Slow start for AVAudioPlayer the first time a sound is played

Question

I'm trying to eliminate startup lag when playing a (very short -- less than 2 seconds) audio file via AVAudioPlayer on the iPhone.

First, the code:

NSString *audioFile = [NSString stringWithFormat:@"%@/%@.caf", [[NSBundle mainBundle] resourcePath], @"audiofile"];
NSData *audioData = [NSData dataWithContentsOfMappedFile:audioFile];

NSError *err;
AVAudioPlayer *audioPlayer = [(AVAudioPlayer*)[AVAudioPlayer alloc] initWithData:audioData error:&err];

audioPlayer.delegate = self;
[audioPlayer play];

I also implement the audioPlayerDidFinishPlaying method to release the AVAudioPlayer once I'm done.

The first time I play the audio the lag is palpable -- at least 2 seconds. However, after that the sound plays immediately. I suspect that the culprit, then, is the [NSData dataWithContentsOfMappedFile] taking a long time reading from the flash initially, but then being fast on later reads. I'm not sure how to test that, though.

Is that the case? If so, should I just pre-cache the NSData objects and be aggressive about clearing them in low memory conditions?

Answer 1

The delay seems to be related to instantiating AVAudioPlayer for the first time. If I load any audio, run [audioPlayer prepareToPlay] and then immediately release it, the load times for all of my other audio is very close to imperceptible. So now I'm doing that in applicationDidFinishLaunching and everything else runs well.

I can't find anything about this in the docs, but it certainly seems to be the case.

Answer 2

Here's what I've done (in a separate thread):

[audioplayer start]
[audioplayer stop]
self.audioplayer = audioplayer

[audioplayer prepareToPlay] seems to be an asynchronous method, so you can't be sure when it returns if the audio is in fact ready to play.

In my case I call start to actually start playing - this appears to be synchronous. Then I stop it immediately. In the simulator anyway I don't hear any sound coming out from this activity. Now that the sound is "really" ready to play, I assign the local variable to a member variable so code outside the thread has access to it.

I must say I find it somewhat surprising that even on iOS 4 it takes some 2 seconds just to load an audio file that is only 4 seconds in length....

Answer 3

If your audio is less than 30 seconds long in length and is in linear PCM or IMA4 format, and is packaged as a .caf, .wav, or .aiff you can use system sounds:

Import the AudioToolbox Framework

In your .h file create this variable:

SystemSoundID mySound;

In your .m file implement it in your init method:

-(id)init{
if (self) {
    //Get path of VICTORY.WAV <-- the sound file in your bundle
    NSString* soundPath = [[NSBundle mainBundle] pathForResource:@"VICTORY" ofType:@"WAV"];
    //If the file is in the bundle
    if (soundPath) {
        //Create a file URL with this path
        NSURL* soundURL = [NSURL fileURLWithPath:soundPath];

        //Register sound file located at that URL as a system sound
        OSStatus err = AudioServicesCreateSystemSoundID((CFURLRef)soundURL, &mySound);

            if (err != kAudioServicesNoError) {
                NSLog(@"Could not load %@, error code: %ld", soundURL, err);
            }
        }
    }
return self;
}

In your IBAction method you call the sound with this:

AudioServicesPlaySystemSound(mySound);

This works for me, plays the sound pretty damn close to when the button is pressed. Hope this helps you.