The following example demonstrates playing an AVI file silently by turning off the MCI audio channels in code.

Example:
uses MMSystem;
procedure SetMediaAudioOff(DeviceID : word);
var
 SetParm : TMCI_SET_PARMS;
begin
  SetParm.dwAudio := MCI_SET_AUDIO_ALL;
  mciSendCommand(DeviceID,
                 MCI_SET,
                 MCI_SET_AUDIO or MCI_SET_OFF,
                 Longint(@SetParm));
end;
Procedure SetMediaAudioOn(DeviceID : word);
var
 SetParm : TMCI_SET_PARMS;
begin
  SetParm.dwAudio := MCI_SET_AUDIO_ALL;
  mciSendCommand(DeviceID,
                 MCI_SET,
                 MCI_SET_AUDIO or MCI_SET_ON,
                 Longint(@SetParm));
end;
procedure TForm .Button Click(Sender: TObject);
begin
 {Play AVI file silently}
  MediaPlayer .FileName := 'C:\TheWall\DELCAR2.AVI';
  MediaPlayer .Display := Panel ;
  MediaPlayer .Open;
  MediaPlayer .Play;
  SetMediaAudioOff(MediaPlayer .DeviceId);
end;
procedure TForm .Button2Click(Sender: TObject);
begin
 {Play AVI with sound}
  MediaPlayer .FileName := 'C:\TheWall\DELCAR2.AVI';
  MediaPlayer .Display := Panel ;
  MediaPlayer .Open;
  MediaPlayer .Play;
  SetMediaAudioOn(MediaPlayer .DeviceId);
end;