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我正在开发一个视频应用程序，它需要在一定时间内在视频上显示文本，我需要在不同的时间范围内显示不同的文本。

我已经创建了一个文本图层并将其组合到视频合成中。但我的问题是我不知道如何根据时间范围更改文本。

这是我到目前为止所做的。

        // init variables
        let videoAsset: AVAsset = AVAsset(url: videoUrl) as AVAsset
        let tracks = videoAsset.tracks(withMediaType: AVMediaType.video)
        let videoAssetTrack = tracks.first!

        let size = videoAssetTrack.naturalSize

        // build video composition
        let videoComposition = AVMutableVideoComposition()
        videoComposition.renderSize = CGSize(width: size.width, height: size.height)
        videoComposition.frameDuration = CMTimeMake(value: 1, timescale: 30)

        // create text Layer
        let titleLayer = CATextLayer()
        titleLayer.backgroundColor = UIColor.yellow.cgColor
        titleLayer.foregroundColor = UIColor.black.cgColor
        titleLayer.string = "Dummy text"
        titleLayer.shadowOpacity = 0.5
        titleLayer.alignmentMode = CATextLayerAlignmentMode.center
        titleLayer.frame = CGRect(x: 0, y: 50, width: size.width, height: size.height / 6)

        let videolayer = CALayer()
        videolayer.frame = CGRect(x: 0, y: 0, width: size.width, height: size.height)

        let parentlayer = CALayer()
        parentlayer.frame = CGRect(x: 0, y: 0, width: size.width, height: size.height)
        parentlayer.addSublayer(videolayer)
        parentlayer.addSublayer(titleLayer)

        let animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videolayer, in: parentlayer)
        videoComposition.animationTool = animationTool

        // create instructions
        let instructionTimeRange = CMTimeRangeMake(start: CMTime.zero, duration: videoAssetTrack.timeRange.duration)
        let instruction = AVMutableVideoCompositionInstruction()
        instruction.timeRange = instructionTimeRange
        let layerinstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoAssetTrack)
        instruction.layerInstructions = NSArray(object: layerinstruction) as! [AVVideoCompositionLayerInstruction]


        videoComposition.instructions = [instruction]


        // create exporter and export
        let exporter = AVAssetExportSession(asset: videoAsset, presetName: AVAssetExportPresetHighestQuality)
        exporter!.videoComposition = videoComposition
        exporter!.outputURL = exportUrl
        exporter!.outputFileType = AVFileType.mov
        exporter!.shouldOptimizeForNetworkUse = true
        exporter!.exportAsynchronously() {
            DispatchQueue.main.async {
                self.exportDidFinish(exporter!)
            }
        }

我想为视频的 x（让它是 30.0）秒到 y（假设 50.0）秒显示“一些其他文本”。

编辑：我已阅读此将带有 AVMutableVideoComposition 的文本覆盖添加到特定时间范围

但是使用 CAKeyframeAnimation 我可以显示或隐藏特定时间范围的文本，我可以使用动画更改文本，还是需要使用多个文本层来实现这一点。

我将不胜感激任何提示或解决方案。TIA。

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