Inside mp3 files there are often some usefull informations stored. Those data are called “id3 tags” and deal with Author name, Title and Album name.
There are also some other informations sometimes: such as the length of the track, or the track number of the album, and more…
Well, all of these infos are packed inside the mp3 into a block of bytes called “header“. When I say packed I mean that they are written in a block of bytes in which each byte must be read as binary data following pre-defined rules. The rules, for the mp3 id3 tags, are defined here in the ID3v2 site (at the chapter 3.1).
Reading binary data means that you have to understand each bit, because each bit as a meaning and the rules can say something like “the first 3 bytes identify the tag: the mp3 contains a ID3 tag if the first 3 bytes are ‘ID3′ string“. This rule is easy because you are used to watch bytes as chars as in text files, so you read the first 3 bytes and compare them to the ‘ID3′ string.
Another rule can say: “after the first 3 bytes you have a byte for the version and a byte for the revision number”. This is more complex because you cannnot use bytes as chars, since the number 3 is this octet 00000011 (an octet is a group of 8 bits), whereas the char “3″ is this octet 00110011, that is the number 51.
This means that you have to use functions like bin2hex and hexdec to convert bytes into chars to understand them.
I’ve found the following function on the Giuseppe Manzavino site and I’ve modified it to fix two really small bugs and I see it works fine with ID3 tags written in some files I’ve edited with iTunes.
<?
// From here: http://www.autistici.org/ermes/index.php?pag=1&post=15
// and fixed here: http://www.barattalo.it
// ------------------------------
// example:
// print_r( tagReader ("myfile.mp3") );
// ------------------------------
function tagReader($file){
$id3v23 = array("TIT2","TALB","TPE1","TRCK","TDRC","TLEN","USLT");
$id3v22 = array("TT2","TAL","TP1","TRK","TYE","TLE","ULT");
$fsize = filesize($file);
$fd = fopen($file,"r");
$tag = fread($fd,$fsize);
$tmp = "";
fclose($fd);
if (substr($tag,0,3) == "ID3") {
$result['FileName'] = $file;
$result['TAG'] = substr($tag,0,3);
$result['Version'] = hexdec(bin2hex(substr($tag,3,1))).".".hexdec(bin2hex(substr($tag,4,1)));
}
if($result['Version'] == "4.0" || $result['Version'] == "3.0"){
for ($i=0;$i<count($id3v23);$i++){
if (strpos($tag,$id3v23[$i].chr(0))!= FALSE){
$pos = strpos($tag, $id3v23[$i].chr(0));
$len = hexdec(bin2hex(substr($tag,($pos+5),3)));
$data = substr($tag, $pos, 9+$len);
for ($a=0;$a<strlen($data);$a++){
$char = substr($data,$a,1);
if($char >= " " && $char <= "~") $tmp.=$char;
}
if(substr($tmp,0,4) == "TIT2") $result['Title'] = substr($tmp,4);
if(substr($tmp,0,4) == "TALB") $result['Album'] = substr($tmp,4);
if(substr($tmp,0,4) == "TPE1") $result['Author'] = substr($tmp,4);
if(substr($tmp,0,4) == "TRCK") $result['Track'] = substr($tmp,4);
if(substr($tmp,0,4) == "TDRC") $result['Year'] = substr($tmp,4);
if(substr($tmp,0,4) == "TLEN") $result['Lenght'] = substr($tmp,4);
if(substr($tmp,0,4) == "USLT") $result['Lyric'] = substr($tmp,7);
$tmp = "";
}
}
}
if($result['Version'] == "2.0"){
for ($i=0;$i<count($id3v22);$i++){
if (strpos($tag,$id3v22[$i].chr(0))!= FALSE){
$pos = strpos($tag, $id3v22[$i].chr(0));
$len = hexdec(bin2hex(substr($tag,($pos+3),3)));
$data = substr($tag, $pos, 6+$len);
for ($a=0;$a<strlen($data);$a++){
$char = substr($data,$a,1);
if($char >= " " && $char <= "~") $tmp.=$char;
}
if(substr($tmp,0,3) == "TT2") $result['Title'] = substr($tmp,3);
if(substr($tmp,0,3) == "TAL") $result['Album'] = substr($tmp,3);
if(substr($tmp,0,3) == "TP1") $result['Author'] = substr($tmp,3);
if(substr($tmp,0,3) == "TRK") $result['Track'] = substr($tmp,3);
if(substr($tmp,0,3) == "TYE") $result['Year'] = substr($tmp,3);
if(substr($tmp,0,3) == "TLE") $result['Lenght'] = substr($tmp,3);
if(substr($tmp,0,3) == "ULT") $result['Lyric'] = substr($tmp,6);
$tmp = "";
}
}
}
return $result;
}
?>
Anyone as seen something similar for reading the EXIF informations on the JPEG files?
Tags: bin2hex, hexdec, id3, id3 tag, mp3
