Using MixerNode to downsample.

[jestrada]

I'm trying to setup AVAudioEngine to read the mic stream with voice processing on, and a downsample mixer to receive a 16khz mic stream. However, I don't see a constructor defined in the MixerNode:

https://github.com/yury/cidre/blob/main/cidre/src/av/audio/mixer_node.rs.

Here's some sample Swift code that I'm trying to use for my solution:

var inputNode = audioEngine.inputNode
var downMixer = AVAudioMixerNode()

//I think you the engine's I/O nodes are already attached to itself by default, so we attach only the downMixer here:
audioEngine.attachNode(downMixer)

//You can tap the downMixer to intercept the audio and do something with it:
downMixer.installTapOnBus(0, bufferSize: 2048, format: downMixer.outputFormatForBus(0), block:  //originally 1024
            { (buffer: AVAudioPCMBuffer!, time: AVAudioTime!) -> Void in
                print(NSString(string: "downMixer Tap"))
                do{
                    print("Downmixer Tap Format: "+self.downMixer.outputFormatForBus(0).description)//buffer.audioBufferList.debugDescription)

        })

//let's get the input audio format right as it is
let format = inputNode.inputFormatForBus(0)
//I initialize a 16KHz format I need:
let format16KHzMono = AVAudioFormat.init(commonFormat: AVAudioCommonFormat.PCMFormatInt16, sampleRate: 11050.0, channels: 1, interleaved: true)

//connect the nodes inside the engine:
//INPUT NODE --format-> downMixer --16Kformat--> mainMixer
//as you can see I m downsampling the default 44khz we get in the input to the 16Khz I want 
audioEngine.connect(inputNode, to: downMixer, format: format)//use default input format
audioEngine.connect(downMixer, to: audioEngine.outputNode, format: format16KHzMono)//use new audio format
//run the engine
audioEngine.prepare()
try! audioEngine.start()

Is this possible with Cidre? I can fallback to using the AVAudioConverter but I'm hoping I can use AVAudioEngine for the complete solution. 🙏

https://stackoverflow.com/a/37547476

Thanks!

[yury]

Added in v0.11.1

[jestrada]

Thanks Yury! 💪

[yury]

@jestrada I added example and missing api in v0.11.2.

[jestrada]

You're amazing Yury, thank you. I'll give this a go.