在Mac OS X 10.7中播放视频

Question

什么是在Mac OS X 10.7（狮子）中通过Objective-C以编程方式播放视频的最简单方法？如果我还想支持OS X 10.6（Snow Leopard），该怎么办？

我注意到iOS AV Foundation 被引入到了OS X 10.7。不幸的是，文档似乎是为iOS编写的，并且我发现它很令人困惑。

- hpique

---

当苹果公司提出建议时，他们几乎总是推荐最新和最闪亮的API，特别是当它使在OS X和iOS之间移植代码变得容易时。这就是你所谓的“推荐”吗？还是你想要其他开发者的个人经验？因为如果是这种情况，你会得到非常不同的答案（可能涉及QTKit和/或CoreAnimation，但具体取决于你想做什么）。 - abarnert

其他开发者的个人经验。我会重新表述为“最简单的”。 - hpique

Answer 1

这是一个使用AV Foundation播放视频的NSView子类，可以通过URL播放视频（仅适用于Mac OS X 10.7或更高版本）。基于AVSimplePlayer示例代码。

头文件：

@interface RMVideoView : NSView

@property (nonatomic, readonly, strong) AVPlayer* player;
@property (nonatomic, readonly, strong) AVPlayerLayer* playerLayer;
@property (nonatomic, retain) NSURL* videoURL;

- (void) play;

@end

实现：

static void *RMVideoViewPlayerLayerReadyForDisplay = &RMVideoViewPlayerLayerReadyForDisplay;
static void *RMVideoViewPlayerItemStatusContext = &RMVideoViewPlayerItemStatusContext;

@interface RMVideoView()

- (void)onError:(NSError*)error;
- (void)onReadyToPlay;
- (void)setUpPlaybackOfAsset:(AVAsset *)asset withKeys:(NSArray *)keys;

@end

@implementation RMVideoView

@synthesize player = _player;
@synthesize playerLayer = _playerLayer;
@synthesize videoURL = _videoURL;

- (id)initWithFrame:(NSRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        self.wantsLayer = YES;
        _player = [[AVPlayer alloc] init];
        [self addObserver:self forKeyPath:@"player.currentItem.status" options:NSKeyValueObservingOptionNew context:RMVideoViewPlayerItemStatusContext];
    }

    return self;
}

- (void) dealloc {
    [self.player pause];
    [self removeObserver:self forKeyPath:@"player.currentItem.status"];
    [self removeObserver:self forKeyPath:@"playerLayer.readyForDisplay"];
    [_player release];
    [_playerLayer release];
    [_videoURL release];
    [super dealloc];
}

- (void) setVideoURL:(NSURL *)videoURL {
    _videoURL = videoURL;

    [self.player pause];
    [self.playerLayer removeFromSuperlayer];

    AVURLAsset *asset = [AVAsset assetWithURL:self.videoURL];
    NSArray *assetKeysToLoadAndTest = [NSArray arrayWithObjects:@"playable", @"hasProtectedContent", @"tracks", @"duration", nil];
    [asset loadValuesAsynchronouslyForKeys:assetKeysToLoadAndTest completionHandler:^(void) {
        dispatch_async(dispatch_get_main_queue(), ^(void) {
            [self setUpPlaybackOfAsset:asset withKeys:assetKeysToLoadAndTest];
        });
    }];
}

#pragma mark - KVO

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if (context == RMVideoViewPlayerItemStatusContext) {
        AVPlayerStatus status = [[change objectForKey:NSKeyValueChangeNewKey] integerValue];
        switch (status) {
            case AVPlayerItemStatusUnknown:
                break;
            case AVPlayerItemStatusReadyToPlay:
                [self onReadyToPlay];
                break;
            case AVPlayerItemStatusFailed:
                [self onError:nil];
                break;
        }
    } else if (context == RMVideoViewPlayerLayerReadyForDisplay) {
        if ([[change objectForKey:NSKeyValueChangeNewKey] boolValue]) {
            self.playerLayer.hidden = NO;
        }
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}


#pragma mark - Private

- (void)onError:(NSError*)error {
    // Notify delegate 
}

- (void)onReadyToPlay {
    // Notify delegate
}

- (void)setUpPlaybackOfAsset:(AVAsset *)asset withKeys:(NSArray *)keys {
    for (NSString *key in keys) {
        NSError *error = nil;
        if ([asset statusOfValueForKey:key error:&error] == AVKeyValueStatusFailed) {
            [self onError:error];
            return;
        }
    }

    if (!asset.isPlayable || asset.hasProtectedContent) {
        [self onError:nil];
        return;
    }

    if ([[asset tracksWithMediaType:AVMediaTypeVideo] count] != 0) { // Asset has video tracks
        _playerLayer = [AVPlayerLayer playerLayerWithPlayer:self.player];
        self.playerLayer.frame = self.layer.bounds;
        self.playerLayer.autoresizingMask = kCALayerWidthSizable | kCALayerHeightSizable;
        self.playerLayer.hidden = YES;
        [self.layer addSublayer:self.playerLayer];
        [self addObserver:self forKeyPath:@"playerLayer.readyForDisplay" options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew context:RMVideoViewPlayerLayerReadyForDisplay];
    }

    // Create a new AVPlayerItem and make it our player's current item.
    AVPlayerItem *playerItem = [AVPlayerItem playerItemWithAsset:asset];
    [self.player replaceCurrentItemWithPlayerItem:playerItem];  
}

#pragma mark - Public

- (void) play {
    [self.player play];
}

@end

- hpique

---

由于OP想要支持10.6，这并不是很有帮助。但他确实也要求对AVFoundation进行澄清。 - abarnert

@abarnert 我是楼主。我想用AV Foundation的方法来补充你的答案。 - hpique

啊，那样的话，你可能比我更清楚 OP 想要什么。 :) - abarnert

Answer 2

“最简单”的方式取决于你想要做什么。如果你想要更多控制（例如将电影呈现为OpenGL纹理）或更少控制（例如一个完全独立的窗口，你可以随意弹出并忽略），可能会有不同的答案。

但对于大多数用例，如果你需要10.6+支持，显示电影的最简单方法是使用QTKit。请参阅Xcode文档中的文章“使用QTKit进行媒体播放”作为一个很好的起点。

- abarnert