how to get the duration of the song in a mp3 file

Hi titcher.

I'm afraid I don't yet have any simple code for you, but there are a few resources that can technically do the job.
So I want to know if you'll accept 3rd party resources?

Here are some resources for you to look at:

0. Here is some C code that you can translate that is BASED ON the Windows Media Player SDK which an easily output the duration of an mp3 or wma file.
http://web.archive.org/web/20040405003445/http://msdn.microsoft.com/library/en-us/dncodefun/html/code4fun01242003.asp

1. XAudio VCL component
Component available from:

http://web.archive.org/web/20040629203345/http://www.cs.ucl.ac.uk/students/S.Lau/delphi001.htm

To distribute an application using this component, you have to buy a license.

2. IF YOU HAVE THE FILESIZE AND BITRATE (doesn't work for Variable Bitrate (VBR) files)
SOURCE: http://www.delphipages.com/threads/thread.cfm?ID=64252&G=64221
QUOTE:
If you have the bitrate and the filesize AND the file is not a variable bit rate (vbr) file, then you simply divide the filesize by the byterate (that's bitrate/8) and you get an approximate playtime in seconds (+-1s, 'cause we didn't compensate for the frame headers):
function GetPlayLength(FileSize, BitRate: integer): integer;
begin
 Result:= round(FileSize / (BitRate shr 3));
end;

procedure TForm1.Button1Click(Sender: TObject);
begin                            //Bitrate FileSize
 caption:= inttostr(GetPlayLength(128000, 4368620));
end;

3. MP3Info v.1.0 component from Torry.net [Freeware, Source Included]
(This will help you calculate the length by calculation)
http://www.torry.net/authorsmore.php?id=3556
"By TRIDENT-Soft. Component which reads information about MPEG version, layer, bitrate and sample frequency from a MP3 file."