在 Mac OS X 10.7 中播放视频

Question

在

Mac OS X 10.7（Lion）中使用Objective-C以编程方式播放视频的最简单方法是什么？如果我也想支持OS X 10.6（Snow Leopard）？

我注意到iOS AV Foundation被引入OS X 10.7。不幸的是，该文档似乎是为iOS编写的，我发现它令人困惑。

Answer 1

这是一个NSView子类，它使用AV Foundation（因此Mac OS X 10.7更高版本）播放给定URL的视频。基于 AVSimplePlayer 示例代码。

页眉：

@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

Answer 2

"

最简单"取决于你想做什么。如果你想要更多的控制（例如，将电影渲染为OpenGL纹理）或更少的控制（例如，一个完全独立的窗口，你可以弹出并忽略），可能会有不同的答案。

但对于大多数用例，如果你想要 10.6+ 支持，最简单的电影放映方式是 QTKit。请参阅 Xcode 文档中的文章"使用 QTKit 进行媒体播放"，以获得良好的起点。