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

Compatibility

Present in every tracked release (6.7.7 to 7.1.0), and compiles on PHP 7.4 through 8.6-dev.

Parameters

$offsetint

$infoarray

$recursivesearchbooloptional

Default: true

$ScanAsCBRbooloptional

Default: false

$FastMPEGheaderScanbooloptional

Default: false

Return value

bool

Performance profile

How much work a call to getid3_mp3::decodeMPEGaudioHeader() does, and what it touches: the algorithmic scaling, the Zend instruction count per call across PHP versions, the hooks it hands control to, and the core code that calls it. Measured from the compiled opcodes, not a stopwatch, so every number is identical on any machine running the same PHP version, and every function in core is ranked by cost.

Cost class

Trivial

Touches nothing outside its own arguments.

Scaling

Constant

No loop in the body: the same number of instructions runs whatever you pass in.

Instructions

62–265

Executed per call on PHP 8.5, depending on the branch taken. The body compiles to 1411.

Plugin surface

None

Nothing here hands control to plugin code.

Called by

2

2 places in core call this, so the cost is paid more often than your own code shows.

What one call costs · 5 distinct outcomes

One number would be a lie: the work depends on which branch runs. These are every distinct cost getid3_mp3::decodeMPEGaudioHeader() can have, taken from its control-flow graph on PHP 8.5.

This body has more branch combinations than are worth enumerating, so the table covers the outcomes found first rather than every one that exists.

Uses · 31

• getid3_mp3::MPEGaudioVersionArray()
• getid3_mp3::MPEGaudioLayerArray()
• getid3_mp3::MPEGaudioBitrateArray()
• getid3_mp3::MPEGaudioFrequencyArray()
• getid3_mp3::MPEGaudioChannelModeArray()
• getid3_mp3::MPEGaudioModeExtensionArray()
• getid3_mp3::MPEGaudioEmphasisArray()
• getid3_mp3::fseek()
• getid3_mp3::error()
• getid3_mp3::fread()
• getid3_lib::PrintHexBytes()
• getid3_mp3::MPEGaudioHeaderDecode()

Used by · 2

• getid3_mp3::RecursiveFrameScanning()
• getid3_mp3::getOnlyMPEGaudioInfo()

Source code

View on Trac ↗View on GitHub ↗

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			}

Changelog

Unchanged from 6.7.7 through 7.1.0.

1. 6.7.7
2. 6.8.8
3. 6.9.7
4. 7.0.4
5. 7.1.0

Signature, return type and hooks compared across 5 parsed releases.

About this page

Parsed data

Generated from the wordpress-develop 7.1.0 tag, from src/wp-includes/ID3/module.audio.mp3.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.

Corrections

Something wrong on this page? Report it and it gets fixed in the next regeneration.