PHP MP3 extract volume peaks - php

Question

say you have a mp3 file.
Is it possible to extract the volume level(set between 0 and 100) for every byte in a mp3 file using PHP ?
This is what I already have, it might help you
function peaks($filename)
{
if (!file_exists($filename)) {
return false;
}
$bitRates = array(
array(0,0,0,0,0),
array(32,32,32,32,8),
array(64,48,40,48,16),
array(96,56,48,56,24),
array(128,64,56,64,32),
array(160,80,64,80,40),
array(192,96,80,96,48),
array(224,112,96,112,56),
array(256,128,112,128,64),
array(288,160,128,144,80),
array(320,192,160,160,96),
array(352,224,192,176,112),
array(384,256,224,192,128),
array(416,320,256,224,144),
array(448,384,320,256,160),
array(-1,-1,-1,-1,-1),
);
$sampleRates = array(
array(11025,12000,8000), //mpeg 2.5
array(0,0,0),
array(22050,24000,16000), //mpeg 2
array(44100,48000,32000), //mpeg 1
);
$bToRead = 1024 * 12;
$fileData = array('bitRate' => 0, 'sampleRate' => 0, 'bits' => 0);
$fp = fopen($filename, 'r');
if (!$fp) {
return false;
}
//seek to 8kb before the end of the file
fseek($fp, -1 * $bToRead, SEEK_END);
$data = fread($fp, $bToRead);
$bytes = unpack('C*', $data);
$frames = array();
$lastFrameVerify = null;
for ($o = 1; $o < count($bytes) - 4; $o++) {
//http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html
//header is AAAAAAAA AAABBCCD EEEEFFGH IIJJKLMM
if (($bytes[$o] & 255) == 255 && ($bytes[$o+1] & 224) == 224) {
$frame = array();
$frame['version'] = ($bytes[$o+1] & 24) >> 3; //get BB (0 -> 3)
$frame['layer'] = abs((($bytes[$o+1] & 6) >> 1) - 4); //get CC (1 -> 3), then invert
$srIndex = ($bytes[$o+2] & 12) >> 2; //get FF (0 -> 3)
$brRow = ($bytes[$o+2] & 240) >> 4; //get EEEE (0 -> 15)
$frame['padding'] = ($bytes[$o+2] & 2) >> 1; //get G
if ($frame['version'] != 1 && $frame['layer'] > 0 && $srIndex < 3 && $brRow != 15 && $brRow != 0 &&
(!$lastFrameVerify || $lastFrameVerify === $bytes[$o+1])) {
//valid frame header
//calculate how much to skip to get to the next header
$frame['sampleRate'] = $sampleRates[$frame['version']][$srIndex];
if ($frame['version'] & 1 == 1) {
$frame['bitRate'] = $bitRates[$brRow][$frame['layer']-1]; //v1 and l1,l2,l3
} else {
$frame['bitRate'] = $bitRates[$brRow][($frame['layer'] & 2 >> 1)+3]; //v2 and l1 or l2/l3 (3 is the offset in the arrays)
}
if ($frame['layer'] == 1) {
$frame['frameLength'] = (12 * $frame['bitRate'] * 1000 / $frame['sampleRate'] + $frame['padding']) * 4;
} else {
$frame['frameLength'] = 144 * $frame['bitRate'] * 1000 / $frame['sampleRate'] + $frame['padding'];
}
$frames[] = $frame;
$lastFrameVerify = $bytes[$o+1];
$o += floor($frame['frameLength'] - 1);
} else {
$frames = array();
$lastFrameVerify = null;
}
}
if (count($frames) < 3) { //verify at least 3 frames to make sure its an mp3
continue;
}
$header = array_pop($frames);
$fileData['sampleRate'] = $header['sampleRate'];
$fileData['bitRate'] = $header['bitRate'];
$fileData['bits'] = $bytes;
break;
}
return $fileData;
}
If this works it will be used to generate waveforms from mp3 files.

Answer 1

this class can be a good starting point too :
http://www.phpclasses.org/browse/file/26606.html
use case here :
http://www.phpclasses.org/browse/file/26607.html