主要通過學習AVAudioPlayer和AVAudioRecorder類來實現(xiàn)應用程序中添加音頻播放及音頻錄制的功能。
AV Foundation定義了7中分類來描述應用程序所使用的音頻行為

AVAudioSessionCategory 7大類別

AVAudioSessionCategoryOptions 類別的子選項

AVAudioSessionMode

配置音頻會話

    AVAudioSession *session = [AVAudioSession sharedInstance];
    NSError *error;
    if (![session setCategory:AVAudioSessionCategoryPlayback error:&error]) {
        NSLog(@"Category Error: %@", [error localizedDescription]);
    }
    // 配置激活
    if (![session setActive:YES error:&error]) {
        NSLog(@"Activation Error: %@", [error localizedDescription]);
    }

/* returns singleton instance */
+ (AVAudioSession *)sharedInstance;

/* Set the session active or inactive. 
*/
- (BOOL)setActive:(BOOL)active error:(NSError **)outError;
- (BOOL)setActive:(BOOL)active withOptions:(AVAudioSessionSetActiveOptions)options error:(NSError **)outError;

/* Asynchronously activate the session. 異步激活會話谚咬，handler是回調(diào)
 */
- (void)activateWithOptions:(AVAudioSessionActivationOptions)options completionHandler:(void (^)(BOOL activated, NSError * _Nullable error))handler;
// 獲取設備可用的SessionCategory
@property (readonly) NSArray<AVAudioSessionCategory> *availableCategories;

/* 設置session的category */
- (BOOL)setCategory:(AVAudioSessionCategory)category error:(NSError **)outError ;
/* set session category with options */
- (BOOL)setCategory:(AVAudioSessionCategory)category withOptions:(AVAudioSessionCategoryOptions)options error:(NSError **)outError;
/* set session category and mode with options */
- (BOOL)setCategory:(AVAudioSessionCategory)category mode:(AVAudioSessionMode)mode options:(AVAudioSessionCategoryOptions)options error:(NSError **)outError ;
- (BOOL)setCategory:(AVAudioSessionCategory)category mode:(AVAudioSessionMode)mode routeSharingPolicy:(AVAudioSessionRouteSharingPolicy)policy options:(AVAudioSessionCategoryOptions)options error:(NSError **)outError;
@property (readonly) AVAudioSessionCategory category;
@property (readonly) AVAudioSessionCategoryOptions categoryOptions;
@property (readonly) AVAudioSessionRouteSharingPolicy routeSharingPolicy;
@property (readonly) NSArray<AVAudioSessionMode> *availableModes;
- (BOOL)setMode:(AVAudioSessionMode)mode error:(NSError **)outError; /* set session mode */
@property (readonly) AVAudioSessionMode mode; /* get session mode */
/* 返回權限*/
@property (readonly) AVAudioSessionRecordPermission recordPermission;

typedef void (^PermissionBlock)(BOOL granted);
- (void)requestRecordPermission:(PermissionBlock)response;
- (BOOL)overrideOutputAudioPort:(AVAudioSessionPortOverride)portOverride error:(NSError **)outError;
@property (readonly, getter=isOtherAudioPlaying) BOOL otherAudioPlaying;
@property (readonly) BOOL secondaryAudioShouldBeSilencedHint;
@property (readonly) AVAudioSessionRouteDescription *currentRoute;
- (BOOL)setPreferredInput:(nullable AVAudioSessionPortDescription *)inPort error:(NSError **)outError API_AVAILABLE(ios(7.0), tvos(9.0)) API_UNAVAILABLE(watchos, macos);
@property (readonly, nullable) AVAudioSessionPortDescription *preferredInput API_AVAILABLE(ios(7.0), tvos(9.0)) API_UNAVAILABLE(watchos, macos); /* Get the preferred input port.  Will be nil if no preference has been set */

@property (readonly, nullable) NSArray<AVAudioSessionPortDescription *> *availableInputs ;

創(chuàng)建AVAudioPlayer

AVAudioPlayer構建與CoreAudio中的C-based Audio Queue Services的最頂層。它可以提供播放尚粘，循環(huán)择卦，音頻計量等簡單友好的Objective-C接口。

- (AVAudioPlayer *)playerForFile:(NSString *)name {

    NSURL *fileURL = [[NSBundle mainBundle] URLForResource:name
                                             withExtension:@"caf"];

    NSError *error;
    AVAudioPlayer *player = [[AVAudioPlayer alloc] initWithContentsOfURL:fileURL
                                                                   error:&error];
    if (player) {
        player.numberOfLoops = -1; // 無限循環(huán)
        player.enableRate = YES;
        [player prepareToPlay];  //相當于預加載Audio Queue的緩沖區(qū)
    } else {
        NSLog(@"Error creating player: %@", [error localizedDescription]);
    }
    return player;
}

播放控制

• 修改播放器的音量
• 修改播放器的pan值 允許使用立體聲播放聲音郎嫁，-1.0 到 1.0 之間
• 調(diào)整播放率rate 0.5表示半速秉继，1表示正常，2表示2倍速播放
• numberOfLoops 實現(xiàn)無縫循環(huán) -1表示無限循環(huán)泽铛，n > 0表示循環(huán)n次

THPlayerController.h
@interface THPlayerController : NSObject
@property (nonatomic, getter = isPlaying) BOOL playing; //是否正在播放
// 播放
- (void)play;
//停止
- (void)stop;
//設置速率
- (void)adjustRate:(float)rate;
// 設置pan值
- (void)adjustPan:(float)pan forPlayerAtIndex:(NSUInteger)index;
//設置音量
- (void)adjustVolume:(float)volume forPlayerAtIndex:(NSUInteger)index;

@end

#import "THPlayerController.h"
#import <AVFoundation/AVFoundation.h>

@interface THPlayerController () <AVAudioPlayerDelegate>
@property (strong, nonatomic) NSArray *players;
@end

@implementation THPlayerController

#pragma mark - Initialization

- (id)init {
    self = [super init];
    if (self) {
        AVAudioPlayer *guitarPlayer = [self playerForFile:@"guitar"];
        AVAudioPlayer *bassPlayer = [self playerForFile:@"bass"];
        AVAudioPlayer *drumsPlayer = [self playerForFile:@"drums"];

        guitarPlayer.delegate = self;

        _players = @[guitarPlayer, bassPlayer, drumsPlayer];
    }
    return self;
}

- (AVAudioPlayer *)playerForFile:(NSString *)name {

    NSURL *fileURL = [[NSBundle mainBundle] URLForResource:name
                                             withExtension:@"caf"];

    NSError *error;
    AVAudioPlayer *player = [[AVAudioPlayer alloc] initWithContentsOfURL:fileURL
                                                                   error:&error];
    if (player) {
        player.numberOfLoops = -1; // loop indefinitely
        player.enableRate = YES;
        [player prepareToPlay];
    } else {
        NSLog(@"Error creating player: %@", [error localizedDescription]);
    }

    return player;
}


#pragma mark - Global playback control methods

- (void)play {
    if (!self.playing) {
        NSTimeInterval delayTime = [self.players[0] deviceCurrentTime] + 0.01;
        for (AVAudioPlayer *player in self.players) {
            [player playAtTime:delayTime];
        }
        self.playing = YES;
    }
}

- (void)stop {
    if (self.playing) {
        for (AVAudioPlayer *player in self.players) {
            [player stop];
            player.currentTime = 0.0f; //player.currentTime回到原點
        }
        self.playing = NO;
    }
}

- (void)adjustRate:(float)rate {
    for (AVAudioPlayer *player in self.players) {
        player.rate = rate;
    }
}
- (void)adjustPan:(float)pan forPlayerAtIndex:(NSUInteger)index {
    if ([self isValidIndex:index]) {
        AVAudioPlayer *player = self.players[index];
        player.pan = pan;
    }
}
- (void)adjustVolume:(float)volume forPlayerAtIndex:(NSUInteger)index {
    if ([self isValidIndex:index]) {
        AVAudioPlayer *player = self.players[index];
        player.volume = volume;
    }
}
- (BOOL)isValidIndex:(NSUInteger)index {
    return index == 0 || index < self.players.count;
}
@end

處理中斷事件

音頻播放過程中尚辑，遇到電話呼入、鬧鐘等事件盔腔，會中斷音頻的播放
設置監(jiān)聽中斷事件

初始化AVAudioPlayer之后設置中斷事件的監(jiān)聽
NSNotificationCenter *nsnc = [NSNotificationCenter defaultCenter];
[nsnc addObserver:self selector:@selector(handleInterruption:) name:AVAudioSessionInterruptionNotification object:[AVAudioSession sharedInstance]];
//相應回調(diào)
-(void)handleInterruption:(NSNotification *)notification{
    NSDictionary *info = notification.userInfo;
    AVAudioSessionInterruptionType type = [info[AVAudioSessionInterruptionTypeKey] unsignedIntegerValue];
    if (type == AVAudioSessionInterruptionTypeBegan) {  //中斷開始
        [self stop]杠茬；  
    }else{
        AVAudioSessionInterruptionOptions options = [info[AVAudioSessionInterruptionTypeKey] unsignedIntegerValue];
        if (options == AVAudioSessionInterruptionOptionShouldResume) {  //恢復
            [self play];
            }
        }
    }
}

對線路改變的響應

線路是指輸出線路從揚聲器模式變?yōu)槎鷻C月褥，或者耳機變?yōu)閾P聲器模式。

線路改變原因的枚舉
AVAudioSessionRouteChangeReasonUnknown = 0,
AVAudioSessionRouteChangeReasonNewDeviceAvailable = 1,
AVAudioSessionRouteChangeReasonOldDeviceUnavailable = 2,
AVAudioSessionRouteChangeReasonCategoryChange = 3,
AVAudioSessionRouteChangeReasonOverride = 4,
AVAudioSessionRouteChangeReasonWakeFromSleep = 6,
AVAudioSessionRouteChangeReasonNoSuitableRouteForCategory = 7,
AVAudioSessionRouteChangeReasonRouteConfigurationChange = 8 

音頻輸入
AVAudioSessionPortUSBAudio,
 AVAudioSessionPortHeadsetMic, 
AVAudioSessionPortBuiltInMic.  
音頻輸出
AVAudioSessionPortUSBAudio,  usb接口
AVAudioSessionPortLineOut, 
AVAudioSessionPortHeadphones,  耳機輸出
AVAudioSessionPortHDMI, 
AVAudioSessionPortBuiltInSpeaker.   內(nèi)置揚聲器

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

//線路的改變  比如耳機斷開是停止播放
- (void)handleRouteChange:(NSNotification *)notification {
    NSDictionary *info = notification.userInfo;
    AVAudioSessionRouteChangeReason reason =
        [info[AVAudioSessionRouteChangeReasonKey] unsignedIntValue];
//舊設備斷開鏈接
    if (reason == AVAudioSessionRouteChangeReasonOldDeviceUnavailable) {
        AVAudioSessionRouteDescription *previousRoute =
            info[AVAudioSessionRouteChangePreviousRouteKey];
//端口描述        
AVAudioSessionPortDescription *previousOutput = previousRoute.outputs[0];
        NSString *portType = previousOutput.portType;
        if ([portType isEqualToString:AVAudioSessionPortHeadphones]) {
            [self stop];
        }
    }
}

音頻錄制AVAudioRecorder

創(chuàng)建AVAudioRecorder實例時需要為其提供數(shù)據(jù)的一些信息

- (nullable instancetype)initWithURL:(NSURL *)url settings:(NSDictionary<NSString *, id> *)settings error:(NSError **)outError;

• 音頻流寫入文件的本地url地址
• 配置錄音會話的設置信息
  在 #import <AVFAudio/AVAudioSettings.h> 文件里有音頻的設置鍵信息瓢喉。

AVFormatIDKey     音頻格式
AVSampleRateKey;    采樣率         
AVNumberOfChannelsKey;      通道數(shù)             

格式：kAudioFormatLinearPCM會將未壓縮的音頻流寫入文件中吓坚。 這中格式保真度最高，kAudioFormatMPEG4AAC的壓縮格式會顯著縮小文件灯荧，還能保證高質(zhì)量的音頻內(nèi)容礁击。
采樣率：對輸入的音頻信號每一秒內(nèi)的采樣數(shù)。一般標準的采樣率為8000逗载、16000哆窿、22050和44100赫茲。
通道數(shù)：定義記錄音頻內(nèi)容的通道數(shù)厉斟。默認值為1意味著使用單聲道錄制挚躯，設置為2采用立體聲錄制。

-(NSURL *)getSavePath{
    NSString *urlStr = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject];
    urlStr = [urlStr stringByAppendingPathComponent:kRecordAudioFile];
    NSLog(@"file path:%@",urlStr);
    NSURL *url = [NSURL fileURLWithPath:urlStr];
    return url;
}

//錄音參數(shù)設置
-(NSDictionary *)getAudioSetting{
    NSMutableDictionary *dicM = @{}.mutableCopy;
    [dicM setObject:@(kAudioFormatLinearPCM) forKey:AVFormatIDKey];
    [dicM setObject:@(44100) forKey:AVSampleRateKey];
    [dicM setObject:@(1) forKey:AVNumberOfChannelsKey];
    [dicM setObject:@(16) forKey:AVEncoderBitDepthHintKey];
    [dicM setObject:@(AVAudioQualityMedium) forKey:AVEncoderAudioQualityKey];
    return dicM;
}
//錄音器
-(AVAudioRecorder *)audioRecorder{
    if (!_audioRecorder) {
        //保存路徑
        NSURL *url = [self getSavePath];
        NSDictionary *setting = [self getAudioSetting];
        NSError *error;
        _audioRecorder = [[AVAudioRecorder alloc] initWithURL:url settings:setting error:&error];
        _audioRecorder.delegate = self;
        _audioRecorder.meteringEnabled = YES;
        [_audioRecorder prepareToRecord];
    }
    return _audioRecorder;
}

//開始錄制
- (BOOL)record {
    return [self.audioRecorder record];
}
//中斷
- (void)pause {
    [self.audioRecorder pause];
}
// 停止
- (void)stop {
    [self.audioRecorder stop];
}
//實現(xiàn)錄制完成代理
- (void)audioRecorderDidFinishRecording:(AVAudioRecorder *)recorder successfully:(BOOL)success {
   
}
//實現(xiàn)代理方法 錄制中斷
- (void)audioRecorderBeginInterruption:(AVAudioRecorder *)recorder {

}

記錄分貝等級

- (float)peakPowerForChannel:(NSUInteger)channelNumber; /* returns peak power in decibels for a given channel */
- (float)averagePowerForChannel:(NSUInteger)channelNumber; /* returns average power in decibels for a given channel */

返回用于表示分貝等級的浮點值擦秽，最大分貝的0dB到最小分貝的-160dB码荔。 在調(diào)用這兩個方法之前需要設置_audioRecorder.meteringEnabled = YES才能使用。

AV Foundation開發(fā)秘籍源碼