Obtenir la longueur d'un son WAV

uses
MPlayer, MMsystem;

type
EMyMCIException = class(Exception);
TWavHeader = record
Marker1: array[0..3] of Char;
BytesFollowing: Longint;
Marker2: array[0..3] of Char;
Marker3: array[0..3] of Char;
Fixed1: Longint;
FormatTag: Word;
Channels: Word;
SampleRate: Longint;
BytesPerSecond: Longint;
BytesPerSample: Word;
BitsPerSample: Word;
Marker4: array[0..3] of Char;
DataBytes: Longint;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
Header: TWavHeader;
begin
with TFileStream.Create('C:WINDOWSMEDIAChimes.wav', fmOpenRead) do
try
ReadBuffer(Header, SizeOf(Header));
finally
Free;
end;
ShowMessage(FloatToStr((Int64(1000) * header.DataBytes div header.BytesPerSecond) / 1000));
end;