getid3_ac3::Analyze() –
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Description
Usage
$bool = getid3_ac3::Analyze();
Parameters
Returns
bool
Source
File name: wordpress/wp-includes/ID3/module.audio.ac3.php
Lines:
1 to 100 of 449
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->getid3_ac3::readHeaderBSI(16)); $thisfile_ac3_raw_bsi['fscod'] = $this->getid3_ac3::readHeaderBSI(2); // 5.4.1.3 $thisfile_ac3_raw_bsi['frmsizecod'] = $this->getid3_ac3::readHeaderBSI(6); // 5.4.1.4 if ($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->getid3_ac3::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->getid3_ac3::readHeaderBSI(3); $thisfile_ac3_raw_bsi['acmod'] = $this->getid3_ac3::readHeaderBSI(3); if ($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->getid3_ac3::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->getid3_ac3::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->getid3_ac3::readHeaderBSI(2); $thisfile_ac3['dolby_surround_mode'] = self::dolbySurroundModeLookup($thisfile_ac3_raw_bsi['dsurmod']); } $thisfile_ac3_raw_bsi['flags']['lfeon'] = (bool) $this->getid3_ac3::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->getid3_ac3::readHeaderBSI(5); // 5.4.2.8 dialnorm: Dialogue Normalization, 5 Bits $thisfile_ac3_raw_bsi['flags']['compr'] = (bool) $this->getid3_ac3::readHeaderBSI(1); // 5.4.2.9 compre: Compression Gain Word Exists, 1 Bit if ($thisfile_ac3_raw_bsi['flags']['compr']) { $thisfile_ac3_raw_bsi['compr'] = $this->getid3_ac3::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) $this->getid3_ac3::readHeaderBSI(1); // 5.4.2.11 langcode: Language Code Exists, 1 Bit if ($thisfile_ac3_raw_bsi['flags']['langcod']) { $thisfile_ac3_raw_bsi['langcod'] = $this->getid3_ac3::readHeaderBSI(8); // 5.4.2.12 langcod: Language Code, 8 Bits } $thisfile_ac3_raw_bsi['flags']['audprodinfo'] = (bool) $this->getid3_ac3::readHeaderBSI(1); // 5.4.2.13 audprodie: Audio Production Information Exists, 1 Bit if ($thisfile_ac3_raw_bsi['flags']['audprodinfo']) {