How to run wake word detection with pocket sphinx on iOS? - ios

Question

I try to run the wake word detection from pocket sphinx on iOS. As base I used TLSphinx and the speech to text works (not good STT, but it recognizes words).
I extended the decoder.swift by a new function:
public func detectWakeWord (complete: #escaping (Bool?) -> ()) throws {
ps_set_keyphrase(psDecoder, "keyphrase_search", "ZWEI")
ps_set_search(psDecoder, "keyphrase_search")
do {
if #available(iOS 10.0, *) {
try AVAudioSession.sharedInstance().setCategory(.playAndRecord, mode: .voiceChat, options: [])
} else {
try AVAudioSession.sharedInstance().setCategory(.playAndRecord)
}
} catch let error as NSError {
print("Error setting the shared AVAudioSession: \(error)")
throw DecodeErrors.CantSetAudioSession(error)
}
engine = AVAudioEngine()
let input = engine.inputNode
let mixer = AVAudioMixerNode()
let output = engine.outputNode
engine.attach(mixer)
engine.connect(input, to: mixer, format: input.outputFormat(forBus: 0))
engine.connect(mixer, to: output, format: input.outputFormat(forBus: 0))
// We forceunwrap this because the docs for AVAudioFormat specify that this constructor return nil when the channels
// are greater than 2.
let formatIn = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: 44100, channels: 1, interleaved: false)!
let formatOut = AVAudioFormat(commonFormat: .pcmFormatInt16, sampleRate: 16000, channels: 1, interleaved: false)!
guard let bufferMapper = AVAudioConverter(from: formatIn, to: formatOut) else {
// Returns nil if the format conversion is not possible.
throw DecodeErrors.CantConvertAudioFormat
}
mixer.installTap(onBus: 0, bufferSize: 2048, format: formatIn, block: {
[unowned self] (buffer: AVAudioPCMBuffer!, time: AVAudioTime!) in
guard let sphinxBuffer = AVAudioPCMBuffer(pcmFormat: formatOut, frameCapacity: buffer.frameCapacity) else {
// Returns nil in the following cases:
// - if the format has zero bytes per frame (format.streamDescription->mBytesPerFrame == 0)
// - if the buffer byte capacity (frameCapacity * format.streamDescription->mBytesPerFrame)
// cannot be represented by an uint32_t
print("Can't create PCM buffer")
return
}
// This is needed because the 'frameLenght' default value is 0 (since iOS 10) and cause the 'convert' call
// to faile with an error (Error Domain=NSOSStatusErrorDomain Code=-50 "(null)")
// More here: http://stackoverflow.com/questions/39714244/avaudioconverter-is-broken-in-ios-10
sphinxBuffer.frameLength = sphinxBuffer.frameCapacity
var error : NSError?
let inputBlock : AVAudioConverterInputBlock = {
inNumPackets, outStatus in
outStatus.pointee = AVAudioConverterInputStatus.haveData
return buffer
}
bufferMapper.convert(to: sphinxBuffer, error: &error, withInputFrom: inputBlock)
print("Error? ", error as Any);
let audioData = sphinxBuffer.toData()
self.process_raw(audioData)
print("Process: \(buffer.frameLength) frames - \(audioData.count) bytes - sample time: \(time.sampleTime)")
self.end_utt()
let hypothesis = self.get_hyp()
print("HYPOTHESIS: ", hypothesis)
DispatchQueue.main.async {
complete(hypothesis != nil)
}
self.start_utt()
})
start_utt()
do {
try engine.start()
} catch let error as NSError {
end_utt()
print("Can't start AVAudioEngine: \(error)")
throw DecodeErrors.CantStartAudioEngine(error)
}
}
There are not errors, but hypothesis is always nil.
My dictionary maps everything to "ZWEI", so the wake word should be detected, if anything is detected.
ZWEI AH P Z EH TS B AAH EX
ZWEI(2) HH IH T
ZWEI(3) F EH EX Q OE F EH N T L IH CC T
ZWEI(4) G AX V AH EX T AX T
...
ZWEI(12113) N AY NZWO B IIH T AX N
Does someone know why hypothesis is always nil?

Answer 1

I had to run self.get_hyp() before self.end_utt().
I'm not sure why, but it is different from speech to text calling order.
Edit
Another tip: For better wake word detection quality increase the buffer size for the microphone input. E.g.:
mixer.installTap(onBus: 0, bufferSize: 8192, format: formatIn, block: [...]