mbirth/php-mp3info
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Added support for informational bits in Mpeg frame header

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Copyright, Original, Private, CRC protected, Padding
This commit is contained in:
Markus Birth 2024-05-28 01:24:46 +01:00
parent 4b2cbfb384
commit 3e1288a68c
1 changed files with 59 additions and 32 deletions
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91
src/Mp3Info.php
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@ -121,6 +121,31 @@ class Mp3Info
*/
public $sampleRate;
/**
* @var bool Header protection by 16 bit CRC
*/
public $isProtected;
/**
* @var bool Frame data is padded with one slot
*/
public $isPadded;
/**
* @var bool Private bit (only informative)
*/
public $isPrivate;
/**
* @var bool Copyright bit (only informative)
*/
public $isCopyright;
/**
* @var bool Original bit (only informative)
*/
public $isOriginal;
/**
* @var boolean Contains true if audio has variable bit rate
*/
@ -318,7 +343,7 @@ class Mp3Info
* Read first N frames
*/
for ($i = 0; $i < self::$framesCountRead; $i++) {
$framesCount = $this->readMpegFrame();
$framesCount = $this->_readMpegFrame();
}
$this->_framesCount = $framesCount !== null
@ -346,56 +371,58 @@ class Mp3Info
return $audioSize;
}
/**
* Read first frame information.
* @return int Number of frames (if present if first frame of VBR-file)
* @throws \Exception
*/
private function readMpegFrame()
private function _findNextMpegFrame(int $headerSeekLimit): ?string
{
$headerSeekMax = $this->fileObj->getFilePos() + self::$headerSeekLimit;
// find frame sync
$headerSeekMax = $this->fileObj->getFilePos() + $headerSeekLimit;
$headerBytes = $this->fileObj->getBytes(3); // preload with 3 Bytes
$pos = false;
do {
$headerBytes .= $this->fileObj->getBytes(1); // load next Byte
$headerBytes = substr($headerBytes, -4); // limit to 4 Bytes
if ((unpack('n', $headerBytes)[1] & self::FRAME_SYNC) === self::FRAME_SYNC) {
$pos = $this->fileObj->getFilePos() - 4;
break;
return $headerBytes;
}
} while ($this->fileObj->getFilePos() <= $headerSeekMax);
return null;
}
if ($pos === false) {
throw new Exception('No Mpeg frame header found up until pos ' . $headerSeekMax . '(0x' . dechex($headerSeekMax).')!');
/**
* Read first frame information.
*
* @link https://www.codeproject.com/Articles/8295/MPEG-Audio-Frame-Header
* @return int Number of frames (if present if first frame of VBR-file)
* @throws \Exception
*/
private function _readMpegFrame()
{
$headerBytes = $this->_findNextMpegFrame(self::$headerSeekLimit);
$pos = $this->fileObj->getFilePos() - 4;
if (is_null($headerBytes)) {
throw new Exception('No Mpeg frame header found up until pos ' . $pos . '(0x' . dechex($pos) . ')!');
}
switch (ord($headerBytes[1]) >> 3 & 0b11) {
case 0b00: $this->codecVersion = self::MPEG_25; break;
case 0b01: echo 'INVALID CODEC VERSION'; return null; break;
case 0b10: $this->codecVersion = self::MPEG_2; break;
case 0b11: $this->codecVersion = self::MPEG_1; break;
}
switch (ord($headerBytes[1]) >> 1 & 0b11) {
case 0b00: echo 'INVALID LAYER VERSION'; return null; break;
case 0b01: $this->layerVersion = self::LAYER_3; break;
case 0b10: $this->layerVersion = self::LAYER_2; break;
case 0b11: $this->layerVersion = self::LAYER_1; break;
}
// 2nd Byte: (rest of frame sync), Version, Layer, Protection
$this->codecVersion = [self::MPEG_25, null, self::MPEG_2, self::MPEG_1][ord($headerBytes[1]) >> 3 & 0b11];
$this->layerVersion = [null, self::LAYER_3, self::LAYER_2, self::LAYER_1][ord($headerBytes[1]) >> 1 & 0b11];
$this->isProtected = ((ord($headerBytes[1]) & 0b1) == 0b1);
// 3rd Byte: Bitrate, Sampling rate, Padding, Private
$this->bitRate = self::$_bitRateTable[$this->codecVersion][$this->layerVersion][ord($headerBytes[2]) >> 4];
$this->sampleRate = self::$_sampleRateTable[$this->codecVersion][(ord($headerBytes[2]) >> 2) & 0b11];
if ($this->sampleRate === false) {
return null;
}
$this->isPadded = ((ord($headerBytes[2]) & 0b10) == 0b10);
$this->isPrivate = ((ord($headerBytes[2]) & 0b1) == 0b1);
switch (ord($headerBytes[3]) >> 6) {
case 0b00: $this->channel = self::STEREO; break;
case 0b01: $this->channel = self::JOINT_STEREO; break;
case 0b10: $this->channel = self::DUAL_MONO; break;
case 0b11: $this->channel = self::MONO; break;
}
// 4th Byte: Channels, Mode extension, Copyright, Original, Emphasis
$this->channel = [self::STEREO, self::JOINT_STEREO, self::DUAL_MONO, self::MONO][ord($headerBytes[3]) >> 6];
// TODO: Mode extension (2 bits)
$this->isCopyright = ((ord($headerBytes[3]) & 0b1000) == 0b1000);
$this->isOriginal = ((ord($headerBytes[3]) & 0b100) == 0b100);
// TODO: Emphasis (2 bits)
$vbr_offset = self::$_vbrOffsets[$this->codecVersion][$this->channel == self::MONO ? 0 : 1];