Merge multiple video clips

MergeClips.swift

// Mark: - Merge Videos and export Finalized Video
    
    private func merge(clips: [Clip]){
        let composition = AVMutableComposition()
        let trackID = kCMPersistentTrackID_Invalid
        let videoTrack = composition.addMutableTrack(withMediaType: AVMediaTypeVideo, preferredTrackID: trackID)
        //let audioTrack = composition.addMutableTrack(withMediaType: AVMediaTypeAudio, preferredTrackID: trackID)
        
        var totalTime = kCMTimeZero
        
        for clip in clips {
            let asset = AVAsset(url: clip.url)
            let range = CMTimeRangeMake(kCMTimeZero, asset.duration)
            let assetTrack = asset.tracks(withMediaType: AVMediaTypeVideo)[0]
            
            // Rotate portrait 90°
            videoTrack.preferredTransform = CGAffineTransform(rotationAngle: .pi/2)
            
            do {
                try videoTrack.insertTimeRange(range, of: assetTrack, at: totalTime)
            } catch{
                print("error: \(error)")
            }
            totalTime = CMTimeAdd(totalTime, asset.duration)
        }
        
        exportMergedVideo(composition: composition, clips: clips)
    }
    
    private func exportMergedVideo(composition: AVMutableComposition, clips: [Clip]){
        let manager = FileManager.default
        
        let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
        
        let outputURL = paths[0].appendingPathComponent("export.mov")
        
        //Remove existing file
        _ = try? manager.removeItem(at: outputURL)
        
        guard let exportSession = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetHighestQuality) else {return}
        exportSession.outputURL = outputURL
        exportSession.outputFileType = AVFileTypeMPEG4
        
        self.outputURL = outputURL
        
        exportSession.exportAsynchronously(completionHandler: {
            switch exportSession.status {
            case .completed:
                //self.prepareForPublish()
                self.deleteClips(clips: clips)
            // To-do: - Save video into Library
            case .failed:
                print("failed \(String(describing: exportSession.error))")
            case .cancelled:
                print("cancelled \(String(describing: exportSession.error))")
            default: break
            }
        })
    }
    
    // Delete single clips from disk
    func deleteClips(clips: [Clip]){
        for clip in clips {
            clip.deleteFromDisk()
        }
        print("\(clips.count) clips deleted from disk!")
    }