swift – 无法使用AVVideoCompositionCoreAnimationTool在视频中

更新6：
我已经设法完全解决了我的问题,但我仍然想要一个更好的解释,而不是我猜的是如果我不正确它是不起作用的原因

我一直试图在视频上制作精灵表,但每次导出视频时,最终结果都是我开始的示例视频.

这是我的代码：

首先我的自定义CALayer来处理我自己的精灵表

class SpriteLayer: CALayer {
    var frameIndex: Int

    override init() {
        // Using 0 as a default state
        self.frameIndex = 0
        super.init()
    }

    required init?(coder aDecoder: NSCoder) {
        self.frameIndex = 0
        super.init(coder: aDecoder)
    }

    override func display() {
        let currentFrameIndex = self.frameIndex
        if currentFrameIndex == 0 {
            return
        }
        let frameSize = self.contentsRect.size
        self.contentsRect = CGRect(x: 0,y: CGFloat(currentFrameIndex - 1) * frameSize.height,width: frameSize.width,height: frameSize.height)
    }

    override func action(forKey event: String) -> CAAction? {
        if event == "contentsRect" {
            return nil
        }
        return super.action(forKey: event)
    }

    override class func needsDisplay(forKey key: String) -> Bool {
        return key == "frameIndex"
    }
}

Gif是一个没有花哨的基本课程,工作得很好. gif.Strip是表示gif的垂直精灵表的UIImage.

现在出现了应该导出新视频的方法(它是用于导出的更大类的一部分.

func convertAndExport(to url :URL,completion: @escaping () -> Void ) {
        // Get Initial info and make sure our destination is available
        self.outputURL = url
        let stripCgImage = self.gif.strip!.cgImage!
        // This is used to time how long the export took
        let start = DispatchTime.now()
        do {
            try FileManager.default.removeItem(at: outputURL)
        } catch {
            print("Remove Error: (error.localizedDescription)")
            print(error)
        }
        // Find and load "sample.mp4" as a AVAsset
        let videoPath = Bundle.main.path(forResource: "sample",ofType: "mp4")!
        let videoUrl = URL(fileURLWithPath: videoPath)
        let videoAsset = AVAsset(url: videoUrl)
        // Start a new mutable Composition with the same base video track
        let mixComposition = AVMutableComposition()
        let compositionVideoTrack = mixComposition.addMutableTrack(withMediaType: .video,preferredTrackID: kCMPersistentTrackID_Invalid)!
        let clipVideoTrack = videoAsset.tracks(withMediaType: .video).first!
        do {
            try compositionVideoTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero,videoAsset.duration),of: clipVideoTrack,at: kCMTimeZero)
        } catch {
            print("Insert Error: (error.localizedDescription)")
            print(error)
            return
        }
        compositionVideoTrack.preferredTransform = clipVideoTrack.preferredTransform
        // Quick access to the video size
        let videoSize = clipVideoTrack.naturalSize
        // Setup CALayer and it's animation
        let aLayer = SpriteLayer()
        aLayer.contents = stripCgImage
        aLayer.frame = CGRect(x: 0,y: 0,width: videoSize.width,height: videoSize.height)
        aLayer.opacity = 1.0
        aLayer.masksToBounds = true
        aLayer.bounds = CGRect(x: 0,height: videoSize.height)
        aLayer.contentsRect = CGRect(x: 0,width: 1,height: 1.0 / 3.0)
        let spriteAnimation = CABasicAnimation(keyPath: "frameIndex")
        spriteAnimation.fromValue = 1
        spriteAnimation.toValue = 4
        spriteAnimation.duration = 2.25
        spriteAnimation.repeatCount = .infinity
        spriteAnimation.autoreverses = false
        spriteAnimation.beginTime = AVCoreAnimationBeginTimeAtZero
        aLayer.add(spriteAnimation,forKey: nil)
        // Setup Layers for AVVideoCompositionCoreAnimationTool
        let parentLayer = CALayer()
        let videoLayer = CALayer()
        parentLayer.frame = CGRect(x: 0,height: videoSize.height)
        videoLayer.frame = CGRect(x: 0,height: videoSize.height)
        parentLayer.addSublayer(videoLayer)
        parentLayer.addSublayer(aLayer)
        // Create the mutable video composition
        let videoComp = AVMutableVideoComposition()
        videoComp.renderSize = videoSize
        videoComp.frameDuration = CMTimeMake(1,30)
        videoComp.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer,in: parentLayer)
        // Set the video composition to apply to the composition's video track
        let instruction = AVMutableVideoCompositionInstruction()
        instruction.timeRange = CMTimeRangeMake(kCMTimeZero,mixComposition.duration)
        let videoTrack = mixComposition.tracks(withMediaType: .video).first!
        let layerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack)
        instruction.layerInstructions = [layerInstruction]
        videoComp.instructions = [instruction]
        // Initialize export session
        let assetExport = AVAssetExportSession(asset: mixComposition,presetName: AVAssetExportPresetPassthrough)!
        assetExport.videoComposition = videoComp
        assetExport.outputFileType = AVFileType.mp4
        assetExport.outputURL = self.outputURL
        assetExport.shouldOptimizeForNetworkUse = true
        // Export
        assetExport.exportAsynchronously {
            let status = assetExport.status
            switch status {
            case .failed:
                print("Export Failed")
                print("Export Error: (assetExport.error!.localizedDescription)")
                print(assetExport.error!)
            case .unknown:
                print("Export Unknown")
            case .exporting:
                print("Export Exporting")
            case .waiting:
                print("Export Waiting")
            case .cancelled:
                print("Export Cancelled")
            case .completed:
                let end = DispatchTime.now()
                let nanoTime = end.uptimeNanoseconds - start.uptimeNanoseconds
                let timeInterval = Double(nanoTime) / 1_000_000_000
                // Function is now over,we can print how long it took
                print("Time to generate video: (timeInterval) seconds")
                completion()
            }
        }
}

编辑：
我将我的代码基于以下链接

> SpriteLayer and how to use it
> CABasicAnimation on a video
> Using AVVideoCompositionCoreAnimationTool and AVAssetExportSession to save the new video

更新1：
我已经尝试删除我的代码中的CABasicAnimation部分并使用我的CALayer,但无济于事.我甚至无法让图像显示出来.
为了测试一下,我尝试使用Xcode Playground中的contentsRect上的CAKeyframeAnimation动画这个精灵表,它运行正常,所以我认为问题不在于CABasicAnimation,甚至可能与CALayer本身无关.我真的可以在这方面使用一些帮助,因为我不明白为什么我甚至无法在导出的示例视频上显示图像.

更新2：
为了回应matt的评论我已经尝试忘记了一点精灵表并将其改成CATextLayer但仍然没有在我的视频上看到任何东西(它有深色图像,所以白色文字应该是完全可见的)

let aLayer = CATextLayer()
aLayer.string = "This is a test"
aLayer.fontSize = videoSize.height / 6
aLayer.alignmentMode = kCAAlignmentCenter
aLayer.foregroundColor = UIColor.white.cgColor
aLayer.bounds = CGRect(x: 0,height: videoSize.height / 6)

更新3：
根据Matt的要求,我尝试将parentLayer.addSublayer(aLayer)更改为videoLayer.addSublayer(aLayer),但仍然没有改变,但我想尽可能多,因为AVVideoCompositionCoreAnimationTool的documentation如下

convenience init(postProcessingAsVideoLayer videoLayer: CALayer,in animationLayer: CALayer)

意思是我的parentLayer是它的animationLayer,可能意味着任何动画应该在这一层完成.

更新4：
我开始疯狂了,我现在已经放弃了显示文字或动画图像的想法,我想以任何可能的方式影响我的视频,所以我将aLayer更改为：

let aLayer = CALayer()
aLayer.frame = CGRect(x: 0,height: videoSize.height)
aLayer.backgroundColor = UIColor.white.cgColor

好吧,这绝对没有,我仍然在我的outputUrl上获取我的示例视频(如果你想“玩”,我开始在操场上用以下代码测试它)

import PlaygroundSupport
import UIKit
import Foundation
import AVFoundation

func convertAndExport(to url :URL,completion: @escaping () -> Void ) {
    let start = DispatchTime.now()
    do {
        try FileManager.default.removeItem(at: url)
    } catch {
        print("Remove Error: (error.localizedDescription)")
        print(error)
    }

    let videoPath = Bundle.main.path(forResource: "sample",ofType: "mp4")!
    let videoUrl = URL(fileURLWithPath: videoPath)
    let videoAsset = AVURLAsset(url: videoUrl)
    let mixComposition = AVMutableComposition()
    let compositionVideoTrack = mixComposition.addMutableTrack(withMediaType: .video,preferredTrackID: kCMPersistentTrackID_Invalid)!
    let clipVideoTrack = videoAsset.tracks(withMediaType: .video).first!

    do {
        try compositionVideoTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero,at: kCMTimeZero)
    } catch {
        print("Insert Error: (error.localizedDescription)")
        print(error)
        return
    }
    compositionVideoTrack.preferredTransform = clipVideoTrack.preferredTransform
    let videoSize = clipVideoTrack.naturalSize
    print("Video Size Detected: (videoSize.width) x (videoSize.height)")

    let aLayer = CALayer()
    aLayer.frame = CGRect(x: 0,height: videoSize.height)
    aLayer.backgroundColor = UIColor.white.cgColor

    let parentLayer = CALayer()
    let videoLayer = CALayer()
    parentLayer.frame = CGRect(x: 0,height: videoSize.height)
    videoLayer.frame = CGRect(x: 0,height: videoSize.height)
    parentLayer.addSublayer(videoLayer)
    parentLayer.addSublayer(aLayer)
    aLayer.setNeedsDisplay()
    let videoComp = AVMutableVideoComposition()
    videoComp.renderSize = videoSize
    videoComp.frameDuration = CMTimeMake(1,30)
    videoComp.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer,in: parentLayer)

    let instruction = AVMutableVideoCompositionInstruction()
    instruction.timeRange = CMTimeRangeMake(kCMTimeZero,mixComposition.duration)
    let videoTrack = mixComposition.tracks(withMediaType: .video).first!
    let layerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack)
    instruction.layerInstructions = [layerInstruction]
    videoComp.instructions = [instruction]

    let assetExport = AVAssetExportSession(asset: mixComposition,presetName: AVAssetExportPresetPassthrough)!
    assetExport.videoComposition = videoComp
    assetExport.outputFileType = AVFileType.mp4
    assetExport.outputURL = url
    assetExport.shouldOptimizeForNetworkUse = true

    assetExport.exportAsynchronously {
        let status = assetExport.status
        switch status {
        case .failed:
            print("Export Failed")
            print("Export Error: (assetExport.error!.localizedDescription)")
            print(assetExport.error!)
        case .unknown:
            print("Export Unknown")
        case .exporting:
            print("Export Exporting")
        case .waiting:
            print("Export Waiting")
        case .cancelled:
            print("Export Cancelled")
        case .completed:
            let end = DispatchTime.now()
            let nanoTime = end.uptimeNanoseconds - start.uptimeNanoseconds
            let timeInterval = Double(nanoTime) / 1_000_000_000
            print("Time to generate video: (timeInterval) seconds")
            completion()
        }
    }
}

let outputUrl = FileManager.default.temporaryDirectory.appendingPathComponent("test.mp4")
convertAndExport(to: outputUrl) {
    print(outputUrl)
}

请有人帮我理解我做错了什么……

更新5：
我正在运行iPad Air 2以外的所有游乐场测试(所以没有模拟器),因为我使用相机拍照,然后将它们拼接成精灵表,然后我计划通过电子邮件发送动画.我开始做Playground测试,因为来自iPad的每个测试都要求我经历整个应用程序周期(倒计时,照片,表单,电子邮件发送/接收)

let assetExport = AVAssetExportSession(asset: mixComposition,presetName: AVAssetExportPresetPassthrough)!

parentLayer.addSublayer(aLayer)

videoLayer.addSublayer(aLayer)

let spriteAnimation = CABasicAnimation(keyPath: "frameIndex")
spriteAnimation.fromValue = 1
spriteAnimation.toValue = 4
spriteAnimation.duration = 2.25
spriteAnimation.repeatCount = .infinity
spriteAnimation.autoreverses = false
spriteAnimation.beginTime = AVCoreAnimationBeginTimeAtZero
aLayer.add(spriteAnimation,forKey: nil)

let animation = CAKeyframeAnimation(keyPath: #keyPath(CALayer.contentsRect))
animation.duration = 2.25
animation.calculationMode = kCAAnimationDiscrete
animation.repeatCount = .infinity
animation.values = [
    CGRect(x: 0,height: 1/3.0),CGRect(x: 0,y: 1/3.0,y: 2/3.0,height: 1/3.0)
    ] as [CGRect]
animation.beginTime = AVCoreAnimationBeginTimeAtZero
animation.fillMode = kCAFillModeBackwards
animation.isRemovedOnCompletion = false
aLayer.add(animation,forKey: nil)