解决方法似乎是确保assetTrackin中的参数AVMutableVideoCompositionLayerInstruction不是来自AVURLAsset对象，而是来自所返回的视频对象addMutableTrackWithMediaType。
换句话说，这一行：
let videoLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: sourceVideoTrack)
应该：
let videoLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack)
啊 数小时无尽的挫败感，因为有时第一行有效，有时却没有。
仍然想将赏金奖励给某人。
如果您可以解释为什么第一行会不确定地失败，而不是每次都失败，或者为AVMutableComposition及其相关类提供更深入的教程-为了向用户录制的视频中添加文字叠加层-赏金全由您自己。:)
解决方法我们在用户录制的视频中添加了字幕，但是AVAssetExportSession对象的导出不确定性失败：有时可以，有时不能。甚至还不清楚如何重现该错误。
我们注意到资产追踪似乎在出口期间丢失了。
导出之前，有两个音轨（一个用于音频，一个用于视频）。但是，检查中的相同文件URL的轨道数exportDidFinish显示为0。因此，导出过程似乎有些问题。
更新：注释掉可以exporter.videoComposition =mutableComposition解决该错误，但是当然不对视频应用任何变换。因此，问题似乎出在create上AVMutableVideoComposition，这在导出期间导致下游问题。文档和教程AVMutableVideoComposition很少，因此，即使您没有解决方案，但可以推荐Apple以外的参考来源，这也会有所帮助。
错误：
错误域= AVFoundationErrorDomain代码= -11841“操作已停止” UserInfo = 0x170676e80
码：
let videoAsset = AVURLAsset(URL: fileUrl,options: nil) let mixComposition = AVMutableComposition() let videoTrack = mixComposition.addMutableTrackWithMediaType(AVMediaTypeVideo,preferredTrackID: CMPersistentTrackID(kCMPersistentTrackID_Invalid)) let audioTrack = mixComposition.addMutableTrackWithMediaType(AVMediaTypeAudio,preferredTrackID: CMPersistentTrackID(kCMPersistentTrackID_Invalid)) let sourceVideoTrack = videoAsset.tracksWithMediaType(AVMediaTypeVideo)[0] as! AVAssetTrack let sourceAudioTrack = videoAsset.tracksWithMediaType(AVMediaTypeAudio)[0] as! AVAssetTrack videoTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero,videoAsset.duration),ofTrack: sourceVideoTrack,atTime: kCMTimeZero,error: nil) audioTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero,ofTrack: sourceAudioTrack,error: nil) // Create something mutable??? // -- Create instruction let instruction = AVMutableVideoCompositionInstruction() instruction.timeRange = CMTimeRangeMake(kCMTimeZero,videoAsset.duration) let videoLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: sourceVideoTrack) instruction.layerInstructions = [videoLayerInstruction] let mutableComposition = AVMutableVideoComposition() //mutableComposition.renderSize = videoTrack.naturalSize mutableComposition.renderSize = CGSize(width: 320,height: 320) mutableComposition.frameDuration = CMTimeMake(1,60) mutableComposition.instructions = [instruction] // Animate mutableComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer,inLayer: parentLayer) // -- Get path let fileName = '/editedVideo-(arc4random() % 10000).mp4' let allPaths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory,.UserDomainMask,true) let docsPath = allPaths[0] as! NSString let exportPath = docsPath.stringByAppendingFormat(fileName) let exportUrl = NSURL.fileURLWithPath(exportPath as String)! println('Tracks before export: (mixComposition.tracks.count). File URL: (exportUrl)') // -- Remove old video? if NSFileManager.defaultManager().fileExistsAtPath(exportPath as String) {println('Deleting existing filen')NSFileManager.defaultManager().removeItemAtPath(exportPath as String,error: nil) } // -- Create exporter let exporter = AVAssetExportSession(asset: mixComposition,presetName: AVAssetExportPresetHighestQuality) exporter.videoComposition = mutableComposition exporter.outputFileType = AVFileTypeMPEG4 exporter.outputURL = exportUrl exporter.shouldOptimizeForNetworkUse = true // -- Export video exporter.exportAsynchronouslyWithCompletionHandler({self.exportDidFinish(exporter) })func exportDidFinish(exporter: AVAssetExportSession) { println('Exported video with status: (getExportStatus(exporter))') // Save video to photo album let assetLibrary = ALAssetsLibrary() assetLibrary.writeVideoAtPathToSavedPhotosAlbum(exporter.outputURL,completionBlock: {(url: NSURL!,error: NSError!) inprintln('Saved video to album (exporter.outputURL)')if (error != nil) { println('Error saving video')} }) // Check asset tracks let asset = AVAsset.assetWithURL(exporter.outputURL) as? AVAsset println('Tracks after export: (asset!.tracks.count). File URL: (exporter.outputURL)')}
问题：
1）是什么引起问题，解决方案是什么？
2）关于如何一致地重现错误的建议，希望可以帮助调试问题？
