Did you know that IE7 does not understand some of CSS properties depending on how classes names are written? How? Here is answer.
// will output i.e. 1KB (function always accepts bytes value)
$sniffer = new Smartycode_Http_Mime();
$contentType = $sniffer->getMime($url);
if('audio/mpeg3' == $contentType) echo 'It is MP3';