1/* 2 * E-AC-3 decoder 3 * Copyright (c) 2007 Bartlomiej Wolowiec <bartek.wolowiec@gmail.com> 4 * Copyright (c) 2008 Justin Ruggles 5 * 6 * This file is part of FFmpeg. 7 * 8 * FFmpeg is free software; you can redistribute it and/or 9 * modify it under the terms of the GNU Lesser General Public 10 * License as published by the Free Software Foundation; either 11 * version 2.1 of the License, or (at your option) any later version. 12 * 13 * FFmpeg is distributed in the hope that it will be useful, 14 * but WITHOUT ANY WARRANTY; without even the implied warranty of 15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 16 * Lesser General Public License for more details. 17 * 18 * You should have received a copy of the GNU Lesser General Public 19 * License along with FFmpeg; if not, write to the Free Software 20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 21 */ 22 23/* 24 * There are several features of E-AC-3 that this decoder does not yet support. 25 * 26 * Enhanced Coupling 27 * No known samples exist. If any ever surface, this feature should not be 28 * too difficult to implement. 29 * 30 * Reduced Sample Rates 31 * No known samples exist. The spec also does not give clear information 32 * on how this is to be implemented. 33 * 34 * Dependent Streams 35 * Only the independent stream is currently decoded. Any dependent 36 * streams are skipped. We have only come across two examples of this, and 37 * they are both just test streams, one for HD-DVD and the other for 38 * Blu-ray. 39 * 40 * Transient Pre-noise Processing 41 * This is side information which a decoder should use to reduce artifacts 42 * caused by transients. There are samples which are known to have this 43 * information, but this decoder currently ignores it. 44 */ 45 46 47#include "avcodec.h" 48#include "internal.h" 49#include "aac_ac3_parser.h" 50#include "ac3.h" 51#include "ac3_parser.h" 52#include "ac3dec.h" 53#include "ac3dec_data.h" 54#include "eac3dec_data.h" 55 56/** gain adaptive quantization mode */ 57typedef enum { 58 EAC3_GAQ_NO =0, 59 EAC3_GAQ_12, 60 EAC3_GAQ_14, 61 EAC3_GAQ_124 62} EAC3GaqMode; 63 64#define EAC3_SR_CODE_REDUCED 3 65 66void ff_eac3_apply_spectral_extension(AC3DecodeContext *s) 67{ 68 int bin, bnd, ch, i; 69 uint8_t wrapflag[SPX_MAX_BANDS]={1,0,}, num_copy_sections, copy_sizes[SPX_MAX_BANDS]; 70 float rms_energy[SPX_MAX_BANDS]; 71 72 /* Set copy index mapping table. Set wrap flags to apply a notch filter at 73 wrap points later on. */ 74 bin = s->spx_dst_start_freq; 75 num_copy_sections = 0; 76 for (bnd = 0; bnd < s->num_spx_bands; bnd++) { 77 int copysize; 78 int bandsize = s->spx_band_sizes[bnd]; 79 if (bin + bandsize > s->spx_src_start_freq) { 80 copy_sizes[num_copy_sections++] = bin - s->spx_dst_start_freq; 81 bin = s->spx_dst_start_freq; 82 wrapflag[bnd] = 1; 83 } 84 for (i = 0; i < bandsize; i += copysize) { 85 if (bin == s->spx_src_start_freq) { 86 copy_sizes[num_copy_sections++] = bin - s->spx_dst_start_freq; 87 bin = s->spx_dst_start_freq; 88 } 89 copysize = FFMIN(bandsize - i, s->spx_src_start_freq - bin); 90 bin += copysize; 91 } 92 } 93 copy_sizes[num_copy_sections++] = bin - s->spx_dst_start_freq; 94 95 for (ch = 1; ch <= s->fbw_channels; ch++) { 96 if (!s->channel_uses_spx[ch]) 97 continue; 98 99 /* Copy coeffs from normal bands to extension bands */ 100 bin = s->spx_src_start_freq; 101 for (i = 0; i < num_copy_sections; i++) { 102 memcpy(&s->transform_coeffs[ch][bin], 103 &s->transform_coeffs[ch][s->spx_dst_start_freq], 104 copy_sizes[i]*sizeof(float)); 105 bin += copy_sizes[i]; 106 } 107 108 /* Calculate RMS energy for each SPX band. */ 109 bin = s->spx_src_start_freq; 110 for (bnd = 0; bnd < s->num_spx_bands; bnd++) { 111 int bandsize = s->spx_band_sizes[bnd]; 112 float accum = 0.0f; 113 for (i = 0; i < bandsize; i++) { 114 float coeff = s->transform_coeffs[ch][bin++]; 115 accum += coeff * coeff; 116 } 117 rms_energy[bnd] = sqrtf(accum / bandsize); 118 } 119 120 /* Apply a notch filter at transitions between normal and extension 121 bands and at all wrap points. */ 122 if (s->spx_atten_code[ch] >= 0) { 123 const float *atten_tab = ff_eac3_spx_atten_tab[s->spx_atten_code[ch]]; 124 bin = s->spx_src_start_freq - 2; 125 for (bnd = 0; bnd < s->num_spx_bands; bnd++) { 126 if (wrapflag[bnd]) { 127 float *coeffs = &s->transform_coeffs[ch][bin]; 128 coeffs[0] *= atten_tab[0]; 129 coeffs[1] *= atten_tab[1]; 130 coeffs[2] *= atten_tab[2]; 131 coeffs[3] *= atten_tab[1]; 132 coeffs[4] *= atten_tab[0]; 133 } 134 bin += s->spx_band_sizes[bnd]; 135 } 136 } 137 138 /* Apply noise-blended coefficient scaling based on previously 139 calculated RMS energy, blending factors, and SPX coordinates for 140 each band. */ 141 bin = s->spx_src_start_freq; 142 for (bnd = 0; bnd < s->num_spx_bands; bnd++) { 143 float nscale = s->spx_noise_blend[ch][bnd] * rms_energy[bnd] * (1.0f/(1<<31)); 144 float sscale = s->spx_signal_blend[ch][bnd]; 145 for (i = 0; i < s->spx_band_sizes[bnd]; i++) { 146 float noise = nscale * (int32_t)av_lfg_get(&s->dith_state); 147 s->transform_coeffs[ch][bin] *= sscale; 148 s->transform_coeffs[ch][bin++] += noise; 149 } 150 } 151 } 152} 153 154 155/** lrint(M_SQRT2*cos(2*M_PI/12)*(1<<23)) */ 156#define COEFF_0 10273905LL 157 158/** lrint(M_SQRT2*cos(0*M_PI/12)*(1<<23)) = lrint(M_SQRT2*(1<<23)) */ 159#define COEFF_1 11863283LL 160 161/** lrint(M_SQRT2*cos(5*M_PI/12)*(1<<23)) */ 162#define COEFF_2 3070444LL 163 164/** 165 * Calculate 6-point IDCT of the pre-mantissas. 166 * All calculations are 24-bit fixed-point. 167 */ 168static void idct6(int pre_mant[6]) 169{ 170 int tmp; 171 int even0, even1, even2, odd0, odd1, odd2; 172 173 odd1 = pre_mant[1] - pre_mant[3] - pre_mant[5]; 174 175 even2 = ( pre_mant[2] * COEFF_0) >> 23; 176 tmp = ( pre_mant[4] * COEFF_1) >> 23; 177 odd0 = ((pre_mant[1] + pre_mant[5]) * COEFF_2) >> 23; 178 179 even0 = pre_mant[0] + (tmp >> 1); 180 even1 = pre_mant[0] - tmp; 181 182 tmp = even0; 183 even0 = tmp + even2; 184 even2 = tmp - even2; 185 186 tmp = odd0; 187 odd0 = tmp + pre_mant[1] + pre_mant[3]; 188 odd2 = tmp + pre_mant[5] - pre_mant[3]; 189 190 pre_mant[0] = even0 + odd0; 191 pre_mant[1] = even1 + odd1; 192 pre_mant[2] = even2 + odd2; 193 pre_mant[3] = even2 - odd2; 194 pre_mant[4] = even1 - odd1; 195 pre_mant[5] = even0 - odd0; 196} 197 198void ff_eac3_decode_transform_coeffs_aht_ch(AC3DecodeContext *s, int ch) 199{ 200 int bin, blk, gs; 201 int end_bap, gaq_mode; 202 GetBitContext *gbc = &s->gbc; 203 int gaq_gain[AC3_MAX_COEFS]; 204 205 gaq_mode = get_bits(gbc, 2); 206 end_bap = (gaq_mode < 2) ? 12 : 17; 207 208 /* if GAQ gain is used, decode gain codes for bins with hebap between 209 8 and end_bap */ 210 gs = 0; 211 if (gaq_mode == EAC3_GAQ_12 || gaq_mode == EAC3_GAQ_14) { 212 /* read 1-bit GAQ gain codes */ 213 for (bin = s->start_freq[ch]; bin < s->end_freq[ch]; bin++) { 214 if (s->bap[ch][bin] > 7 && s->bap[ch][bin] < end_bap) 215 gaq_gain[gs++] = get_bits1(gbc) << (gaq_mode-1); 216 } 217 } else if (gaq_mode == EAC3_GAQ_124) { 218 /* read 1.67-bit GAQ gain codes (3 codes in 5 bits) */ 219 int gc = 2; 220 for (bin = s->start_freq[ch]; bin < s->end_freq[ch]; bin++) { 221 if (s->bap[ch][bin] > 7 && s->bap[ch][bin] < 17) { 222 if (gc++ == 2) { 223 int group_code = get_bits(gbc, 5); 224 if (group_code > 26) { 225 av_log(s->avctx, AV_LOG_WARNING, "GAQ gain group code out-of-range\n"); 226 group_code = 26; 227 } 228 gaq_gain[gs++] = ff_ac3_ungroup_3_in_5_bits_tab[group_code][0]; 229 gaq_gain[gs++] = ff_ac3_ungroup_3_in_5_bits_tab[group_code][1]; 230 gaq_gain[gs++] = ff_ac3_ungroup_3_in_5_bits_tab[group_code][2]; 231 gc = 0; 232 } 233 } 234 } 235 } 236 237 gs=0; 238 for (bin = s->start_freq[ch]; bin < s->end_freq[ch]; bin++) { 239 int hebap = s->bap[ch][bin]; 240 int bits = ff_eac3_bits_vs_hebap[hebap]; 241 if (!hebap) { 242 /* zero-mantissa dithering */ 243 for (blk = 0; blk < 6; blk++) { 244 s->pre_mantissa[ch][bin][blk] = (av_lfg_get(&s->dith_state) & 0x7FFFFF) - 0x400000; 245 } 246 } else if (hebap < 8) { 247 /* Vector Quantization */ 248 int v = get_bits(gbc, bits); 249 for (blk = 0; blk < 6; blk++) { 250 s->pre_mantissa[ch][bin][blk] = ff_eac3_mantissa_vq[hebap][v][blk] << 8; 251 } 252 } else { 253 /* Gain Adaptive Quantization */ 254 int gbits, log_gain; 255 if (gaq_mode != EAC3_GAQ_NO && hebap < end_bap) { 256 log_gain = gaq_gain[gs++]; 257 } else { 258 log_gain = 0; 259 } 260 gbits = bits - log_gain; 261 262 for (blk = 0; blk < 6; blk++) { 263 int mant = get_sbits(gbc, gbits); 264 if (log_gain && mant == -(1 << (gbits-1))) { 265 /* large mantissa */ 266 int b; 267 int mbits = bits - (2 - log_gain); 268 mant = get_sbits(gbc, mbits); 269 mant <<= (23 - (mbits - 1)); 270 /* remap mantissa value to correct for asymmetric quantization */ 271 if (mant >= 0) 272 b = 1 << (23 - log_gain); 273 else 274 b = ff_eac3_gaq_remap_2_4_b[hebap-8][log_gain-1] << 8; 275 mant += ((ff_eac3_gaq_remap_2_4_a[hebap-8][log_gain-1] * (int64_t)mant) >> 15) + b; 276 } else { 277 /* small mantissa, no GAQ, or Gk=1 */ 278 mant <<= 24 - bits; 279 if (!log_gain) { 280 /* remap mantissa value for no GAQ or Gk=1 */ 281 mant += (ff_eac3_gaq_remap_1[hebap-8] * (int64_t)mant) >> 15; 282 } 283 } 284 s->pre_mantissa[ch][bin][blk] = mant; 285 } 286 } 287 idct6(s->pre_mantissa[ch][bin]); 288 } 289} 290 291int ff_eac3_parse_header(AC3DecodeContext *s) 292{ 293 int i, blk, ch; 294 int ac3_exponent_strategy, parse_aht_info, parse_spx_atten_data; 295 int parse_transient_proc_info; 296 int num_cpl_blocks; 297 GetBitContext *gbc = &s->gbc; 298 299 /* An E-AC-3 stream can have multiple independent streams which the 300 application can select from. each independent stream can also contain 301 dependent streams which are used to add or replace channels. */ 302 if (s->frame_type == EAC3_FRAME_TYPE_DEPENDENT) { 303 av_log_missing_feature(s->avctx, "Dependent substream decoding", 1); 304 return AAC_AC3_PARSE_ERROR_FRAME_TYPE; 305 } else if (s->frame_type == EAC3_FRAME_TYPE_RESERVED) { 306 av_log(s->avctx, AV_LOG_ERROR, "Reserved frame type\n"); 307 return AAC_AC3_PARSE_ERROR_FRAME_TYPE; 308 } 309 310 /* The substream id indicates which substream this frame belongs to. each 311 independent stream has its own substream id, and the dependent streams 312 associated to an independent stream have matching substream id's. */ 313 if (s->substreamid) { 314 /* only decode substream with id=0. skip any additional substreams. */ 315 av_log_missing_feature(s->avctx, "Additional substreams", 1); 316 return AAC_AC3_PARSE_ERROR_FRAME_TYPE; 317 } 318 319 if (s->bit_alloc_params.sr_code == EAC3_SR_CODE_REDUCED) { 320 /* The E-AC-3 specification does not tell how to handle reduced sample 321 rates in bit allocation. The best assumption would be that it is 322 handled like AC-3 DolbyNet, but we cannot be sure until we have a 323 sample which utilizes this feature. */ 324 av_log_missing_feature(s->avctx, "Reduced sampling rates", 1); 325 return -1; 326 } 327 skip_bits(gbc, 5); // skip bitstream id 328 329 /* volume control params */ 330 for (i = 0; i < (s->channel_mode ? 1 : 2); i++) { 331 skip_bits(gbc, 5); // skip dialog normalization 332 if (get_bits1(gbc)) { 333 skip_bits(gbc, 8); // skip compression gain word 334 } 335 } 336 337 /* dependent stream channel map */ 338 if (s->frame_type == EAC3_FRAME_TYPE_DEPENDENT) { 339 if (get_bits1(gbc)) { 340 skip_bits(gbc, 16); // skip custom channel map 341 } 342 } 343 344 /* mixing metadata */ 345 if (get_bits1(gbc)) { 346 /* center and surround mix levels */ 347 if (s->channel_mode > AC3_CHMODE_STEREO) { 348 skip_bits(gbc, 2); // skip preferred stereo downmix mode 349 if (s->channel_mode & 1) { 350 /* if three front channels exist */ 351 skip_bits(gbc, 3); //skip Lt/Rt center mix level 352 s->center_mix_level = get_bits(gbc, 3); 353 } 354 if (s->channel_mode & 4) { 355 /* if a surround channel exists */ 356 skip_bits(gbc, 3); //skip Lt/Rt surround mix level 357 s->surround_mix_level = get_bits(gbc, 3); 358 } 359 } 360 361 /* lfe mix level */ 362 if (s->lfe_on && get_bits1(gbc)) { 363 // TODO: use LFE mix level 364 skip_bits(gbc, 5); // skip LFE mix level code 365 } 366 367 /* info for mixing with other streams and substreams */ 368 if (s->frame_type == EAC3_FRAME_TYPE_INDEPENDENT) { 369 for (i = 0; i < (s->channel_mode ? 1 : 2); i++) { 370 // TODO: apply program scale factor 371 if (get_bits1(gbc)) { 372 skip_bits(gbc, 6); // skip program scale factor 373 } 374 } 375 if (get_bits1(gbc)) { 376 skip_bits(gbc, 6); // skip external program scale factor 377 } 378 /* skip mixing parameter data */ 379 switch(get_bits(gbc, 2)) { 380 case 1: skip_bits(gbc, 5); break; 381 case 2: skip_bits(gbc, 12); break; 382 case 3: { 383 int mix_data_size = (get_bits(gbc, 5) + 2) << 3; 384 skip_bits_long(gbc, mix_data_size); 385 break; 386 } 387 } 388 /* skip pan information for mono or dual mono source */ 389 if (s->channel_mode < AC3_CHMODE_STEREO) { 390 for (i = 0; i < (s->channel_mode ? 1 : 2); i++) { 391 if (get_bits1(gbc)) { 392 /* note: this is not in the ATSC A/52B specification 393 reference: ETSI TS 102 366 V1.1.1 394 section: E.1.3.1.25 */ 395 skip_bits(gbc, 8); // skip pan mean direction index 396 skip_bits(gbc, 6); // skip reserved paninfo bits 397 } 398 } 399 } 400 /* skip mixing configuration information */ 401 if (get_bits1(gbc)) { 402 for (blk = 0; blk < s->num_blocks; blk++) { 403 if (s->num_blocks == 1 || get_bits1(gbc)) { 404 skip_bits(gbc, 5); 405 } 406 } 407 } 408 } 409 } 410 411 /* informational metadata */ 412 if (get_bits1(gbc)) { 413 skip_bits(gbc, 3); // skip bit stream mode 414 skip_bits(gbc, 2); // skip copyright bit and original bitstream bit 415 if (s->channel_mode == AC3_CHMODE_STEREO) { 416 skip_bits(gbc, 4); // skip Dolby surround and headphone mode 417 } 418 if (s->channel_mode >= AC3_CHMODE_2F2R) { 419 skip_bits(gbc, 2); // skip Dolby surround EX mode 420 } 421 for (i = 0; i < (s->channel_mode ? 1 : 2); i++) { 422 if (get_bits1(gbc)) { 423 skip_bits(gbc, 8); // skip mix level, room type, and A/D converter type 424 } 425 } 426 if (s->bit_alloc_params.sr_code != EAC3_SR_CODE_REDUCED) { 427 skip_bits1(gbc); // skip source sample rate code 428 } 429 } 430 431 /* converter synchronization flag 432 If frames are less than six blocks, this bit should be turned on 433 once every 6 blocks to indicate the start of a frame set. 434 reference: RFC 4598, Section 2.1.3 Frame Sets */ 435 if (s->frame_type == EAC3_FRAME_TYPE_INDEPENDENT && s->num_blocks != 6) { 436 skip_bits1(gbc); // skip converter synchronization flag 437 } 438 439 /* original frame size code if this stream was converted from AC-3 */ 440 if (s->frame_type == EAC3_FRAME_TYPE_AC3_CONVERT && 441 (s->num_blocks == 6 || get_bits1(gbc))) { 442 skip_bits(gbc, 6); // skip frame size code 443 } 444 445 /* additional bitstream info */ 446 if (get_bits1(gbc)) { 447 int addbsil = get_bits(gbc, 6); 448 for (i = 0; i < addbsil + 1; i++) { 449 skip_bits(gbc, 8); // skip additional bit stream info 450 } 451 } 452 453 /* audio frame syntax flags, strategy data, and per-frame data */ 454 455 if (s->num_blocks == 6) { 456 ac3_exponent_strategy = get_bits1(gbc); 457 parse_aht_info = get_bits1(gbc); 458 } else { 459 /* less than 6 blocks, so use AC-3-style exponent strategy syntax, and 460 do not use AHT */ 461 ac3_exponent_strategy = 1; 462 parse_aht_info = 0; 463 } 464 465 s->snr_offset_strategy = get_bits(gbc, 2); 466 parse_transient_proc_info = get_bits1(gbc); 467 468 s->block_switch_syntax = get_bits1(gbc); 469 if (!s->block_switch_syntax) 470 memset(s->block_switch, 0, sizeof(s->block_switch)); 471 472 s->dither_flag_syntax = get_bits1(gbc); 473 if (!s->dither_flag_syntax) { 474 for (ch = 1; ch <= s->fbw_channels; ch++) 475 s->dither_flag[ch] = 1; 476 } 477 s->dither_flag[CPL_CH] = s->dither_flag[s->lfe_ch] = 0; 478 479 s->bit_allocation_syntax = get_bits1(gbc); 480 if (!s->bit_allocation_syntax) { 481 /* set default bit allocation parameters */ 482 s->bit_alloc_params.slow_decay = ff_ac3_slow_decay_tab[2]; 483 s->bit_alloc_params.fast_decay = ff_ac3_fast_decay_tab[1]; 484 s->bit_alloc_params.slow_gain = ff_ac3_slow_gain_tab [1]; 485 s->bit_alloc_params.db_per_bit = ff_ac3_db_per_bit_tab[2]; 486 s->bit_alloc_params.floor = ff_ac3_floor_tab [7]; 487 } 488 489 s->fast_gain_syntax = get_bits1(gbc); 490 s->dba_syntax = get_bits1(gbc); 491 s->skip_syntax = get_bits1(gbc); 492 parse_spx_atten_data = get_bits1(gbc); 493 494 /* coupling strategy occurance and coupling use per block */ 495 num_cpl_blocks = 0; 496 if (s->channel_mode > 1) { 497 for (blk = 0; blk < s->num_blocks; blk++) { 498 s->cpl_strategy_exists[blk] = (!blk || get_bits1(gbc)); 499 if (s->cpl_strategy_exists[blk]) { 500 s->cpl_in_use[blk] = get_bits1(gbc); 501 } else { 502 s->cpl_in_use[blk] = s->cpl_in_use[blk-1]; 503 } 504 num_cpl_blocks += s->cpl_in_use[blk]; 505 } 506 } else { 507 memset(s->cpl_in_use, 0, sizeof(s->cpl_in_use)); 508 } 509 510 /* exponent strategy data */ 511 if (ac3_exponent_strategy) { 512 /* AC-3-style exponent strategy syntax */ 513 for (blk = 0; blk < s->num_blocks; blk++) { 514 for (ch = !s->cpl_in_use[blk]; ch <= s->fbw_channels; ch++) { 515 s->exp_strategy[blk][ch] = get_bits(gbc, 2); 516 } 517 } 518 } else { 519 /* LUT-based exponent strategy syntax */ 520 for (ch = !((s->channel_mode > 1) && num_cpl_blocks); ch <= s->fbw_channels; ch++) { 521 int frmchexpstr = get_bits(gbc, 5); 522 for (blk = 0; blk < 6; blk++) { 523 s->exp_strategy[blk][ch] = ff_eac3_frm_expstr[frmchexpstr][blk]; 524 } 525 } 526 } 527 /* LFE exponent strategy */ 528 if (s->lfe_on) { 529 for (blk = 0; blk < s->num_blocks; blk++) { 530 s->exp_strategy[blk][s->lfe_ch] = get_bits1(gbc); 531 } 532 } 533 /* original exponent strategies if this stream was converted from AC-3 */ 534 if (s->frame_type == EAC3_FRAME_TYPE_INDEPENDENT && 535 (s->num_blocks == 6 || get_bits1(gbc))) { 536 skip_bits(gbc, 5 * s->fbw_channels); // skip converter channel exponent strategy 537 } 538 539 /* determine which channels use AHT */ 540 if (parse_aht_info) { 541 /* For AHT to be used, all non-zero blocks must reuse exponents from 542 the first block. Furthermore, for AHT to be used in the coupling 543 channel, all blocks must use coupling and use the same coupling 544 strategy. */ 545 s->channel_uses_aht[CPL_CH]=0; 546 for (ch = (num_cpl_blocks != 6); ch <= s->channels; ch++) { 547 int use_aht = 1; 548 for (blk = 1; blk < 6; blk++) { 549 if ((s->exp_strategy[blk][ch] != EXP_REUSE) || 550 (!ch && s->cpl_strategy_exists[blk])) { 551 use_aht = 0; 552 break; 553 } 554 } 555 s->channel_uses_aht[ch] = use_aht && get_bits1(gbc); 556 } 557 } else { 558 memset(s->channel_uses_aht, 0, sizeof(s->channel_uses_aht)); 559 } 560 561 /* per-frame SNR offset */ 562 if (!s->snr_offset_strategy) { 563 int csnroffst = (get_bits(gbc, 6) - 15) << 4; 564 int snroffst = (csnroffst + get_bits(gbc, 4)) << 2; 565 for (ch = 0; ch <= s->channels; ch++) 566 s->snr_offset[ch] = snroffst; 567 } 568 569 /* transient pre-noise processing data */ 570 if (parse_transient_proc_info) { 571 for (ch = 1; ch <= s->fbw_channels; ch++) { 572 if (get_bits1(gbc)) { // channel in transient processing 573 skip_bits(gbc, 10); // skip transient processing location 574 skip_bits(gbc, 8); // skip transient processing length 575 } 576 } 577 } 578 579 /* spectral extension attenuation data */ 580 for (ch = 1; ch <= s->fbw_channels; ch++) { 581 if (parse_spx_atten_data && get_bits1(gbc)) { 582 s->spx_atten_code[ch] = get_bits(gbc, 5); 583 } else { 584 s->spx_atten_code[ch] = -1; 585 } 586 } 587 588 /* block start information */ 589 if (s->num_blocks > 1 && get_bits1(gbc)) { 590 /* reference: Section E2.3.2.27 591 nblkstrtbits = (numblks - 1) * (4 + ceiling(log2(words_per_frame))) 592 The spec does not say what this data is or what it's used for. 593 It is likely the offset of each block within the frame. */ 594 int block_start_bits = (s->num_blocks-1) * (4 + av_log2(s->frame_size-2)); 595 skip_bits_long(gbc, block_start_bits); 596 av_log_missing_feature(s->avctx, "Block start info", 1); 597 } 598 599 /* syntax state initialization */ 600 for (ch = 1; ch <= s->fbw_channels; ch++) { 601 s->first_spx_coords[ch] = 1; 602 s->first_cpl_coords[ch] = 1; 603 } 604 s->first_cpl_leak = 1; 605 606 return 0; 607} 608