According to the Apple docs, you should be able to connect audio nodes to an AVAudioEngine instance during runtime, but I'm getting a crash while trying to do so, in particular, when trying to connect instances of AVAudioUnitTimePitch or AVAudioUnitVarispeed to an AVAudioEngine with manual rendering mode enabled. The error message I get is:
Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason:
'player started when in a disconnected state'
In my code, first, I configure the audio engine:
let engine = AVAudioEngine()
let format = AVAudioFormat(standardFormatWithSampleRate: 48000, channels: 2)!
try! engine.enableManualRenderingMode(.offline, format: format, maximumFrameCount: 1024)
try! engine.start()
Then, I try to attach the player to the engine:
let player = AVAudioPlayerNode()
configureEngine(player: player, useVarispeed: true)
player.play() // this is the line that causes the crash
Finally, this is the function I use to configure the engine nodes graph:
func configureEngine(player: AVAudioPlayerNode, useVarispeed: Bool) {
engine.attach(player)
guard useVarispeed else {
engine.connect(player, to: engine.mainMixerNode, format: format)
return
}
let varispeed = AVAudioUnitVarispeed()
engine.attach(varispeed)
engine.connect(player, to: varispeed, format: format)
engine.connect(varispeed, to: engine.mainMixerNode, format: format)
}
If I pass false as the value for the useVarispeed parameter, the crash goes away. What is even more interesting is that if I add a dummy player node before starting the engine, the crash goes away too 🤷♂️
Could anyone please add clarity on what's going on here? Is this a bug or a limitation of the framework that I'm not aware of?
Here's a simple project demonstrating the problem: https://github.com/rlaguilar/AVAudioEngineBug