Play video synthesized by AVMutableComposition in AVPlayer with error - swift

Question

I am creating an IOS video editing tool by AVMutableComposition.
If I combine multiple videos in a single video mutabletrack, it works fine. However, when I create mutabletrack per video and synthesize the video and play it in AVPlayer, only sound plays and video stops when move on the next video. However, if I seek video, it works normally. What's the cause?
The following is the code in which the current situation occur.
static func mergeClips(
videos: [ExCAVideoLayer]?,
audios: [ExCAAudioLayer]? = nil
) -> AVPlayerItem? {
guard let videos = videos else {
return nil
}
let mixComposition = AVMutableComposition()
var layerInstructions = [AVMutableVideoCompositionLayerInstruction]()
do {
// Determind video aspect ratio
var aspectRatio: Double = 0.00001
for video in videos {
guard let url = video.videoUrl else {
continue
}
if let naturalSize = self.resolutionForLocalVideo(url: url) {
let naturalAspectRatio = naturalSize.height == 0 ? 1 : naturalSize.width / naturalSize.height
if aspectRatio < naturalAspectRatio {
aspectRatio = naturalAspectRatio
}
}
}
var frameWidth = UIScreen.main.bounds.width
var frameHeight = round(UIScreen.main.bounds.width / aspectRatio)
if frameWidth.truncatingRemainder(dividingBy: 2) > 0 {
frameWidth = frameWidth - 1
}
if frameHeight.truncatingRemainder(dividingBy: 2) > 0 {
frameHeight = frameHeight - 1
}
let frameSize = CGSize(width: frameWidth, height: frameHeight)
// Video composition
var currentDuration = mixComposition.duration
for video in videos {
guard let url = video.videoUrl else {
continue
}
let videoTrack = mixComposition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
let audioTrack = mixComposition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)
let avAsset = AVAsset(url: url)
if let layerInstruction = self.videoCompositionInstruction(videoTrack, asset: avAsset, frameSize: frameSize) {
layerInstructions.append(layerInstruction)
}
let streamRange = CMTimeRangeMake(start: CMTime.zero, duration: CMTimeAdd(avAsset.duration, CMTimeMakeWithSeconds(video.gap, preferredTimescale: 1)))
if let streamVideoTrack = avAsset.tracks(withMediaType: .video).first {
try videoTrack?.insertTimeRange(streamRange, of: streamVideoTrack, at: currentDuration)
videoTrack?.preferredTransform = streamVideoTrack.preferredTransform
}
if let streamAudioTrack = avAsset.tracks(withMediaType: .audio).first {
try audioTrack?.insertTimeRange(streamRange, of: streamAudioTrack, at: currentDuration)
}
currentDuration = mixComposition.duration
}
// Audio composition
if let audios = audios {
for audio in audios {
guard let url = audio.audioUrl else {
continue
}
let audioTrack = mixComposition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)
let avAsset = AVAsset(url: url)
let streamRange = CMTimeRangeMake(start: CMTime.zero, duration: avAsset.duration)
if let streamAudioTrack = avAsset.tracks(withMediaType: .audio).first {
try audioTrack?.insertTimeRange(streamRange, of: streamAudioTrack, at: CMTimeMakeWithSeconds(audio.startTime, preferredTimescale: 1))
}
}
}
//AVVideoComposition and layout
let videoComposition = AVMutableVideoComposition()
videoComposition.frameDuration = CMTime(value: 1, timescale: 30)
videoComposition.renderSize = CGSize(width: frameSize.width, height: frameSize.height)
let mainInstruction = AVMutableVideoCompositionInstruction()
mainInstruction .timeRange = CMTimeRange(start: .zero, duration: mixComposition.duration)
mainInstruction.backgroundColor = UIColor.black.cgColor
mainInstruction.layerInstructions = layerInstructions
videoComposition.instructions = [mainInstruction]
let assetKeys = [
"playable",
"hasProtectedContent"
]
let avPlayItem = AVPlayerItem(asset: mixComposition, automaticallyLoadedAssetKeys: assetKeys)
avPlayItem.videoComposition = videoComposition
return avPlayItem
}
catch(let error) {
print("Could not create mixComposition \(error.localizedDescription)")
return nil
}
}
func PlayVideo() {
guard let avPlayerItem = VideoComposition.mergeClips(videos: self.projectRender?.videoItems) else {
return
}
self.avPlayer = AVPlayer(playerItem: avPlayerItem)
self.avPlayerLayer = AVPlayerLayer(player: self.avPlayer)
self.avPlayerLayer?.needsDisplayOnBoundsChange = true
if let avPlayerLayer = self.avPlayerLayer {
self.videoContainer?.layer.addSublayer(avPlayerLayer)
}
self.avPlayer?.play()
}