SpeechToTextImplementation.cs

using AVFoundation;
using Foundation;
using Speech;
using System;
using Xamarin.Forms;
using XFSpeechDemo.iOS;

[assembly: Xamarin.Forms.Dependency(typeof(SpeechToTextImplementation))]
namespace XFSpeechDemo.iOS
{
    public class SpeechToTextImplementation : ISpeechToText
    {
        private AVAudioEngine _audioEngine = new AVAudioEngine();
        private SFSpeechRecognizer _speechRecognizer = new SFSpeechRecognizer();
        private SFSpeechAudioBufferRecognitionRequest _recognitionRequest;
        private SFSpeechRecognitionTask _recognitionTask;
        private string _recognizedString;
        private NSTimer _timer;
        private bool isNotContinious;


        public SpeechToTextImplementation()
        {
            AskForSpeechPermission();
        }
        public void StartSpeechToText()
        {

            if (_audioEngine.Running)
            {
                StopRecordingAndRecognition();

            }
            StartRecordingAndRecognizing();
        }

        public void StopSpeechToText()
        {
            _audioEngine?.Stop();
            _recognitionRequest.EndAudio();
        }

        private void AskForSpeechPermission()
        {
            SFSpeechRecognizer.RequestAuthorization((SFSpeechRecognizerAuthorizationStatus status) =>
            {
                switch (status)
                {
                    case SFSpeechRecognizerAuthorizationStatus.Authorized:
                        MessagingCenter.Send<ISpeechToText>(this, "Authorized");
                        break;
                    case SFSpeechRecognizerAuthorizationStatus.Denied:
                        throw new Exception("Audio permission denied");

                    case SFSpeechRecognizerAuthorizationStatus.NotDetermined:
                        throw new Exception("Audio permission not available");
                    case SFSpeechRecognizerAuthorizationStatus.Restricted:
                        throw new Exception("Audio permission denied");
                }
            });
        }

        private void DidFinishTalk()
        {
            MessagingCenter.Send<ISpeechToText>(this, "Final");
            if (_timer != null)
            {
                _timer.Invalidate();
                _timer = null;
            }


            if (_audioEngine.Running)
            {
                StopRecordingAndRecognition();
            }

        }

        private void StartRecordingAndRecognizing()
        {
            if(isNotContinious)
            {
                _timer = NSTimer.CreateRepeatingScheduledTimer(5, delegate
                {
                    DidFinishTalk();
                });
            }
            

            _recognitionTask?.Cancel();
            _recognitionTask = null;

            var audioSession = AVAudioSession.SharedInstance();
            NSError nsError;
            nsError = audioSession.SetCategory(AVAudioSessionCategory.Record);
            audioSession.SetMode(AVAudioSession.ModeMeasurement, out nsError);
            nsError = audioSession.SetActive(true, AVAudioSessionSetActiveOptions.NotifyOthersOnDeactivation);

            _recognitionRequest = new SFSpeechAudioBufferRecognitionRequest();

            var inputNode = _audioEngine.InputNode;
            if (inputNode == null)
            {
                throw new Exception();
            }

            var recordingFormat = inputNode.GetBusOutputFormat(0);
            inputNode.InstallTapOnBus(0, 1024, recordingFormat, (buffer, when) =>
            {
                _recognitionRequest?.Append(buffer);
            });

            _audioEngine.Prepare();
            _audioEngine.StartAndReturnError(out nsError);

            _recognitionTask = _speechRecognizer.GetRecognitionTask(_recognitionRequest, (result, error) =>
            {
                var isFinal = false;
                if (result != null)
                {
                    _recognizedString = result.BestTranscription.FormattedString;
                    MessagingCenter.Send<ISpeechToText, string>(this, "STT", _recognizedString);
                    Console.WriteLine("result");
                    if(isNotContinious)
                    {
                        _timer.Invalidate();
                        _timer = null;
                        _timer = NSTimer.CreateRepeatingScheduledTimer(3, delegate
                        {
                            DidFinishTalk();
                        });
                    }
                    
                }
                if (error != null || isFinal)
                {
                    MessagingCenter.Send<ISpeechToText>(this, "Final");
                    StopRecordingAndRecognition();
                }
            });

        }

        private void StopRecordingAndRecognition()
        {
            _audioEngine.Stop();
            _audioEngine.InputNode.RemoveTapOnBus(0);
            _recognitionTask?.Cancel();
            _recognitionRequest = null;
            _recognitionTask = null;
        }


    }
}