Trouble hooking up AVAudioUnitEffect with AVAudioEngine - objective-c

Question

I've been poking around with AVAudioEngine and I'm having trouble integrating AVAudioUnitEffect classes. For example, with AVAudioUnitDelay...
#implementation ViewController {
AVAudioEngine *engine;
AVAudioPlayerNode *player;
}
...
- (IBAction)playButtonHit:(id)sender {
if (!player){
NSURL *bandsURL = [[NSBundle mainBundle] URLForResource:#"Bands With Managers" withExtension:#"mp3"];
AVAudioFile *file = [[AVAudioFile alloc] initForReading:bandsURL error:nil];
engine = [[AVAudioEngine alloc] init];
player = [[AVAudioPlayerNode alloc] init];
[engine attachNode:player];
AVAudioUnitDelay *delay = [[AVAudioUnitDelay alloc] init];
delay.wetDryMix = 50;
[engine connect:player to:delay format:file.processingFormat];
[engine connect:delay to:[engine outputNode] format:file.processingFormat];
[player scheduleFile:file atTime:nil completionHandler:nil];
[engine prepare];
[engine startAndReturnError:nil];
}
[player play];
}
When the method is called the app crashes and I get this error: "* Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: [_nodes containsObject: node1] && [_nodes containsObject: node2]'"
I'm modeling this after some of the examples from the "AVAudioEngine in Practice" session from WWDC. I know there's probably something obvious I'm missing but can't figure it out....

Answer 1

You forgot to attach your AvAudioUnitDelay object to your AvAudioEngine nodes before linking them ;)
Here is the working code :
- (IBAction)playMusic:(id)sender {
if (!player){
NSURL *bandsURL = [[NSBundle mainBundle] URLForResource:#"Bands With Managers" withExtension:#"mp3"];
AVAudioFile *file = [[AVAudioFile alloc] initForReading:bandsURL error:nil];
engine = [[AVAudioEngine alloc] init];
player = [[AVAudioPlayerNode alloc] init];
[engine attachNode:player];
AVAudioUnitDelay *delay = [[AVAudioUnitDelay alloc] init];
delay.wetDryMix = 50;
[engine attachNode:delay];
[engine connect:player to:delay format:file.processingFormat];
[engine connect:delay to:[engine outputNode] format:file.processingFormat];
[player scheduleFile:file atTime:nil completionHandler:nil];
[engine prepare];
[engine startAndReturnError:nil];
}
[player play];
}

Answer 2

It is not a problem of the AVAudioUnitEffect! I tried it with that code
NSError *err = nil;
self.engine = [[AVAudioEngine alloc] init];
AVAudioPlayerNode *player = [[AVAudioPlayerNode alloc] init];
[self.engine attachNode:player];
NSURL *fileURL = [[NSBundle mainBundle] URLForResource:#"sound" withExtension:#"m4a"];
AVAudioFile *file = [[AVAudioFile alloc] initForReading:fileURL error:&err];
AVAudioMixerNode *mainMixer = [self.engine mainMixerNode];
[self.engine connect:player to:mainMixer format:file.processingFormat];
[player scheduleFile:file atTime:nil completionHandler:nil];
[self.engine startAndReturnError:&err];
if (err != nil) {
NSLog(#"An error occured");
}
[player play];
while self.engine is defined by
#property (nonatomic, strong) AVAudioEngine *engine;
I think that is a bug in AVAudioEngine, because it causes a memory leak: It starts playing the first samples and then it crashes because of heavy memory usage (more than 300 MB in my case of a 16 kB m4a file).
Update 12/07/2014: Apple fixed this issue with iOS 8 Seed 3 (Build 12A4318c)!