Question

我目前正在使用AVMutableComposition在视频中叠加一些文本，我想根据某个时间间隔重复更改字符串。我正在尝试使用核心动画来实现这一目标；但是，string属性似乎无法设置动画。还有其他方法可以实现目标吗？谢谢。

代码（不起作用）：

func getSubtitlesAnimation(withFrames frames: [String], duration: CFTimeInterval)->CAKeyframeAnimation {
    let animation = CAKeyframeAnimation(keyPath:"string")
    animation.calculationMode = kCAAnimationDiscrete
    animation.duration = duration
    animation.values = frames
    animation.keyTimes = [0,0.5,1]
    animation.repeatCount = Float(frames.count)
    animation.isRemovedOnCompletion = false
    animation.fillMode = kCAFillModeForwards
    animation.beginTime = AVCoreAnimationBeginTimeAtZero
    return animation
}

Answer 1

字符串不是CATextLayer上的动画路径。这是list of keyPaths，您可以在任何CALayer上使用。

关于将Core Animation与AVFoundation一起使用的其他一些重要事项。

所有动画都必须已删除Completion of false。
您只能将一个关键路径动画应用于图层一次。意味着如果要添加淡入和淡出的不透明度，则需要将其合并为单个关键帧动画。在核心动画中，您可以使用beginTime并应用两个不同的不透明度动画，但是以我对AVFoundation和Core Animation的经验来看，这是行不通的。因此，如果要在CALayer的同一关键路径上使用两个不同的（不透明）动画，则必须弄清楚要发生的事件的关键时间和值。
您的离散曲线仍然可以使用，但是您必须计算关键时间和值。
因为不能将字符串用作可设置动画的属性，所以下一个最好的方法是使用多个CATextLayers，然后将它们彼此淡入淡出。这是一个例子。将CACurrentMediaTime（）替换为AVCoreAnimationBeginTimeAtZero以与AVFoundation一起使用。这只是一个示例，因此您可以可视化您想要的内容。

Example1Using-Discrete

 import UIKit

class ViewController: UIViewController {

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        //center the frame
        let textFrame = CGRect(x: (self.view.bounds.width - 200)/2, y: (self.view.bounds.height - 100)/2, width: 200, height: 50)

        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now()) {
            //animation spacing could be a negative value of half the animation to appear to fade between strings
            self.animateText(subtitles: ["Hello","Good Morning","Good Afternoon","Good Evening","Goodnight","Goodbye"], duration: 2, animationSpacing: 0, frame: textFrame, targetLayer: self.view.layer)
        }
    }

    func animateText(subtitles:[String],duration:Double,animationSpacing:Double,frame:CGRect,targetLayer:CALayer){
        var currentTime : Double = 0
        for x in 0..<subtitles.count{
            let string = subtitles[x]
            let textLayer = CATextLayer()
            textLayer.frame = frame
            textLayer.string = string
            textLayer.font = UIFont.systemFont(ofSize: 20)
            textLayer.foregroundColor = UIColor.black.cgColor
            textLayer.fontSize = 20.0
            textLayer.alignmentMode = kCAAlignmentCenter
            let anim = getSubtitlesAnimation(duration: duration, startTime: currentTime)
            targetLayer.addSublayer(textLayer)
            textLayer.add(anim, forKey: "opacityLayer\(x)")
            currentTime += duration + animationSpacing
        }
    }
    func getSubtitlesAnimation(duration: CFTimeInterval,startTime:Double)->CAKeyframeAnimation {
        let animation = CAKeyframeAnimation(keyPath:"opacity")
        animation.duration = duration
        animation.calculationMode = kCAAnimationDiscrete
        //have to fade in and out with a single animation because AVFoundation
        //won't allow you to animate the same propery on the same layer with
        //two different animations
        animation.values = [0,1,1,0,0]
        animation.keyTimes = [0,0.001,0.99,0.999,1]
        animation.isRemovedOnCompletion = false
        animation.fillMode = kCAFillModeBoth
        //Replace with AVCoreAnimationBeginTimeAtZero for AVFoundation
        animation.beginTime = CACurrentMediaTime() + startTime
        return animation
    }
}

示例2-使用带有较长淡入效果的Gif附件

import UIKit

class ViewController: UIViewController {

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        //center the frame
        let textFrame = CGRect(x: (self.view.bounds.width - 200)/2, y: (self.view.bounds.height - 100)/2, width: 200, height: 50)

        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now()) {
            //animation spacing could be a negative value of half the animation to appear to fade between strings
            self.animateText(subtitles: ["Hello","Good Morning","Good Afternoon","Good Evening","Goodnight","Goodbye"], duration: 4, animationSpacing: -2, frame: textFrame, targetLayer: self.view.layer)
        }
    }

    func animateText(subtitles:[String],duration:Double,animationSpacing:Double,frame:CGRect,targetLayer:CALayer){
        var currentTime : Double = 0
        for x in 0..<subtitles.count{
            let string = subtitles[x]
            let textLayer = CATextLayer()
            textLayer.frame = frame
            textLayer.string = string
            textLayer.font = UIFont.systemFont(ofSize: 20)
            textLayer.foregroundColor = UIColor.black.cgColor
            textLayer.fontSize = 20.0
            textLayer.alignmentMode = kCAAlignmentCenter
            let anim = getSubtitlesAnimation(duration: duration, startTime: currentTime)
            targetLayer.addSublayer(textLayer)
            textLayer.add(anim, forKey: "opacityLayer\(x)")
            currentTime += duration + animationSpacing
        }
    }
    func getSubtitlesAnimation(duration: CFTimeInterval,startTime:Double)->CAKeyframeAnimation {
        let animation = CAKeyframeAnimation(keyPath:"opacity")
        animation.duration = duration
        //have to fade in and out with a single animation because AVFoundation
        //won't allow you to animate the same propery on the same layer with
        //two different animations
        animation.values = [0,0.5,1,0.5,0]
        animation.keyTimes = [0,0.25,0.5,0.75,1]
        animation.isRemovedOnCompletion = false
        animation.fillMode = kCAFillModeBoth
        //Replace with AVCoreAnimationBeginTimeAtZero for AVFoundation
        animation.beginTime = CACurrentMediaTime() + startTime
        return animation
    }
}

结果：持续2秒和持续2秒的持续时间。可能是立即的。

Answer 2

Swift 5解决方案：

喜欢@ agibson007的答案

在0.25的持续时间内无法进行优化。（存在褪色/闪烁的问题）

func animateText(subtitles:[String],duration:Double,animationSpacing:Double,frame:CGRect,targetLayer:CALayer){
        var currentTime : Double = 0
        for x in 0..<subtitles.count{
            let textLayer = CATextLayer()
            textLayer.frame = frame
            textLayer.string = subtitles[x]
            textLayer.font = UIFont.systemFont(ofSize: 20)
            textLayer.foregroundColor = UIColor.black.cgColor
            textLayer.fontSize = 40.0
            textLayer.alignmentMode = .center
            let anim = getSubtitlesAnimation(duration: duration, startTime: currentTime)
            textLayer.add(anim, forKey: "opacityLayer\(x)")
            targetLayer.addSublayer(textLayer)
            currentTime += duration + animationSpacing
        }
    }

    func getSubtitlesAnimation(duration: CFTimeInterval,startTime:Double)->CAKeyframeAnimation {
        let animation = CAKeyframeAnimation(keyPath:"opacity")
        animation.duration = duration
        animation.calculationMode = .discrete
        animation.values = [0,1,1,0,0]
        animation.keyTimes = [0,0.00000001,0.999,0.999995,1]
        animation.isRemovedOnCompletion = false
        animation.fillMode = .both
        animation.beginTime = AVCoreAnimationBeginTimeAtZero + startTime // CACurrentMediaTime() <- NO AV Foundation
        return animation
    }

    let steps = 0.25
    let duration = 8.0
    let textFrame = CGRect( x: (videoSize.width / 2) - (90 / 2) , y: videoSize.height * 0.2, width: 90, height: 50)

    var subtitles:[String] = []
    for i in 0...Int(duration / steps) {
        let time = i > 0 ? steps * Double(i) : Double(i)
        subtitles.append(String(format: "%0.1f", time) )
    }

    animateText(subtitles: subtitles, duration: steps, animationSpacing: 0, frame: textFrame, targetLayer: layer)

Answer 3

使用 CATextLayer 和 CAKeyframeAnimation 的文本动画解决方案。现在 string 属性是可动画的。不知道过去怎么样。

func addTextLayer(to layer: CALayer) {
    let myAnimation = CAKeyframeAnimation(keyPath: "string");
    myAnimation.beginTime = 0;
    myAnimation.duration = 1.0;
    myAnimation.values = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12"]
    myAnimation.fillMode = CAMediaTimingFillMode.forwards;
    myAnimation.isRemovedOnCompletion = false;
    myAnimation.repeatCount = 1;
    
    let textLayer = CATextLayer();
    textLayer.frame = CGRect(x: 200, y: 300, width: 100, height: 100);
    textLayer.string = "0";
    textLayer.font = UIFont.systemFont(ofSize: 20)
    textLayer.foregroundColor = UIColor.black.cgColor
    textLayer.fontSize = 40.0
    textLayer.alignmentMode = .center
    textLayer.add(myAnimation, forKey: nil);

    layer.addSublayer(textLayer);
}

Answer 4

尝试思考电影中如何添加字幕？

字幕文件包含时间戳记值，例如00:31:21：“某些文本”。因此，当电影的搜索栏位于00:31:21时，您会看到“某些文本”作为字幕。

类似地，根据您的要求，您将需要多个CATextLayers，它们具有与它们相对应的动画（每个CATExtLayer相同或不同）。当一个CATextLayer动画结束时，您可以淡入第二个CATextLayer，淡入第一个。

我记得上一次这样做，可以对动画进行分组，并且您实际上可以指定动画的起点。检查beginTime的{{1}}属性

如何为CATextLayer的字符串设置动画？

4 个答案: