textospeechimpl.m

#import "TSTextToSpeechUtils.h"
 
@interface TSTextToSpeechUtils ()
 
@property (strong, nonatomic) AVSpeechSynthesizer *synthesizer;
@property (strong, nonatomic) AVSpeechUtterance *lastPlayingUtterance;
@property (strong, nonatomic) AVAudioSession *audioSession;
 
@end
 
@implementation TSTextToSpeechUtils
 
- (instancetype)init
{
    if ((self = [super init])) {
        _synthesizer = [[AVSpeechSynthesizer alloc] init];
        _synthesizer.delegate = self;
    }
    return self;
}
 
- (void)synthesizeSpeechForText:(NSString *)text
{
    if ([text length] == 0) {
        return;
    }
     
    self.audioSession = [AVAudioSession sharedInstance];
     
    NSError *error;
     
    // activate audioSession to play utterance
    [self.audioSession setCategory:AVAudioSessionCategoryPlayback withOptions:AVAudioSessionCategoryOptionDuckOthers error:&error];
    [self.audioSession setActive:YES error:&error];
     
    AVSpeechUtterance *utterance = [[AVSpeechUtterance alloc] initWithString:text];
    utterance.rate = AVSpeechUtteranceDefaultSpeechRate;
    utterance.voice = [AVSpeechSynthesisVoice voiceWithLanguage:[self detectLanguageFromText:text]];
    utterance.volume = 0.7;
    [self.synthesizer speakUtterance:utterance];
     
    self.lastPlayingUtterance = utterance;
}
 
- (void)speechSynthesizer:(AVSpeechSynthesizer *)synthesizer didFinishSpeechUtterance:(AVSpeechUtterance *)utterance
{
    if (synthesizer == self.synthesizer && self.lastPlayingUtterance == utterance) {
        NSError *error;
        // after last utterance has played - deactivate the audio session
        [self.audioSession setActive:NO error:&error];
    }
}
 
- (NSString *)detectLanguageFromText:(NSString *)text
{
    NSArray *tagSchemes = [NSArray arrayWithObjects:NSLinguisticTagSchemeLanguage, nil];
    NSLinguisticTagger *tagger = [[NSLinguisticTagger alloc] initWithTagSchemes:tagSchemes options:0];
    [tagger setString:text];
    NSString *textLanguage = [tagger tagAtIndex:0 scheme:NSLinguisticTagSchemeLanguage tokenRange:nil sentenceRange:nil];
     
    NSString *detectedLanguage = nil;
     
    // check if the text language exists within installed languages
    for (id installedLanguage in [AVSpeechSynthesisVoice speechVoices]) {
        NSArray *languageStringParts = [[installedLanguage language] componentsSeparatedByString:@"-"];
        if (languageStringParts.count > 0 && [languageStringParts[0] isEqualToString:textLanguage]) {
            detectedLanguage = [installedLanguage language];
            break;
        }
    }
     
    if (detectedLanguage == nil) {
        // if language could not be detected assign to default
        detectedLanguage = @"en-US";
    }
    return detectedLanguage;
}
 
@end