How to change speed

[developer-poplar]

Excuse me, how to changed speed.I use SFBAudioPlayer on iOS

[sbooth]

The general method mentioned in #245 should work except by using AVAudioUnitVarispeed instead of an equalizer.

[developer-poplar]

I tried to write it that way, but it didn't work。Can I give some hints? Thank you very much.

[self.audioPlayer withEngine:(^(AVAudioEngine * _Nonnull engine) {
        NSError *error;
        AVAudioPlayerNode *playerNode = [AVAudioPlayerNode new];
        AVAudioMixerNode *mixer = [[AVAudioMixerNode alloc] init];
        AVAudioUnitVarispeed *variSpeed = [AVAudioUnitVarispeed new];
        
        [engine attachNode:playerNode];
        [engine attachNode:variSpeed];
        [engine attachNode:mixer];
        
        [engine connect:playerNode to:variSpeed format:self.audioPlayer.playerNode.renderingFormat];
        [engine connect:variSpeed to:mixer format:self.audioPlayer.playerNode.renderingFormat];
        [engine connect:variSpeed to:engine.mainMixerNode format:self.audioPlayer.playerNode.renderingFormat];

        variSpeed.rate = rate;
        mixer.pan = -1;

        [engine prepare];
        [engine startAndReturnError:&error];
    })];

[sbooth]

This example is in Swift but should be a start.

(assuming an ivar varispeed of type AVAudioUnitVarispeed!)

withEngine { engine in
	let mainMixer = engine.mainMixerNode
	guard let mainMixerInputConnectionPoint = engine.inputConnectionPoint(for: mainMixer, inputBus: 0) else {
		os_log(.error, "AVAudioEngine missing main mixer node")
		return
	}

	self.varispeed = AVAudioUnitVarispeed()
	guard self.varispeed != nil else {
		return
	}

	self.varispeed.auAudioUnit.shouldBypassEffect = false
	self.varispeed.rate = 0.75

	engine.attach(self.varispeed)

	engine.disconnectNodeInput(mainMixer, bus: 0)

	engine.connect(self.varispeed, to: mainMixer, format: nil)

	guard let mainMixerInputNode = mainMixerInputConnectionPoint.node else {
		os_log(.error, "AVAudioEngine missing input node to main mixer node")
		return
	}

	engine.connect(mainMixerInputNode, to: self.varispeed, format: nil)
}

[fig7]

I was basically trying to do the same thing and I had a little bit of trouble because I wasn't very familar with the AVAudioEngine. I think I figured it out, though. I made one change to the code above and I also had to add the reconfigureProcessingGraph() function:

I think the line from your example:

engine.connect(self.varispeed, to: mainMixer, format: nil)

should be

engine.connect(self.varispeed, to: mainMixer, format: mainMixer.inputFormat(forBus: 0))

because you do want the varispeed unit to take its output format from the mixer.

Similarly, you have to make sure the varispeed unit gets re-configured after a format change:

func audioPlayer(_ audioPlayer: AudioPlayer, reconfigureProcessingGraph engine: AVAudioEngine, with format: AVAudioFormat) -> AVAudioNode {
    let mainMixer = engine.mainMixerNode
    engine.disconnectNodeInput(mainMixer, bus: 0)
    engine.connect(self.varispeed, to: mainMixer, format: format)

    return self.varispeed
  }