哪位大师能教我一下怎样调用API函数,如:midiOutGetDevCaps...

首先应把MMSYSTEM单元加入，然后进行调用。先用midiOutGetNumDevs获得系统所带设备数，再用midiOutGetDevCapS获得设备说明。我写了个程序试验了一下。  
unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls,mmsystem;type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.DFM}procedure TForm1.Button1Click(Sender: TObject);
var
  num:uint;
  i:Cardinal ;
  midi:MIDIOUTCAPS;
  mhr:MMRESULT ;
begin
  num:=midioutGetNumDevs;
  if (num=0) then
  begin
   showmessage('no device');
   exit;
  end;
  for i:=0 to num-1 do
  begin
   mhr:=midiOutGetDevCaps(i,@midi,sizeof(midi));
    case mhr of
     MMSYSERR_BADDEVICEID:
                        showmessage('bad');
     MMSYSERR_INVALPARAM:
                         showmessage('invalid');
     MMSYSERR_NODRIVER:
                           showmessage('nodriver');
     MMSYSERR_NOMEM:
                      showmessage('nomem');
      MMSYSERR_NOERROR:
                      begin
                      showmessage('The Driver version is'+midi.szPname );
                      end;     end;
   end;
end;
end.