iOS音频视频简单介绍

音频##

常用的音频API######

• SystemSoundServices
• AVAudioPlayer
• MPMusicPlayerController
• AVAudioRecorder
• OpenAL
• AudioUnits
  其中最常用的还是 SystemSoundServices 和 AVAudioPlayer

---

System Sound Services######

C形式接口，属于AudioToolBox框架，这个框架可以将比较短的声音注册到 system sound服务上。被注册到system sound服务上的声音称之为 system sounds。比如其中的播放API AudioServicesPlaySystemSound()，但是只可以播放一些简单的音频文件，此方法它只适合播放一些很小的提示或者是警告音，并有很多限制：
1> 长度小于30秒的Core Audio Format (.caf), Waveform audio (.wav), 或者 Audio Interchange File (.aiff)
2> 调用后立即播放，并且声音的进度无法控制
3> 没有循环播放和立体声控制

SystemSound常用的方法######

• AudioServicesCreateSystemSoundID 从URL创建声音
• AydioServicesDisposeSystemSoundID 播放完成时删除声音
• AudioServicesAddSystemSoundCompletion 播放完成时回调
• AudioServicesRemoveSystemSoundCompletion 播放完成时删除回调
• AudioServicesPlaySystemSound 播放

Demo示例(首先要把push.wav托到项目中去)：
导入 AudioToolbox.framework 并且
#import

@interface RootViewController ()

@property(nonatomic) SystemSoundID soundID;
@end

@implementation RootViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    UILabel *label        = [[UILabel alloc] initWithFrame:CGRectMake(20, 40, self.view.bounds.size.width - 40, 40)];
    label.backgroundColor = [UIColor darkGrayColor];
    label.textAlignment   = NSTextAlignmentCenter;
    label.text      = @"System Sound Services 方式";
    label.textColor = [UIColor whiteColor];
    [self.view addSubview:label];
    UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
    CGRect frame     = label.frame;
    frame.origin.y   = CGRectGetMaxY(label.frame) + 10.0;
    button.frame = frame;
    [button setTitle:@"播放" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(systemSoundPlay:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
}

static void finishCompletion()
{
    UIAlertView *alert = [[UIAlertView alloc]
                               initWithTitle:@"提示"
                               message:@"播放结束"
                               delegate:nil
                               cancelButtonTitle:@"确定"
                               otherButtonTitles:nil,
                               nil];
    [alert show];
    [alert release];
    
    // 震动设备
    AudioServicesPlaySystemSound(kSystemSoundID_Vibrate);
    
    /**
     enum
     {
         #if TARGET_OS_IPHONE
         kSystemSoundID_Vibrate              = 0x00000FFF
         #else
         kSystemSoundID_UserPreferredAlert   = 0x00001000,
         kSystemSoundID_FlashScreen          = 0x00000FFE,
         // this has been renamed to be consistent
         kUserPreferredAlert     = kSystemSoundID_UserPreferredAlert
         #endif
     };
     */
}

- (void)systemSoundPlay:(UIButton *)button
{
    // 初始化URL
    NSString *path = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"push.wav"]; // 注意，首先要把push.wav文件放到项目中
    NSURL *url = [NSURL fileURLWithPath:path];
    
    // 创建声音
    OSStatus error = AudioServicesCreateSystemSoundID((CFURLRef)url, &_soundID);

    // 增加回调 simpleSoundFinishCompletion
    AudioServicesAddSystemSoundCompletion(self.soundID, nil, nil, finishCompletion, nil);
    
    if (error) {
        UIAlertView *alert = [[UIAlertView alloc]
                              initWithTitle:@"提示"
                              message:@"加载声音文件错误!"
                              delegate:nil
                              cancelButtonTitle:@"确定"
                              otherButtonTitles:nil,
                              nil];
        [alert show];
        [alert release];
    } else {
        AudioServicesPlaySystemSound(self.soundID);
    }
}

@end

---

AVAudioPlayer######

AVAudioPlayer属于AVFoundation框架，对于压缩过Audio文件，或者超过30秒的音频文件，可以使用AVAudioPlayer类，这个类定义在AVFoundation framework中，因此要导入 AVFoundation framwork, 并且 #import
下面通过一个录音和播放录音的Demo示例展示：

#import "RootViewController.h"
#import 

@interface RootViewController () 

@property (nonatomic, retain) NSURL *soundURL;

@property (nonatomic, retain) UIButton *recordBtn;
@property (nonatomic, retain) UIButton *playBtn;

@property (nonatomic, retain) AVAudioRecorder *recorder;
@property (nonatomic, retain) AVAudioPlayer *player;
@end

@implementation RootViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    [self initUI];
    
    // 初始化录音文件的路径
    NSString *soundFilePath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"sound.caf"];
    self.soundURL = [NSURL fileURLWithPath:soundFilePath];
    
    // 建立音频会话
    AVAudioSession *audioSession = [AVAudioSession sharedInstance];
    [[NSNotificationCenter defaultCenter] addObserver: self
                                             selector: @selector(handleInterruption:)
                                                 name: AVAudioSessionInterruptionNotification
                                               object: audioSession];
    [audioSession setActive:YES error:nil];
    /**
        AudioSession ...
     */
}

- (void)handleInterruption:(NSNotification *)notification
{
    NSLog(@"%s", __func__);
}

- (void)initUI
{
    UILabel *label        = [[UILabel alloc] initWithFrame:CGRectMake(20, 40, self.view.bounds.size.width - 40, 40)];
    label.backgroundColor = [UIColor darkGrayColor];
    label.textAlignment   = NSTextAlignmentCenter;
    label.text            = @"AVAudioRecorder/AVAudioPlayer";
    label.textColor       = [UIColor whiteColor];
    [self.view addSubview:label];
    
    self.recordBtn       = [UIButton buttonWithType:UIButtonTypeSystem];
    CGRect frame         = label.frame;
    frame.origin.y       = CGRectGetMaxY(label.frame) + 10.0;
    frame.size.width     = frame.size.width / 2.0;
    self.recordBtn.frame = frame;
    [self.recordBtn setTitle:@"录制" forState:UIControlStateNormal];
    [self.recordBtn addTarget:self action:@selector(record:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:self.recordBtn];
    
    self.playBtn       = [UIButton buttonWithType:UIButtonTypeSystem];
    frame.origin.x    += frame.size.width;
    self.playBtn.frame = frame;
    [self.playBtn setTitle:@"播放" forState:UIControlStateNormal];
    [self.playBtn addTarget:self action:@selector(play:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:self.playBtn];
}

- (void)record:(UIButton *)button
{
    if (self.recorder.isRecording) {
        [self stopRecord];
    } else {
        [self beginRecord];
    }
}

- (void)play:(UIButton *)button
{
    if (self.recorder.isRecording) {
        [self stopRecord];
    }
    if (self.player.isPlaying) {
        [self stopPlay];
    } else {
        [self beginPlay];
    }
}

- (void)beginRecord
{
    // 更新 AVAudioSession 状态
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryRecord error:nil];
    
    // 设置属性
    NSDictionary *recordSettings =
    [[NSDictionary alloc] initWithObjectsAndKeys:
     [NSNumber numberWithFloat: 44100.0],                 AVSampleRateKey,
     [NSNumber numberWithInt: kAudioFormatAppleLossless], AVFormatIDKey,
     [NSNumber numberWithInt: 1],                         AVNumberOfChannelsKey,
     [NSNumber numberWithInt: AVAudioQualityMax],         AVEncoderAudioQualityKey,
     nil];
    
    // 创建 AVAudioRecorder
    AVAudioRecorder *recorder = [[AVAudioRecorder alloc] initWithURL:self.soundURL
                                                            settings:recordSettings
                                                               error:nil];
    self.recorder = recorder;
    [recorder release];
    [self.recorder prepareToRecord];
    [self.recorder record];
    
    [self.recordBtn setTitle:@"停止" forState:UIControlStateNormal];
}

- (void)stopRecord
{
    [self.recorder stop];
    [self.recordBtn setTitle:@"录制" forState:UIControlStateNormal];
    [[AVAudioSession sharedInstance] setActive:NO error:nil];
}

- (void)beginPlay
{
    NSError *error = nil;
    AVAudioSession *session = [AVAudioSession sharedInstance];
    [session setCategory:AVAudioSessionCategoryPlayback error:&error];
    if (error) {
        NSLog(@"error occured: %@", error.userInfo);
        [self stopPlay];
        return ;
    }
    AVAudioPlayer *player = [[AVAudioPlayer alloc] initWithContentsOfURL:self.soundURL error:&error];
    self.player = player;
    if (error) {
        NSLog(@"error occured: %@", error.userInfo);
        return ;
    }
    [self.player setDelegate:self];
    [self.player prepareToPlay];
    
    [self.playBtn setTitle:@"停止" forState:UIControlStateNormal];
}

- (void)stopPlay
{
    [self.player stop];
    [self.playBtn setTitle:@"播放" forState:UIControlStateNormal];
}

#pragma mark - 
- (void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag
{}

#pragma mark - dealloc
- (void)dealloc
{
    [_soundURL release];
    [_recordBtn release];
    [_playBtn release];
    [_recorder release];
    [_player release];
    [super dealloc];
}

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