AVF 6 - 视频播放

一、相关说明

1、相关类

• AVPlayerItem，相比 AVAsset（描述资源静态数据），可以描述资源的动态数据，如播放状态等。
• AVPlayer
• AVPlayerLayer

2、精细监听

• 定期监听
• 边界时间监听
• 条目结束监听

二、使用

1、播放视频

// AVPlayerItem's status property
#define STATUS_KEYPATH @"status"

// Refresh interval for timed observations of AVPlayer
#define REFRESH_INTERVAL 0.5f

// Define this constant for the key-value observation context.
static const NSString *PlayerItemStatusContext;


@interface VideoPlayer ()


@property (strong, nonatomic) AVAsset *asset;
@property (strong, nonatomic) AVPlayerItem *playerItem;
@property (strong, nonatomic) AVPlayer *player;  

@property (nonatomic, strong) NSWindow *window;


@end

@implementation VideoPlayer

- (void)setup{
    
    NSString *fileName = @"ElephantSeals.mov";
    NSURL *fileURL = [[NSBundle mainBundle] URLForResource:fileName
                                             withExtension:nil];
    self.asset = [AVAsset assetWithURL:fileURL];
    
    NSArray *keys = @[
        @"tracks",
        @"duration",
        @"commonMetadata",
        @"availableMediaCharacteristicsWithMediaSelectionOptions"
    ];
    self.playerItem = [AVPlayerItem playerItemWithAsset:self.asset
                           automaticallyLoadedAssetKeys:keys]; // 自动异步载入
    
    [self.playerItem addObserver:self
                      forKeyPath:STATUS_KEYPATH
                         options:0
                         context:&PlayerItemStatusContext];
    
    self.player = [AVPlayer playerWithPlayerItem:self.playerItem];
    
    
    // 创建 playerLayer 存放资源内容
    AVPlayerLayer *playerLayer = [AVPlayerLayer playerLayerWithPlayer:self.player];
    playerLayer.videoGravity = AVLayerVideoGravityResizeAspect;
    playerLayer.frame = NSMakeRect(0, 0, 300, 300);
    playerLayer.backgroundColor = [NSColor yellowColor].CGColor;
    
    
    NSUInteger style = NSWindowStyleMaskTitled | NSWindowStyleMaskClosable | NSWindowStyleMaskMiniaturizable;
    self.window = [[NSWindow alloc]initWithContentRect:CGRectMake(0, 0, 400, 400) styleMask:style backing:NSBackingStoreBuffered defer:YES];
    self.window.contentView.wantsLayer = YES;
    self.window.contentView.layer.backgroundColor = [NSColor cyanColor].CGColor;
    [self.window.contentView.layer addSublayer:playerLayer];
    [self.window orderFront:nil];
    self.window.title = @"123";
    
    
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(playOverNotification:) name:AVPlayerItemDidPlayToEndTimeNotification object:self.playerItem];
    
}

#pragma mark - 播放完成
- (void)playOverNotification:(NSNotification *)notification {
    
    
    [self.player seekToTime:kCMTimeZero completionHandler:^(BOOL finished) {
        //        self.playButton.selected = NO;
        //        self.timeLabel.text = @"0/0"; 
    }];
}

#pragma mark - 监听播放状态
- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context {
    
    if (context == &PlayerItemStatusContext) {
        
        dispatch_async(dispatch_get_main_queue(), ^{                        // 1
            
            [self.playerItem removeObserver:self forKeyPath:STATUS_KEYPATH];
            
            if (self.playerItem.status == AVPlayerItemStatusReadyToPlay) { 
                CMTime duration = self.playerItem.duration; 
                [self.player play];              
            } else { 
                NSLog(@"Failed to load video");
            }
        });
    }
}

2、时间监听

#pragma mark - Time Observers
// 更精确的时间监听

// 定期监听
- (void)addPlayerItemTimeObserver {
    
    // Create 0.5 second refresh interval - REFRESH_INTERVAL == 0.5
    CMTime interval =
        CMTimeMakeWithSeconds(REFRESH_INTERVAL, NSEC_PER_SEC);              // 1
    
    // Main dispatch queue
    dispatch_queue_t queue = dispatch_get_main_queue();                     // 2
    
    // Create callback block for time observer
    __weak THPlayerController *weakSelf = self;                             // 3
    void (^callback)(CMTime time) = ^(CMTime time) {
        NSTimeInterval currentTime = CMTimeGetSeconds(time);
        NSTimeInterval duration = CMTimeGetSeconds(weakSelf.playerItem.duration);
        [weakSelf.transport setCurrentTime:currentTime duration:duration];  // 4
    };
    
    // Add observer and store pointer for future use
    self.timeObserver =                                                     // 5
        [self.player addPeriodicTimeObserverForInterval:interval
                                                  queue:queue
                                             usingBlock:callback];
}

// 条目结束监听
- (void)addItemEndObserverForPlayerItem {

    NSString *name = AVPlayerItemDidPlayToEndTimeNotification;

    NSOperationQueue *queue = [NSOperationQueue mainQueue];

    __weak THPlayerController *weakSelf = self;                             // 1
    void (^callback)(NSNotification *note) = ^(NSNotification *notification) {
        [weakSelf.player seekToTime:kCMTimeZero                             // 2
                  completionHandler:^(BOOL finished) {
            [weakSelf.transport playbackComplete];                          // 3
        }];
    };

    self.itemEndObserver =                                                  // 4
        [[NSNotificationCenter defaultCenter] addObserverForName:name
                                                          object:self.playerItem
                                                           queue:queue
                                                      usingBlock:callback];
}

3、生成缩略图

#pragma mark - Thumbnail Generation

- (void)generateThumbnails {
    
    self.imageGenerator =                                                   // 1
        [AVAssetImageGenerator assetImageGeneratorWithAsset:self.asset];
    
    // Generate the @2x equivalent
    self.imageGenerator.maximumSize = CGSizeMake(200.0f, 0.0f);             // 2

    CMTime duration = self.asset.duration;

    NSMutableArray *times = [NSMutableArray array];                         // 3
    CMTimeValue increment = duration.value / 20;
    CMTimeValue currentValue = 2.0 * duration.timescale;
    while (currentValue <= duration.value) {
        CMTime time = CMTimeMake(currentValue, duration.timescale);
        [times addObject:[NSValue valueWithCMTime:time]];
        currentValue += increment;
    }

    __block NSUInteger imageCount = times.count;                            // 4
    __block NSMutableArray *images = [NSMutableArray array];

    AVAssetImageGeneratorCompletionHandler handler;                         // 5
    
    handler = ^(CMTime requestedTime,
                CGImageRef imageRef,
                CMTime actualTime,
                AVAssetImageGeneratorResult result,
                NSError *error) {

        if (result == AVAssetImageGeneratorSucceeded) {                     // 6
            UIImage *image = [UIImage imageWithCGImage:imageRef];
            id thumbnail =
                [THThumbnail thumbnailWithImage:image time:actualTime];
            [images addObject:thumbnail];
        } else {
            NSLog(@"Error: %@", [error localizedDescription]);
        }

        // If the decremented image count is at 0, we're all done.
        if (--imageCount == 0) {                                            // 7
            dispatch_async(dispatch_get_main_queue(), ^{
                NSString *name = THThumbnailsGeneratedNotification;
                NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
                [nc postNotificationName:name object:images];
            });
        }
    };

    [self.imageGenerator generateCGImagesAsynchronouslyForTimes:times       // 8
                                              completionHandler:handler];
}