如何在 AVSpeechUtterance 之后始终停止 AVAudioSession

Question

我想要做的是让我的应用在后台音频应用正在播放音频时使用AVSpeechSynthesizer 说出话语。在我的应用说话时，我希望后台应用的音频“变暗”，然后在我的应用说完后恢复到原来的音量。

在我的AudioFeedback 类中，我初始化我设置AVAudioSessions，如下所示：

    self.session = [AVAudioSession sharedInstance];
    NSError *error;
    [self.session setCategory:AVAudioSessionCategoryPlayback withOptions:AVAudioSessionCategoryOptionDuckOthers error:&error];

每当我想说出新的话语时，我都会执行以下操作。我遵循An issue with AVSpeechSynthesizer, Any workarounds? 的建议，每次都创建一个新的 AVSpeechSynthesizer 以“确保”始终收到取消（它似乎有效，我不知道为什么）。

- (AVSpeechUtterance *) utteranceWithString: (NSString *) string
{
    AVSpeechUtterance *utterance = [AVSpeechUtterance  speechUtteranceWithString:string];
    utterance.voice = [AVSpeechSynthesisVoice voiceWithLanguage:@"en-ES"];
    [utterance setRate:(AVSpeechUtteranceDefaultSpeechRate+AVSpeechUtteranceMinimumSpeechRate)/2.0];
    return utterance;
}

- (void) sayString: (NSString *) string cancelPrevious: (BOOL) cancelPrevious
{
    [self.session setActive:enabled error:nil];
    if (cancelPrevious) {
        AVSpeechSynthesizer *oldSynthesizer = self.voice;
        self.voice = nil;
        [oldSynthesizer stopSpeakingAtBoundary:AVSpeechBoundaryImmediate];
        self.voice = [[AVSpeechSynthesizer alloc] init];
        self.voice.delegate = self;
    }

    // Keep track of the final utterance, we'll use this to determine whether or not we should stop the audio session
    self.finalUtterance = [self utteranceWithString:string];
    [self.voice speakUtterance:self.finalUtterance];
}

在我的 AVSpeechSynthesizer 委托方法中，如果当前 AVSpeechSynthesizer 和当前 AVSpeechUtterance 与最后一个已知的合成器和话语匹配，我检查是否应该停止音频会话以将背景音频恢复到正常音量。

-(void)speechSynthesizer:(AVSpeechSynthesizer *)synthesizer didFinishSpeechUtterance:(AVSpeechUtterance *)utterance
{
    NSError *error;
    // Only stop the audio session if this is the last created synthesizer
    if (synthesizer == self.voice  && self.finalUtterance == utterance) {
        if ([self.session setActive:enabled error:&error]]) {
            NSLog(@"Stopped the audio session: Speech synthesizer still speaking %d", synthesizer.speaking);
        } else {
            NSLog(@"ERROR failed to stop the audio session: %@. Speech synthesizer still speaking %d", error, synthesizer.speaking);
        }
    }
}

我遇到的问题是，有时，音频会话会毫无问题地停止，而其他时候，音频会话将无法停止并出现以下错误：

Error Domain=NSOSStatusErrorDomain Code=2003329396 “操作无法完成。（OSStatus 错误 2003329396。）”

我不确定如何保证我可以停止 AVAudioSession。只要我无法停止音频会话，我就一直尝试拨打[[AVAudioSession sharedInstance] setActive:NO error:&error]，但这似乎不起作用。任何帮助将不胜感激。谢谢！

Answer 1

我发现，如果我在几秒钟后再试一次，它就会起作用。我正在使用此代码。

-(void)configureAVAudioSession:(bool)active {

    AVAudioSession *audioSession = [AVAudioSession sharedInstance];

    if (deactivationAttempt < 3) {  // This doesn't always work first time, but don't want to keep trying forever if it decides not to work ever.

        NSError *activationError = nil;
        success = [audioSession setActive:active error:&activationError];

        if (!success) {
            NSLog(@"(de)activation ERROR");
            ++deactivationAttempt;
            [self performSelector:@selector(configureAVAudioSession:) withObject:false afterDelay:2.0];
        }
        else {  // Success!
            deactivationAttempt = 0;
        }
    }
    else {  // Failed, but reset the counter in case we have more luck next time
        deactivationAttempt = 0;
    }
}

来自文档：

如果任何关联的音频对象（例如队列、转换器、播放器或录音机）当前正在运行，则停用会话将失败。

我想从队列中清除话语需要一段时间。

Answer 2

我也遇到过同样的问题，我相信我已经找到了原因。对我来说，如果我说的短语太短，就会出错。如果它“足够长”，则没有错误。

我测试过

NSString *phraseToSay = [NSString stringWithFormat:@"One Two Three Four Five"]; // Gives the error
NSString *phraseToSay = [NSString stringWithFormat:@"One Two Three Four Five Six"]; // No error

我找到的唯一解决方案是让短语ToSay 更长。