The resolution status of the issue I registered through Feedback Assistant is set to "Potential fix identified - In iOS 14.5" now. Also, when I tried some unsync cases in iOS 14.6, the problem is not reproduced.

I use AVAssetReader and AVAssetWriter to export edited video. Since iOS 14.5.1, -11819 errors have occurred a lot too.

The feedback ID is FB8811460. Thanks!

I uploaded same question to Feedback Assistant. I hope this problem will be resolved well and I will cooperate actively.

Yes, but it has still a sync problem. Also, AVAsset.duration and AVAssetTrack.timeRange.duration is actually the same in the log. FYI, here is the stackoverflow link - https://stackoverflow.com/questions/64349186/out-of-sync-between-video-and-audio-of-video-exported-by-avassetexportsession of my question. It has an image about audio tracks between source and exported video.

Thank you for the reply. Here is my code I use to construct AVMutableComposition. let composition = AVMutableComposition() let videoTrack = composition.addMutableTrack(   withMediaType: AVMediaType.video,   preferredTrackID: kCMPersistentTrackID_Invalid ) let audioTrack = composition.addMutableTrack(   withMediaType: AVMediaType.audio,   preferredTrackID: kCMPersistentTrackID_Invalid ) let assetVideoTrack = asset.tracks(withMediaType: AVMediaType.video).first let assetAudioTrack = asset.tracks(withMediaType: AVMediaType.audio).first let assetDuration = assetVideoTrack?.timeRange.duration   ?? assetAudioTrack?.timeRange.duration   ?? CMTime.zero let timeRange = CMTimeRangeMake(start: CMTime.zero, duration: assetDuration) let atTime = CMTime.zero do {   if let assetVideoTrack = assetVideoTrack {   	try videoTrack?.insertTimeRange(    	 timeRange,    	 of: assetVideoTrack,    	 at: atTime   	)   }   if let assetAudioTrack = assetAudioTrack {   	try audioTrack?.insertTimeRange(    	 timeRange,    	 of: assetAudioTrack,    	 at: atTime   	)   } } catch { }