getid3_ac3

21class getid3_ac3 extends getid3_handler22{23	/**24	 * @var array25	 */26	private $AC3header = array();27 28	/**29	 * @var int30	 */31	private $BSIoffset = 0;32 33	const syncword = 0x0B77;34 35	/**36	 * @return bool37	 */38	public function Analyze() {39		$info = &$this->getid3->info;40 41		///AH42		$info['ac3']['raw']['bsi'] = array();43		$thisfile_ac3              = &$info['ac3'];44		$thisfile_ac3_raw          = &$thisfile_ac3['raw'];45		$thisfile_ac3_raw_bsi      = &$thisfile_ac3_raw['bsi'];46 47 48		// http://www.atsc.org/standards/a_52a.pdf49 50		$info['fileformat'] = 'ac3';51 52		// An AC-3 serial coded audio bit stream is made up of a sequence of synchronization frames53		// Each synchronization frame contains 6 coded audio blocks (AB), each of which represent 25654		// new audio samples per channel. A synchronization information (SI) header at the beginning55		// of each frame contains information needed to acquire and maintain synchronization. A56		// bit stream information (BSI) header follows SI, and contains parameters describing the coded57		// audio service. The coded audio blocks may be followed by an auxiliary data (Aux) field. At the58		// end of each frame is an error check field that includes a CRC word for error detection. An59		// additional CRC word is located in the SI header, the use of which, by a decoder, is optional.60		//61		// syncinfo() | bsi() | AB0 | AB1 | AB2 | AB3 | AB4 | AB5 | Aux | CRC62 63		// syncinfo() {64		// 	 syncword    1665		// 	 crc1        1666		// 	 fscod        267		// 	 frmsizecod   668		// } /* end of syncinfo */69 70		$this->fseek($info['avdataoffset']);71		$tempAC3header = $this->fread(100); // should be enough to cover all data, there are some variable-length fields...?72		$this->AC3header['syncinfo']  =     getid3_lib::BigEndian2Int(substr($tempAC3header, 0, 2));73		$this->AC3header['bsi']       =     getid3_lib::BigEndian2Bin(substr($tempAC3header, 2));74		$thisfile_ac3_raw_bsi['bsid'] = (getid3_lib::LittleEndian2Int(substr($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 sense75		unset($tempAC3header);76 77		if ($this->AC3header['syncinfo'] !== self::syncword) {78			if (!$this->isDependencyFor('matroska')) {79				unset($info['fileformat'], $info['ac3']);80				return $this->error('Expecting "'.dechex(self::syncword).'" at offset '.$info['avdataoffset'].', found "'.dechex($this->AC3header['syncinfo']).'"');81			}82		}83 84		$info['audio']['dataformat']   = 'ac3';85		$info['audio']['bitrate_mode'] = 'cbr';86		$info['audio']['lossless']     = false;87 88		if ($thisfile_ac3_raw_bsi['bsid'] <= 8) {89 90			$thisfile_ac3_raw_bsi['crc1']       = getid3_lib::Bin2Dec($this->readHeaderBSI(16));91			$thisfile_ac3_raw_bsi['fscod']      =                     $this->readHeaderBSI(2);   // 5.4.1.392			$thisfile_ac3_raw_bsi['frmsizecod'] =                     $this->readHeaderBSI(6);   // 5.4.1.493			if ($thisfile_ac3_raw_bsi['frmsizecod'] > 37) { // binary: 100101 - see Table 5.18 Frame Size Code Table (1 word = 16 bits)94				$this->warning('Unexpected ac3.bsi.frmsizecod value: '.$thisfile_ac3_raw_bsi['frmsizecod'].', bitrate not set correctly');95			}96 97			$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 intended98			$thisfile_ac3_raw_bsi['bsmod'] = $this->readHeaderBSI(3);99			$thisfile_ac3_raw_bsi['acmod'] = $this->readHeaderBSI(3);100