Determine size/aspect ratio of video for SKVideoNode in SceneKit

问题

How can I get the video size of a video from AVPlayer to set the geometry size of my node?

For example, I have an SCNPlane with a width and height

let planeGeo = SCNPlane(width: 5, height: 5)

So now I instantiate my video player

let videoURL = NSURL(string: someURL)
let player = AVPlayer(URL: videoURL!)

and my SKVideoNode

let spriteKitScene = SKScene(size: CGSize(width: 1920, height: 1080))
spriteKitScene.scaleMode = .AspectFit

videoSpriteKitNode = SKVideoNode(AVPlayer: player)
videoSpriteKitNode.anchorPoint = CGPointMake(0,0)
videoSpriteKitNode.size.width = spriteKitScene.size.width
videoSpriteKitNode.size.height = spriteKitScene.size.height

spriteKitScene.addChild(videoSpriteKitNode)

planeGeo!.firstMaterial.diffuse.contents = spriteKitScene
videoSpriteKitNode.play()

So now I want to have the video size to resize my plane to a correct aspect ratio. I already fiddled around with AVLPlayerLayer but this gives me always 0

let avLayer = AVPlayerLayer(player: player)
print(avLayer.videoRect.width) //0
print(avLayer.videoRect.height) //0

Also I tried that here but it doesn't work as well

let avLayer = AVPlayerLayer(player: player)
let layer = avLayer.sublayers![0]
let transformedBounds = CGRectApplyAffineTransform(layer.bounds, CATransform3DGetAffineTransform(layer.sublayerTransform))
print(transformedBounds.width) //0
print(transformedBounds.height) //0

回答1:

Ok I figured it out, KVO is the way to go. Add in viewDidLoad:

player.currentItem?.addObserver(self, forKeyPath: "presentationSize", options: .New, context: nil)

in deinit:

player.currentItem?.removeObserver(self, forKeyPath: "presentationSize")

and then add:

override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {

    if keyPath == "presentationSize" {
        if let item = object as? AVPlayerItem {
            let size = item.presentationSize
            let width = size.width
            let height = size.height

            //Set size of geometry here
        }
    }
}

来源：https://stackoverflow.com/questions/34928396/determine-size-aspect-ratio-of-video-for-skvideonode-in-scenekit