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，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（因此仅适用于 Mac OS X 10.7 以上）播放给定 URL 的视频。基于AVSimplePlayer 示例代码。

标题：

@interface RMVideoView : NSView

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

- (void) play;

@end

实施：

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”取决于您想要做什么。如果您想要更多控制（例如，将影片渲染为 OpenGL 纹理）或更少（例如，您可以弹出并忽略的完全独立的窗口），可能会有不同的答案。

但是对于大多数用例，如果您想要 10.6+ 的支持，那么显示电影的最简单方法是 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。