Merge Videos Array in Swift - iphone

Question

I am trying to merge the videos from the array of avssets but I am able to get only first and last video. Videos between the array are showing black area.
Check the code I am using.
func mergeVideoArray() {
let mixComposition = AVMutableComposition()
for videoAsset in videoURLArray {
let videoTrack =
mixComposition.addMutableTrack(withMediaType: AVMediaType.video,
preferredTrackID: Int32(kCMPersistentTrackID_Invalid))
do {
try videoTrack?.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration),
of: videoAsset.tracks(withMediaType: AVMediaType.video).first!,
at: totalTime)
videoSize = (videoTrack?.naturalSize)!
} catch let error as NSError {
print("error: \(error)")
}
let trackArray = videoAsset.tracks(withMediaType: .audio)
if trackArray.count > 0 {
let audioTrack =
mixComposition.addMutableTrack(withMediaType: AVMediaType.audio,
preferredTrackID: Int32(kCMPersistentTrackID_Invalid))
do {
try audioTrack?.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration), of: videoAsset.tracks(withMediaType: AVMediaType.audio).first!, at: audioTime)
audioTime = audioTime + videoAsset.duration
}
catch {
}
}
totalTime = totalTime + videoAsset.duration
let videoInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack!)
if videoAsset != videoURLArray.last{
videoInstruction.setOpacity(0.0, at: videoAsset.duration)
}
layerInstructionsArray.append(videoInstruction)
}
let mainInstruction = AVMutableVideoCompositionInstruction()
mainInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, totalTime)
mainInstruction.layerInstructions = layerInstructionsArray
let mainComposition = AVMutableVideoComposition()
mainComposition.instructions = [mainInstruction]
mainComposition.frameDuration = CMTimeMake(1, 30)
mainComposition.renderSize = CGSize(width: videoSize.width, height: videoSize.height)
let url = "merge_video".outputURL
let exporter = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality)
exporter!.outputURL = url
exporter!.outputFileType = AVFileType.mov
exporter!.shouldOptimizeForNetworkUse = false
exporter!.videoComposition = mainComposition
exporter!.exportAsynchronously {
let video = AVAsset(url: url)
let playerItem = AVPlayerItem(asset: video)
let player = AVPlayer(playerItem: playerItem)
self.playerViewController.player = player
self.present(self.playerViewController, animated: true) {
self.playerViewController.player!.play()
}
}
}
Please help me resolving this issue. Thanks in advance.
Note I am able to create a video from the array but only first and last index values are showing in videos. For rest of the values only blank screen is showing.

Answer 1

I just solved my question just need to update the one line in the code. Please have a look in to the code.
if videoAsset != videoURLArray.last{
videoInstruction.setOpacity(0.0, at: totalTime)
}
Note: just need to change the at position of the next video for the every value of array.

Answer 2

Right way to do it would be to change
if videoAsset != videoURLArray.last{
videoInstruction.setOpacity(0.0, at: videoAsset.duration)
}
to:
videoInstruction.setOpacity(0.0, at: totalTime)
I want to emphasize here that adding
totalTime = totalTime + videoAsset.duration
before setting opacity to layer instruction makes all the difference. Otherwise videos are black screen.