getid3_mp3::getOnlyMPEGaudioInfo( int $avdataoffset, bool $BitrateHistogram = false ): bool

1454	public function getOnlyMPEGaudioInfo($avdataoffset, $BitrateHistogram=false) {1455		// looks for synch, decodes MPEG audio header1456 1457		$info = &$this->getid3->info;1458 1459		static $MPEGaudioVersionLookup;1460		static $MPEGaudioLayerLookup;1461		static $MPEGaudioBitrateLookup;1462		if (empty($MPEGaudioVersionLookup)) {1463			$MPEGaudioVersionLookup = self::MPEGaudioVersionArray();1464			$MPEGaudioLayerLookup   = self::MPEGaudioLayerArray();1465			$MPEGaudioBitrateLookup = self::MPEGaudioBitrateArray();1466		}1467 1468		$this->fseek($avdataoffset);1469		$sync_seek_buffer_size = min(128 * 1024, $info['avdataend'] - $avdataoffset);1470		if ($sync_seek_buffer_size <= 0) {1471			$this->error('Invalid $sync_seek_buffer_size at offset '.$avdataoffset);1472			return false;1473		}1474		$header = $this->fread($sync_seek_buffer_size);1475		$sync_seek_buffer_size = strlen($header);1476		$SynchSeekOffset = 0;1477		$SyncSeekAttempts = 0;1478		$SyncSeekAttemptsMax = 1000;1479		$FirstFrameThisfileInfo = null;1480		while ($SynchSeekOffset < $sync_seek_buffer_size) {1481			if ((($avdataoffset + $SynchSeekOffset)  < $info['avdataend']) && !$this->feof()) {1482 1483				if ($SynchSeekOffset > $sync_seek_buffer_size) {1484					// if a synch's not found within the first 128k bytes, then give up1485					$this->error('Could not find valid MPEG audio synch within the first '.round($sync_seek_buffer_size / 1024).'kB');1486					if (isset($info['audio']['bitrate'])) {1487						unset($info['audio']['bitrate']);1488					}1489					if (isset($info['mpeg']['audio'])) {1490						unset($info['mpeg']['audio']);1491					}1492					if (empty($info['mpeg'])) {1493						unset($info['mpeg']);1494					}1495					return false;1496				}1497			}1498 1499			if (($SynchSeekOffset + 1) >= strlen($header)) {1500				$this->error('Could not find valid MPEG synch before end of file');1501				return false;1502			}1503 1504			if (($header[$SynchSeekOffset] == "\xFF") && ($header[($SynchSeekOffset + 1)] > "\xE0")) { // possible synch detected1505				if (++$SyncSeekAttempts >= $SyncSeekAttemptsMax) {1506					// https://github.com/JamesHeinrich/getID3/issues/2861507					// corrupt files claiming to be MP3, with a large number of 0xFF bytes near the beginning, can cause this loop to take a very long time1508					// should have escape condition to avoid spending too much time scanning a corrupt file1509					// if a synch's not found within the first 128k bytes, then give up1510					$this->error('Could not find valid MPEG audio synch after scanning '.$SyncSeekAttempts.' candidate offsets');1511					if (isset($info['audio']['bitrate'])) {1512						unset($info['audio']['bitrate']);1513					}1514					if (isset($info['mpeg']['audio'])) {1515						unset($info['mpeg']['audio']);1516					}1517					if (empty($info['mpeg'])) {1518						unset($info['mpeg']);1519					}1520					return false;1521				}1522				$FirstFrameAVDataOffset = null;1523				if (!isset($FirstFrameThisfileInfo) && !isset($info['mpeg']['audio'])) {1524					$FirstFrameThisfileInfo = $info;1525					$FirstFrameAVDataOffset = $avdataoffset + $SynchSeekOffset;1526					if (!$this->decodeMPEGaudioHeader($FirstFrameAVDataOffset, $FirstFrameThisfileInfo, false)) {1527						// if this is the first valid MPEG-audio frame, save it in case it's a VBR header frame and there's1528						// garbage between this frame and a valid sequence of MPEG-audio frames, to be restored below1529						unset($FirstFrameThisfileInfo);1530					}1531				}1532 1533				$dummy = $info; // only overwrite real data if valid header found