function extract($start, $length)
{
$maxStrLen = strlen($this->str);
$currentStrPos = $this->getStart();
$framesCount = 0;
$time = 0;
$startCount = -1;
$endCount = -1;
while ($currentStrPos < $maxStrLen) {
if ($startCount == -1 && $time >= $start) {
$startCount = $currentStrPos;
}
if ($endCount == -1 && $time >= $start + $length) {
$endCount = $currentStrPos - $startCount;
}
$doFrame = true;
$str = substr($this->str, $currentStrPos, 4);
$strlen = strlen($str);
$parts = array();
for ($i = 0; $i < $strlen; $i++) {
$parts[] = $this->decbinFill(ord($str[$i]), 8);
}
if ($parts[0] != "11111111") {
if ($maxStrLen - 128 > $currentStrPos) {
$doFrame = false;
} else {
$doFrame = false;
}
}
if ($doFrame) {
$a = $this->doFrameStuff($parts);
$currentStrPos += $a[0];
$time += $a[1];
$framesCount++;
} else {
break;
}
}
$mp3 = new mp3();
if ($endCount == -1) {
$endCount = $maxStrLen - $startCount;
}
if ($startCount != -1 && $endCount != -1) {
$mp3->setStr(substr($this->str, $startCount, $endCount));
}
return $mp3;
}
