AVAudioRecorder - 如何从来电中恢复

Question

我正在努力实现我认为非常容易但事实并非如此的事情。

我正在玩 "react-native-audio" 库的源代码。但是你可以假设我是为了这个问题而在本地工作。

这是我正在玩的 reference for the source code。

我的目标很简单，我正在使用 AVAudioRecorder 录制会议（大约需要 30 分钟）。如果在录音过程中有来电，我希望我的应用能够 "recover" 通过执行以下选项之一：

1) "pause" "incoming call" 和 "resume" 当应用回到前台时的记录。

2) 来电时 - 关闭当前文件，当应用程序返回前台时，使用新文件开始新录音（第 2 部分）。

显然选项 (1) 是首选。

请注意，我很清楚如何使用 AVAudioSessionInterruptionNotification 并在我的实验中使用它，但到目前为止运气不佳，例如：

- (void) receiveAudioSessionNotification:(NSNotification *) notification
{
    if ([notification.name isEqualToString:AVAudioSessionInterruptionNotification]) {
        NSLog(@"AVAudioSessionInterruptionNotification");
        NSNumber *type = [notification.userInfo valueForKey:AVAudioSessionInterruptionTypeKey];

        if ([type isEqualToNumber:[NSNumber numberWithInt:AVAudioSessionInterruptionTypeBegan]]) {
            NSLog(@"*** InterruptionTypeBegan");
            [self pauseRecording];
        } else {
            NSLog(@"*** InterruptionTypeEnded");
            [_recordSession setActive:YES error:nil];            
        }
    }
}

请注意，我会为这个问题设置悬赏，但唯一可接受的答案是针对真实世界的工作代码，而不是 "should work in theory"。非常感谢您的帮助:)

Answer 1

我选择了AVAudioEngine和AVAudioFile作为解决方案，因为代码很简短，AVFoundation的中断处理是particularly simple（你的player/recorderobjects被暂停了，并且取消暂停会重新激活您的音频 session)。

N.B AVAudioFile 没有明确的关闭方法，而是写入 headers 并在 [=14= 期间关闭文件] 令人遗憾的是，这个选择使原本简单的 API.

复杂化了

@interface ViewController ()

@property (nonatomic) AVAudioEngine *audioEngine;
@property AVAudioFile *outputFile;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    AVAudioSession *session = [AVAudioSession sharedInstance];
    NSError *error;
    if (![session setCategory:AVAudioSessionCategoryRecord error:&error])  {
        NSLog(@"Failed to set session category: %@", error);
    }

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(audioInterruptionHandler:) name:AVAudioSessionInterruptionNotification object:nil];

    NSURL *outputURL = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask][0] URLByAppendingPathComponent:@"output.aac"];

    __block BOOL outputFileInited = NO;

    self.audioEngine = [[AVAudioEngine alloc] init];

    AVAudioInputNode *inputNode = self.audioEngine.inputNode;

    [inputNode installTapOnBus:0 bufferSize:512 format:nil block:^(AVAudioPCMBuffer *buffer, AVAudioTime * when) {
        NSError *error;

        if (self.outputFile == nil && !outputFileInited) {
            NSDictionary *settings = @{
               AVFormatIDKey: @(kAudioFormatMPEG4AAC),
               AVNumberOfChannelsKey: @(buffer.format.channelCount),
               AVSampleRateKey: @(buffer.format.sampleRate)
            };

            self.outputFile = [[AVAudioFile alloc] initForWriting:outputURL settings:settings error:&error];

            if (!self.outputFile) {
                NSLog(@"output file error: %@", error);
                abort();
            }

            outputFileInited = YES;
        }

        if (self.outputFile && ![self.outputFile writeFromBuffer:buffer error:&error]) {
            NSLog(@"AVAudioFile write error: %@", error);
        }
    }];

    if (![self.audioEngine startAndReturnError:&error]) {
        NSLog(@"engine start error: %@", error);
    }

    // To stop recording, nil the outputFile at some point in the future.
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(20 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        NSLog(@"Finished");
         self.outputFile = nil;
    });
}

// https://developer.apple.com/library/archive/documentation/Audio/Conceptual/AudioSessionProgrammingGuide/HandlingAudioInterruptions/HandlingAudioInterruptions.html
- (void)audioInterruptionHandler:(NSNotification *)notification {
    NSDictionary *info = notification.userInfo;
    AVAudioSessionInterruptionType type = [info[AVAudioSessionInterruptionTypeKey] unsignedIntegerValue];

    switch (type) {
        case AVAudioSessionInterruptionTypeBegan:
            NSLog(@"Begin interruption");
            break;
        case AVAudioSessionInterruptionTypeEnded:
            NSLog(@"End interruption");
            // or ignore shouldResume if you're really keen to resume recording
            AVAudioSessionInterruptionOptions endOptions = [info[AVAudioSessionInterruptionOptionKey] unsignedIntegerValue];
            if (AVAudioSessionInterruptionOptionShouldResume == endOptions) {
                NSError *error;
                if (![self.audioEngine startAndReturnError:&error]) {
                    NSLog(@"Error restarting engine: %@", error);
                }
            }
            break;
    }
}
@end

N.B。您可能想要启用背景音频（当然还要在 Info.plist 中添加一个 NSMicrophoneUsageDescription 字符串）。

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