CONST
  MaxSize : Longint = 1440000;  //байт


function ExtractFileNames(FileNames:string):string; 
var 
  S:string; 
begin 
  S:=''; 
  while Pos('.', FileNames) > 0 do 
  begin 
    S:=S+Copy(FileNames,1,Pos('.',FileNames)-1); 
    Delete(FileNames,1,Pos('.',FileNames)); 
  end; 
  result:=S; 
end; 

procedure TForm1.SpeedButton1Click(Sender: TObject); 
var 
  InFile,OutFile: FILE; 
  CopyBuffer : POINTER; { buffer for copying } 
  iRecsOK, iRecsWr, index: Integer; 
  sFileName,sFileExt,sFileFullName:string; 
  fFileSize: file of Byte; 
  Size:LongInt; 
begin 
  sFileFullName:='C:\1\1.mp3'; 
  sFileName:=ExtractFileName(sFileFullName); 
  sFileExt:=ExtractFileExt(sFileName); 
  sFileName:=ExtractFileNames(sFileName); 

  ShowMessage(sFileFullName+#13+sFilename+#13+sFileExt);

  if FileExists(sFileFullName) then 
  begin 
    AssignFile(fFileSize, sFileFullName); 
    FileMode := 0;  {Set file access to read only } 
    Reset(fFileSize); 
    Size := FileSize(fFileSize); {Get File Size} 
    CloseFile(fFileSize); 
    ShowMessage(IntToStr(Size)); 

    if Size>MaxSize then 
    begin {Divide} 
      Getmem(CopyBuffer, MaxSize); { allocate the buffer } 

      Assignfile(inFile,sFileFullName );//+ '.ZIP'); 
      Reset(inFile,1); 

      index := 1; 
      repeat 
        AssignFile(outFile,sFileName + '-'+IntToStr(index) + sFileExt); 
        Rewrite(OutFile,1); 
        inc(index); 
        BlockRead(InFile, CopyBuffer^, MaxSize, iRecsOK); 
        BlockWrite(OutFile, CopyBuffer^, iRecsOK, iRecsWr); 
        CloseFile(OutFile); 
      until (iRecsOK < MaxSize); 
      CloseFile(InFile); 
      FreeMem(CopyBuffer, MaxSize); { free the buffer } 
      ShowMessage('Done..!'); 

    end
    else
    begin
      ShowMessage('Do nothing..!');
    end;
  end
  else
    ShowMessage('File: '+sFileFullName+' not found');
end;

// Чтобы склеить файлы обратно в один,
// можно воспользоваться DOS функцией copy;

// copy /b file-1.xxx+file-2.xxx+file-3.xxx file.mp3