动画AVPlayerLayer videoGravity属性 [英] Animate AVPlayerLayer videoGravity property

问题描述

我正在尝试复制Apple在视频播放中的行为，允许用户拉伸视频图像以填充边界。

I'm trying to copy Apple's behavior in video playback that allows the user to stretch the video image to fill the bounds.

@interface FHVideoPlayerView : UIView
@end
@interface FHVideoPlayerView

+ (Class)layerClass
{
    return [AVPlayerLayer class];
}

- (void)setAspectMode:(FHVideoPlayerAspectMode)aspectMode animated:(BOOL)animated
{
    FHVideoPlayerAspectMode current = [self aspectMode];
    FHVideoPlayerAspectMode final   = aspectMode;

    NSString *fromValue;
    NSString *toValue;

    AVPlayerLayer *layer = (AVPlayerLayer *)[self layer];

    switch (current) {
        case FHVideoPlayerAspectFill:
            fromValue = AVLayerVideoGravityResizeAspectFill;
            break;
        case FHVideoPlayerAspectFit:
            fromValue = AVLayerVideoGravityResizeAspect;
            break;
       default:
           break;
    }

    switch (final) {
        case FHVideoPlayerAspectFill:
            toValue = AVLayerVideoGravityResizeAspectFill;
            break;
        case FHVideoPlayerAspectFit:
            toValue = AVLayerVideoGravityResizeAspect;
            break;
        default:
            break;
    }

    if (toValue != fromValue) {
        if (animated == YES) {
            // Manually added CABasicAnimation based on the understanding the implicit animations are disabled for CALayers that back a UIView
            CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"videoGravity"];
            [layer addAnimation:animation forKey:@"animateVideoGravity"];

            [CATransaction begin];
            [CATransaction setAnimationDuration:0.333];
        }

        [layer setVideoGravity:toValue];

        if (animated == YES) {
            [CATransaction commit];
        }
    }
}

我工作正常尝试为不透明度等数字属性设置动画。但是，你会从类引用中注意到，AVPlayerLayer的videoGravity属性是一个NSString。类引用确实指出它是可动画的。

This works just fine when I try and animate a numeric property such as opacity. But, you'll notice from the class reference, AVPlayerLayer's videoGravity property is an NSString. The class reference does points out that it is animatable.

所以我的问题是：如何！？

So my question is: How!?

I相信这可能与CALayer的内容属性以及可能的contentsGravity有关。

I believe this is probably related somehow to CALayer's content property and possibly contentsGravity.

推荐答案

正如voromax所指出的，这是iOS中的一个错误5.0。我在iOS 5.1中反向设计了 - [AVPlayerLayer setVideoGravity：] 实现，以便了解动画应该如何工作。以下是如何解决这个错误，并在iOS 5.0上有一个很好的动画。

As voromax pointed out, this is a bug in iOS 5.0. I reverse engineered -[AVPlayerLayer setVideoGravity:] implementation in iOS 5.1 in order to understand how the animation was supposed to work. Here is how to workaround the bug and have a nice animation on iOS 5.0.

@implementation VideoPlayerView

+ (Class) layerClass
{
    return [AVPlayerLayer class];
}

- (AVPlayerLayer *) playerLayer
{
    return (AVPlayerLayer *)[self layer];
}

- (NSString *) videoGravity
{
    return self.playerLayer.videoGravity;
}

- (void) setVideoGravity:(NSString *)videoGravity
{
    self.playerLayer.videoGravity = videoGravity;

    // Workaround a bug in iOS 5.0
    float avFoundationVersion = [[[NSBundle bundleForClass:[AVPlayerLayer class]] objectForInfoDictionaryKey:(NSString *)kCFBundleVersionKey] floatValue];
    if (avFoundationVersion < 292.24f)
    {
        @try
        {
            NSString *contentLayerKeyPath = [NSString stringWithFormat:@"%1$@%2$@.%3$@%2$@", @"player", [@"layer" capitalizedString], @"content"]; // playerLayer.contentLayer
            CALayer *contentLayer = [self.playerLayer valueForKeyPath:contentLayerKeyPath];
            if ([contentLayer isKindOfClass:[CALayer class]])
                [contentLayer addAnimation:[CABasicAnimation animation] forKey:@"sublayerTransform"];
        }
        @catch (NSException *exception)
        {
        }
        self.bounds = self.bounds;
    }
}

@end

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