多媒体

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一、音频

iOS里面有四种专门实现播放音频的方式：
1、system sound services（系统声音服务）
2、OpenAL（跨平台的开放音频处理借口）
3、audio queue services（播放和录制音频的服务）
4、AVAudioPlayer（高级音频播放器）

system sound services

适用场景：播放一些很小的提示，或者警告音
局限性：
1、声音长度要小于30秒
2、格式：IMA4
3、不能控制播放的进度
4、调用方法后立即播放声音
5、没有循环播放和立体声播放

实例代码

//路径NSString* path = [[NSBundle mainBundle] pathForResource:@"news" ofType:@"wav"];    //播放指定音频时，需要的路径为url    NSURL *musicPath = [NSURL fileURLWithPath:path];    //创建soundID，播放系统提示音，或者指定的音频文件，系统都是根据soundID来寻找音频文件。大小范围为1000-2000    SystemSoundID mySoundID;    //创建播放器并播放    AudioServicesCreateSystemSoundID((__bridge CFURLRef)musicPath, &mySoundID);    AudioServicesPlaySystemSound(mySoundID);

还有另外一种播放的方法

    //路径    CFBundleRef mainBundle;    //系统声音    SystemSoundID soundID;    mainBundle = CFBundleGetMainBundle();    CFURLRef URLRef = CFBundleCopyResourceURL(mainBundle, CFSTR("news"), CFSTR("wav"), NULL);    AudioServicesCreateSystemSoundID(URLRef, &soundID);    AudioServicesPlaySystemSound(soundID);

OpenAL

OpenAL是一套跨平台的开源的音频处理接口
最适合开发游戏的音频
OpenAL包括三个实体
listener（听者）
source（资源）
buffer（缓存）
OpenAL资料网址：
网址一
网址二

Audio Queue Services

audio queue services主要用来实现录制音频，为了简化音频文件的处理，通常哈需要使用到Audio file services。
相对底层的api，参考
http://blog.csdn.net/midfar/article/details/7233454
我们可以吧AVAudioPlayer看做是一个高级播放器，它支持的音频格式，如下：
* AAC
* AMR
* ALAC
* iLBC
* IMA4
* linearPCM
* MP3
开发步骤：
首先，导入AVFoundation框架
其次，AVAudioPlayer在初始化的时候要给一个播放文件
再然后，就是对一些属性进行设置了。
代码如下：

//得到音频资源    NSString *musicPath = [[NSBundle mainBundle] pathForResource:@"112" ofType:@"mp3"];    //转化文件地址    NSURL* url = [NSURL fileURLWithPath:musicPath];    _player = [[AVAudioPlayer alloc] initWithContentsOfURL:url error:nil];    //设置声音    [_player setVolume:1.0];    self.valumSlider.value = self.player.volume;    self.volumValue.text = [NSString stringWithFormat:@"%.0f", self.player.volume*100];    //准备播放    [_player prepareToPlay];    //播放//    [_player play];

播放暂停按钮的逻辑

if ([_play.titleLabel.text isEqualToString:@"播放"]) {        [_play setTitle:@"暂停" forState:UIControlStateNormal];         BOOL isplay = [_player play];        if (isplay) {            [self.timer setFireDate:[NSDate distantPast]];        }else{            NSLog(@"播放有误");        }        NSLog(@"点击了播放");    }    else{        [_play setTitle:@"播放" forState:UIControlStateNormal];        [_player pause];        [self.timer setFireDate:[NSDate distantFuture]];        NSLog(@"点击了暂停");    }

停止播放按钮的逻辑

 NSLog(@"停止");    //归零    [_player setCurrentTime:0];    [_player stop];    [self.timer setFireDate:[NSDate distantFuture]];    self.progressSlider.value = 0;    if ([self.play.titleLabel.text isEqualToString:@"暂停"]) {        [self.play setTitle:@"播放" forState:UIControlStateNormal];    }

二、视频

iOS里面的视频播放用到的是AVPlayer（包含在AVFoundation里面）与AVAudioPlayer有点类似，但是其功能更加强大
直接上代码：
一些控件的初始化：

@property (nonatomic, retain)AVPlayer*player;@property (nonatomic, retain)AVPlayerItem*playerItem;//播放元素@property (nonatomic, retain)AVPlayerLayer*playerLayer;//显示视屏的层@property (nonatomic, assign)BOOL isreadtoplay;//判断是否已经开始视屏_isreadtoplay = NO;    //监听通知中心中的某一条消息    //关心对象，回调方法，消息名称，标记    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(videofinish:) name:AVPlayerItemDidPlayToEndTimeNotification object:nil];    self.navigationItem.title = @"高级播放";//        [self localMusicalPlay];    NSLog(@"进入页面");    //滑竿    UISlider *progressSilder = [[UISlider alloc]initWithFrame:CGRectMake(50, 400, 150, 80)];    [self.view addSubview:progressSilder];    progressSilder.tag = 1000;    progressSilder.minimumValue = 0;    progressSilder.value = 0;    [progressSilder addTarget:self action:@selector(didChangeValue:) forControlEvents:UIControlEventValueChanged];     [self localVadio];

-(void)localVadio{    NSString *stringPath = [[NSBundle mainBundle] pathForResource:@"9533522808" ofType:@"mp4"];    NSURL* url = [NSURL fileURLWithPath:stringPath];    //时间监听者监听事键    _playerItem = [AVPlayerItem playerItemWithURL:url];    _player = [AVPlayer playerWithPlayerItem:_playerItem];    //初始化layer    _playerLayer = [AVPlayerLayer playerLayerWithPlayer:_player];    //将视屏层添加到当前界面的layer上    [self.view.layer addSublayer:_playerLayer];    _playerLayer.frame = CGRectMake(0, 60, 400, 300);    _playerLayer.videoGravity = AVLayerVideoGravityResizeAspect;    //为视屏添加观察者    [_playerItem addObserver:self forKeyPath:@"status" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];}

-(void)localMusicalPlay{    //先取得本地音频文件    NSString *stringPath = [[NSBundle mainBundle] pathForResource:@"113" ofType:@"mp3"];    NSURL* url = [NSURL fileURLWithPath:stringPath];    _playerItem = [AVPlayerItem playerItemWithURL:url];    //kvo 观察某对象属性的变化    [_playerItem addObserver:self forKeyPath:@"status" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];    //初始化播放器    _player = [AVPlayer playerWithPlayerItem:_playerItem];    //播放    [_player play];

#pragma kvo 的回调方法-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context{    AVPlayerItem* item = (AVPlayerItem*)object;//    AVPlayerStatus status = change[NSKeyValueChangeNewKey];    NSLog(@"%@",change[NSKeyValueChangeNewKey]);    NSLog(@"old%@",change[NSKeyValueChangeOldKey]);    NSLog(@"%@",item);    //得到改变之后的属性    AVPlayerStatus status = [change [NSKeyValueChangeNewKey] intValue];    switch (status) {        case AVPlayerStatusUnknown:            NSLog(@"未知");            break;        case AVPlayerStatusFailed:            NSLog(@"失败");            break;        case AVPlayerStatusReadyToPlay:{            NSLog(@"准备");            [_player play];            float sum = self.playerItem.duration.value/self.playerItem.duration.timescale*1.0;            UISlider* temop = [self.view viewWithTag:1000];            temop.maximumValue = sum;             _isreadtoplay = YES;            NSLog(@"%f------",sum);        }            break;        default:            break;    }    //移除观察者；    [item removeObserver:self forKeyPath:@"status"];}

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