blog-speech-framework-07.swift

private func startRecording() throws {
        // 1
        if let recognitionTask = self.recognitionTask {
            recognitionTask.cancel()
            self.recognitionTask = nil
        }
        
        // 2
        let audioSession = AVAudioSession.sharedInstance()
        try audioSession.setCategory(AVAudioSessionCategoryRecord)
        try audioSession.setMode(AVAudioSessionModeMeasurement)
        try audioSession.setActive(true, with: .notifyOthersOnDeactivation)
        guard let inputNode = audioEngine.inputNode else { fatalError("Audio engine has no input node") }
        
        // 3
        self.recognitionRequest = SFSpeechAudioBufferRecognitionRequest()
        guard let recognitionRequest = recognitionRequest else { fatalError("Unable to created a SFSpeechAudioBufferRecognitionRequest object") }
        self.recognitionRequest.shouldReportPartialResults = true
        
        // 4
        self.recognitionTask = self.speechRecognizer.recognitionTask(with: recognitionRequest) { result, error in 
            
            var isFinal = false
            
            // 5
            if let result = result {
                self.textView.text = result.bestTranscription.formattedString
                isFinal = result.isFinal
            }
            
            // 6
            if error != nil || isFinal {
                self.audioEngine.stop()
                inputNode.removeTap(onBus: 0)
                
                self.recognitionRequest = nil
                self.recognitionTask = nil
                
                self.recordButton.isEnabled = true
            }
        }
        
        // 7
        let recordingFormat = inputNode.outputFormat(forBus: 0)
        inputNode.installTap(onBus: 0, bufferSize: 1024, format: recordingFormat) { (buffer: AVAudioPCMBuffer, when: AVAudioTime) in
            self.recognitionRequest?.append(buffer)
        }
  
        audioEngine.prepare()
        
        try audioEngine.start()
}