getid3_mp3::decodeMPEGaudioHeader( int $offset, array $info, bool $recursivesearch = true, bool $ScanAsCBR = false, bool $FastMPEGheaderScan = false ): bool

453	public function decodeMPEGaudioHeader($offset, &$info, $recursivesearch=true, $ScanAsCBR=false, $FastMPEGheaderScan=false) {454		static $MPEGaudioVersionLookup;455		static $MPEGaudioLayerLookup;456		static $MPEGaudioBitrateLookup;457		static $MPEGaudioFrequencyLookup;458		static $MPEGaudioChannelModeLookup;459		static $MPEGaudioModeExtensionLookup;460		static $MPEGaudioEmphasisLookup;461		if (empty($MPEGaudioVersionLookup)) {462			$MPEGaudioVersionLookup       = self::MPEGaudioVersionArray();463			$MPEGaudioLayerLookup         = self::MPEGaudioLayerArray();464			$MPEGaudioBitrateLookup       = self::MPEGaudioBitrateArray();465			$MPEGaudioFrequencyLookup     = self::MPEGaudioFrequencyArray();466			$MPEGaudioChannelModeLookup   = self::MPEGaudioChannelModeArray();467			$MPEGaudioModeExtensionLookup = self::MPEGaudioModeExtensionArray();468			$MPEGaudioEmphasisLookup      = self::MPEGaudioEmphasisArray();469		}470 471		if ($this->fseek($offset) != 0) {472			$this->error('decodeMPEGaudioHeader() failed to seek to next offset at '.$offset);473			return false;474		}475		//$headerstring = $this->fread(1441); // worst-case max length = 32kHz @ 320kbps layer 3 = 1441 bytes/frame476		$headerstring = $this->fread(226); // LAME header at offset 36 + 190 bytes of Xing/LAME data477 478		// MP3 audio frame structure:479		// $aa $aa $aa $aa [$bb $bb] $cc...480		// where $aa..$aa is the four-byte mpeg-audio header (below)481		// $bb $bb is the optional 2-byte CRC482		// and $cc... is the audio data483 484		$head4 = substr($headerstring, 0, 4);485		$head4_key = getid3_lib::PrintHexBytes($head4, true, false, false);486		static $MPEGaudioHeaderDecodeCache = array();487		if (isset($MPEGaudioHeaderDecodeCache[$head4_key])) {488			$MPEGheaderRawArray = $MPEGaudioHeaderDecodeCache[$head4_key];489		} else {490			$MPEGheaderRawArray = self::MPEGaudioHeaderDecode($head4);491			$MPEGaudioHeaderDecodeCache[$head4_key] = $MPEGheaderRawArray;492		}493 494		static $MPEGaudioHeaderValidCache = array();495		if (!isset($MPEGaudioHeaderValidCache[$head4_key])) { // Not in cache496			//$MPEGaudioHeaderValidCache[$head4_key] = self::MPEGaudioHeaderValid($MPEGheaderRawArray, false, true);  // allow badly-formatted freeformat (from LAME 3.90 - 3.93.1)497			$MPEGaudioHeaderValidCache[$head4_key] = self::MPEGaudioHeaderValid($MPEGheaderRawArray, false, false);498		}499 500		// shortcut501		if (!isset($info['mpeg']['audio'])) {502			$info['mpeg']['audio'] = array();503		}504		$thisfile_mpeg_audio = &$info['mpeg']['audio'];505 506		if ($MPEGaudioHeaderValidCache[$head4_key]) {507			$thisfile_mpeg_audio['raw'] = $MPEGheaderRawArray;508		} else {509			$this->warning('Invalid MPEG audio header ('.getid3_lib::PrintHexBytes($head4).') at offset '.$offset);510			return false;511		}512 513		if (!$FastMPEGheaderScan) {514			$thisfile_mpeg_audio['version']       = $MPEGaudioVersionLookup[$thisfile_mpeg_audio['raw']['version']];515			$thisfile_mpeg_audio['layer']         = $MPEGaudioLayerLookup[$thisfile_mpeg_audio['raw']['layer']];516 517			$thisfile_mpeg_audio['channelmode']   = $MPEGaudioChannelModeLookup[$thisfile_mpeg_audio['raw']['channelmode']];518			$thisfile_mpeg_audio['channels']      = (($thisfile_mpeg_audio['channelmode'] == 'mono') ? 1 : 2);519			$thisfile_mpeg_audio['sample_rate']   = $MPEGaudioFrequencyLookup[$thisfile_mpeg_audio['version']][$thisfile_mpeg_audio['raw']['sample_rate']];520			$thisfile_mpeg_audio['protection']    = !$thisfile_mpeg_audio['raw']['protection'];521			$thisfile_mpeg_audio['private']       = (bool) $thisfile_mpeg_audio['raw']['private'];522			$thisfile_mpeg_audio['modeextension'] = $MPEGaudioModeExtensionLookup[$thisfile_mpeg_audio['layer']][$thisfile_mpeg_audio['raw']['modeextension']];523			$thisfile_mpeg_audio['copyright']     = (bool) $thisfile_mpeg_audio['raw']['copyright'];524			$thisfile_mpeg_audio['original']      = (bool) $thisfile_mpeg_audio['raw']['original'];525			$thisfile_mpeg_audio['emphasis']      = $MPEGaudioEmphasisLookup[$thisfile_mpeg_audio['raw']['emphasis']];526 527			$info['audio']['channels']    = $thisfile_mpeg_audio['channels'];528			$info['audio']['sample_rate'] = $thisfile_mpeg_audio['sample_rate'];529 530			if ($thisfile_mpeg_audio['protection']) {531				$thisfile_mpeg_audio['crc'] = getid3_lib::BigEndian2Int(substr($headerstring, 4, 2));532			}