Skip to content
This repository

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
tree: 1e9caf9c92
Fetching contributors…

Cannot retrieve contributors at this time

file 1516 lines (1384 sloc) 56.459 kb
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516
/*
* AC-3 Audio Decoder
* This code was developed as part of Google Summer of Code 2006.
* E-AC-3 support was added as part of Google Summer of Code 2007.
*
* Copyright (c) 2006 Kartikey Mahendra BHATT (bhattkm at gmail dot com)
* Copyright (c) 2007-2008 Bartlomiej Wolowiec <bartek.wolowiec@gmail.com>
* Copyright (c) 2007 Justin Ruggles <justin.ruggles@gmail.com>
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/

#include <stdio.h>
#include <stddef.h>
#include <math.h>
#include <string.h>

#include "libavutil/crc.h"
#include "libavutil/opt.h"
#include "internal.h"
#include "aac_ac3_parser.h"
#include "ac3_parser.h"
#include "ac3dec.h"
#include "ac3dec_data.h"
#include "kbdwin.h"

/**
* table for ungrouping 3 values in 7 bits.
* used for exponents and bap=2 mantissas
*/
static uint8_t ungroup_3_in_7_bits_tab[128][3];

/** tables for ungrouping mantissas */
static int b1_mantissas[32][3];
static int b2_mantissas[128][3];
static int b3_mantissas[8];
static int b4_mantissas[128][2];
static int b5_mantissas[16];

/**
* Quantization table: levels for symmetric. bits for asymmetric.
* reference: Table 7.18 Mapping of bap to Quantizer
*/
static const uint8_t quantization_tab[16] = {
    0, 3, 5, 7, 11, 15,
    5, 6, 7, 8, 9, 10, 11, 12, 14, 16
};

/** dynamic range table. converts codes to scale factors. */
static float dynamic_range_tab[256];

/** Adjustments in dB gain */
static const float gain_levels[9] = {
    LEVEL_PLUS_3DB,
    LEVEL_PLUS_1POINT5DB,
    LEVEL_ONE,
    LEVEL_MINUS_1POINT5DB,
    LEVEL_MINUS_3DB,
    LEVEL_MINUS_4POINT5DB,
    LEVEL_MINUS_6DB,
    LEVEL_ZERO,
    LEVEL_MINUS_9DB
};

/**
* Table for default stereo downmixing coefficients
* reference: Section 7.8.2 Downmixing Into Two Channels
*/
static const uint8_t ac3_default_coeffs[8][5][2] = {
    { { 2, 7 }, { 7, 2 }, },
    { { 4, 4 }, },
    { { 2, 7 }, { 7, 2 }, },
    { { 2, 7 }, { 5, 5 }, { 7, 2 }, },
    { { 2, 7 }, { 7, 2 }, { 6, 6 }, },
    { { 2, 7 }, { 5, 5 }, { 7, 2 }, { 8, 8 }, },
    { { 2, 7 }, { 7, 2 }, { 6, 7 }, { 7, 6 }, },
    { { 2, 7 }, { 5, 5 }, { 7, 2 }, { 6, 7 }, { 7, 6 }, },
};

/**
* Symmetrical Dequantization
* reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization
* Tables 7.19 to 7.23
*/
static inline int
symmetric_dequant(int code, int levels)
{
    return ((code - (levels >> 1)) << 24) / levels;
}

/*
* Initialize tables at runtime.
*/
static av_cold void ac3_tables_init(void)
{
    int i;

    /* generate table for ungrouping 3 values in 7 bits
reference: Section 7.1.3 Exponent Decoding */
    for (i = 0; i < 128; i++) {
        ungroup_3_in_7_bits_tab[i][0] = i / 25;
        ungroup_3_in_7_bits_tab[i][1] = (i % 25) / 5;
        ungroup_3_in_7_bits_tab[i][2] = (i % 25) % 5;
    }

    /* generate grouped mantissa tables
reference: Section 7.3.5 Ungrouping of Mantissas */
    for (i = 0; i < 32; i++) {
        /* bap=1 mantissas */
        b1_mantissas[i][0] = symmetric_dequant(ff_ac3_ungroup_3_in_5_bits_tab[i][0], 3);
        b1_mantissas[i][1] = symmetric_dequant(ff_ac3_ungroup_3_in_5_bits_tab[i][1], 3);
        b1_mantissas[i][2] = symmetric_dequant(ff_ac3_ungroup_3_in_5_bits_tab[i][2], 3);
    }
    for (i = 0; i < 128; i++) {
        /* bap=2 mantissas */
        b2_mantissas[i][0] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][0], 5);
        b2_mantissas[i][1] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][1], 5);
        b2_mantissas[i][2] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][2], 5);

        /* bap=4 mantissas */
        b4_mantissas[i][0] = symmetric_dequant(i / 11, 11);
        b4_mantissas[i][1] = symmetric_dequant(i % 11, 11);
    }
    /* generate ungrouped mantissa tables
reference: Tables 7.21 and 7.23 */
    for (i = 0; i < 7; i++) {
        /* bap=3 mantissas */
        b3_mantissas[i] = symmetric_dequant(i, 7);
    }
    for (i = 0; i < 15; i++) {
        /* bap=5 mantissas */
        b5_mantissas[i] = symmetric_dequant(i, 15);
    }

    /* generate dynamic range table
reference: Section 7.7.1 Dynamic Range Control */
    for (i = 0; i < 256; i++) {
        int v = (i >> 5) - ((i >> 7) << 3) - 5;
        dynamic_range_tab[i] = powf(2.0f, v) * ((i & 0x1F) | 0x20);
    }
}

/**
* AVCodec initialization
*/
static av_cold int ac3_decode_init(AVCodecContext *avctx)
{
    AC3DecodeContext *s = avctx->priv_data;
    s->avctx = avctx;

    ff_ac3_common_init();
    ac3_tables_init();
    ff_mdct_init(&s->imdct_256, 8, 1, 1.0);
    ff_mdct_init(&s->imdct_512, 9, 1, 1.0);
    ff_kbd_window_init(s->window, 5.0, 256);
    ff_dsputil_init(&s->dsp, avctx);
    ff_ac3dsp_init(&s->ac3dsp, avctx->flags & CODEC_FLAG_BITEXACT);
    ff_fmt_convert_init(&s->fmt_conv, avctx);
    av_lfg_init(&s->dith_state, 0);

    /* set scale value for float to int16 conversion */
    if (avctx->request_sample_fmt == AV_SAMPLE_FMT_FLT) {
        s->mul_bias = 1.0f;
        avctx->sample_fmt = AV_SAMPLE_FMT_FLT;
    } else {
        s->mul_bias = 32767.0f;
        avctx->sample_fmt = AV_SAMPLE_FMT_S16;
    }

    /* allow downmixing to stereo or mono */
    if (avctx->channels > 0 && avctx->request_channels > 0 &&
            avctx->request_channels < avctx->channels &&
            avctx->request_channels <= 2) {
        avctx->channels = avctx->request_channels;
    }
    s->downmixed = 1;

    avcodec_get_frame_defaults(&s->frame);
    avctx->coded_frame = &s->frame;

    return 0;
}

/**
* Parse the 'sync info' and 'bit stream info' from the AC-3 bitstream.
* GetBitContext within AC3DecodeContext must point to
* the start of the synchronized AC-3 bitstream.
*/
static int ac3_parse_header(AC3DecodeContext *s)
{
    GetBitContext *gbc = &s->gbc;
    int i;

    /* read the rest of the bsi. read twice for dual mono mode. */
    i = !s->channel_mode;
    do {
        skip_bits(gbc, 5); // skip dialog normalization
        if (get_bits1(gbc))
            skip_bits(gbc, 8); //skip compression
        if (get_bits1(gbc))
            skip_bits(gbc, 8); //skip language code
        if (get_bits1(gbc))
            skip_bits(gbc, 7); //skip audio production information
    } while (i--);

    skip_bits(gbc, 2); //skip copyright bit and original bitstream bit

    /* skip the timecodes (or extra bitstream information for Alternate Syntax)
TODO: read & use the xbsi1 downmix levels */
    if (get_bits1(gbc))
        skip_bits(gbc, 14); //skip timecode1 / xbsi1
    if (get_bits1(gbc))
        skip_bits(gbc, 14); //skip timecode2 / xbsi2

    /* skip additional bitstream info */
    if (get_bits1(gbc)) {
        i = get_bits(gbc, 6);
        do {
            skip_bits(gbc, 8);
        } while (i--);
    }

    return 0;
}

/**
* Common function to parse AC-3 or E-AC-3 frame header
*/
static int parse_frame_header(AC3DecodeContext *s)
{
    AC3HeaderInfo hdr;
    int err;

    err = avpriv_ac3_parse_header(&s->gbc, &hdr);
    if (err)
        return err;

    /* get decoding parameters from header info */
    s->bit_alloc_params.sr_code = hdr.sr_code;
    s->bitstream_mode = hdr.bitstream_mode;
    s->channel_mode = hdr.channel_mode;
    s->channel_layout = hdr.channel_layout;
    s->lfe_on = hdr.lfe_on;
    s->bit_alloc_params.sr_shift = hdr.sr_shift;
    s->sample_rate = hdr.sample_rate;
    s->bit_rate = hdr.bit_rate;
    s->channels = hdr.channels;
    s->fbw_channels = s->channels - s->lfe_on;
    s->lfe_ch = s->fbw_channels + 1;
    s->frame_size = hdr.frame_size;
    s->center_mix_level = hdr.center_mix_level;
    s->surround_mix_level = hdr.surround_mix_level;
    s->num_blocks = hdr.num_blocks;
    s->frame_type = hdr.frame_type;
    s->substreamid = hdr.substreamid;

    if (s->lfe_on) {
        s->start_freq[s->lfe_ch] = 0;
        s->end_freq[s->lfe_ch] = 7;
        s->num_exp_groups[s->lfe_ch] = 2;
        s->channel_in_cpl[s->lfe_ch] = 0;
    }

    if (hdr.bitstream_id <= 10) {
        s->eac3 = 0;
        s->snr_offset_strategy = 2;
        s->block_switch_syntax = 1;
        s->dither_flag_syntax = 1;
        s->bit_allocation_syntax = 1;
        s->fast_gain_syntax = 0;
        s->first_cpl_leak = 0;
        s->dba_syntax = 1;
        s->skip_syntax = 1;
        memset(s->channel_uses_aht, 0, sizeof(s->channel_uses_aht));
        return ac3_parse_header(s);
    } else if (CONFIG_EAC3_DECODER) {
        s->eac3 = 1;
        return ff_eac3_parse_header(s);
    } else {
        av_log(s->avctx, AV_LOG_ERROR, "E-AC-3 support not compiled in\n");
        return -1;
    }
}

/**
* Set stereo downmixing coefficients based on frame header info.
* reference: Section 7.8.2 Downmixing Into Two Channels
*/
static void set_downmix_coeffs(AC3DecodeContext *s)
{
    int i;
    float cmix = gain_levels[s-> center_mix_level];
    float smix = gain_levels[s->surround_mix_level];
    float norm0, norm1;

    for (i = 0; i < s->fbw_channels; i++) {
        s->downmix_coeffs[i][0] = gain_levels[ac3_default_coeffs[s->channel_mode][i][0]];
        s->downmix_coeffs[i][1] = gain_levels[ac3_default_coeffs[s->channel_mode][i][1]];
    }
    if (s->channel_mode > 1 && s->channel_mode & 1) {
        s->downmix_coeffs[1][0] = s->downmix_coeffs[1][1] = cmix;
    }
    if (s->channel_mode == AC3_CHMODE_2F1R || s->channel_mode == AC3_CHMODE_3F1R) {
        int nf = s->channel_mode - 2;
        s->downmix_coeffs[nf][0] = s->downmix_coeffs[nf][1] = smix * LEVEL_MINUS_3DB;
    }
    if (s->channel_mode == AC3_CHMODE_2F2R || s->channel_mode == AC3_CHMODE_3F2R) {
        int nf = s->channel_mode - 4;
        s->downmix_coeffs[nf][0] = s->downmix_coeffs[nf+1][1] = smix;
    }

    /* renormalize */
    norm0 = norm1 = 0.0;
    for (i = 0; i < s->fbw_channels; i++) {
        norm0 += s->downmix_coeffs[i][0];
        norm1 += s->downmix_coeffs[i][1];
    }
    norm0 = 1.0f / norm0;
    norm1 = 1.0f / norm1;
    for (i = 0; i < s->fbw_channels; i++) {
        s->downmix_coeffs[i][0] *= norm0;
        s->downmix_coeffs[i][1] *= norm1;
    }

    if (s->output_mode == AC3_CHMODE_MONO) {
        for (i = 0; i < s->fbw_channels; i++)
            s->downmix_coeffs[i][0] = (s->downmix_coeffs[i][0] +
                                       s->downmix_coeffs[i][1]) * LEVEL_MINUS_3DB;
    }
}

/**
* Decode the grouped exponents according to exponent strategy.
* reference: Section 7.1.3 Exponent Decoding
*/
static int decode_exponents(GetBitContext *gbc, int exp_strategy, int ngrps,
                            uint8_t absexp, int8_t *dexps)
{
    int i, j, grp, group_size;
    int dexp[256];
    int expacc, prevexp;

    /* unpack groups */
    group_size = exp_strategy + (exp_strategy == EXP_D45);
    for (grp = 0, i = 0; grp < ngrps; grp++) {
        expacc = get_bits(gbc, 7);
        dexp[i++] = ungroup_3_in_7_bits_tab[expacc][0];
        dexp[i++] = ungroup_3_in_7_bits_tab[expacc][1];
        dexp[i++] = ungroup_3_in_7_bits_tab[expacc][2];
    }

    /* convert to absolute exps and expand groups */
    prevexp = absexp;
    for (i = 0, j = 0; i < ngrps * 3; i++) {
        prevexp += dexp[i] - 2;
        if (prevexp > 24U)
            return -1;
        switch (group_size) {
        case 4: dexps[j++] = prevexp;
                dexps[j++] = prevexp;
        case 2: dexps[j++] = prevexp;
        case 1: dexps[j++] = prevexp;
        }
    }
    return 0;
}

/**
* Generate transform coefficients for each coupled channel in the coupling
* range using the coupling coefficients and coupling coordinates.
* reference: Section 7.4.3 Coupling Coordinate Format
*/
static void calc_transform_coeffs_cpl(AC3DecodeContext *s)
{
    int bin, band, ch;

    bin = s->start_freq[CPL_CH];
    for (band = 0; band < s->num_cpl_bands; band++) {
        int band_start = bin;
        int band_end = bin + s->cpl_band_sizes[band];
        for (ch = 1; ch <= s->fbw_channels; ch++) {
            if (s->channel_in_cpl[ch]) {
                int cpl_coord = s->cpl_coords[ch][band] << 5;
                for (bin = band_start; bin < band_end; bin++) {
                    s->fixed_coeffs[ch][bin] =
                        MULH(s->fixed_coeffs[CPL_CH][bin] << 4, cpl_coord);
                }
                if (ch == 2 && s->phase_flags[band]) {
                    for (bin = band_start; bin < band_end; bin++)
                        s->fixed_coeffs[2][bin] = -s->fixed_coeffs[2][bin];
                }
            }
        }
        bin = band_end;
    }
}

/**
* Grouped mantissas for 3-level 5-level and 11-level quantization
*/
typedef struct {
    int b1_mant[2];
    int b2_mant[2];
    int b4_mant;
    int b1;
    int b2;
    int b4;
} mant_groups;

/**
* Decode the transform coefficients for a particular channel
* reference: Section 7.3 Quantization and Decoding of Mantissas
*/
static void ac3_decode_transform_coeffs_ch(AC3DecodeContext *s, int ch_index, mant_groups *m)
{
    int start_freq = s->start_freq[ch_index];
    int end_freq = s->end_freq[ch_index];
    uint8_t *baps = s->bap[ch_index];
    int8_t *exps = s->dexps[ch_index];
    int *coeffs = s->fixed_coeffs[ch_index];
    int dither = (ch_index == CPL_CH) || s->dither_flag[ch_index];
    GetBitContext *gbc = &s->gbc;
    int freq;

    for (freq = start_freq; freq < end_freq; freq++) {
        int bap = baps[freq];
        int mantissa;
        switch (bap) {
        case 0:
            if (dither)
                mantissa = (av_lfg_get(&s->dith_state) & 0x7FFFFF) - 0x400000;
            else
                mantissa = 0;
            break;
        case 1:
            if (m->b1) {
                m->b1--;
                mantissa = m->b1_mant[m->b1];
            } else {
                int bits = get_bits(gbc, 5);
                mantissa = b1_mantissas[bits][0];
                m->b1_mant[1] = b1_mantissas[bits][1];
                m->b1_mant[0] = b1_mantissas[bits][2];
                m->b1 = 2;
            }
            break;
        case 2:
            if (m->b2) {
                m->b2--;
                mantissa = m->b2_mant[m->b2];
            } else {
                int bits = get_bits(gbc, 7);
                mantissa = b2_mantissas[bits][0];
                m->b2_mant[1] = b2_mantissas[bits][1];
                m->b2_mant[0] = b2_mantissas[bits][2];
                m->b2 = 2;
            }
            break;
        case 3:
            mantissa = b3_mantissas[get_bits(gbc, 3)];
            break;
        case 4:
            if (m->b4) {
                m->b4 = 0;
                mantissa = m->b4_mant;
            } else {
                int bits = get_bits(gbc, 7);
                mantissa = b4_mantissas[bits][0];
                m->b4_mant = b4_mantissas[bits][1];
                m->b4 = 1;
            }
            break;
        case 5:
            mantissa = b5_mantissas[get_bits(gbc, 4)];
            break;
        default: /* 6 to 15 */
            /* Shift mantissa and sign-extend it. */
            mantissa = get_sbits(gbc, quantization_tab[bap]);
            mantissa <<= 24 - quantization_tab[bap];
            break;
        }
        coeffs[freq] = mantissa >> exps[freq];
    }
}

/**
* Remove random dithering from coupling range coefficients with zero-bit
* mantissas for coupled channels which do not use dithering.
* reference: Section 7.3.4 Dither for Zero Bit Mantissas (bap=0)
*/
static void remove_dithering(AC3DecodeContext *s) {
    int ch, i;

    for (ch = 1; ch <= s->fbw_channels; ch++) {
        if (!s->dither_flag[ch] && s->channel_in_cpl[ch]) {
            for (i = s->start_freq[CPL_CH]; i < s->end_freq[CPL_CH]; i++) {
                if (!s->bap[CPL_CH][i])
                    s->fixed_coeffs[ch][i] = 0;
            }
        }
    }
}

static void decode_transform_coeffs_ch(AC3DecodeContext *s, int blk, int ch,
                                       mant_groups *m)
{
    if (!s->channel_uses_aht[ch]) {
        ac3_decode_transform_coeffs_ch(s, ch, m);
    } else {
        /* if AHT is used, mantissas for all blocks are encoded in the first
block of the frame. */
        int bin;
        if (!blk && CONFIG_EAC3_DECODER)
            ff_eac3_decode_transform_coeffs_aht_ch(s, ch);
        for (bin = s->start_freq[ch]; bin < s->end_freq[ch]; bin++) {
            s->fixed_coeffs[ch][bin] = s->pre_mantissa[ch][bin][blk] >> s->dexps[ch][bin];
        }
    }
}

/**
* Decode the transform coefficients.
*/
static void decode_transform_coeffs(AC3DecodeContext *s, int blk)
{
    int ch, end;
    int got_cplchan = 0;
    mant_groups m;

    m.b1 = m.b2 = m.b4 = 0;

    for (ch = 1; ch <= s->channels; ch++) {
        /* transform coefficients for full-bandwidth channel */
        decode_transform_coeffs_ch(s, blk, ch, &m);
        /* tranform coefficients for coupling channel come right after the
coefficients for the first coupled channel*/
        if (s->channel_in_cpl[ch]) {
            if (!got_cplchan) {
                decode_transform_coeffs_ch(s, blk, CPL_CH, &m);
                calc_transform_coeffs_cpl(s);
                got_cplchan = 1;
            }
            end = s->end_freq[CPL_CH];
        } else {
            end = s->end_freq[ch];
        }
        do
            s->fixed_coeffs[ch][end] = 0;
        while (++end < 256);
    }

    /* zero the dithered coefficients for appropriate channels */
    remove_dithering(s);
}

/**
* Stereo rematrixing.
* reference: Section 7.5.4 Rematrixing : Decoding Technique
*/
static void do_rematrixing(AC3DecodeContext *s)
{
    int bnd, i;
    int end, bndend;

    end = FFMIN(s->end_freq[1], s->end_freq[2]);

    for (bnd = 0; bnd < s->num_rematrixing_bands; bnd++) {
        if (s->rematrixing_flags[bnd]) {
            bndend = FFMIN(end, ff_ac3_rematrix_band_tab[bnd + 1]);
            for (i = ff_ac3_rematrix_band_tab[bnd]; i < bndend; i++) {
                int tmp0 = s->fixed_coeffs[1][i];
                s->fixed_coeffs[1][i] += s->fixed_coeffs[2][i];
                s->fixed_coeffs[2][i] = tmp0 - s->fixed_coeffs[2][i];
            }
        }
    }
}

/**
* Inverse MDCT Transform.
* Convert frequency domain coefficients to time-domain audio samples.
* reference: Section 7.9.4 Transformation Equations
*/
static inline void do_imdct(AC3DecodeContext *s, int channels)
{
    int ch;

    for (ch = 1; ch <= channels; ch++) {
        if (s->block_switch[ch]) {
            int i;
            float *x = s->tmp_output + 128;
            for (i = 0; i < 128; i++)
                x[i] = s->transform_coeffs[ch][2 * i];
            s->imdct_256.imdct_half(&s->imdct_256, s->tmp_output, x);
            s->dsp.vector_fmul_window(s->output[ch - 1], s->delay[ch - 1],
                                      s->tmp_output, s->window, 128);
            for (i = 0; i < 128; i++)
                x[i] = s->transform_coeffs[ch][2 * i + 1];
            s->imdct_256.imdct_half(&s->imdct_256, s->delay[ch - 1], x);
        } else {
            s->imdct_512.imdct_half(&s->imdct_512, s->tmp_output, s->transform_coeffs[ch]);
            s->dsp.vector_fmul_window(s->output[ch - 1], s->delay[ch - 1],
                                      s->tmp_output, s->window, 128);
            memcpy(s->delay[ch - 1], s->tmp_output + 128, 128 * sizeof(float));
        }
    }
}

/**
* Downmix the output to mono or stereo.
*/
void ff_ac3_downmix_c(float (*samples)[256], float (*matrix)[2],
                      int out_ch, int in_ch, int len)
{
    int i, j;
    float v0, v1;
    if (out_ch == 2) {
        for (i = 0; i < len; i++) {
            v0 = v1 = 0.0f;
            for (j = 0; j < in_ch; j++) {
                v0 += samples[j][i] * matrix[j][0];
                v1 += samples[j][i] * matrix[j][1];
            }
            samples[0][i] = v0;
            samples[1][i] = v1;
        }
    } else if (out_ch == 1) {
        for (i = 0; i < len; i++) {
            v0 = 0.0f;
            for (j = 0; j < in_ch; j++)
                v0 += samples[j][i] * matrix[j][0];
            samples[0][i] = v0;
        }
    }
}

/**
* Upmix delay samples from stereo to original channel layout.
*/
static void ac3_upmix_delay(AC3DecodeContext *s)
{
    int channel_data_size = sizeof(s->delay[0]);
    switch (s->channel_mode) {
    case AC3_CHMODE_DUALMONO:
    case AC3_CHMODE_STEREO:
        /* upmix mono to stereo */
        memcpy(s->delay[1], s->delay[0], channel_data_size);
        break;
    case AC3_CHMODE_2F2R:
        memset(s->delay[3], 0, channel_data_size);
    case AC3_CHMODE_2F1R:
        memset(s->delay[2], 0, channel_data_size);
        break;
    case AC3_CHMODE_3F2R:
        memset(s->delay[4], 0, channel_data_size);
    case AC3_CHMODE_3F1R:
        memset(s->delay[3], 0, channel_data_size);
    case AC3_CHMODE_3F:
        memcpy(s->delay[2], s->delay[1], channel_data_size);
        memset(s->delay[1], 0, channel_data_size);
        break;
    }
}

/**
* Decode band structure for coupling, spectral extension, or enhanced coupling.
* The band structure defines how many subbands are in each band. For each
* subband in the range, 1 means it is combined with the previous band, and 0
* means that it starts a new band.
*
* @param[in] gbc bit reader context
* @param[in] blk block number
* @param[in] eac3 flag to indicate E-AC-3
* @param[in] ecpl flag to indicate enhanced coupling
* @param[in] start_subband subband number for start of range
* @param[in] end_subband subband number for end of range
* @param[in] default_band_struct default band structure table
* @param[out] num_bands number of bands (optionally NULL)
* @param[out] band_sizes array containing the number of bins in each band (optionally NULL)
*/
static void decode_band_structure(GetBitContext *gbc, int blk, int eac3,
                                  int ecpl, int start_subband, int end_subband,
                                  const uint8_t *default_band_struct,
                                  int *num_bands, uint8_t *band_sizes)
{
    int subbnd, bnd, n_subbands, n_bands=0;
    uint8_t bnd_sz[22];
    uint8_t coded_band_struct[22];
    const uint8_t *band_struct;

    n_subbands = end_subband - start_subband;

    /* decode band structure from bitstream or use default */
    if (!eac3 || get_bits1(gbc)) {
        for (subbnd = 0; subbnd < n_subbands - 1; subbnd++) {
            coded_band_struct[subbnd] = get_bits1(gbc);
        }
        band_struct = coded_band_struct;
    } else if (!blk) {
        band_struct = &default_band_struct[start_subband+1];
    } else {
        /* no change in band structure */
        return;
    }

    /* calculate number of bands and band sizes based on band structure.
note that the first 4 subbands in enhanced coupling span only 6 bins
instead of 12. */
    if (num_bands || band_sizes ) {
        n_bands = n_subbands;
        bnd_sz[0] = ecpl ? 6 : 12;
        for (bnd = 0, subbnd = 1; subbnd < n_subbands; subbnd++) {
            int subbnd_size = (ecpl && subbnd < 4) ? 6 : 12;
            if (band_struct[subbnd - 1]) {
                n_bands--;
                bnd_sz[bnd] += subbnd_size;
            } else {
                bnd_sz[++bnd] = subbnd_size;
            }
        }
    }

    /* set optional output params */
    if (num_bands)
        *num_bands = n_bands;
    if (band_sizes)
        memcpy(band_sizes, bnd_sz, n_bands);
}

/**
* Decode a single audio block from the AC-3 bitstream.
*/
static int decode_audio_block(AC3DecodeContext *s, int blk)
{
    int fbw_channels = s->fbw_channels;
    int channel_mode = s->channel_mode;
    int i, bnd, seg, ch;
    int different_transforms;
    int downmix_output;
    int cpl_in_use;
    GetBitContext *gbc = &s->gbc;
    uint8_t bit_alloc_stages[AC3_MAX_CHANNELS] = { 0 };

    /* block switch flags */
    different_transforms = 0;
    if (s->block_switch_syntax) {
        for (ch = 1; ch <= fbw_channels; ch++) {
            s->block_switch[ch] = get_bits1(gbc);
            if (ch > 1 && s->block_switch[ch] != s->block_switch[1])
                different_transforms = 1;
        }
    }

    /* dithering flags */
    if (s->dither_flag_syntax) {
        for (ch = 1; ch <= fbw_channels; ch++) {
            s->dither_flag[ch] = get_bits1(gbc);
        }
    }

    /* dynamic range */
    i = !s->channel_mode;
    do {
        if (get_bits1(gbc)) {
            s->dynamic_range[i] = ((dynamic_range_tab[get_bits(gbc, 8)] - 1.0) *
                                  s->drc_scale) + 1.0;
        } else if (blk == 0) {
            s->dynamic_range[i] = 1.0f;
        }
    } while (i--);

    /* spectral extension strategy */
    if (s->eac3 && (!blk || get_bits1(gbc))) {
        s->spx_in_use = get_bits1(gbc);
        if (s->spx_in_use) {
            int dst_start_freq, dst_end_freq, src_start_freq,
                start_subband, end_subband;

            /* determine which channels use spx */
            if (s->channel_mode == AC3_CHMODE_MONO) {
                s->channel_uses_spx[1] = 1;
            } else {
                for (ch = 1; ch <= fbw_channels; ch++)
                    s->channel_uses_spx[ch] = get_bits1(gbc);
            }

            /* get the frequency bins of the spx copy region and the spx start
and end subbands */
            dst_start_freq = get_bits(gbc, 2);
            start_subband = get_bits(gbc, 3) + 2;
            if (start_subband > 7)
                start_subband += start_subband - 7;
            end_subband = get_bits(gbc, 3) + 5;
            if (end_subband > 7)
                end_subband += end_subband - 7;
            dst_start_freq = dst_start_freq * 12 + 25;
            src_start_freq = start_subband * 12 + 25;
            dst_end_freq = end_subband * 12 + 25;

            /* check validity of spx ranges */
            if (start_subband >= end_subband) {
                av_log(s->avctx, AV_LOG_ERROR, "invalid spectral extension "
                       "range (%d >= %d)\n", start_subband, end_subband);
                return -1;
            }
            if (dst_start_freq >= src_start_freq) {
                av_log(s->avctx, AV_LOG_ERROR, "invalid spectral extension "
                       "copy start bin (%d >= %d)\n", dst_start_freq, src_start_freq);
                return -1;
            }

            s->spx_dst_start_freq = dst_start_freq;
            s->spx_src_start_freq = src_start_freq;
            s->spx_dst_end_freq = dst_end_freq;

            decode_band_structure(gbc, blk, s->eac3, 0,
                                  start_subband, end_subband,
                                  ff_eac3_default_spx_band_struct,
                                  &s->num_spx_bands,
                                  s->spx_band_sizes);
        } else {
            for (ch = 1; ch <= fbw_channels; ch++) {
                s->channel_uses_spx[ch] = 0;
                s->first_spx_coords[ch] = 1;
            }
        }
    }

    /* spectral extension coordinates */
    if (s->spx_in_use) {
        for (ch = 1; ch <= fbw_channels; ch++) {
            if (s->channel_uses_spx[ch]) {
                if (s->first_spx_coords[ch] || get_bits1(gbc)) {
                    float spx_blend;
                    int bin, master_spx_coord;

                    s->first_spx_coords[ch] = 0;
                    spx_blend = get_bits(gbc, 5) * (1.0f/32);
                    master_spx_coord = get_bits(gbc, 2) * 3;

                    bin = s->spx_src_start_freq;
                    for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
                        int bandsize;
                        int spx_coord_exp, spx_coord_mant;
                        float nratio, sblend, nblend, spx_coord;

                        /* calculate blending factors */
                        bandsize = s->spx_band_sizes[bnd];
                        nratio = ((float)((bin + (bandsize >> 1))) / s->spx_dst_end_freq) - spx_blend;
                        nratio = av_clipf(nratio, 0.0f, 1.0f);
                        nblend = sqrtf(3.0f * nratio); // noise is scaled by sqrt(3)
                                                       // to give unity variance
                        sblend = sqrtf(1.0f - nratio);
                        bin += bandsize;

                        /* decode spx coordinates */
                        spx_coord_exp = get_bits(gbc, 4);
                        spx_coord_mant = get_bits(gbc, 2);
                        if (spx_coord_exp == 15) spx_coord_mant <<= 1;
                        else spx_coord_mant += 4;
                        spx_coord_mant <<= (25 - spx_coord_exp - master_spx_coord);
                        spx_coord = spx_coord_mant * (1.0f / (1 << 23));

                        /* multiply noise and signal blending factors by spx coordinate */
                        s->spx_noise_blend [ch][bnd] = nblend * spx_coord;
                        s->spx_signal_blend[ch][bnd] = sblend * spx_coord;
                    }
                }
            } else {
                s->first_spx_coords[ch] = 1;
            }
        }
    }

    /* coupling strategy */
    if (s->eac3 ? s->cpl_strategy_exists[blk] : get_bits1(gbc)) {
        memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
        if (!s->eac3)
            s->cpl_in_use[blk] = get_bits1(gbc);
        if (s->cpl_in_use[blk]) {
            /* coupling in use */
            int cpl_start_subband, cpl_end_subband;

            if (channel_mode < AC3_CHMODE_STEREO) {
                av_log(s->avctx, AV_LOG_ERROR, "coupling not allowed in mono or dual-mono\n");
                return -1;
            }

            /* check for enhanced coupling */
            if (s->eac3 && get_bits1(gbc)) {
                /* TODO: parse enhanced coupling strategy info */
                av_log_missing_feature(s->avctx, "Enhanced coupling", 1);
                return -1;
            }

            /* determine which channels are coupled */
            if (s->eac3 && s->channel_mode == AC3_CHMODE_STEREO) {
                s->channel_in_cpl[1] = 1;
                s->channel_in_cpl[2] = 1;
            } else {
                for (ch = 1; ch <= fbw_channels; ch++)
                    s->channel_in_cpl[ch] = get_bits1(gbc);
            }

            /* phase flags in use */
            if (channel_mode == AC3_CHMODE_STEREO)
                s->phase_flags_in_use = get_bits1(gbc);

            /* coupling frequency range */
            cpl_start_subband = get_bits(gbc, 4);
            cpl_end_subband = s->spx_in_use ? (s->spx_src_start_freq - 37) / 12 :
                                              get_bits(gbc, 4) + 3;
            if (cpl_start_subband >= cpl_end_subband) {
                av_log(s->avctx, AV_LOG_ERROR, "invalid coupling range (%d >= %d)\n",
                       cpl_start_subband, cpl_end_subband);
                return -1;
            }
            s->start_freq[CPL_CH] = cpl_start_subband * 12 + 37;
            s->end_freq[CPL_CH] = cpl_end_subband * 12 + 37;

            decode_band_structure(gbc, blk, s->eac3, 0, cpl_start_subband,
                                  cpl_end_subband,
                                  ff_eac3_default_cpl_band_struct,
                                  &s->num_cpl_bands, s->cpl_band_sizes);
        } else {
            /* coupling not in use */
            for (ch = 1; ch <= fbw_channels; ch++) {
                s->channel_in_cpl[ch] = 0;
                s->first_cpl_coords[ch] = 1;
            }
            s->first_cpl_leak = s->eac3;
            s->phase_flags_in_use = 0;
        }
    } else if (!s->eac3) {
        if (!blk) {
            av_log(s->avctx, AV_LOG_ERROR, "new coupling strategy must "
                   "be present in block 0\n");
            return -1;
        } else {
            s->cpl_in_use[blk] = s->cpl_in_use[blk-1];
        }
    }
    cpl_in_use = s->cpl_in_use[blk];

    /* coupling coordinates */
    if (cpl_in_use) {
        int cpl_coords_exist = 0;

        for (ch = 1; ch <= fbw_channels; ch++) {
            if (s->channel_in_cpl[ch]) {
                if ((s->eac3 && s->first_cpl_coords[ch]) || get_bits1(gbc)) {
                    int master_cpl_coord, cpl_coord_exp, cpl_coord_mant;
                    s->first_cpl_coords[ch] = 0;
                    cpl_coords_exist = 1;
                    master_cpl_coord = 3 * get_bits(gbc, 2);
                    for (bnd = 0; bnd < s->num_cpl_bands; bnd++) {
                        cpl_coord_exp = get_bits(gbc, 4);
                        cpl_coord_mant = get_bits(gbc, 4);
                        if (cpl_coord_exp == 15)
                            s->cpl_coords[ch][bnd] = cpl_coord_mant << 22;
                        else
                            s->cpl_coords[ch][bnd] = (cpl_coord_mant + 16) << 21;
                        s->cpl_coords[ch][bnd] >>= (cpl_coord_exp + master_cpl_coord);
                    }
                } else if (!blk) {
                    av_log(s->avctx, AV_LOG_ERROR, "new coupling coordinates must "
                           "be present in block 0\n");
                    return -1;
                }
            } else {
                /* channel not in coupling */
                s->first_cpl_coords[ch] = 1;
            }
        }
        /* phase flags */
        if (channel_mode == AC3_CHMODE_STEREO && cpl_coords_exist) {
            for (bnd = 0; bnd < s->num_cpl_bands; bnd++) {
                s->phase_flags[bnd] = s->phase_flags_in_use? get_bits1(gbc) : 0;
            }
        }
    }

    /* stereo rematrixing strategy and band structure */
    if (channel_mode == AC3_CHMODE_STEREO) {
        if ((s->eac3 && !blk) || get_bits1(gbc)) {
            s->num_rematrixing_bands = 4;
            if (cpl_in_use && s->start_freq[CPL_CH] <= 61) {
                s->num_rematrixing_bands -= 1 + (s->start_freq[CPL_CH] == 37);
            } else if (s->spx_in_use && s->spx_src_start_freq <= 61) {
                s->num_rematrixing_bands--;
            }
            for (bnd = 0; bnd < s->num_rematrixing_bands; bnd++)
                s->rematrixing_flags[bnd] = get_bits1(gbc);
        } else if (!blk) {
            av_log(s->avctx, AV_LOG_WARNING, "Warning: "
                   "new rematrixing strategy not present in block 0\n");
            s->num_rematrixing_bands = 0;
        }
    }

    /* exponent strategies for each channel */
    for (ch = !cpl_in_use; ch <= s->channels; ch++) {
        if (!s->eac3)
            s->exp_strategy[blk][ch] = get_bits(gbc, 2 - (ch == s->lfe_ch));
        if (s->exp_strategy[blk][ch] != EXP_REUSE)
            bit_alloc_stages[ch] = 3;
    }

    /* channel bandwidth */
    for (ch = 1; ch <= fbw_channels; ch++) {
        s->start_freq[ch] = 0;
        if (s->exp_strategy[blk][ch] != EXP_REUSE) {
            int group_size;
            int prev = s->end_freq[ch];
            if (s->channel_in_cpl[ch])
                s->end_freq[ch] = s->start_freq[CPL_CH];
            else if (s->channel_uses_spx[ch])
                s->end_freq[ch] = s->spx_src_start_freq;
            else {
                int bandwidth_code = get_bits(gbc, 6);
                if (bandwidth_code > 60) {
                    av_log(s->avctx, AV_LOG_ERROR, "bandwidth code = %d > 60\n", bandwidth_code);
                    return -1;
                }
                s->end_freq[ch] = bandwidth_code * 3 + 73;
            }
            group_size = 3 << (s->exp_strategy[blk][ch] - 1);
            s->num_exp_groups[ch] = (s->end_freq[ch] + group_size-4) / group_size;
            if (blk > 0 && s->end_freq[ch] != prev)
                memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
        }
    }
    if (cpl_in_use && s->exp_strategy[blk][CPL_CH] != EXP_REUSE) {
        s->num_exp_groups[CPL_CH] = (s->end_freq[CPL_CH] - s->start_freq[CPL_CH]) /
                                    (3 << (s->exp_strategy[blk][CPL_CH] - 1));
    }

    /* decode exponents for each channel */
    for (ch = !cpl_in_use; ch <= s->channels; ch++) {
        if (s->exp_strategy[blk][ch] != EXP_REUSE) {
            s->dexps[ch][0] = get_bits(gbc, 4) << !ch;
            if (decode_exponents(gbc, s->exp_strategy[blk][ch],
                                 s->num_exp_groups[ch], s->dexps[ch][0],
                                 &s->dexps[ch][s->start_freq[ch]+!!ch])) {
                av_log(s->avctx, AV_LOG_ERROR, "exponent out-of-range\n");
                return -1;
            }
            if (ch != CPL_CH && ch != s->lfe_ch)
                skip_bits(gbc, 2); /* skip gainrng */
        }
    }

    /* bit allocation information */
    if (s->bit_allocation_syntax) {
        if (get_bits1(gbc)) {
            s->bit_alloc_params.slow_decay = ff_ac3_slow_decay_tab[get_bits(gbc, 2)] >> s->bit_alloc_params.sr_shift;
            s->bit_alloc_params.fast_decay = ff_ac3_fast_decay_tab[get_bits(gbc, 2)] >> s->bit_alloc_params.sr_shift;
            s->bit_alloc_params.slow_gain = ff_ac3_slow_gain_tab[get_bits(gbc, 2)];
            s->bit_alloc_params.db_per_bit = ff_ac3_db_per_bit_tab[get_bits(gbc, 2)];
            s->bit_alloc_params.floor = ff_ac3_floor_tab[get_bits(gbc, 3)];
            for (ch = !cpl_in_use; ch <= s->channels; ch++)
                bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
        } else if (!blk) {
            av_log(s->avctx, AV_LOG_ERROR, "new bit allocation info must "
                   "be present in block 0\n");
            return -1;
        }
    }

    /* signal-to-noise ratio offsets and fast gains (signal-to-mask ratios) */
    if (!s->eac3 || !blk) {
        if (s->snr_offset_strategy && get_bits1(gbc)) {
            int snr = 0;
            int csnr;
            csnr = (get_bits(gbc, 6) - 15) << 4;
            for (i = ch = !cpl_in_use; ch <= s->channels; ch++) {
                /* snr offset */
                if (ch == i || s->snr_offset_strategy == 2)
                    snr = (csnr + get_bits(gbc, 4)) << 2;
                /* run at least last bit allocation stage if snr offset changes */
                if (blk && s->snr_offset[ch] != snr) {
                    bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 1);
                }
                s->snr_offset[ch] = snr;

                /* fast gain (normal AC-3 only) */
                if (!s->eac3) {
                    int prev = s->fast_gain[ch];
                    s->fast_gain[ch] = ff_ac3_fast_gain_tab[get_bits(gbc, 3)];
                    /* run last 2 bit allocation stages if fast gain changes */
                    if (blk && prev != s->fast_gain[ch])
                        bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
                }
            }
        } else if (!s->eac3 && !blk) {
            av_log(s->avctx, AV_LOG_ERROR, "new snr offsets must be present in block 0\n");
            return -1;
        }
    }

    /* fast gain (E-AC-3 only) */
    if (s->fast_gain_syntax && get_bits1(gbc)) {
        for (ch = !cpl_in_use; ch <= s->channels; ch++) {
            int prev = s->fast_gain[ch];
            s->fast_gain[ch] = ff_ac3_fast_gain_tab[get_bits(gbc, 3)];
            /* run last 2 bit allocation stages if fast gain changes */
            if (blk && prev != s->fast_gain[ch])
                bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
        }
    } else if (s->eac3 && !blk) {
        for (ch = !cpl_in_use; ch <= s->channels; ch++)
            s->fast_gain[ch] = ff_ac3_fast_gain_tab[4];
    }

    /* E-AC-3 to AC-3 converter SNR offset */
    if (s->frame_type == EAC3_FRAME_TYPE_INDEPENDENT && get_bits1(gbc)) {
        skip_bits(gbc, 10); // skip converter snr offset
    }

    /* coupling leak information */
    if (cpl_in_use) {
        if (s->first_cpl_leak || get_bits1(gbc)) {
            int fl = get_bits(gbc, 3);
            int sl = get_bits(gbc, 3);
            /* run last 2 bit allocation stages for coupling channel if
coupling leak changes */
            if (blk && (fl != s->bit_alloc_params.cpl_fast_leak ||
                sl != s->bit_alloc_params.cpl_slow_leak)) {
                bit_alloc_stages[CPL_CH] = FFMAX(bit_alloc_stages[CPL_CH], 2);
            }
            s->bit_alloc_params.cpl_fast_leak = fl;
            s->bit_alloc_params.cpl_slow_leak = sl;
        } else if (!s->eac3 && !blk) {
            av_log(s->avctx, AV_LOG_ERROR, "new coupling leak info must "
                   "be present in block 0\n");
            return -1;
        }
        s->first_cpl_leak = 0;
    }

    /* delta bit allocation information */
    if (s->dba_syntax && get_bits1(gbc)) {
        /* delta bit allocation exists (strategy) */
        for (ch = !cpl_in_use; ch <= fbw_channels; ch++) {
            s->dba_mode[ch] = get_bits(gbc, 2);
            if (s->dba_mode[ch] == DBA_RESERVED) {
                av_log(s->avctx, AV_LOG_ERROR, "delta bit allocation strategy reserved\n");
                return -1;
            }
            bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
        }
        /* channel delta offset, len and bit allocation */
        for (ch = !cpl_in_use; ch <= fbw_channels; ch++) {
            if (s->dba_mode[ch] == DBA_NEW) {
                s->dba_nsegs[ch] = get_bits(gbc, 3) + 1;
                for (seg = 0; seg < s->dba_nsegs[ch]; seg++) {
                    s->dba_offsets[ch][seg] = get_bits(gbc, 5);
                    s->dba_lengths[ch][seg] = get_bits(gbc, 4);
                    s->dba_values[ch][seg] = get_bits(gbc, 3);
                }
                /* run last 2 bit allocation stages if new dba values */
                bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
            }
        }
    } else if (blk == 0) {
        for (ch = 0; ch <= s->channels; ch++) {
            s->dba_mode[ch] = DBA_NONE;
        }
    }

    /* Bit allocation */
    for (ch = !cpl_in_use; ch <= s->channels; ch++) {
        if (bit_alloc_stages[ch] > 2) {
            /* Exponent mapping into PSD and PSD integration */
            ff_ac3_bit_alloc_calc_psd(s->dexps[ch],
                                      s->start_freq[ch], s->end_freq[ch],
                                      s->psd[ch], s->band_psd[ch]);
        }
        if (bit_alloc_stages[ch] > 1) {
            /* Compute excitation function, Compute masking curve, and
Apply delta bit allocation */
            if (ff_ac3_bit_alloc_calc_mask(&s->bit_alloc_params, s->band_psd[ch],
                                           s->start_freq[ch], s->end_freq[ch],
                                           s->fast_gain[ch], (ch == s->lfe_ch),
                                           s->dba_mode[ch], s->dba_nsegs[ch],
                                           s->dba_offsets[ch], s->dba_lengths[ch],
                                           s->dba_values[ch], s->mask[ch])) {
                av_log(s->avctx, AV_LOG_ERROR, "error in bit allocation\n");
                return -1;
            }
        }
        if (bit_alloc_stages[ch] > 0) {
            /* Compute bit allocation */
            const uint8_t *bap_tab = s->channel_uses_aht[ch] ?
                                     ff_eac3_hebap_tab : ff_ac3_bap_tab;
            s->ac3dsp.bit_alloc_calc_bap(s->mask[ch], s->psd[ch],
                                      s->start_freq[ch], s->end_freq[ch],
                                      s->snr_offset[ch],
                                      s->bit_alloc_params.floor,
                                      bap_tab, s->bap[ch]);
        }
    }

    /* unused dummy data */
    if (s->skip_syntax && get_bits1(gbc)) {
        int skipl = get_bits(gbc, 9);
        while (skipl--)
            skip_bits(gbc, 8);
    }

    /* unpack the transform coefficients
this also uncouples channels if coupling is in use. */
    decode_transform_coeffs(s, blk);

    /* TODO: generate enhanced coupling coordinates and uncouple */

    /* recover coefficients if rematrixing is in use */
    if (s->channel_mode == AC3_CHMODE_STEREO)
        do_rematrixing(s);

    /* apply scaling to coefficients (headroom, dynrng) */
    for (ch = 1; ch <= s->channels; ch++) {
        float gain = s->mul_bias / 4194304.0f;
        if (s->channel_mode == AC3_CHMODE_DUALMONO) {
            gain *= s->dynamic_range[2 - ch];
        } else {
            gain *= s->dynamic_range[0];
        }
        s->fmt_conv.int32_to_float_fmul_scalar(s->transform_coeffs[ch],
                                               s->fixed_coeffs[ch], gain, 256);
    }

    /* apply spectral extension to high frequency bins */
    if (s->spx_in_use && CONFIG_EAC3_DECODER) {
        ff_eac3_apply_spectral_extension(s);
    }

    /* downmix and MDCT. order depends on whether block switching is used for
any channel in this block. this is because coefficients for the long
and short transforms cannot be mixed. */
    downmix_output = s->channels != s->out_channels &&
                     !((s->output_mode & AC3_OUTPUT_LFEON) &&
                     s->fbw_channels == s->out_channels);
    if (different_transforms) {
        /* the delay samples have already been downmixed, so we upmix the delay
samples in order to reconstruct all channels before downmixing. */
        if (s->downmixed) {
            s->downmixed = 0;
            ac3_upmix_delay(s);
        }

        do_imdct(s, s->channels);

        if (downmix_output) {
            s->dsp.ac3_downmix(s->output, s->downmix_coeffs,
                               s->out_channels, s->fbw_channels, 256);
        }
    } else {
        if (downmix_output) {
            s->dsp.ac3_downmix(s->transform_coeffs + 1, s->downmix_coeffs,
                               s->out_channels, s->fbw_channels, 256);
        }

        if (downmix_output && !s->downmixed) {
            s->downmixed = 1;
            s->dsp.ac3_downmix(s->delay, s->downmix_coeffs, s->out_channels,
                               s->fbw_channels, 128);
        }

        do_imdct(s, s->out_channels);
    }

    return 0;
}

/**
* Decode a single AC-3 frame.
*/
static int ac3_decode_frame(AVCodecContext * avctx, void *data,
                            int *got_frame_ptr, AVPacket *avpkt)
{
    const uint8_t *buf = avpkt->data;
    int buf_size = avpkt->size;
    AC3DecodeContext *s = avctx->priv_data;
    float *out_samples_flt;
    int16_t *out_samples_s16;
    int blk, ch, err, ret;
    const uint8_t *channel_map;
    const float *output[AC3_MAX_CHANNELS];

    /* copy input buffer to decoder context to avoid reading past the end
of the buffer, which can be caused by a damaged input stream. */
    if (buf_size >= 2 && AV_RB16(buf) == 0x770B) {
        // seems to be byte-swapped AC-3
        int cnt = FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE) >> 1;
        s->dsp.bswap16_buf((uint16_t *)s->input_buffer, (const uint16_t *)buf, cnt);
    } else
        memcpy(s->input_buffer, buf, FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE));
    buf = s->input_buffer;
    /* initialize the GetBitContext with the start of valid AC-3 Frame */
    init_get_bits(&s->gbc, buf, buf_size * 8);

    /* parse the syncinfo */
    err = parse_frame_header(s);

    if (err) {
        switch (err) {
        case AAC_AC3_PARSE_ERROR_SYNC:
            av_log(avctx, AV_LOG_ERROR, "frame sync error\n");
            return -1;
        case AAC_AC3_PARSE_ERROR_BSID:
            av_log(avctx, AV_LOG_ERROR, "invalid bitstream id\n");
            break;
        case AAC_AC3_PARSE_ERROR_SAMPLE_RATE:
            av_log(avctx, AV_LOG_ERROR, "invalid sample rate\n");
            break;
        case AAC_AC3_PARSE_ERROR_FRAME_SIZE:
            av_log(avctx, AV_LOG_ERROR, "invalid frame size\n");
            break;
        case AAC_AC3_PARSE_ERROR_FRAME_TYPE:
            /* skip frame if CRC is ok. otherwise use error concealment. */
            /* TODO: add support for substreams and dependent frames */
            if (s->frame_type == EAC3_FRAME_TYPE_DEPENDENT || s->substreamid) {
                av_log(avctx, AV_LOG_ERROR, "unsupported frame type : "
                       "skipping frame\n");
                *got_frame_ptr = 0;
                return s->frame_size;
            } else {
                av_log(avctx, AV_LOG_ERROR, "invalid frame type\n");
            }
            break;
        default:
            av_log(avctx, AV_LOG_ERROR, "invalid header\n");
            break;
        }
    } else {
        /* check that reported frame size fits in input buffer */
        if (s->frame_size > buf_size) {
            av_log(avctx, AV_LOG_ERROR, "incomplete frame\n");
            err = AAC_AC3_PARSE_ERROR_FRAME_SIZE;
        } else if (avctx->err_recognition & (AV_EF_CRCCHECK|AV_EF_CAREFUL)) {
            /* check for crc mismatch */
            if (av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, &buf[2],
                       s->frame_size - 2)) {
                av_log(avctx, AV_LOG_ERROR, "frame CRC mismatch\n");
                err = AAC_AC3_PARSE_ERROR_CRC;
            }
        }
    }

    /* if frame is ok, set audio parameters */
    if (!err) {
        avctx->sample_rate = s->sample_rate;
        avctx->bit_rate = s->bit_rate;

        /* channel config */
        s->out_channels = s->channels;
        s->output_mode = s->channel_mode;
        if (s->lfe_on)
            s->output_mode |= AC3_OUTPUT_LFEON;
        if (avctx->request_channels > 0 && avctx->request_channels <= 2 &&
                avctx->request_channels < s->channels) {
            s->out_channels = avctx->request_channels;
            s->output_mode = avctx->request_channels == 1 ? AC3_CHMODE_MONO : AC3_CHMODE_STEREO;
            s->channel_layout = avpriv_ac3_channel_layout_tab[s->output_mode];
        }
        avctx->channels = s->out_channels;
        avctx->channel_layout = s->channel_layout;

        s->loro_center_mix_level = gain_levels[s-> center_mix_level];
        s->loro_surround_mix_level = gain_levels[s->surround_mix_level];
        s->ltrt_center_mix_level = LEVEL_MINUS_3DB;
        s->ltrt_surround_mix_level = LEVEL_MINUS_3DB;
        /* set downmixing coefficients if needed */
        if (s->channels != s->out_channels && !((s->output_mode & AC3_OUTPUT_LFEON) &&
                s->fbw_channels == s->out_channels)) {
            set_downmix_coeffs(s);
        }
    } else if (!s->out_channels) {
        s->out_channels = avctx->channels;
        if (s->out_channels < s->channels)
            s->output_mode = s->out_channels == 1 ? AC3_CHMODE_MONO : AC3_CHMODE_STEREO;
    }
    if (avctx->channels != s->out_channels) {
        av_log(avctx, AV_LOG_ERROR, "channel number mismatching on damaged frame\n");
        return AVERROR_INVALIDDATA;
    }
    /* set audio service type based on bitstream mode for AC-3 */
    avctx->audio_service_type = s->bitstream_mode;
    if (s->bitstream_mode == 0x7 && s->channels > 1)
        avctx->audio_service_type = AV_AUDIO_SERVICE_TYPE_KARAOKE;

    /* get output buffer */
    s->frame.nb_samples = s->num_blocks * 256;
    if ((ret = avctx->get_buffer(avctx, &s->frame)) < 0) {
        av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
        return ret;
    }
    out_samples_flt = (float *)s->frame.data[0];
    out_samples_s16 = (int16_t *)s->frame.data[0];

    /* decode the audio blocks */
    channel_map = ff_ac3_dec_channel_map[s->output_mode & ~AC3_OUTPUT_LFEON][s->lfe_on];
    for (ch = 0; ch < s->out_channels; ch++)
        output[ch] = s->output[channel_map[ch]];
    for (blk = 0; blk < s->num_blocks; blk++) {
        if (!err && decode_audio_block(s, blk)) {
            av_log(avctx, AV_LOG_ERROR, "error decoding the audio block\n");
            err = 1;
        }
        if (avctx->sample_fmt == AV_SAMPLE_FMT_FLT) {
            s->fmt_conv.float_interleave(out_samples_flt, output, 256,
                                         s->out_channels);
            out_samples_flt += 256 * s->out_channels;
        } else {
            s->fmt_conv.float_to_int16_interleave(out_samples_s16, output, 256,
                                                  s->out_channels);
            out_samples_s16 += 256 * s->out_channels;
        }
    }

    s->frame.decode_error_flags = err ? FF_DECODE_ERROR_INVALID_BITSTREAM : 0;

    *got_frame_ptr = 1;
    *(AVFrame *)data = s->frame;

    return FFMIN(buf_size, s->frame_size);
}

/**
* Uninitialize the AC-3 decoder.
*/
static av_cold int ac3_decode_end(AVCodecContext *avctx)
{
    AC3DecodeContext *s = avctx->priv_data;
    ff_mdct_end(&s->imdct_512);
    ff_mdct_end(&s->imdct_256);

    return 0;
}

#define OFFSET(x) offsetof(AC3DecodeContext, x)
#define PAR (AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_AUDIO_PARAM)
static const AVOption options[] = {
    { "drc_scale", "percentage of dynamic range compression to apply", OFFSET(drc_scale), AV_OPT_TYPE_FLOAT, {.dbl = 1.0}, 0.0, 1.0, PAR },

{"dmix_mode", "Preferred Stereo Downmix Mode", OFFSET(preferred_stereo_downmix), AV_OPT_TYPE_INT, {.i64 = -1 }, -1, 2, 0, "dmix_mode"},
{"ltrt_cmixlev", "Lt/Rt Center Mix Level", OFFSET(ltrt_center_mix_level), AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"ltrt_surmixlev", "Lt/Rt Surround Mix Level", OFFSET(ltrt_surround_mix_level), AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"loro_cmixlev", "Lo/Ro Center Mix Level", OFFSET(loro_center_mix_level), AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"loro_surmixlev", "Lo/Ro Surround Mix Level", OFFSET(loro_surround_mix_level), AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},

    { NULL},
};

static const AVClass ac3_decoder_class = {
    .class_name = "AC3 decoder",
    .item_name = av_default_item_name,
    .option = options,
    .version = LIBAVUTIL_VERSION_INT,
};

AVCodec ff_ac3_decoder = {
    .name = "ac3",
    .type = AVMEDIA_TYPE_AUDIO,
    .id = AV_CODEC_ID_AC3,
    .priv_data_size = sizeof (AC3DecodeContext),
    .init = ac3_decode_init,
    .close = ac3_decode_end,
    .decode = ac3_decode_frame,
    .capabilities = CODEC_CAP_DR1,
    .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
    .sample_fmts = (const enum AVSampleFormat[]) { AV_SAMPLE_FMT_FLT,
                                                      AV_SAMPLE_FMT_S16,
                                                      AV_SAMPLE_FMT_NONE },
    .priv_class = &ac3_decoder_class,
};

#if CONFIG_EAC3_DECODER
static const AVClass eac3_decoder_class = {
    .class_name = "E-AC3 decoder",
    .item_name = av_default_item_name,
    .option = options,
    .version = LIBAVUTIL_VERSION_INT,
};

AVCodec ff_eac3_decoder = {
    .name = "eac3",
    .type = AVMEDIA_TYPE_AUDIO,
    .id = AV_CODEC_ID_EAC3,
    .priv_data_size = sizeof (AC3DecodeContext),
    .init = ac3_decode_init,
    .close = ac3_decode_end,
    .decode = ac3_decode_frame,
    .capabilities = CODEC_CAP_DR1,
    .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52B (AC-3, E-AC-3)"),
    .sample_fmts = (const enum AVSampleFormat[]) { AV_SAMPLE_FMT_FLT,
                                                      AV_SAMPLE_FMT_S16,
                                                      AV_SAMPLE_FMT_NONE },
    .priv_class = &eac3_decoder_class,
};
#endif
Something went wrong with that request. Please try again.