Merge Videos with different aspectRatios about cabbage HOT 6 CLOSED

let item1 = TrackItem(resource: resource)
// Set all item's base content mode to .aspectFit
item1.configuration.videoConfiguration.baseContentMode = .aspectFit
....
item2.configuration.videoConfiguration.baseContentMode = .aspectFit
....
itemN.configuration.videoConfiguration.baseContentMode = .aspectFit

let timeline = Timeline()
timeline.videoChannel = [item1, item2, ..., itemN]
timeline.audioChannel = [item1, item2, ..., itemN]

let compositionGenerator = CompositionGenerator(timeline: timeline)
// Set canvas to first video's size
compositionGenerator.renderSize = item1.resource.size
let playerItem = compositionGenerator.buildPlayerItem()

                let tLine = Timeline()
                var vChannel = [TrackItem]()
                var aChannel = [TrackItem]()
                for clip: G8Clip in self._clips {
                    if let asset = clip.asset {
                        let resource = AVAssetTrackResource(asset: asset)
                        // Create a TrackItem instance, TrackItem can configure video&audio configuration
                        let trackItem = TrackItem(resource: resource)
                        // Set the video scale mode on canvas
                        trackItem.configuration.videoConfiguration.baseContentMode = .aspectFit
                        vChannel.append(trackItem)
                        aChannel.append(trackItem)
                    }
                }
                tLine.videoChannel = vChannel
                tLine.audioChannel = aChannel
                
                // Use CompositionGenerator to create AVAssetExportSession/AVAssetImageGenerator/AVPlayerItem
                let compositionGenerator = CompositionGenerator(timeline: tLine)
                // Set the video canvas's size
                var firstVideoDimensions = CGSize(width: 1920, height: 1080)
                if(self._clips.count > 0){
                    let firstVTrack = self._clips.first?.asset?.tracks(withMediaType: AVMediaType.video).first
                    firstVideoDimensions = CGSize(width: firstVTrack!.naturalSize.width, height: firstVTrack!.naturalSize.height)
                }
                compositionGenerator.renderSize = firstVideoDimensions
                
                //Create the Export Session
                if let exportURL = outputURL {
                    self.removeFile(fileUrl: exportURL)
                    if let exportSession = compositionGenerator.buildExportSession(presetName: preset){
                        exportSession.shouldOptimizeForNetworkUse = true
                        exportSession.outputURL = exportURL
                        exportSession.outputFileType = self.fileType
                        exportSession.exportAsynchronously {
                            DispatchQueue.main.async {
                                completionHandler(exportURL, exportSession.error)
                            }
                        }
                        return
                    }
                    
                }

tLine.videoChannel = vChannel
tLine.audioChannel = aChannel

// Call this after you set videoChannel. This method will correct the video's start time, base on your order
try! Timeline.reloadVideoStartTime(providers: tLine.videoChannel)