n = av_log2(vmax);
 378                 /* n is the position of the MSB of vmax. now
 379                    use at most 2 compares to find the index */
 380                 index = (21 - n) * 3 - 3;
 381                 if (index >= 0) {
 382                     while (vmax <= scale_factor_table[index+1])
 383                         index++;
 384                 } else {
 385                     index = 0; /* very unlikely case of overflow */
 386                 }
 387             } else {
 388                 index = 62; /* value 63 is not allowed */
 389             }
 390
 391 #if 0
 392             printf("%2d:%d in=%x %x %d\n",
 393                    j, i, vmax, scale_factor_table[index], index);
 394 #endif
 395             /* store the scale factor */
 396             assert(index >=0 && index <= 63);
 397             sf[i] = index;
 398         }
 399
 400         /* compute the transmission factor : look if the scale factors
 401            are close enough to each other */
 402         d1 = scale_diff_table[sf[0] - sf[1] + 64];
 403         d2 = scale_diff_table[sf[1] - sf[2] + 64];
 404
 405         /* handle the 25 cases */
 406         switch(d1 * 5 + d2) {
 407         case 0*5+0:
 408         case 0*5+4:
 409         case 3*5+4:
 410         case 4*5+0:
 411         case 4*5+4:
 412             code = 0;
 413             break;
 414         case 0*5+1:
 415         case 0*5+2:
 416         case 4*5+1:
 417         case 4*5+2:
 418             code = 3;
 419             sf[2] = sf[1];
 420             break;
 421         case 0*5+3:
 422         case 4*5+3:
 423             code = 3;
 424             sf[1] = sf[2];
 425             break;
 426         case 1*5+0:
 427         case 1*5+4:
 428         case 2*5+4:
 429             code = 1;
 430             sf[1] = sf[0];
 431             break;
 432         case 1*5+1:
 433         case 1*5+2:
 434         case 2*5+0:
 435         case 2*5+1:
 436         case 2*5+2:
 437             code = 2;
 438             sf[1] = sf[2] = sf[0];
 439             break;
 440         case 2*5+3:
 441         case 3*5+3:
 442             code = 2;
 443             sf[0] = sf[1] = sf[2];
 444             break;
 445         case 3*5+0:
 446         case 3*5+1:
 447         case 3*5+2:
 448             code = 2;
 449             sf[0] = sf[2] = sf[1];
 450             break;
 451         case 1*5+3:
 452             code = 2;
 453             if (sf[0] > sf[2])
 454               sf[0] = sf[2];
 455             sf[1] = sf[2] = sf[0];
 456             break;
 457         default:
 458             abort();
 459         }
 460
 461 #if 0
 462         printf("%d: %2d %2d %2d %d %d -> %d\n", j,
 463                sf[0], sf[1], sf[2], d1, d2, code);
 464 #endif
 465         scale_code[j] = code;
 466         sf += 3;
 467     }
 468 }
 469
 470 /* The most important function : psycho acoustic module. In this
 471    encoder there is basically none, so this is the worst you can do,
 472    but also this is the simpler. */
 473 static void psycho_acoustic_model(MpegAudioContext *s, short smr[SBLIMIT])
 474 {
 475     int i;
 476
 477     for(i=0;i<s->sblimit;i++) {
 478         smr[i] = (int)(fixed_smr[i] * 10);
 479     }
 480 }
 481
 482
 483 #define SB_NOTALLOCATED  0
 484 #define SB_ALLOCATED     1
 485 #define SB_NOMORE        2
 486
 487 /* Try to maximize the smr while using a number of bits inferior to
 488    the frame size. I tried to make the code simpler, faster and
 489    smaller than other encoders :-) */
 490 static void compute_bit_allocation(MpegAudioContext *s,
 491                                    short smr1[MPA_MAX_CHANNELS][SBLIMIT],
 492                                    unsigned char bit_alloc[MPA_MAX_CHANNELS][SBLIMIT],
 493                                    int *padding)
 494 {
 495     int i, ch, b, max_smr, max_ch, max_sb, current_frame_size, max_frame_size;
 496     int incr;
 497     short smr[MPA_MAX_CHANNELS][SBLIMIT];
 498     unsigned char subband_status[MPA_MAX_CHANNELS][SBLIMIT];
 499     const unsigned char *alloc;
 500
 501     memcpy(smr, smr1, s->nb_channels * sizeof(short) * SBLIMIT);
 502     memset(subband_status, SB_NOTALLOCATED, s->nb_channels * SBLIMIT);
 503     memset(bit_alloc, 0, s->nb_channels * SBLIMIT);
 504
 505     /* compute frame size and padding */
 506     max_frame_size = s->frame_size;
 507     s->frame_frac += s->frame_frac_incr;
 508     if (s->frame_frac >= 65536) {
 509         s->frame_frac -= 65536;
 510         s->do_padding = 1;
 511         max_frame_size += 8;
 512     } else {
 513         s->do_padding = 0;
 514     }
 515
 516     /* compute the header + bit alloc size */
 517     current_frame_size = 32;
 518     alloc = s->alloc_table;
 519     for(i=0;i<s->sblimit;i++) {
 520         incr = alloc[0];
 521         current_frame_size += incr * s->nb_channels;
 522         alloc += 1 << incr;
 523     }
 524     for(;;) {
 525         /* look for the subband with the largest signal to mask ratio */
 526         max_sb = -1;
 527         max_ch = -1;
 528         max_smr = 0x80000000;
 529         for(ch=0;ch<s->nb_channels;ch++) {
 530             for(i=0;i<s->sblimit;i++) {
 531                 if (smr[ch][i] > max_smr && subband_status[ch][i] != SB_NOMORE) {
 532                     max_smr = smr[ch][i];
 533                     max_sb = i;
 534                     max_ch = ch;
 535                 }
 536             }
 537         }
 538 #if 0
 539         printf("current=%d max=%d max_sb=%d alloc=%d\n",
 540                current_frame_size, max_frame_size, max_sb,
 541                bit_alloc[max_sb]);
 542 #endif
 543         if (max_sb < 0)
 544             break;
 545
 546         /* find alloc table entry (XXX: not optimal, should use
 547            pointer table) */
 548         alloc = s->alloc_table;
 549         for(i=0;i<max_sb;i++) {
 550             alloc += 1 << alloc[0];
 551         }
 552
 553         if (subband_status[max_ch][max_sb] == SB_NOTALLOCATED) {
 554             /* nothing was coded for this band: add the necessary bits */
 555             incr = 2 + nb_scale_factors[s->scale_code[max_ch][max_sb]] * 6;
 556             incr += total_quant_bits[alloc[1]];
 557         } else {
 558             /* increments bit allocation */
 559             b = bit_alloc[max_ch][max_sb];
 560             incr = total_quant_bits[alloc[b + 1]] -
 561                 total_quant_bits[alloc[b]];
 562         }
 563
 564         if (current_frame_size + incr <= max_frame_size) {
 565             /* can increase size */
 566             b = ++bit_alloc[max_ch][max_sb];
 567             current_frame_size += incr;
 568             /* decrease smr by the resolution we added */
 569             smr[max_ch][max_sb] = smr1[max_ch][max_sb] - quant_snr[alloc[b]];
 570             /* max allocation size reached ? */
 571             if (b == ((1 << alloc[0]) - 1))
 572                 subband_status[max_ch][max_sb] = SB_NOMORE;
 573             else
 574                 subband_status[max_ch][max_sb] = SB_ALLOCATED;
 575         } else {
 576             /* cannot increase the size of this subband */
 577             subband_status[max_ch][max_sb] = SB_NOMORE;
 578         }
 579     }
 580     *padding = max_frame_size - current_frame_size;
 581     assert(*padding >= 0);
 582
 583 #if 0
 584     for(i=0;i<s->sblimit;i++) {
 585         printf("%d ", bit_alloc[i]);
 586     }
 587     printf("\n");
 588 #endif
 589 }
 590
 591 /*
 592  * Output the mpeg audio layer 2 frame. Note how the code is small
 593  * compared to other encoders :-)
 594  */
 595 static void encode_frame(MpegAudioContext *s,
 596                          unsigned char bit_alloc[MPA_MAX_CHANNELS][SBLIMIT],
 597                          int padding)
 598 {
 599     int i, j, k, l, bit_alloc_bits, b, ch;
 600     unsigned char *sf;
 601     int q[3];
 602     PutBitContext *p = &s->pb;
 603
 604     /* header */
 605
 606     put_bits(p, 12, 0xfff);
 607     put_bits(p, 1, 1 - s->lsf); /* 1 = mpeg1 ID, 0 = mpeg2 lsf ID */
 608     put_bits(p, 2, 4-2);  /* layer 2 */
 609     put_bits(p, 1, 1); /* no error protection */
 610     put_bits(p, 4, s->bitrate_index);
 611     put_bits(p, 2, s->freq_index);
 612     put_bits(p, 1, s->do_padding); /* use padding */
 613     put_bits(p, 1, 0);             /* private_bit */
 614     put_bits(p, 2, s->nb_channels == 2 ? MPA_STEREO : MPA_MONO);
 615     put_bits(p, 2, 0); /* mode_ext */
 616     put_bits(p, 1, 0); /* no copyright */
 617     put_bits(p, 1, 1); /* original */
 618     put_bits(p, 2, 0); /* no emphasis */
 619
 620     /* bit allocation */
 621     j = 0;
 622     for(i=0;i<s->sblimit;i++) {
 623         bit_alloc_bits = s->alloc_table[j];
 624         for(ch=0;ch<s->nb_channels;ch++) {
 625             put_bits(p, bit_alloc_bits, bit_alloc[ch][i]);
 626         }
 627         j += 1 << bit_alloc_bits;
 628     }
 629
 630     /* scale codes */
 631     for(i=0;i<s->sblimit;i++) {
 632         for(ch=0;ch<s->nb_channels;ch++) {
 633             if (bit_alloc[ch][i])
 634                 put_bits(p, 2, s->scale_code[ch][i]);
 635         }
 636     }
 637
 638     /* scale factors */
 639     for(i=0;i<s->sblimit;i++) {
 640         for(ch=0;ch<s->nb_channels;ch++) {
 641             if (bit_alloc[ch][i]) {
 642                 sf = &s->scale_factors[ch][i][0];
 643                 switch(s->scale_code[ch][i]) {
 644                 case 0:
 645                     put_bits(p, 6, sf[0]);
 646                     put_bits(p, 6, sf[1]);
 647                     put_bits(p, 6, sf[2]);
 648                     break;
 649                 case 3:
 650                 case 1:
 651                     put_bits(p, 6, sf[0]);
 652                     put_bits(p, 6, sf[2]);
 653                     break;
 654                 case 2:
 655                     put_bits(p, 6, sf[0]);
 656                     break;
 657                 }
 658             }
 659         }
 660     }
 661
 662     /* quantization & write sub band samples */
 663
 664     for(k=0;k<3;k++) {
 665         for(l=0;l<12;l+=3) {
 666             j = 0;
 667             for(i=0;i<s->sblimit;i++) {
 668                 bit_alloc_bits = s->alloc_table[j];
 669                 for(ch=0;ch<s->nb_channels;ch++) {
 670                     b = bit_alloc[ch][i];
 671                     if (b) {
 672                         int qindex, steps, m, sample, bits;
 673                         /* we encode 3 sub band samples of the same sub band at a time */
 674                         qindex = s->alloc_table[j+b];
 675                         steps = quant_steps[qindex];
 676                         for(m=0;m<3;m++) {
 677                             sample = s->sb_samples[ch][k][l + m][i];
 678                             /* divide by scale factor */
 679 #ifdef USE_FLOATS
 680                             {
 681                                 float a;
 682                                 a = (float)sample * scale_factor_inv_table[s->scale_factors[ch][i][k]];
 683                                 q[m] = (int)((a + 1.0) * steps * 0.5);
 684                             }
 685 #else
 686                             {
 687                                 int q1, e, shift, mult;
 688                                 e = s->scale_factors[ch][i][k];
 689                                 shift = scale_factor_shift[e];
 690                                 mult = scale_factor_mult[e];
 691
 692                                 /* normalize to P bits */
 693                                 if (shift < 0)
 694                                     q1 = sample << (-shift);
 695                                 else
 696                                     q1 = sample >> shift;
 697                                 q1 = (q1 * mult) >> P;
 698                                 q[m] = ((q1 + (1 << P)) * steps) >> (P + 1);
 699                             }
 700 #endif
 701                             if (q[m] >= steps)
 702                                 q[m] = steps - 1;
 703                             assert(q[m] >= 0 && q[m] < steps);
 704                         }
 705                         bits = quant_bits[qindex];
 706                         if (bits < 0) {
 707                             /* group the 3 values to save bits */
 708                             put_bits(p, -bits,
 709                                      q[0] + steps * (q[1] + steps * q[2]));
 710 #if 0
 711                             printf("%d: gr1 %d\n",
 712                                    i, q[0] + steps * (q[1] + steps * q[2]));
 713 #endif
 714                         } else {
 715 #if 0
 716                             printf("%d: gr3 %d %d %d\n",
 717                                    i, q[0], q[1], q[2]);
 718 #endif
 719                             put_bits(p, bits, q[0]);
 720                             put_bits(p, bits, q[1]);
 721                             put_bits(p, bits, q[2]);
 722                         }
 723                     }
 724                 }
 725                 /* next subband in alloc table */
 726                 j += 1 << bit_alloc_bits;
 727             }
 728         }
 729     }
 730
 731     /* padding */
 732     for(i=0;i<padding;i++)
 733         put_bits(p, 1, 0);
 734
 735     /* flush */
 736     flush_put_bits(p);
 737 }
 738
 739 int MPA_encode_frame(AVCodecContext *avctx,
 740                      unsigned char *frame, int buf_size, void *data)
 741 {
 742     MpegAudioContext *s = avctx->priv_data;
 743     short *samples = data;
 744     short smr[MPA_MAX_CHANNELS][SBLIMIT];
 745     unsigned char bit_alloc[MPA_MAX_CHANNELS][SBLIMIT];
 746     int padding, i;
 747
 748     for(i=0;i<s->nb_channels;i++) {
 749         filter(s, i, samples + i, s->nb_channels);
 750     }
 751
 752     for(i=0;i<s->nb_channels;i++) {
 753         compute_scale_factors(s->scale_code[i], s->scale_factors[i],
 754                               s->sb_samples[i], s->sblimit);
 755     }
 756     for(i=0;i<s->nb_channels;i++) {
 757         psycho_acoustic_model(s, smr[i]);
 758     }
 759     compute_bit_allocation(s, smr, bit_alloc, &padding);
 760
 761     init_put_bits(&s->pb, frame, MPA_MAX_CODED_FRAME_SIZE, NULL, NULL);
 762
 763     encode_frame(s, bit_alloc, padding);
 764
 765     s->nb_samples += MPA_FRAME_SIZE;
 766     return pbBufPtr(&s->pb) - s->pb.buf;
 767 }
 768
 769
 770 AVCodec mp2_encoder = {
 771     "mp2",
 772     CODEC_TYPE_AUDIO,
 773     CODEC_ID_MP2,
 774     sizeof(MpegAudioContext),
 775     MPA_encode_init,
 776     MPA_encode_frame,
 777     NULL,
 778 };