AVAudioEngine multiple AVAudioInputNodes do not play in perfect sync

Question

I\'ve been trying to use AVAudioEngine to schedule multiple audio files to play in perfect sync, but when listening to the output there seems to be a very slight delay betwe

Answer 1

I used Apple developer support ticket for my own problems with AVAudioEngine in which one problem was (is) exactly the same as yours. I got this code to try:

AudioTimeStamp myAudioQueueStartTime = {0};
UInt32 theNumberOfSecondsInTheFuture = 5;
Float64 hostTimeFreq = CAHostTimeBase::GetFrequency();
UInt64 startHostTime = CAHostTimeBase::GetCurrentTime()+theNumberOfSecondsInTheFuture*hostTimeFreq;
myAudioQueueStartTime.mFlags = kAudioTimeStampHostTimeValid;
myAudioQueueStartTime.mHostTime = startHostTime;
AVAudioTime *time = [AVAudioTime timeWithAudioTimeStamp:&myAudioQueueStartTime sampleRate:_file.processingFormat.sampleRate];

Aside from scheduling play in Skynet era instead of 5 seconds in the future, it still didn't sync two AVAudioPlayerNodes (when I switched GetCurrentTime() for some arbitrary value to actually manage to play the nodes).

So not being able to sync two and more nodes together is a bug (confirmed by Apple support). Generally, if you don't have to use something that was introduced with AVAudioEngine (and you don't know how to translate it into AUGraph), I advise to use AUGraph instead. It's a bit more overhead to implement but you have more control over it.