AKOfflineRenderNode - Scheduling AKAudioPlayers, only the last player renders - swift

Question

Getting some weird results when trying to render a sequence of AKAudioPlayers with AudioKit 4.0, Swift 4 on iOS 11.1
I'm aware of AudioKit.renderToFile alternative on the development branch (https://github.com/AudioKit/AudioKit/commit/09aedf7c119a399ab00026ddfb91ae6778570176) but would like to cover iOS 9+ if possible
Expected result:
A long audio file with the each file (URL) rendered in sequence
Actual result:
Only the last scheduled file is rendered (at the correct offset in the resulting wav file)
Weirdly, if I schedule them all at the 0 offset, they all get rendered. Also, if I play things back without rendering, it sounds correct (though I have to adjust the AVAudioTime to use mach_absolute_time)
It almost seems like scheduling an AKAudioPlayer cancels the previous one.
Setup:
class func initialize (){
// ....
do {
try AKSettings.setSession(category: .playAndRecord, with: .allowBluetoothA2DP)
} catch {
AKLog("Could not set session category.")
}
//AKSettings.playbackWhileMuted = true
AKSettings.defaultToSpeaker = true
mainMixer = AKMixer()
offlineRender = AKOfflineRenderNode()
mainMixer! >>> offlineRender!
AudioKit.output = offlineRender!
AudioKit.start()
// ....
Rendering:
class func testRender(urls: [URL], dest: URL, offset: TimeInterval = 2){
// Stop / Start AudioKit when switching internalRenderEnabled, otherwise I get the following error:
// *** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'player started when engine not running'
AudioKit.stop()
var players = [AKAudioPlayer]()
var scheduleTime : TimeInterval = 0
// create players
for url in urls {
do {
let file = try AKAudioFile(forReading: url)
let player = try AKAudioPlayer(file: file)
players.append(player)
player.connect(to: mainMixer!)
print("Connecting player")
} catch {
print("error reading")
}
}
offlineRender!.internalRenderEnabled = false
AudioKit.start()
for player in players{
do {
// 0 instead of mach_absolute_time(), otherwise the result is silent
let avTime = AKAudioPlayer.secondsToAVAudioTime(hostTime: 0, time: scheduleTime)
// schedule and play according to:
// https://stackoverflow.com/questions/45799686/how-to-apply-audio-effect-to-a-file-and-write-to-filesystem-ios/45807586#45807586
player.schedule(from: 0, to: player.duration, avTime: nil)
player.play(at: avTime);
scheduleTime += offset
} catch {
print("error reading")
}
}
// add some padding
scheduleTime += 3
let duration = scheduleTime
do {
try offlineRender!.renderToURL(dest, seconds: duration)
} catch {
print("error rendering")
}
// cleanup
players.forEach { $0.schedule(from: 0, to: $0.duration, avTime: nil)}
players.forEach({$0.stop()})
players.forEach({$0.disconnectOutput()})
offlineRender!.internalRenderEnabled = true
}
Appreciate any help!

Answer 1

AKOfflineRenderNode has been deprecated as of iOS 11.0. Version 4.0.4 has an AudioKit.renderToFile method to replace it. It was updated recently (in late 2017).

Answer 2

So it looks like the AKOFflineRednerNode is indeed deprecated in the coming versions of AudioKit and is not working on iOS11. Reading comments discussing the issue on GitHub it sounds like the plan is to encapsulate both the new (iOS11+) offline rendering and the old (iOS9-10) under a common interface (AudioKit.renderToFile). However for now it seems to be iOS11 only.
After some testing with the dev version (install instructions here: https://github.com/audiokit/AudioKit/blob/master/Frameworks/README.md) I got the following code to work as intended:
try AudioKit.renderToFile(outputFile, seconds: duration, prerender: {
var scheduleTime : TimeInterval = 0
for player in players{
let dspTime = AVAudioTime(sampleTime: AVAudioFramePosition(scheduleTime * AKSettings.sampleRate), atRate: AKSettings.sampleRate)
player.play(at: dspTime)
scheduleTime += offset
}
})
Unless someone can provide a workaround that gets the OfflineRenderNode working on iOS11 and until the official release of AudioKit with the renderToFile implemented this is the best answer I could find.