播放音频

1.配置音频回话

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    AVAudioSession *session = [AVAudioSession sharedInstance];

    NSError *error;
    if (![session setCategory:AVAudioSessionCategoryPlayback error:&error]) {
        NSLog(@"Category Error: %@", [error localizedDescription]);
    }

    if (![session setActive:YES error:&error]) {
        NSLog(@"Activation Error: %@", [error localizedDescription]);
    }
    
    return YES;
}

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2.播放音频
创建AVAudioPlayer

  NSError *error;
    AVAudioPlayer *player = [[AVAudioPlayer alloc] initWithContentsOfURL:fileURL
                                                                   error:&error];
 player.numberOfLoops = -1; // loop indefinitely
     player.enableRate = YES;//指定是否为音频播放器启用播放速率调整。
        [player prepareToPlay];//准备播放，会在播放时自动调用此方法。
[player play];

volume:调节声音的音量
pan：修改播放器的pan值。允许使用立方声播放声音。
rate：调整播放速率。
numberOfLoops:如果设置的值大于0，可以实现设置值的循环播放。如果设置的是-1，无限循环.
3.设置后台播放音频
在plist文件中设置添加一个新的，Required background modes类型数组，在其中添加名为App plays audio or streams audio/video using AirPlay。
4.处理中断时间

        NSNotificationCenter *nsnc = [NSNotificationCenter defaultCenter];
        [nsnc addObserver:self selector:@selector(handleInterruptionNotification:) name:AVAudioSessionInterruptionNotification object:[AVAudioSession sharedInstance]];

5.处理线路改变相应

        NSNotificationCenter *nsnc = [NSNotificationCenter defaultCenter];
        [nsnc addObserver:self
                 selector:@selector(handleRouteChange:)
                     name:AVAudioSessionRouteChangeNotification
                   object:[AVAudioSession sharedInstance]];

录制音频

1.设置音频会话

    AVAudioSession *session = [AVAudioSession sharedInstance];

    NSError *error;
    if (![session setCategory:AVAudioSessionCategoryPlayAndRecord error:&error]) {
        NSLog(@"Category Error: %@", [error localizedDescription]);
    }

    if (![session setActive:YES error:&error]) {
        NSLog(@"Activation Error: %@", [error localizedDescription]);
    }

2.初始化音频录制对象。

 NSString *tmpDir = NSTemporaryDirectory();
        NSString *filePath = [tmpDir stringByAppendingPathComponent:@"memo.caf"];
        NSURL *fileURL = [NSURL fileURLWithPath:filePath];

        NSDictionary *settings = @{
                              //值是CoreAudioTypes.h中的整数（格式ID）
                                  AVFormatIDKey : @(kAudioFormatAppleIMA4), 
                                  //采样率
                                   AVSampleRateKey : @44100.0f,
                                  //表示为NSNumber整数值的通道数。
                                   AVNumberOfChannelsKey : @1,
                                   //value is an integer from 8 to 32
                                   AVEncoderBitDepthHintKey : @16,
                                  //音频质量
                                   AVEncoderAudioQualityKey : @(AVAudioQualityMedium)
                                   };

        NSError *error;
        self.recorder = [[AVAudioRecorder alloc] initWithURL:fileURL settings:settings error:&error];
        if (self.recorder) {
            self.recorder.delegate = self;
            self.recorder.meteringEnabled = YES;
            [self.recorder prepareToRecord];
        } else {
            NSLog(@"Error: %@", [error localizedDescription]);
        }

AVFormatIDKey：音频格式kAudioFormatMPEG4AAC是最常用的
AVSampleRateKey：采样率
AVNumberOfChannelsKey：设置2说明是立体的