如何在 AVFoundation 中显示视频的剪切/部分

Question

我正在尝试在 AVFoundation 中裁剪视频/显示视频的一部分。 到目前为止，我的代码对我来说是正确的，但 output 不是我想要的。 我看不出有什么问题。 有任何想法吗？

let item = AVPlayerItem(url: nextVideoItem.url)
let cropRect = CGRect(x: 200, y: 200, width: 300, height: 300)
let cropComposition = AVMutableVideoComposition(asset: item.asset, applyingCIFiltersWithHandler: { request in    
    let cropFilter = CIFilter(name: "CICrop")!
    cropFilter.setValue(request.sourceImage, forKey: kCIInputImageKey)
    cropFilter.setValue(CIVector(cgRect: cropRect), forKey: "inputRectangle")
    
    let imageAtOrigin = cropFilter.outputImage!.transformed(by: CGAffineTransform(translationX: -cropRect.origin.x, y: -cropRect.origin.y))
    request.finish(with: imageAtOrigin, context: nil)
})
cropComposition.renderSize = cropRect.size
item.videoComposition = cropComposition
self.player.replaceCurrentItem(with: item)
self.player.play()

Answer 1

上面的代码本身运行良好，您看不到它的原因可能是您没有在周围的 UI 代码中正确设置 AVPlayerViewController 视图或 AVPlayerLayer 的框架。 这是一个 Swift Playground 代码片段，它使用您在上面指定的裁剪来播放视频资产：

import UIKit
import AVKit
import PlaygroundSupport

class MyViewController : UIViewController {
    var player: AVPlayer!
    var avLayer: AVPlayerLayer!
    
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white

        player = AVPlayer()
        
        let item = AVPlayerItem(url: #fileLiteral(resourceName: "logos.mov"))
        
        let cropRect = CGRect(x: 500, y: 250, width: 480, height: 320)
        let cropComposition = AVMutableVideoComposition(asset: item.asset, applyingCIFiltersWithHandler: { request in
            let cropFilter = CIFilter(name: "CICrop")!
            cropFilter.setValue(request.sourceImage, forKey: kCIInputImageKey)
            cropFilter.setValue(CIVector(cgRect: cropRect), forKey: "inputRectangle")
            
            let imageAtOrigin = cropFilter.outputImage!.transformed(by: CGAffineTransform(translationX: -cropRect.origin.x, y: -cropRect.origin.y))
            request.finish(with: imageAtOrigin, context: nil)
        })
        cropComposition.renderSize = cropRect.size
        item.videoComposition = cropComposition
        self.player.replaceCurrentItem(with: item)
        self.player.play()
        
        avLayer = AVPlayerLayer()
        avLayer.player = self.player
        view.layer.addSublayer(avLayer)
        self.view = view
    }
    
    override func viewDidAppear(_ animated: Bool) {
        // this is the important bit
        avLayer.frame = view.bounds
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()

Answer 2

cropScaleComposition未定义，但在以下行中使用：

item.videoComposition = cropScaleComposition

缩放到零/空/未定义，如果甚至可以编译？，肯定会导致空屏幕。