macOS Play Alert Sound

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This article applies to macOS only.

See also: Multiplatform Programming Guide

Overview

The Apple macOS operating system has many possible alert sounds which you can play to alert your user to various situation that need their attention. You can use System Sound Services to play short (30 seconds or shorter) sounds. The interface does not provide level, positioning, looping, or timing control, and does not support simultaneous playback: You can play only one sound at a time and the sound only plays once. You can, however, use System Sound Services to provide audible alerts.

System Sound Services supported audio formats:

  • It only supports audio data formats linear PCM or IMA4.
  • It only supports audio file formats CAF, AIF, or WAV.

If these limitations on System Sound Services are an issue, check out the AVFoundation AVAudioPlayer which does not suffer from the limitations.

Alert Sound Identifiers

These are the AudioToolbox identifiers for System Sound Services alert sounds and alternatives to sounds, for use with the AudioServicesPlayAlertSound:

Identifier Description
kSystemSoundID_Vibrate On the iPhone, use this constant with the AudioServicesPlayAlertSound function to invoke a brief vibration. On the iPod touch, does nothing.
kSystemSoundID_UserPreferredAlert On the desktop, use this constant with the AudioServicesPlayAlertSound function to play the alert specified in the Sound preference pane.
kSystemSoundID_FlashScreen On the desktop, use this constant with the AudioServicesPlayAlertSound function to display a flash of light on the screen.
kUserPreferredAlert Deprecated. Use kSystemSoundID_UserPreferredAlert instead.

When a user has configured System Preferences to flash the screen for alerts, or if sound cannot be rendered, calling AudioServicesPlayAlertSound will result in the screen flashing. In macOS, pass the constant kSystemSoundID_UserPreferredAlert to play the alert sound selected by the user in System Preferences.

Result codes

This table lists the result codes defined for System Sound Services:

Constant Value Description
kAudioServicesNoError 0 No error has occurred
kAudioServicesUnsupportedPropertyError 'pty?' The property is not supported
kAudioServicesBadPropertySizeError '!siz' The size of the property data was not correct
kAudioServicesBadSpecifierSizeError '!spc' The size of the specifier data was not correct
kAudioServicesSystemSoundUnspecifiedError -1500 An unspecified error has occurred
kAudioServicesSystemSoundClientTimedOutError -1501 System sound client message timed out

Example code

The example application code below shows how to play those alert sounds. In this example the alert sound is being played by choosing a menu item which is just for the purposes of the demonstration.

Note that the choice of 2 for the alert sound to play in this example is purely arbitrary. You should choose the number for the appropriate sound you want to play. Sound number 4096 is particularly interesting for deaf users. Try it :-)

Alternatively, you can use the sound identifier variables listed in the section above.

unit unit1;

{$mode objfpc}{$H+}
{$linkframework AudioToolbox}

interface

uses
  Forms,
  Menus;

type

  { TForm1 }

  TForm1 = class(TForm)
    MainMenu1: TMainMenu;
    MenuItem1: TMenuItem;
    procedure MenuItem1PlaySoundClick(Sender: TObject);
    MenuItem2: TMenuItem;
    procedure MenuItem2PlaySoundClick(Sender: TObject);

  private

  public

  end;

var
  Form1: TForm1;

implementation

{$R *.lfm}

{ TForm1 }

// Sound procedure declaration 
Procedure AudioServicesPlayAlertSound (inSystemSoundID: UInt32)
   external name '_AudioServicesPlayAlertSound';

// Menu item1 OnClick Event
procedure TForm1.MenuItem1PlaySoundClick(Sender: TObject);
begin
  AudioServicesPlayAlertSound(2);  // Use the appropriate value for the sound you want
end;

// Menu item2 OnClick Event
procedure TForm1.MenuItem2PlaySoundClick(Sender: TObject);
begin
  AudioServicesPlayAlertSound(kSystemSoundID_UserPreferredAlert);  // Use the user's preferred alert sound
end;

end.


Playing an alert sound from a file

Not only can you play the existing operating system alert sounds, you can also play your own .wav sound files. The example application below demonstrates this. The Button1 OnClick event handler plays your sound from the specified file and updates the button caption with the SoundID assigned to the sound.

unit Unit1;

{$mode objfpc}{$H+}
{$modeswitch objectivec1}
{$linkframework AudioToolbox}

interface

{$DEFINE DEBUG}  // Comment if console log messages may required

uses
 Classes,
 SysUtils,
 Forms,
 Controls,
 StdCtrls,
 Dialogs,
 {$IFDEF DEBUG}
 CocoaAll,
 {$ENDIF}
 MacOSAll;

type

 TSystemSoundID = UInt32;
 pSystemSoundID = ^TSystemSoundID;

 { TForm1 }

 TForm1 = class(TForm)
   Button1: TButton;
   procedure Button1Click(Sender: TObject);
 private

 public

 end;


var
 Form1: TForm1;


implementation


{$R *.lfm}

// Completion handler: Executed when the sound file finishes playing
procedure myCompletionHandler(SoundID: SystemSoundID; inClientData: CFStringRef);
begin
  AudioServicesDisposeSystemSoundID(SoundID);  // Dispose of a system sound object and associated resources
  {$IFDEF DEBUG}
  NSLog(NSStr('Completion handler called'));
  {$ENDIF}
end;

// System Sound Services procedure and function declarations
procedure AudioServicesPlayAlertSound (inSystemSoundID: TSystemSoundID); 
  external name '_AudioServicesPlayAlertSound';
function AudioServicesCreateSystemSoundID(inFileURL: CFURLRef; outSystemSoundID: pSystemSoundID): OSStatus; 
  external name '_AudioServicesCreateSystemSoundID';
function AudioServicesAddSystemSoundCompletion (inSystemSoundID: TSystemSoundID; inRunLoop: CFRunLoopRef; inRunLoopMode: CFStringRef; inCompletionRoutine: Pointer; inClientData: CFURLRef): OSStatus; cdecl; 
  external name 'AudioServicesAddSystemSoundCompletion';
function AudioServicesDisposeSystemSoundID(inSystemSoundID: TSystemSoundID): OSStatus; cdecl; 
  external name '_AudioServicesDisposeSystemSoundID';

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
var
   newSoundID: TSystemSoundID;
   filePathURL: CFURLRef;
   filePathCFStringRef: CFStringRef;
   filePathStr: String;
   status: Integer = -1;
begin
 // Sound file to play
 filePathStr := '/usr/local/share/fpcsrc/fpc-3.0.4/packages/libndsfpc/examples/audio/maxmod/basic_sound/audio/Ambulance.wav';
 filePathCFStringRef := CFStringCreateWithPascalString(kCFAllocatorDefault, filePathStr, CFStringGetSystemEncoding);
 filePathURL := CFURLCreateWithFileSystemPath(kCFAllocatorDefault, filePathCFStringRef, kCFURLPOSIXPathStyle, false);

 // Create a new system sound object
 status := AudioServicesCreateSystemSoundID(filePathURL, @newSoundID); 
 if(status = kAudioServicesNoError) then
   begin
      Button1.Caption := IntToStr(newSoundID);

      // Register a callback function, invoked when specified system sound finishes playing
      status := AudioServicesAddSystemSoundCompletion(newSoundID, Nil, Nil, @myCompletionHandler, Nil);
      if(status <> kAudioServicesNoError) then
        ShowMessage('Error in AudioServicesAddSystemSoundCompletion() : ' + IntToStr(status));

      // Play sound
      AudioServicesPlayAlertSound(newSoundID);
   end
 else
   ShowMessage('Error in AudioServicesCreateSystemSoundID() : ' + IntToStr(status));
end;

end.

In the code above we are disposing of the system sound object and its associated resources in the completion handler procedure. You will not want to do this if you wish to replay the sound using it SoundID at a later time in the application (eg in a game).

See also

External links