module.audio.ac3.php 38.5 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
<?php

/////////////////////////////////////////////////////////////////
/// getID3() by James Heinrich <info@getid3.org>               //
//  available at https://github.com/JamesHeinrich/getID3       //
//            or https://www.getid3.org                        //
//            or http://getid3.sourceforge.net                 //
//  see readme.txt for more details                            //
/////////////////////////////////////////////////////////////////
//                                                             //
// module.audio.ac3.php                                        //
// module for analyzing AC-3 (aka Dolby Digital) audio files   //
// dependencies: NONE                                          //
//                                                            ///
/////////////////////////////////////////////////////////////////

if (!defined('GETID3_INCLUDEPATH')) { // prevent path-exposing attacks that access modules directly on public webservers
	exit;
}

class getid3_ac3 extends getid3_handler
{
	/**
	 * @var array
	 */
	private $AC3header = array();

	/**
	 * @var int
	 */
	private $BSIoffset = 0;

	const syncword = 0x0B77;

	/**
	 * @return bool
	 */
	public function Analyze() {
		$info = &$this->getid3->info;

		///AH
		$info['ac3']['raw']['bsi'] = array();
		$thisfile_ac3              = &$info['ac3'];
		$thisfile_ac3_raw          = &$thisfile_ac3['raw'];
		$thisfile_ac3_raw_bsi      = &$thisfile_ac3_raw['bsi'];


		// http://www.atsc.org/standards/a_52a.pdf

		$info['fileformat'] = 'ac3';

		// An AC-3 serial coded audio bit stream is made up of a sequence of synchronization frames
		// Each synchronization frame contains 6 coded audio blocks (AB), each of which represent 256
		// new audio samples per channel. A synchronization information (SI) header at the beginning
		// of each frame contains information needed to acquire and maintain synchronization. A
		// bit stream information (BSI) header follows SI, and contains parameters describing the coded
		// audio service. The coded audio blocks may be followed by an auxiliary data (Aux) field. At the
		// end of each frame is an error check field that includes a CRC word for error detection. An
		// additional CRC word is located in the SI header, the use of which, by a decoder, is optional.
		//
		// syncinfo() | bsi() | AB0 | AB1 | AB2 | AB3 | AB4 | AB5 | Aux | CRC

		// syncinfo() {
		// 	 syncword    16
		// 	 crc1        16
		// 	 fscod        2
		// 	 frmsizecod   6
		// } /* end of syncinfo */

		$this->fseek($info['avdataoffset']);
		$tempAC3header = $this->fread(100); // should be enough to cover all data, there are some variable-length fields...?
		$this->AC3header['syncinfo']  =     getid3_lib::BigEndian2Int(substr($tempAC3header, 0, 2));
		$this->AC3header['bsi']       =     getid3_lib::BigEndian2Bin(substr($tempAC3header, 2));
		$thisfile_ac3_raw_bsi['bsid'] = (getid3_lib::LittleEndian2Int(substr($tempAC3header, 5, 1)) & 0xF8) >> 3; // AC3 and E-AC3 put the "bsid" version identifier in the same place, but unfortnately the 4 bytes between the syncword and the version identifier are interpreted differently, so grab it here so the following code structure can make sense
		unset($tempAC3header);

		if ($this->AC3header['syncinfo'] !== self::syncword) {
			if (!$this->isDependencyFor('matroska')) {
				unset($info['fileformat'], $info['ac3']);
				return $this->error('Expecting "'.dechex(self::syncword).'" at offset '.$info['avdataoffset'].', found "'.dechex($this->AC3header['syncinfo']).'"');
			}
		}

		$info['audio']['dataformat']   = 'ac3';
		$info['audio']['bitrate_mode'] = 'cbr';
		$info['audio']['lossless']     = false;

		if ($thisfile_ac3_raw_bsi['bsid'] <= 8) {

			$thisfile_ac3_raw_bsi['crc1']       = getid3_lib::Bin2Dec($this->readHeaderBSI(16));
			$thisfile_ac3_raw_bsi['fscod']      =                     $this->readHeaderBSI(2);   // 5.4.1.3
			$thisfile_ac3_raw_bsi['frmsizecod'] =                     $this->readHeaderBSI(6);   // 5.4.1.4
			if ($thisfile_ac3_raw_bsi['frmsizecod'] > 37) { // binary: 100101 - see Table 5.18 Frame Size Code Table (1 word = 16 bits)
				$this->warning('Unexpected ac3.bsi.frmsizecod value: '.$thisfile_ac3_raw_bsi['frmsizecod'].', bitrate not set correctly');
			}

			$thisfile_ac3_raw_bsi['bsid']  = $this->readHeaderBSI(5); // we already know this from pre-parsing the version identifier, but re-read it to let the bitstream flow as intended
			$thisfile_ac3_raw_bsi['bsmod'] = $this->readHeaderBSI(3);
			$thisfile_ac3_raw_bsi['acmod'] = $this->readHeaderBSI(3);

			if ($thisfile_ac3_raw_bsi['acmod'] & 0x01) {
				// If the lsb of acmod is a 1, center channel is in use and cmixlev follows in the bit stream.
				$thisfile_ac3_raw_bsi['cmixlev'] = $this->readHeaderBSI(2);
				$thisfile_ac3['center_mix_level'] = self::centerMixLevelLookup($thisfile_ac3_raw_bsi['cmixlev']);
			}

			if ($thisfile_ac3_raw_bsi['acmod'] & 0x04) {
				// If the msb of acmod is a 1, surround channels are in use and surmixlev follows in the bit stream.
				$thisfile_ac3_raw_bsi['surmixlev'] = $this->readHeaderBSI(2);
				$thisfile_ac3['surround_mix_level'] = self::surroundMixLevelLookup($thisfile_ac3_raw_bsi['surmixlev']);
			}

			if ($thisfile_ac3_raw_bsi['acmod'] == 0x02) {
				// When operating in the two channel mode, this 2-bit code indicates whether or not the program has been encoded in Dolby Surround.
				$thisfile_ac3_raw_bsi['dsurmod'] = $this->readHeaderBSI(2);
				$thisfile_ac3['dolby_surround_mode'] = self::dolbySurroundModeLookup($thisfile_ac3_raw_bsi['dsurmod']);
			}

			$thisfile_ac3_raw_bsi['flags']['lfeon'] = (bool) $this->readHeaderBSI(1);

			// This indicates how far the average dialogue level is below digital 100 percent. Valid values are 1-31.
			// The value of 0 is reserved. The values of 1 to 31 are interpreted as -1 dB to -31 dB with respect to digital 100 percent.
			$thisfile_ac3_raw_bsi['dialnorm'] = $this->readHeaderBSI(5);                 // 5.4.2.8 dialnorm: Dialogue Normalization, 5 Bits

			$thisfile_ac3_raw_bsi['flags']['compr'] = (bool) $this->readHeaderBSI(1);       // 5.4.2.9 compre: Compression Gain Word Exists, 1 Bit
			if ($thisfile_ac3_raw_bsi['flags']['compr']) {
				$thisfile_ac3_raw_bsi['compr'] = $this->readHeaderBSI(8);                // 5.4.2.10 compr: Compression Gain Word, 8 Bits
				$thisfile_ac3['heavy_compression'] = self::heavyCompression($thisfile_ac3_raw_bsi['compr']);
			}

			$thisfile_ac3_raw_bsi['flags']['langcod'] = (bool) $this->readHeaderBSI(1);     // 5.4.2.11 langcode: Language Code Exists, 1 Bit
			if ($thisfile_ac3_raw_bsi['flags']['langcod']) {
				$thisfile_ac3_raw_bsi['langcod'] = $this->readHeaderBSI(8);              // 5.4.2.12 langcod: Language Code, 8 Bits
			}

			$thisfile_ac3_raw_bsi['flags']['audprodinfo'] = (bool) $this->readHeaderBSI(1);  // 5.4.2.13 audprodie: Audio Production Information Exists, 1 Bit
			if ($thisfile_ac3_raw_bsi['flags']['audprodinfo']) {
				$thisfile_ac3_raw_bsi['mixlevel'] = $this->readHeaderBSI(5);             // 5.4.2.14 mixlevel: Mixing Level, 5 Bits
				$thisfile_ac3_raw_bsi['roomtyp']  = $this->readHeaderBSI(2);             // 5.4.2.15 roomtyp: Room Type, 2 Bits

				$thisfile_ac3['mixing_level'] = (80 + $thisfile_ac3_raw_bsi['mixlevel']).'dB';
				$thisfile_ac3['room_type']    = self::roomTypeLookup($thisfile_ac3_raw_bsi['roomtyp']);
			}


			$thisfile_ac3_raw_bsi['dialnorm2'] = $this->readHeaderBSI(5);                // 5.4.2.16 dialnorm2: Dialogue Normalization, ch2, 5 Bits
			$thisfile_ac3['dialogue_normalization2'] = '-'.$thisfile_ac3_raw_bsi['dialnorm2'].'dB';  // This indicates how far the average dialogue level is below digital 100 percent. Valid values are 1-31. The value of 0 is reserved. The values of 1 to 31 are interpreted as -1 dB to -31 dB with respect to digital 100 percent.

			$thisfile_ac3_raw_bsi['flags']['compr2'] = (bool) $this->readHeaderBSI(1);       // 5.4.2.17 compr2e: Compression Gain Word Exists, ch2, 1 Bit
			if ($thisfile_ac3_raw_bsi['flags']['compr2']) {
				$thisfile_ac3_raw_bsi['compr2'] = $this->readHeaderBSI(8);               // 5.4.2.18 compr2: Compression Gain Word, ch2, 8 Bits
				$thisfile_ac3['heavy_compression2'] = self::heavyCompression($thisfile_ac3_raw_bsi['compr2']);
			}

			$thisfile_ac3_raw_bsi['flags']['langcod2'] = (bool) $this->readHeaderBSI(1);    // 5.4.2.19 langcod2e: Language Code Exists, ch2, 1 Bit
			if ($thisfile_ac3_raw_bsi['flags']['langcod2']) {
				$thisfile_ac3_raw_bsi['langcod2'] = $this->readHeaderBSI(8);             // 5.4.2.20 langcod2: Language Code, ch2, 8 Bits
			}

			$thisfile_ac3_raw_bsi['flags']['audprodinfo2'] = (bool) $this->readHeaderBSI(1); // 5.4.2.21 audprodi2e: Audio Production Information Exists, ch2, 1 Bit
			if ($thisfile_ac3_raw_bsi['flags']['audprodinfo2']) {
				$thisfile_ac3_raw_bsi['mixlevel2'] = $this->readHeaderBSI(5);            // 5.4.2.22 mixlevel2: Mixing Level, ch2, 5 Bits
				$thisfile_ac3_raw_bsi['roomtyp2']  = $this->readHeaderBSI(2);            // 5.4.2.23 roomtyp2: Room Type, ch2, 2 Bits

				$thisfile_ac3['mixing_level2'] = (80 + $thisfile_ac3_raw_bsi['mixlevel2']).'dB';
				$thisfile_ac3['room_type2']    = self::roomTypeLookup($thisfile_ac3_raw_bsi['roomtyp2']);
			}

			$thisfile_ac3_raw_bsi['copyright'] = (bool) $this->readHeaderBSI(1);         // 5.4.2.24 copyrightb: Copyright Bit, 1 Bit

			$thisfile_ac3_raw_bsi['original']  = (bool) $this->readHeaderBSI(1);         // 5.4.2.25 origbs: Original Bit Stream, 1 Bit

			$thisfile_ac3_raw_bsi['flags']['timecod1'] = $this->readHeaderBSI(2);            // 5.4.2.26 timecod1e, timcode2e: Time Code (first and second) Halves Exist, 2 Bits
			if ($thisfile_ac3_raw_bsi['flags']['timecod1'] & 0x01) {
				$thisfile_ac3_raw_bsi['timecod1'] = $this->readHeaderBSI(14);            // 5.4.2.27 timecod1: Time code first half, 14 bits
				$thisfile_ac3['timecode1'] = 0;
				$thisfile_ac3['timecode1'] += (($thisfile_ac3_raw_bsi['timecod1'] & 0x3E00) >>  9) * 3600;  // The first 5 bits of this 14-bit field represent the time in hours, with valid values of 0�23
				$thisfile_ac3['timecode1'] += (($thisfile_ac3_raw_bsi['timecod1'] & 0x01F8) >>  3) *   60;  // The next 6 bits represent the time in minutes, with valid values of 0�59
				$thisfile_ac3['timecode1'] += (($thisfile_ac3_raw_bsi['timecod1'] & 0x0003) >>  0) *    8;  // The final 3 bits represents the time in 8 second increments, with valid values of 0�7 (representing 0, 8, 16, ... 56 seconds)
			}
			if ($thisfile_ac3_raw_bsi['flags']['timecod1'] & 0x02) {
				$thisfile_ac3_raw_bsi['timecod2'] = $this->readHeaderBSI(14);            // 5.4.2.28 timecod2: Time code second half, 14 bits
				$thisfile_ac3['timecode2'] = 0;
				$thisfile_ac3['timecode2'] += (($thisfile_ac3_raw_bsi['timecod2'] & 0x3800) >> 11) *   1;              // The first 3 bits of this 14-bit field represent the time in seconds, with valid values from 0�7 (representing 0-7 seconds)
				$thisfile_ac3['timecode2'] += (($thisfile_ac3_raw_bsi['timecod2'] & 0x07C0) >>  6) *  (1 / 30);        // The next 5 bits represents the time in frames, with valid values from 0�29 (one frame = 1/30th of a second)
				$thisfile_ac3['timecode2'] += (($thisfile_ac3_raw_bsi['timecod2'] & 0x003F) >>  0) * ((1 / 30) / 60);  // The final 6 bits represents fractions of 1/64 of a frame, with valid values from 0�63
			}

			$thisfile_ac3_raw_bsi['flags']['addbsi'] = (bool) $this->readHeaderBSI(1);
			if ($thisfile_ac3_raw_bsi['flags']['addbsi']) {
				$thisfile_ac3_raw_bsi['addbsi_length'] = $this->readHeaderBSI(6) + 1; // This 6-bit code, which exists only if addbside is a 1, indicates the length in bytes of additional bit stream information. The valid range of addbsil is 0�63, indicating 1�64 additional bytes, respectively.

				$this->AC3header['bsi'] .= getid3_lib::BigEndian2Bin($this->fread($thisfile_ac3_raw_bsi['addbsi_length']));

				$thisfile_ac3_raw_bsi['addbsi_data'] = substr($this->AC3header['bsi'], $this->BSIoffset, $thisfile_ac3_raw_bsi['addbsi_length'] * 8);
				$this->BSIoffset += $thisfile_ac3_raw_bsi['addbsi_length'] * 8;
			}


		} elseif ($thisfile_ac3_raw_bsi['bsid'] <= 16) { // E-AC3


			$this->error('E-AC3 parsing is incomplete and experimental in this version of getID3 ('.$this->getid3->version().'). Notably the bitrate calculations are wrong -- value might (or not) be correct, but it is not calculated correctly. Email info@getid3.org if you know how to calculate EAC3 bitrate correctly.');
			$info['audio']['dataformat'] = 'eac3';

			$thisfile_ac3_raw_bsi['strmtyp']          =        $this->readHeaderBSI(2);
			$thisfile_ac3_raw_bsi['substreamid']      =        $this->readHeaderBSI(3);
			$thisfile_ac3_raw_bsi['frmsiz']           =        $this->readHeaderBSI(11);
			$thisfile_ac3_raw_bsi['fscod']            =        $this->readHeaderBSI(2);
			if ($thisfile_ac3_raw_bsi['fscod'] == 3) {
				$thisfile_ac3_raw_bsi['fscod2']       =        $this->readHeaderBSI(2);
				$thisfile_ac3_raw_bsi['numblkscod'] = 3; // six blocks per syncframe
			} else {
				$thisfile_ac3_raw_bsi['numblkscod']   =        $this->readHeaderBSI(2);
			}
			$thisfile_ac3['bsi']['blocks_per_sync_frame'] = self::blocksPerSyncFrame($thisfile_ac3_raw_bsi['numblkscod']);
			$thisfile_ac3_raw_bsi['acmod']            =        $this->readHeaderBSI(3);
			$thisfile_ac3_raw_bsi['flags']['lfeon']   = (bool) $this->readHeaderBSI(1);
			$thisfile_ac3_raw_bsi['bsid']             =        $this->readHeaderBSI(5); // we already know this from pre-parsing the version identifier, but re-read it to let the bitstream flow as intended
			$thisfile_ac3_raw_bsi['dialnorm']         =        $this->readHeaderBSI(5);
			$thisfile_ac3_raw_bsi['flags']['compr']       = (bool) $this->readHeaderBSI(1);
			if ($thisfile_ac3_raw_bsi['flags']['compr']) {
				$thisfile_ac3_raw_bsi['compr']        =        $this->readHeaderBSI(8);
			}
			if ($thisfile_ac3_raw_bsi['acmod'] == 0) { // if 1+1 mode (dual mono, so some items need a second value)
				$thisfile_ac3_raw_bsi['dialnorm2']    =        $this->readHeaderBSI(5);
				$thisfile_ac3_raw_bsi['flags']['compr2']  = (bool) $this->readHeaderBSI(1);
				if ($thisfile_ac3_raw_bsi['flags']['compr2']) {
					$thisfile_ac3_raw_bsi['compr2']   =        $this->readHeaderBSI(8);
				}
			}
			if ($thisfile_ac3_raw_bsi['strmtyp'] == 1) { // if dependent stream
				$thisfile_ac3_raw_bsi['flags']['chanmap'] = (bool) $this->readHeaderBSI(1);
				if ($thisfile_ac3_raw_bsi['flags']['chanmap']) {
					$thisfile_ac3_raw_bsi['chanmap']  =        $this->readHeaderBSI(8);
				}
			}
			$thisfile_ac3_raw_bsi['flags']['mixmdat']     = (bool) $this->readHeaderBSI(1);
			if ($thisfile_ac3_raw_bsi['flags']['mixmdat']) { // Mixing metadata
				if ($thisfile_ac3_raw_bsi['acmod'] > 2) { // if more than 2 channels
					$thisfile_ac3_raw_bsi['dmixmod']  =        $this->readHeaderBSI(2);
				}
				if (($thisfile_ac3_raw_bsi['acmod'] & 0x01) && ($thisfile_ac3_raw_bsi['acmod'] > 2)) { // if three front channels exist
					$thisfile_ac3_raw_bsi['ltrtcmixlev'] =        $this->readHeaderBSI(3);
					$thisfile_ac3_raw_bsi['lorocmixlev'] =        $this->readHeaderBSI(3);
				}
				if ($thisfile_ac3_raw_bsi['acmod'] & 0x04) { // if a surround channel exists
					$thisfile_ac3_raw_bsi['ltrtsurmixlev'] =        $this->readHeaderBSI(3);
					$thisfile_ac3_raw_bsi['lorosurmixlev'] =        $this->readHeaderBSI(3);
				}
				if ($thisfile_ac3_raw_bsi['flags']['lfeon']) { // if the LFE channel exists
					$thisfile_ac3_raw_bsi['flags']['lfemixlevcod'] = (bool) $this->readHeaderBSI(1);
					if ($thisfile_ac3_raw_bsi['flags']['lfemixlevcod']) {
						$thisfile_ac3_raw_bsi['lfemixlevcod']  =        $this->readHeaderBSI(5);
					}
				}
				if ($thisfile_ac3_raw_bsi['strmtyp'] == 0) { // if independent stream
					$thisfile_ac3_raw_bsi['flags']['pgmscl'] = (bool) $this->readHeaderBSI(1);
					if ($thisfile_ac3_raw_bsi['flags']['pgmscl']) {
						$thisfile_ac3_raw_bsi['pgmscl']  =        $this->readHeaderBSI(6);
					}
					if ($thisfile_ac3_raw_bsi['acmod'] == 0) { // if 1+1 mode (dual mono, so some items need a second value)
						$thisfile_ac3_raw_bsi['flags']['pgmscl2'] = (bool) $this->readHeaderBSI(1);
						if ($thisfile_ac3_raw_bsi['flags']['pgmscl2']) {
							$thisfile_ac3_raw_bsi['pgmscl2']  =        $this->readHeaderBSI(6);
						}
					}
					$thisfile_ac3_raw_bsi['flags']['extpgmscl'] = (bool) $this->readHeaderBSI(1);
					if ($thisfile_ac3_raw_bsi['flags']['extpgmscl']) {
						$thisfile_ac3_raw_bsi['extpgmscl']  =        $this->readHeaderBSI(6);
					}
					$thisfile_ac3_raw_bsi['mixdef']  =        $this->readHeaderBSI(2);
					if ($thisfile_ac3_raw_bsi['mixdef'] == 1) { // mixing option 2
						$thisfile_ac3_raw_bsi['premixcmpsel']  = (bool) $this->readHeaderBSI(1);
						$thisfile_ac3_raw_bsi['drcsrc']        = (bool) $this->readHeaderBSI(1);
						$thisfile_ac3_raw_bsi['premixcmpscl']  =        $this->readHeaderBSI(3);
					} elseif ($thisfile_ac3_raw_bsi['mixdef'] == 2) { // mixing option 3
						$thisfile_ac3_raw_bsi['mixdata']       =        $this->readHeaderBSI(12);
					} elseif ($thisfile_ac3_raw_bsi['mixdef'] == 3) { // mixing option 4
						$mixdefbitsread = 0;
						$thisfile_ac3_raw_bsi['mixdeflen']     =        $this->readHeaderBSI(5); $mixdefbitsread += 5;
						$thisfile_ac3_raw_bsi['flags']['mixdata2'] = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
						if ($thisfile_ac3_raw_bsi['flags']['mixdata2']) {
							$thisfile_ac3_raw_bsi['premixcmpsel']  = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
							$thisfile_ac3_raw_bsi['drcsrc']        = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
							$thisfile_ac3_raw_bsi['premixcmpscl']  =        $this->readHeaderBSI(3); $mixdefbitsread += 3;
							$thisfile_ac3_raw_bsi['flags']['extpgmlscl']   = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
							if ($thisfile_ac3_raw_bsi['flags']['extpgmlscl']) {
								$thisfile_ac3_raw_bsi['extpgmlscl']    =        $this->readHeaderBSI(4); $mixdefbitsread += 4;
							}
							$thisfile_ac3_raw_bsi['flags']['extpgmcscl']   = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
							if ($thisfile_ac3_raw_bsi['flags']['extpgmcscl']) {
								$thisfile_ac3_raw_bsi['extpgmcscl']    =        $this->readHeaderBSI(4); $mixdefbitsread += 4;
							}
							$thisfile_ac3_raw_bsi['flags']['extpgmrscl']   = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
							if ($thisfile_ac3_raw_bsi['flags']['extpgmrscl']) {
								$thisfile_ac3_raw_bsi['extpgmrscl']    =        $this->readHeaderBSI(4);
							}
							$thisfile_ac3_raw_bsi['flags']['extpgmlsscl']  = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
							if ($thisfile_ac3_raw_bsi['flags']['extpgmlsscl']) {
								$thisfile_ac3_raw_bsi['extpgmlsscl']   =        $this->readHeaderBSI(4); $mixdefbitsread += 4;
							}
							$thisfile_ac3_raw_bsi['flags']['extpgmrsscl']  = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
							if ($thisfile_ac3_raw_bsi['flags']['extpgmrsscl']) {
								$thisfile_ac3_raw_bsi['extpgmrsscl']   =        $this->readHeaderBSI(4); $mixdefbitsread += 4;
							}
							$thisfile_ac3_raw_bsi['flags']['extpgmlfescl'] = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
							if ($thisfile_ac3_raw_bsi['flags']['extpgmlfescl']) {
								$thisfile_ac3_raw_bsi['extpgmlfescl']  =        $this->readHeaderBSI(4); $mixdefbitsread += 4;
							}
							$thisfile_ac3_raw_bsi['flags']['dmixscl']      = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
							if ($thisfile_ac3_raw_bsi['flags']['dmixscl']) {
								$thisfile_ac3_raw_bsi['dmixscl']       =        $this->readHeaderBSI(4); $mixdefbitsread += 4;
							}
							$thisfile_ac3_raw_bsi['flags']['addch']        = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
							if ($thisfile_ac3_raw_bsi['flags']['addch']) {
								$thisfile_ac3_raw_bsi['flags']['extpgmaux1scl']   = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
								if ($thisfile_ac3_raw_bsi['flags']['extpgmaux1scl']) {
									$thisfile_ac3_raw_bsi['extpgmaux1scl']    =        $this->readHeaderBSI(4); $mixdefbitsread += 4;
								}
								$thisfile_ac3_raw_bsi['flags']['extpgmaux2scl']   = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
								if ($thisfile_ac3_raw_bsi['flags']['extpgmaux2scl']) {
									$thisfile_ac3_raw_bsi['extpgmaux2scl']    =        $this->readHeaderBSI(4); $mixdefbitsread += 4;
								}
							}
						}
						$thisfile_ac3_raw_bsi['flags']['mixdata3'] = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
						if ($thisfile_ac3_raw_bsi['flags']['mixdata3']) {
							$thisfile_ac3_raw_bsi['spchdat']   =        $this->readHeaderBSI(5); $mixdefbitsread += 5;
							$thisfile_ac3_raw_bsi['flags']['addspchdat'] = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
							if ($thisfile_ac3_raw_bsi['flags']['addspchdat']) {
								$thisfile_ac3_raw_bsi['spchdat1']   =         $this->readHeaderBSI(5); $mixdefbitsread += 5;
								$thisfile_ac3_raw_bsi['spchan1att'] =         $this->readHeaderBSI(2); $mixdefbitsread += 2;
								$thisfile_ac3_raw_bsi['flags']['addspchdat1'] = (bool) $this->readHeaderBSI(1); $mixdefbitsread += 1;
								if ($thisfile_ac3_raw_bsi['flags']['addspchdat1']) {
									$thisfile_ac3_raw_bsi['spchdat2']   =         $this->readHeaderBSI(5); $mixdefbitsread += 5;
									$thisfile_ac3_raw_bsi['spchan2att'] =         $this->readHeaderBSI(3); $mixdefbitsread += 3;
								}
							}
						}
						$mixdata_bits = (8 * ($thisfile_ac3_raw_bsi['mixdeflen'] + 2)) - $mixdefbitsread;
						$mixdata_fill = (($mixdata_bits % 8) ? 8 - ($mixdata_bits % 8) : 0);
						$thisfile_ac3_raw_bsi['mixdata']     =        $this->readHeaderBSI($mixdata_bits);
						$thisfile_ac3_raw_bsi['mixdatafill'] =        $this->readHeaderBSI($mixdata_fill);
						unset($mixdefbitsread, $mixdata_bits, $mixdata_fill);
					}
					if ($thisfile_ac3_raw_bsi['acmod'] < 2) { // if mono or dual mono source
						$thisfile_ac3_raw_bsi['flags']['paninfo'] = (bool) $this->readHeaderBSI(1);
						if ($thisfile_ac3_raw_bsi['flags']['paninfo']) {
							$thisfile_ac3_raw_bsi['panmean']   =        $this->readHeaderBSI(8);
							$thisfile_ac3_raw_bsi['paninfo']   =        $this->readHeaderBSI(6);
						}
						if ($thisfile_ac3_raw_bsi['acmod'] == 0) { // if 1+1 mode (dual mono, so some items need a second value)
							$thisfile_ac3_raw_bsi['flags']['paninfo2'] = (bool) $this->readHeaderBSI(1);
							if ($thisfile_ac3_raw_bsi['flags']['paninfo2']) {
								$thisfile_ac3_raw_bsi['panmean2']   =        $this->readHeaderBSI(8);
								$thisfile_ac3_raw_bsi['paninfo2']   =        $this->readHeaderBSI(6);
							}
						}
					}
					$thisfile_ac3_raw_bsi['flags']['frmmixcfginfo'] = (bool) $this->readHeaderBSI(1);
					if ($thisfile_ac3_raw_bsi['flags']['frmmixcfginfo']) { // mixing configuration information
						if ($thisfile_ac3_raw_bsi['numblkscod'] == 0) {
							$thisfile_ac3_raw_bsi['blkmixcfginfo'][0]  =        $this->readHeaderBSI(5);
						} else {
							for ($blk = 0; $blk < $thisfile_ac3_raw_bsi['numblkscod']; $blk++) {
								$thisfile_ac3_raw_bsi['flags']['blkmixcfginfo'.$blk] = (bool) $this->readHeaderBSI(1);
								if ($thisfile_ac3_raw_bsi['flags']['blkmixcfginfo'.$blk]) { // mixing configuration information
									$thisfile_ac3_raw_bsi['blkmixcfginfo'][$blk]  =        $this->readHeaderBSI(5);
								}
							}
						}
					}
				}
			}
			$thisfile_ac3_raw_bsi['flags']['infomdat']          = (bool) $this->readHeaderBSI(1);
			if ($thisfile_ac3_raw_bsi['flags']['infomdat']) { // Informational metadata
				$thisfile_ac3_raw_bsi['bsmod']                  =        $this->readHeaderBSI(3);
				$thisfile_ac3_raw_bsi['flags']['copyrightb']    = (bool) $this->readHeaderBSI(1);
				$thisfile_ac3_raw_bsi['flags']['origbs']        = (bool) $this->readHeaderBSI(1);
				if ($thisfile_ac3_raw_bsi['acmod'] == 2) { //  if in 2/0 mode
					$thisfile_ac3_raw_bsi['dsurmod']            =        $this->readHeaderBSI(2);
					$thisfile_ac3_raw_bsi['dheadphonmod']       =        $this->readHeaderBSI(2);
				}
				if ($thisfile_ac3_raw_bsi['acmod'] >= 6) { //  if both surround channels exist
					$thisfile_ac3_raw_bsi['dsurexmod']          =        $this->readHeaderBSI(2);
				}
				$thisfile_ac3_raw_bsi['flags']['audprodi']      = (bool) $this->readHeaderBSI(1);
				if ($thisfile_ac3_raw_bsi['flags']['audprodi']) {
					$thisfile_ac3_raw_bsi['mixlevel']           =        $this->readHeaderBSI(5);
					$thisfile_ac3_raw_bsi['roomtyp']            =        $this->readHeaderBSI(2);
					$thisfile_ac3_raw_bsi['flags']['adconvtyp'] = (bool) $this->readHeaderBSI(1);
				}
				if ($thisfile_ac3_raw_bsi['acmod'] == 0) { //  if 1+1 mode (dual mono, so some items need a second value)
					$thisfile_ac3_raw_bsi['flags']['audprodi2']      = (bool) $this->readHeaderBSI(1);
					if ($thisfile_ac3_raw_bsi['flags']['audprodi2']) {
						$thisfile_ac3_raw_bsi['mixlevel2']           =        $this->readHeaderBSI(5);
						$thisfile_ac3_raw_bsi['roomtyp2']            =        $this->readHeaderBSI(2);
						$thisfile_ac3_raw_bsi['flags']['adconvtyp2'] = (bool) $this->readHeaderBSI(1);
					}
				}
				if ($thisfile_ac3_raw_bsi['fscod'] < 3) { // if not half sample rate
					$thisfile_ac3_raw_bsi['flags']['sourcefscod'] = (bool) $this->readHeaderBSI(1);
				}
			}
			if (($thisfile_ac3_raw_bsi['strmtyp'] == 0) && ($thisfile_ac3_raw_bsi['numblkscod'] != 3)) { //  if both surround channels exist
				$thisfile_ac3_raw_bsi['flags']['convsync'] = (bool) $this->readHeaderBSI(1);
			}
			if ($thisfile_ac3_raw_bsi['strmtyp'] == 2) { //  if bit stream converted from AC-3
				if ($thisfile_ac3_raw_bsi['numblkscod'] != 3) { // 6 blocks per syncframe
					$thisfile_ac3_raw_bsi['flags']['blkid']  = 1;
				} else {
					$thisfile_ac3_raw_bsi['flags']['blkid']  = (bool) $this->readHeaderBSI(1);
				}
				if ($thisfile_ac3_raw_bsi['flags']['blkid']) {
					$thisfile_ac3_raw_bsi['frmsizecod']  =        $this->readHeaderBSI(6);
				}
			}
			$thisfile_ac3_raw_bsi['flags']['addbsi']  = (bool) $this->readHeaderBSI(1);
			if ($thisfile_ac3_raw_bsi['flags']['addbsi']) {
				$thisfile_ac3_raw_bsi['addbsil']  =        $this->readHeaderBSI(6);
				$thisfile_ac3_raw_bsi['addbsi']   =        $this->readHeaderBSI(($thisfile_ac3_raw_bsi['addbsil'] + 1) * 8);
			}

		} else {

			$this->error('Bit stream identification is version '.$thisfile_ac3_raw_bsi['bsid'].', but getID3() only understands up to version 16. Please submit a support ticket with a sample file.');
			unset($info['ac3']);
			return false;

		}

		if (isset($thisfile_ac3_raw_bsi['fscod2'])) {
			$thisfile_ac3['sample_rate'] = self::sampleRateCodeLookup2($thisfile_ac3_raw_bsi['fscod2']);
		} else {
			$thisfile_ac3['sample_rate'] = self::sampleRateCodeLookup($thisfile_ac3_raw_bsi['fscod']);
		}
		if ($thisfile_ac3_raw_bsi['fscod'] <= 3) {
			$info['audio']['sample_rate'] = $thisfile_ac3['sample_rate'];
		} else {
			$this->warning('Unexpected ac3.bsi.fscod value: '.$thisfile_ac3_raw_bsi['fscod']);
		}
		if (isset($thisfile_ac3_raw_bsi['frmsizecod'])) {
			$thisfile_ac3['frame_length'] = self::frameSizeLookup($thisfile_ac3_raw_bsi['frmsizecod'], $thisfile_ac3_raw_bsi['fscod']);
			$thisfile_ac3['bitrate']      = self::bitrateLookup($thisfile_ac3_raw_bsi['frmsizecod']);
		} elseif (!empty($thisfile_ac3_raw_bsi['frmsiz'])) {
			// this isn't right, but it's (usually) close, roughly 5% less than it should be.
			// but WHERE is the actual bitrate value stored in EAC3?? email info@getid3.org if you know!
			$thisfile_ac3['bitrate']      = ($thisfile_ac3_raw_bsi['frmsiz'] + 1) * 16 * 30; // The frmsiz field shall contain a value one less than the overall size of the coded syncframe in 16-bit words. That is, this field may assume a value ranging from 0 to 2047, and these values correspond to syncframe sizes ranging from 1 to 2048.
			// kludge-fix to make it approximately the expected value, still not "right":
			$thisfile_ac3['bitrate'] = round(($thisfile_ac3['bitrate'] * 1.05) / 16000) * 16000;
		}
		$info['audio']['bitrate'] = $thisfile_ac3['bitrate'];

		if (isset($thisfile_ac3_raw_bsi['bsmod']) && isset($thisfile_ac3_raw_bsi['acmod'])) {
			$thisfile_ac3['service_type'] = self::serviceTypeLookup($thisfile_ac3_raw_bsi['bsmod'], $thisfile_ac3_raw_bsi['acmod']);
		}
		$ac3_coding_mode = self::audioCodingModeLookup($thisfile_ac3_raw_bsi['acmod']);
		foreach($ac3_coding_mode as $key => $value) {
			$thisfile_ac3[$key] = $value;
		}
		switch ($thisfile_ac3_raw_bsi['acmod']) {
			case 0:
			case 1:
				$info['audio']['channelmode'] = 'mono';
				break;
			case 3:
			case 4:
				$info['audio']['channelmode'] = 'stereo';
				break;
			default:
				$info['audio']['channelmode'] = 'surround';
				break;
		}
		$info['audio']['channels'] = $thisfile_ac3['num_channels'];

		$thisfile_ac3['lfe_enabled'] = $thisfile_ac3_raw_bsi['flags']['lfeon'];
		if ($thisfile_ac3_raw_bsi['flags']['lfeon']) {
			$info['audio']['channels'] .= '.1';
		}

		$thisfile_ac3['channels_enabled'] = self::channelsEnabledLookup($thisfile_ac3_raw_bsi['acmod'], $thisfile_ac3_raw_bsi['flags']['lfeon']);
		$thisfile_ac3['dialogue_normalization'] = '-'.$thisfile_ac3_raw_bsi['dialnorm'].'dB';

		return true;
	}

	/**
	 * @param int $length
	 *
	 * @return int
	 */
	private function readHeaderBSI($length) {
		$data = substr($this->AC3header['bsi'], $this->BSIoffset, $length);
		$this->BSIoffset += $length;

		return bindec($data);
	}

	/**
	 * @param int $fscod
	 *
	 * @return int|string|false
	 */
	public static function sampleRateCodeLookup($fscod) {
		static $sampleRateCodeLookup = array(
			0 => 48000,
			1 => 44100,
			2 => 32000,
			3 => 'reserved' // If the reserved code is indicated, the decoder should not attempt to decode audio and should mute.
		);
		return (isset($sampleRateCodeLookup[$fscod]) ? $sampleRateCodeLookup[$fscod] : false);
	}

	/**
	 * @param int $fscod2
	 *
	 * @return int|string|false
	 */
	public static function sampleRateCodeLookup2($fscod2) {
		static $sampleRateCodeLookup2 = array(
			0 => 24000,
			1 => 22050,
			2 => 16000,
			3 => 'reserved' // If the reserved code is indicated, the decoder should not attempt to decode audio and should mute.
		);
		return (isset($sampleRateCodeLookup2[$fscod2]) ? $sampleRateCodeLookup2[$fscod2] : false);
	}

	/**
	 * @param int $bsmod
	 * @param int $acmod
	 *
	 * @return string|false
	 */
	public static function serviceTypeLookup($bsmod, $acmod) {
		static $serviceTypeLookup = array();
		if (empty($serviceTypeLookup)) {
			for ($i = 0; $i <= 7; $i++) {
				$serviceTypeLookup[0][$i] = 'main audio service: complete main (CM)';
				$serviceTypeLookup[1][$i] = 'main audio service: music and effects (ME)';
				$serviceTypeLookup[2][$i] = 'associated service: visually impaired (VI)';
				$serviceTypeLookup[3][$i] = 'associated service: hearing impaired (HI)';
				$serviceTypeLookup[4][$i] = 'associated service: dialogue (D)';
				$serviceTypeLookup[5][$i] = 'associated service: commentary (C)';
				$serviceTypeLookup[6][$i] = 'associated service: emergency (E)';
			}

			$serviceTypeLookup[7][1]      = 'associated service: voice over (VO)';
			for ($i = 2; $i <= 7; $i++) {
				$serviceTypeLookup[7][$i] = 'main audio service: karaoke';
			}
		}
		return (isset($serviceTypeLookup[$bsmod][$acmod]) ? $serviceTypeLookup[$bsmod][$acmod] : false);
	}

	/**
	 * @param int $acmod
	 *
	 * @return array|false
	 */
	public static function audioCodingModeLookup($acmod) {
		// array(channel configuration, # channels (not incl LFE), channel order)
		static $audioCodingModeLookup = array (
			0 => array('channel_config'=>'1+1', 'num_channels'=>2, 'channel_order'=>'Ch1,Ch2'),
			1 => array('channel_config'=>'1/0', 'num_channels'=>1, 'channel_order'=>'C'),
			2 => array('channel_config'=>'2/0', 'num_channels'=>2, 'channel_order'=>'L,R'),
			3 => array('channel_config'=>'3/0', 'num_channels'=>3, 'channel_order'=>'L,C,R'),
			4 => array('channel_config'=>'2/1', 'num_channels'=>3, 'channel_order'=>'L,R,S'),
			5 => array('channel_config'=>'3/1', 'num_channels'=>4, 'channel_order'=>'L,C,R,S'),
			6 => array('channel_config'=>'2/2', 'num_channels'=>4, 'channel_order'=>'L,R,SL,SR'),
			7 => array('channel_config'=>'3/2', 'num_channels'=>5, 'channel_order'=>'L,C,R,SL,SR'),
		);
		return (isset($audioCodingModeLookup[$acmod]) ? $audioCodingModeLookup[$acmod] : false);
	}

	/**
	 * @param int $cmixlev
	 *
	 * @return int|float|string|false
	 */
	public static function centerMixLevelLookup($cmixlev) {
		static $centerMixLevelLookup;
		if (empty($centerMixLevelLookup)) {
			$centerMixLevelLookup = array(
				0 => pow(2, -3.0 / 6), // 0.707 (-3.0 dB)
				1 => pow(2, -4.5 / 6), // 0.595 (-4.5 dB)
				2 => pow(2, -6.0 / 6), // 0.500 (-6.0 dB)
				3 => 'reserved'
			);
		}
		return (isset($centerMixLevelLookup[$cmixlev]) ? $centerMixLevelLookup[$cmixlev] : false);
	}

	/**
	 * @param int $surmixlev
	 *
	 * @return int|float|string|false
	 */
	public static function surroundMixLevelLookup($surmixlev) {
		static $surroundMixLevelLookup;
		if (empty($surroundMixLevelLookup)) {
			$surroundMixLevelLookup = array(
				0 => pow(2, -3.0 / 6),
				1 => pow(2, -6.0 / 6),
				2 => 0,
				3 => 'reserved'
			);
		}
		return (isset($surroundMixLevelLookup[$surmixlev]) ? $surroundMixLevelLookup[$surmixlev] : false);
	}

	/**
	 * @param int $dsurmod
	 *
	 * @return string|false
	 */
	public static function dolbySurroundModeLookup($dsurmod) {
		static $dolbySurroundModeLookup = array(
			0 => 'not indicated',
			1 => 'Not Dolby Surround encoded',
			2 => 'Dolby Surround encoded',
			3 => 'reserved'
		);
		return (isset($dolbySurroundModeLookup[$dsurmod]) ? $dolbySurroundModeLookup[$dsurmod] : false);
	}

	/**
	 * @param int  $acmod
	 * @param bool $lfeon
	 *
	 * @return array
	 */
	public static function channelsEnabledLookup($acmod, $lfeon) {
		$lookup = array(
			'ch1'=>($acmod == 0),
			'ch2'=>($acmod == 0),
			'left'=>($acmod > 1),
			'right'=>($acmod > 1),
			'center'=>(bool) ($acmod & 0x01),
			'surround_mono'=>false,
			'surround_left'=>false,
			'surround_right'=>false,
			'lfe'=>$lfeon);
		switch ($acmod) {
			case 4:
			case 5:
				$lookup['surround_mono']  = true;
				break;
			case 6:
			case 7:
				$lookup['surround_left']  = true;
				$lookup['surround_right'] = true;
				break;
		}
		return $lookup;
	}

	/**
	 * @param int $compre
	 *
	 * @return float|int
	 */
	public static function heavyCompression($compre) {
		// The first four bits indicate gain changes in 6.02dB increments which can be
		// implemented with an arithmetic shift operation. The following four bits
		// indicate linear gain changes, and require a 5-bit multiply.
		// We will represent the two 4-bit fields of compr as follows:
		//   X0 X1 X2 X3 . Y4 Y5 Y6 Y7
		// The meaning of the X values is most simply described by considering X to represent a 4-bit
		// signed integer with values from -8 to +7. The gain indicated by X is then (X + 1) * 6.02 dB. The
		// following table shows this in detail.

		// Meaning of 4 msb of compr
		//  7    +48.16 dB
		//  6    +42.14 dB
		//  5    +36.12 dB
		//  4    +30.10 dB
		//  3    +24.08 dB
		//  2    +18.06 dB
		//  1    +12.04 dB
		//  0     +6.02 dB
		// -1         0 dB
		// -2     -6.02 dB
		// -3    -12.04 dB
		// -4    -18.06 dB
		// -5    -24.08 dB
		// -6    -30.10 dB
		// -7    -36.12 dB
		// -8    -42.14 dB

		$fourbit = str_pad(decbin(($compre & 0xF0) >> 4), 4, '0', STR_PAD_LEFT);
		if ($fourbit[0] == '1') {
			$log_gain = -8 + bindec(substr($fourbit, 1));
		} else {
			$log_gain = bindec(substr($fourbit, 1));
		}
		$log_gain = ($log_gain + 1) * getid3_lib::RGADamplitude2dB(2);

		// The value of Y is a linear representation of a gain change of up to -6 dB. Y is considered to
		// be an unsigned fractional integer, with a leading value of 1, or: 0.1 Y4 Y5 Y6 Y7 (base 2). Y can
		// represent values between 0.111112 (or 31/32) and 0.100002 (or 1/2). Thus, Y can represent gain
		// changes from -0.28 dB to -6.02 dB.

		$lin_gain = (16 + ($compre & 0x0F)) / 32;

		// The combination of X and Y values allows compr to indicate gain changes from
		//  48.16 - 0.28 = +47.89 dB, to
		// -42.14 - 6.02 = -48.16 dB.

		return $log_gain - $lin_gain;
	}

	/**
	 * @param int $roomtyp
	 *
	 * @return string|false
	 */
	public static function roomTypeLookup($roomtyp) {
		static $roomTypeLookup = array(
			0 => 'not indicated',
			1 => 'large room, X curve monitor',
			2 => 'small room, flat monitor',
			3 => 'reserved'
		);
		return (isset($roomTypeLookup[$roomtyp]) ? $roomTypeLookup[$roomtyp] : false);
	}

	/**
	 * @param int $frmsizecod
	 * @param int $fscod
	 *
	 * @return int|false
	 */
	public static function frameSizeLookup($frmsizecod, $fscod) {
		// LSB is whether padding is used or not
		$padding     = (bool) ($frmsizecod & 0x01);
		$framesizeid =        ($frmsizecod & 0x3E) >> 1;

		static $frameSizeLookup = array();
		if (empty($frameSizeLookup)) {
			$frameSizeLookup = array (
				0  => array( 128,  138,  192),  //  32 kbps
				1  => array( 160,  174,  240),  //  40 kbps
				2  => array( 192,  208,  288),  //  48 kbps
				3  => array( 224,  242,  336),  //  56 kbps
				4  => array( 256,  278,  384),  //  64 kbps
				5  => array( 320,  348,  480),  //  80 kbps
				6  => array( 384,  416,  576),  //  96 kbps
				7  => array( 448,  486,  672),  // 112 kbps
				8  => array( 512,  556,  768),  // 128 kbps
				9  => array( 640,  696,  960),  // 160 kbps
				10 => array( 768,  834, 1152),  // 192 kbps
				11 => array( 896,  974, 1344),  // 224 kbps
				12 => array(1024, 1114, 1536),  // 256 kbps
				13 => array(1280, 1392, 1920),  // 320 kbps
				14 => array(1536, 1670, 2304),  // 384 kbps
				15 => array(1792, 1950, 2688),  // 448 kbps
				16 => array(2048, 2228, 3072),  // 512 kbps
				17 => array(2304, 2506, 3456),  // 576 kbps
				18 => array(2560, 2786, 3840)   // 640 kbps
			);
		}
		$paddingBytes = 0;
		if (($fscod == 1) && $padding) {
			// frame lengths are padded by 1 word (16 bits) at 44100
			// (fscode==1) means 44100Hz (see sampleRateCodeLookup)
			$paddingBytes = 2;
		}
		return (isset($frameSizeLookup[$framesizeid][$fscod]) ? $frameSizeLookup[$framesizeid][$fscod] + $paddingBytes : false);
	}

	/**
	 * @param int $frmsizecod
	 *
	 * @return int|false
	 */
	public static function bitrateLookup($frmsizecod) {
		// LSB is whether padding is used or not
		$padding     = (bool) ($frmsizecod & 0x01);
		$framesizeid =        ($frmsizecod & 0x3E) >> 1;

		static $bitrateLookup = array(
			 0 =>  32000,
			 1 =>  40000,
			 2 =>  48000,
			 3 =>  56000,
			 4 =>  64000,
			 5 =>  80000,
			 6 =>  96000,
			 7 => 112000,
			 8 => 128000,
			 9 => 160000,
			10 => 192000,
			11 => 224000,
			12 => 256000,
			13 => 320000,
			14 => 384000,
			15 => 448000,
			16 => 512000,
			17 => 576000,
			18 => 640000,
		);
		return (isset($bitrateLookup[$framesizeid]) ? $bitrateLookup[$framesizeid] : false);
	}

	/**
	 * @param int $numblkscod
	 *
	 * @return int|false
	 */
	public static function blocksPerSyncFrame($numblkscod) {
		static $blocksPerSyncFrameLookup = array(
			0 => 1,
			1 => 2,
			2 => 3,
			3 => 6,
		);
		return (isset($blocksPerSyncFrameLookup[$numblkscod]) ? $blocksPerSyncFrameLookup[$numblkscod] : false);
	}


}