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const   WINAMP_BUTTON1   : integer = 40044; // previous title
        WINAMP_BUTTON2   : integer = 40045; // play
        WINAMP_BUTTON3   : integer = 40046; // pause
        WINAMP_BUTTON4   : integer = 40047; // stop
        WINAMP_BUTTON5   : integer = 40048; // next title
        WINAMP_VOLUMEUP  : integer = 40058; // volume up
        WINAMP_VOLUMEDOWN: integer = 40059; // volume down
//[...]
procedure WinampPlay;
var hwndWinamp: THandle;
begin
    hwndWinamp:= FindWindow('Winamp v1.x',nil);
    if hwndWinamp<>0 then SendMessage(hwndWinamp,WM_COMMAND, WinAmp_Button2, 0);
end;

procedure WinampPause;
var hwndWinamp: THandle;
begin
    hwndWinamp:= FindWindow('Winamp v1.x',nil);
    if hwndWinamp<>0 then SendMessage(hwndWinamp,WM_COMMAND, WinAmp_Button3, 0);
end;