Some of my code for combining an .mp4 and an .aac file together into an .mov file worked just fine since its very beginning, it creats an AVMutableComposition with 1 video track and 1 audio track from the input audio and video files. After exportAsynchronously(), the AVAssetExportSession gets AVAssetExportSession.Status.completed. Here is the Swift source code of the key function: func compileAudioAndVideoToMovie(audioInputURL:URL, videoInputURL:URL) { let docPath:String = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]; let videoOutputURL:URL = URL(fileURLWithPath: docPath).appendingPathComponent("video_output.mov"); do { try FileManager.default.removeItem(at: videoOutputURL); } catch {} let mixComposition = AVMutableComposition(); let videoTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.video, preferredTrackID: kCMPersistentTrackID_Invalid); let videoInputAsset = AVURLAsset(url: videoInputURL); let audioTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.audio, preferredTrackID: kCMPersistentTrackID_Invalid); let audioInputAsset = AVURLAsset(url: audioInputURL); do { try videoTrack?.insertTimeRange(CMTimeRangeMake(start: CMTimeMake(value: 0, timescale: 1000), duration: CMTimeMake(value: 3000, timescale: 1000)), of: videoInputAsset.tracks(withMediaType: AVMediaType.video)[0], at: CMTimeMake(value: 0, timescale: 1000));// Insert an 3-second video clip into the video track try audioTrack?.insertTimeRange(CMTimeRangeMake(start: CMTimeMake(value: 0, timescale: 1000), duration: CMTimeMake(value: 3000, timescale: 1000)), of: audioInputAsset.tracks(withMediaType: AVMediaType.audio)[0], at: CMTimeMake(value: 0, timescale: 1000));// Insert an 3-second audio clip into the audio track let assetExporter = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetPassthrough); assetExporter?.outputFileType = AVFileType.mov; assetExporter?.outputURL = videoOutputURL; assetExporter?.shouldOptimizeForNetworkUse = false; assetExporter?.exportAsynchronously { switch (assetExporter?.status) { case .cancelled: print("Exporting cancelled"); case .completed: print("Exporting completed"); case .exporting: print("Exporting ..."); case .failed: print("Exporting failed"); default: print("Exporting with other result"); } if let error = assetExporter?.error { print("Error:\n\(error)"); } } } catch { print("Exception when compiling movie"); } }However, after I upgraded my iPhone to iOS13(beta), it always ends up with .failed status, and the AVAssetExportSession.error reads: Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed" UserInfo={NSLocalizedFailureReason=An unknown error occurred (-12735), NSLocalizedDescription=The operation could not be completed, NSUnderlyingError=0x2815e9bc0 {Error Domain=NSOSStatusErrorDomain Code=-12735 "(null)”}}I've tested this on iPhone6Plus and iPhone7, both given the same result.You can clone my minimal demo project with sample input audio and video files embedded in its bundle from here:https://github.com/chenqiu1024/iOS13VideoRecordingError.git, run it and check the console output.Is there any explanation and suggestion?