要合并多个视频并在视频之间添加动画，可以使用AVFoundation框架。以下是一个示例代码解决方案。

import AVFoundation

class VideoMerger {
    func mergeVideosWithAnimation(videos: [AVAsset], animationDuration: CMTime, completion: @escaping (AVAsset?, Error?) -> Void) {
        let composition = AVMutableComposition()
        let videoTrack = composition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
        let audioTrack = composition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)
        
        var currentTime = CMTime.zero
        
        for video in videos {
            do {
                let videoAssetTrack = video.tracks(withMediaType: .video)[0]
                let audioAssetTrack = video.tracks(withMediaType: .audio)[0]
                
                try videoTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: videoAssetTrack.timeRange.duration), of: videoAssetTrack, at: currentTime)
                try audioTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: videoAssetTrack.timeRange.duration), of: audioAssetTrack, at: currentTime)
                
                currentTime = CMTimeAdd(currentTime, videoAssetTrack.timeRange.duration)
                
                // 添加动画
                if let lastVideo = videos.last, video != lastVideo {
                    let animationStartTime = CMTimeSubtract(currentTime, animationDuration)
                    let animationEndTime = currentTime
                    let animationComposition = AVMutableVideoComposition()
                    animationComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoTrack!, in: animationComposition)
                    
                    let fadeAnimation = CABasicAnimation(keyPath: "opacity")
                    fadeAnimation.fromValue = 0.0
                    fadeAnimation.toValue = 1.0
                    fadeAnimation.beginTime = AVCoreAnimationBeginTimeAtZero
                    fadeAnimation.duration = CMTimeGetSeconds(animationDuration)
                    
                    let animationLayer = CALayer()
                    animationLayer.frame = CGRect(x: 0, y: 0, width: videoAssetTrack.naturalSize.width, height: videoAssetTrack.naturalSize.height)
                    animationLayer.add(fadeAnimation, forKey: nil)
                    
                    let videoLayer = CALayer()
                    videoLayer.frame = CGRect(x: 0, y: 0, width: videoAssetTrack.naturalSize.width, height: videoAssetTrack.naturalSize.height)
                    videoLayer.addSublayer(animationLayer)
                    
                    let animationInstruction = AVMutableVideoCompositionInstruction()
                    animationInstruction.timeRange = CMTimeRangeMake(start: animationStartTime, duration: animationDuration)
                    animationInstruction.layerInstructions = [AVMutableVideoCompositionLayerInstruction(assetTrack: videoAssetTrack)]
                    
                    animationComposition.instructions = [animationInstruction]
                    animationComposition.animationTool?.setTargetLayer(videoLayer)
                    
                    composition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)?.insertTimeRange(CMTimeRangeMake(start: animationStartTime, duration: animationDuration), of: animationComposition, at: animationStartTime)
                }
            } catch {
                completion(nil, error)
                return
            }
        }
        
        // 导出合并后的视频
        guard let exportSession = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetHighestQuality) else {
            completion(nil, nil)
            return
        }
        
        let outputURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent("output.mp4")
        exportSession.outputURL = outputURL
        exportSession.outputFileType = .mp4
        
        exportSession.exportAsynchronously {
            switch exportSession.status {
            case .completed:
                let mergedVideo = AVAsset(url: outputURL)
                completion(mergedVideo, nil)
            case .failed, .cancelled:
                completion(nil, exportSession.error)
            default:
                break
            }
        }
    }
}

使用示例：

let videoURL1 = URL(fileURLWithPath: Bundle.main.path(forResource: "video1", ofType: "mov")!)
let videoURL2 = URL(fileURLWithPath: Bundle.main.path(forResource: "video2", ofType: "mov")!)

let videoAsset1 = AVAsset(url: videoURL1)
let videoAsset2 = AVAsset(url: videoURL2)

let videoMerger = VideoMerger()
videoMerger.mergeVideosWithAnimation(videos: [videoAsset1, videoAsset2], animationDuration: CMTime(seconds: 1, preferredTimescale: 1)) { (mergedVideo, error) in
    if let mergedVideo = mergedVideo {
        // 处理