iOS What is happening here? cached sound?

[dantastic]

I've a timer and at the end of it an alarm.

The alarm sits in a function like this:

- (void) soundAlarm {
	[alarmTimer invalidate];
	alarmTimer = nil;
	SystemSoundID sound;
	AudioServicesCreateSystemSoundID((CFURLRef)[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"ALARM" ofType:@"WAV"]], &sound);
	AudioServicesPlaySystemSound (sound); 	
}

The first time the alarm sounds it's off by 0.5 sec or so. Any subsequent call to this function and there is no delay.

I have tried to put the

AudioServicesCreateSystemSoundID((CFURLRef)[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"ALARM" ofType:@"WAV"]], &sound);

In the initialization code and just call the PlaySound from my function but the result is the same.

In the function above though, I'm not retaining anything so I should have to create the sound every time, no?

I can accept a delay, but why is there no delay the second & 3rd time I sound the alarm?

Is there any way of making this a bit more consistent? Perhaps playing the sound in the initialization code but in mute, can I do that?

 

[nickculbertson]

The NSTimer has a delay the first time an instance is called. You could do a self performSelector in your viewDidLoad to get that first fire out of the way. There would be a random alarm sound though.

Where are you firing the timer from? Button? viewDidLoad?

You could probably do some kind of switch case statement where case 1 is

[alarmTimer invalidate];
	alarmTimer = nil;

and all other cases are

SystemSoundID sound;
	AudioServicesCreateSystemSoundID((CFURLRef)[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"ALARM" ofType:@"WAV"]], &sound);
	AudioServicesPlaySystemSound (sound); 
[alarmTimer invalidate];
	alarmTimer = nil;

 

[dantastic]

So it's the timer firing that's causing this.

I'm firing from a button with this when the button is pressed

alarmTimer = [NSTimer scheduledTimerWithTimeInterval:(countdownSeconds) 
				target:self selector:@selector(soundAlarm) userInfo:nil repeats:NO];

The first time I press the button there's a 0.5 delay. any subsequent press and there's no delay.

Could I do a

alarmTimer = [NSTimer scheduledTimerWithTimeInterval:0.0 
				target:self selector:@selector(doNothingFunction) userInfo:nil repeats:NO];

in my viewDidLoad? you think that would cure the lag?

 

[nickculbertson]

Yeah that might work.

To make sure the timer is the reason for the delay put a NSLog at the end of your timer and see if it shows on the console after a delay.

If you are firing from a button push IBAction then put the code to play the sound in that method, not at the end of the timer... unless you mean that there is a delay after ( countdownSeconds ) ?

If the delay is after the countdownSeconds a hacky fix could be...

-(void)viewDidLoad{
    alarmTimer = [NSTimer scheduledTimerWithTimeInterval:.02 
				target:self selector:@selector(soundAlarm) userInfo:nil repeats:NO];
}
 -(void)soundAlarm{
   switch(){
     case1://no sound
break; 
     case2://sound
break; 
     case3://sound... this could work unless you fire the method a bizillion times 
break; 
      default:
    break; 
}
}

but I'd try the (doNothingFunction) first.

Nick

 

[dejo]

Is there any way of making this a bit more consistent? Perhaps playing the sound in the initialization code but in mute, can I do that?

Yeah, I've experienced something similar with the sound playing a bit delayed the first time. Even if you create the system sound earlier, there seems to be a hitch the first time it's played. Turning down the volume while playing the sound during init seems to be a plausible workaround. You should try it out.

 

[dantastic]

I've done some more testing now.

1) Added some NSLogging. The timer is actually firing accurately enough. It's the sound playing that is delayed the first time.

2) I did set the timer to fire against a 'doNothing' function in my viewDidLoad but as expected with the result from test 1 that didn't do anything at all.

I suspect Apple won't be cool about me fiddling with the volume up and down in my app so I need to find a way of playing this without it being played. on the iPhone, is there something like /dev/null I can use to play my sound to or how would I go about playing it?

 

[nickculbertson]

I see.

The delay occurs the first time with AudioServicesPlaySystemSound. In that case, create a short soundless audio track to play in your viewDidLoad. This will get that first fire out of the way silently.

 

[dantastic]

I see.

The delay occurs the first time with AudioServicesPlaySystemSound. In that case, create a short soundless audio track to play in your viewDidLoad. This will get that first fire out of the way silently.

Aaah! Good thinking 99!

AudioServicesCreateSystemSoundID((CFURLRef)[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"SILENCE" ofType:@"WAV"]], &alarm); 
	AudioServicesPlaySystemSound (alarm); 
	AudioServicesCreateSystemSoundID((CFURLRef)[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"ALARM" ofType:@"WAV"]], &alarm);

Playing one sec of silence in the viewDidLoad solved it. sneaky!