- substr: documentation ( source)
- str_replace: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$fileName = "140908181323-q6nr12vo-8900001-08031970805-byC1.mp3";
$downloadFile["file_name"] = $fileName;
$downloadFile["view_fileName"] = date('Y-m-d H:i:s', strtotime("20".str_replace("_","",substr($downloadFile["file_name"],0,12)))).substr($downloadFile["file_name"],13);
echo $downloadFile["view_fileName"];