mbirth/php-mp3info
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Optimise searching for Mpeg frame

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Markus Birth 2024-05-27 20:55:51 +01:00
parent 2a16b836b7
commit 3184973867
1 changed files with 23 additions and 28 deletions
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51
src/Mp3Info.php
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@ -353,48 +353,43 @@ class Mp3Info
*/
private function readMpegFrame()
{
$header_seek_pos = $this->fileObj->getFilePos() + self::$headerSeekLimit;
$headerSeekMax = $this->fileObj->getFilePos() + self::$headerSeekLimit;
$headerBytes = $this->fileObj->getBytes(3); // preload with 3 Bytes
$pos = false;
do {
$pos = $this->fileObj->getFilePos();
$first_header_byte = $this->fileObj->getBytes(1);
if (ord($first_header_byte[0]) === 0xFF) {
$second_header_byte = $this->fileObj->getBytes(1);
if (((ord($second_header_byte[0]) >> 5) & 0b111) == 0b111) {
$this->fileObj->seekTo($pos);
$header_bytes = $this->fileObj->getBytes(4);
break;
} else {
$this->fileObj->seekForward(-1);
}
} else {
$this->fileObj->seekForward(-1);
}
$this->fileObj->seekForward(1);
} while ($this->fileObj->getFilePos() <= $header_seek_pos);
$headerBytes .= $this->fileObj->getBytes(1); // load next Byte
$headerBytes = substr($headerBytes, -4); // limit to 4 Bytes
if (!isset($header_bytes) || ord($header_bytes[0]) !== 0xFF || ((ord($header_bytes[1]) >> 5) & 0b111) != 0b111) {
throw new \Exception('At '.$pos
.'(0x'.dechex($pos).') should be a frame header!');
if (unpack('n', $headerBytes)[1] & self::FRAME_SYNC === self::FRAME_SYNC) {
$pos = $this->fileObj->getFilePos() - 4;
break;
}
} while ($this->fileObj->getFilePos() <= $headerSeekMax);
if (!$pos) {
throw new Exception('No Mpeg frame header found up until pos ' . $headerSeekMax . '(0x' . dechex($headerSeekMax).')!');
}
switch (ord($header_bytes[1]) >> 3 & 0b11) {
switch (ord($headerBytes[1]) >> 3 & 0b11) {
case 0b00: $this->codecVersion = self::MPEG_25; break;
case 0b01: return null; break;
case 0b10: $this->codecVersion = self::MPEG_2; break;
case 0b11: $this->codecVersion = self::MPEG_1; break;
}
switch (ord($header_bytes[1]) >> 1 & 0b11) {
switch (ord($headerBytes[1]) >> 1 & 0b11) {
case 0b01: $this->layerVersion = self::LAYER_3; break;
case 0b10: $this->layerVersion = self::LAYER_2; break;
case 0b11: $this->layerVersion = self::LAYER_1; break;
}
$this->bitRate = self::$_bitRateTable[$this->codecVersion][$this->layerVersion][ord($header_bytes[2]) >> 4];
$this->sampleRate = self::$_sampleRateTable[$this->codecVersion][(ord($header_bytes[2]) >> 2) & 0b11];
if ($this->sampleRate === false) return null;
$this->bitRate = self::$_bitRateTable[$this->codecVersion][$this->layerVersion][ord($headerBytes[2]) >> 4];
$this->sampleRate = self::$_sampleRateTable[$this->codecVersion][(ord($headerBytes[2]) >> 2) & 0b11];
if ($this->sampleRate === false) {
return null;
}
switch (ord($header_bytes[3]) >> 6) {
switch (ord($headerBytes[3]) >> 6) {
case 0b00: $this->channel = self::STEREO; break;
case 0b01: $this->channel = self::JOINT_STEREO; break;
case 0b10: $this->channel = self::DUAL_MONO; break;
@ -429,9 +424,9 @@ class Mp3Info
// go to the end of frame
if ($this->layerVersion == self::LAYER_1) {
$this->_cbrFrameSize = floor((12 * $this->bitRate / $this->sampleRate + (ord($header_bytes[2]) >> 1 & 0b1)) * 4);
$this->_cbrFrameSize = floor((12 * $this->bitRate / $this->sampleRate + (ord($headerBytes[2]) >> 1 & 0b1)) * 4);
} else {
$this->_cbrFrameSize = floor(144 * $this->bitRate / $this->sampleRate + (ord($header_bytes[2]) >> 1 & 0b1));
$this->_cbrFrameSize = floor(144 * $this->bitRate / $this->sampleRate + (ord($headerBytes[2]) >> 1 & 0b1));
}
$this->fileObj->seekTo($pos + $this->_cbrFrameSize);