iOS使用AVPlayer播放视频

在iOS开发中，播放视频通常有两种方式，一种是使用MPMoviePlayerController（需要导入MediaPlayer.Framework），还有一种是使用AVPlayer。关于这两个类的区别可以参考http://stackoverflow.com/questions/8146942/avplayer-and-mpmovieplayercontroller-differences，简而言之就是MPMoviePlayerController使用更简单，功能不如AVPlayer强大，而AVPlayer使用稍微麻烦点，不过功能更加强大。这篇博客主要介绍下AVPlayer的基本使用，由于博主也是刚刚接触，所以有问题大家直接指出~

0x01.新建一个ViewController类并添加下面代码

在开发中，单纯使用AVPlayer类是无法显示视频的，要将视频层添加至AVPlayerLayer中，这样才能将视频显示出来，所以先在ViewController的@interface中添加以下属性

viewController.m

@property (nonatomic,strong) AVPlayer      *avPlayer;
@property (nonatomic,strong) AVPlayerItem  *avPlayerItem;
@property (nonatomic,strong) AVPlayerLayer *avPlayerLayer;

在viewDidLoad中写下下面代码。

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    self.avPlayerItem = [AVPlayerItem playerItemWithURL:self.videoUrl];
    //对item添加监听
    [self.avPlayerItem addObserver:self forKeyPath:@"status" options:NSKeyValueObservingOptionNew context:nil];
    [self.avPlayerItem addObserver:self forKeyPath:@"loadedTimeRanges" options:NSKeyValueObservingOptionNew context:nil];
    //[self.playItem addObserver:self forKeyPath:@"playbackBufferEmpty" options:NSKeyValueObservingOptionNew context:nil];
    
    self.avPlayer      = [AVPlayer playerWithPlayerItem:self.avPlayerItem];
    self.avPlayerLayer = [AVPlayerLayer playerLayerWithPlayer:self.avPlayer];

    AVPlayView *avPlayerView = [[AVPlayView alloc] initWithMoviePlayerLayer:self.avPlayerLayer frame:self.view.bounds];
    avPlayerView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    [self.view addSubview:avPlayerView];
    
    //这里可以实现界面代码。
    //[self initSubViews];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(moviePlayDidEnd) name:AVPlayerItemDidPlayToEndTimeNotification object:nil];
}

- (void)moviePlayDidEnd
{
    NSLog(@"播放完成");
    [self.avPlayer pause];
    [self.link invalidate];
    [self dismissViewControllerAnimated:YES completion:nil];
}

其中playerView继承自UIView，不过重写了set和get方法，用于将player添加至playerView的AVPlayerLayer中，这样才能顺利将视频显示出来

0x02.新建一个AVPlayerView:UIView类并添加下面代码。

在PlayerView.h中声明一个AVPlayer对象，由于默认的layer是CALayer，而AVPlayer只能添加至AVPlayerLayer中，所以我们改变一下layerClass，这样PlayerView的默认layer就变了，之后我们可以把在viewController中初始化的AVPlayer对象赋给AVPlayerLayer的player属性。

AVPlayerView.h

　@property (nonatomic ,strong) AVPlayer *player;

AVPlayerView.m

#import "AVPlayView.h"


@interface AVPlayView()
{
    AVPlayerLayer *_playerlayer;
}
@end

@implementation AVPlayView

-(instancetype)initWithMoviePlayerLayer:(AVPlayerLayer *)playerLayer frame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        _playerlayer = playerLayer;
        playerLayer.backgroundColor =  [UIColor blackColor].CGColor;
        _playerlayer.videoGravity   = AVLayerVideoGravityResizeAspect;
        _playerlayer.contentsScale  = [UIScreen mainScreen].scale;
        [self.layer addSublayer:_playerlayer];
    }
    return self;
}

-(void)layoutSublayersOfLayer:(CALayer *)layer{
    [super layoutSublayersOfLayer:layer];
    
    _playerlayer.bounds   = self.layer.bounds;
    _playerlayer.position = self.layer.position;
}

0x03.实现视频的播放：

第一步在viewDidLoad中执行初始化：

先将在线视频链接存放在videoUrl中，然后初始化playerItem，playerItem是管理资源的对象

然后监听playerItem的status和loadedTimeRange属性，status有三种状态：

AVPlayerStatusUnknown,
AVPlayerStatusReadyToPlay,
AVPlayerStatusFailed

当status等于AVPlayerStatusReadyToPlay时代表视频已经可以播放了，我们就可以调用play方法播放了。
loadedTimeRange属性代表已经缓冲的进度，监听此属性可以在UI中更新缓冲进度，也是很有用的一个属性。
最后添加一个通知，用于监听视频是否已经播放完毕，然后实现KVO的方法：

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    AVPlayerItem *playerItem = (AVPlayerItem *)object;
    
    if ([keyPath isEqualToString:@"loadedTimeRanges"]){
        NSTimeInterval loadedTime = [self availableDurationWithplayerItem:playerItem];
        NSTimeInterval totalTime = CMTimeGetSeconds(playerItem.duration);
        
        //if (!self.slider.isSliding) {
            //self.slider.progressPercent = loadedTime/totalTime;
        //}
        
    }else if ([keyPath isEqualToString:@"status"]){
        if (playerItem.status == AVPlayerItemStatusReadyToPlay){
            //NSLog(@"playerItem is ready");
            
            [self.avPlayer play];
            self.slider.enabled = YES;
            self.playButton.enabled = YES;
        } else{
            NSLog(@"load break");
            //self.faildView.hidden = NO;
        }
    }
}

- (NSTimeInterval)availableDurationWithplayerItem:(AVPlayerItem *)playerItem
{
    NSArray *loadedTimeRanges = [playerItem loadedTimeRanges];
    CMTimeRange timeRange = [loadedTimeRanges.firstObject CMTimeRangeValue];// 获取缓冲区域
    NSTimeInterval startSeconds = CMTimeGetSeconds(timeRange.start);
    NSTimeInterval durationSeconds = CMTimeGetSeconds(timeRange.duration);
    NSTimeInterval result = startSeconds + durationSeconds;// 计算缓冲总进度
    return result;
}

此方法主要对status和loadedTimeRanges属性做出响应，status状态变为AVPlayerStatusReadyToPlay时，说明视频已经可以播放了，这时我们可以获取一些视频的信息，包含视频长度等，把播放按钮设备enabled，点击就可以调用play方法播放视频了。在AVPlayerStatusReadyToPlay的底部还有个monitoringPlayback方法：

- (void)monitoringPlayback:(AVPlayerItem *)playerItem {
  self.playbackTimeObserver = [self.playerView.player addPeriodicTimeObserverForInterval:CMTimeMake(1, 1) queue:NULL usingBlock:^(CMTime time) {   
  CGFloat currentSecond = playerItem.currentTime.value/playerItem.currentTime.timescale;
 // 计算当前在第几秒 
  [self updateVideoSlider:currentSecond]; 
 NSString *timeString = [self convertTime:currentSecond]; 
 self.timeLabel.text = [NSString stringWithFormat:@"%@/%@",timeString,_totalTime]; }]; 
}

monitoringPlayback用于监听每秒的状态，- (id)addPeriodicTimeObserverForInterval:(CMTime)interval queue:(dispatch_queue_t)queue usingBlock:(void (^)(CMTime time))block;此方法就是关键，interval参数为响应的间隔时间，这里设为每秒都响应，queue是队列，传NULL代表在主线程执行。可以更新一个UI，比如进度条的当前时间等。

0x04.播放器其他元素。

这里只介绍播放方法，具体暂停功能、播放进度、时间显示等在这里不做讨论。