求助： AVAssetExportSession 在正常runtime下不工作

[weixin_42659924]

我想把一个音频和视频merge到一起，但是output的时候总是会跳出NSUncaught exception，奇怪的是如果是一行一行stepover就可以正常工作。我感觉应该是thread出了问题，但是找不到具体的点。

这是我merge的函数。

    /// Merges video and sound while keeping sound of the video too
    ///
    /// - Parameters:
    ///   - videoUrl: URL to video file
    ///   - audioUrl: URL to audio file
    ///   - shouldFlipHorizontally: pass True if video was recorded using frontal camera otherwise pass False
    ///   - completion: completion of saving: error or url with final video
    func mergeVideoAndAudio(videoUrl: URL,
                            audioUrl: URL,
                            shouldFlipHorizontally: Bool = false,
                            completion: @escaping (_ error: Error?, _ url: URL?) -> Void) {
        
        let mixComposition = AVMutableComposition()
        var mutableCompositionVideoTrack = [AVMutableCompositionTrack]()
        var mutableCompositionAudioTrack = [AVMutableCompositionTrack]()
        var mutableCompositionAudioOfVideoTrack = [AVMutableCompositionTrack]()
        
        //start merge
        
        let aVideoAsset = AVAsset(url: videoUrl)
        let aAudioAsset = AVAsset(url: audioUrl)
        
        let compositionAddVideo = mixComposition.addMutableTrack(withMediaType: AVMediaType.video,
                                                                 preferredTrackID: kCMPersistentTrackID_Invalid)
        
        let compositionAddAudio = mixComposition.addMutableTrack(withMediaType: AVMediaType.audio,
                                                                 preferredTrackID: kCMPersistentTrackID_Invalid)
        
        let compositionAddAudioOfVideo = mixComposition.addMutableTrack(withMediaType: AVMediaType.audio,
                                                                        preferredTrackID: kCMPersistentTrackID_Invalid)
        
        let aVideoAssetTrack: AVAssetTrack = aVideoAsset.tracks(withMediaType: AVMediaType.video)[0]
        let aAudioOfVideoAssetTrack: AVAssetTrack? = aVideoAsset.tracks(withMediaType: AVMediaType.audio).first
        let aAudioAssetTrack: AVAssetTrack = aAudioAsset.tracks(withMediaType: AVMediaType.audio)[0]
        
        // Default must have tranformation
        compositionAddVideo?.preferredTransform = aVideoAssetTrack.preferredTransform
        
        if shouldFlipHorizontally {
            // Flip video horizontally
            var frontalTransform: CGAffineTransform = CGAffineTransform(scaleX: -1.0, y: 1.0)
            frontalTransform = frontalTransform.translatedBy(x: -aVideoAssetTrack.naturalSize.width, y: 0.0)
            frontalTransform = frontalTransform.translatedBy(x: 0.0, y: -aVideoAssetTrack.naturalSize.width)
            compositionAddVideo?.preferredTransform = frontalTransform
        }
        
        mutableCompositionVideoTrack.append(compositionAddVideo!)
        mutableCompositionAudioTrack.append(compositionAddAudio!)
        mutableCompositionAudioOfVideoTrack.append(compositionAddAudioOfVideo!)
        
        do {
            try mutableCompositionVideoTrack[0].insertTimeRange(CMTimeRangeMake(kCMTimeZero,
                                                                                aVideoAssetTrack.timeRange.duration),
                                                                of: aVideoAssetTrack,
                                                                at: kCMTimeZero)
            
            //In my case my audio file is longer then video file so i took videoAsset duration
            //instead of audioAsset duration
            try mutableCompositionAudioTrack[0].insertTimeRange(CMTimeRangeMake(kCMTimeZero,
                                                                                aVideoAssetTrack.timeRange.duration),
                                                                of: aAudioAssetTrack,
                                                                at: kCMTimeZero)
            
            // adding audio (of the video if exists) asset to the final composition
            if let aAudioOfVideoAssetTrack = aAudioOfVideoAssetTrack {
                try mutableCompositionAudioOfVideoTrack[0].insertTimeRange(CMTimeRangeMake(kCMTimeZero,
                                                                                           aVideoAssetTrack.timeRange.duration),
                                                                           of: aAudioOfVideoAssetTrack,
                                                                           at: kCMTimeZero)
            }
        } catch {
            print(error.localizedDescription)
        }
        
        // Exporting
        let savePathUrl: URL = URL(fileURLWithPath: NSHomeDirectory() + "/Documents/newVideo.mp4")
        do { // delete old video
            try FileManager.default.removeItem(at: savePathUrl)
        } catch { print(error.localizedDescription) }
        
        let assetExport: AVAssetExportSession = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality)!
        assetExport.outputFileType = AVFileType.mp4
        assetExport.outputURL = savePathUrl
        assetExport.shouldOptimizeForNetworkUse = true
        
        assetExport.exportAsynchronously{ () -> Void in
            
            switch assetExport.status {
            case AVAssetExportSessionStatus.completed:
                print("success")
                completion(nil, savePathUrl)
            case AVAssetExportSessionStatus.failed:
                print("failed \(assetExport.error?.localizedDescription ?? "error nil")")
                completion(assetExport.error, nil)
            case AVAssetExportSessionStatus.cancelled:
                print("cancelled \(assetExport.error?.localizedDescription ?? "error nil")")
                completion(assetExport.error, nil)
            default:
                print("complete")
                completion(assetExport.error, nil)
            }
            
            
        }
        
    }

这是我call function的地方。

@objc func touchCameraButton(){
soundFileURL!, completion: {(err, url) in print("fuck")})

    if isVideoRecordingOn{

        if isFirstTouch{
            startCapture()
            recordAudio()
            isFirstTouch = false
        }else{
            startCapture()
            recordAudio()
            self.mergeVideoAndAudio(videoUrl: videoFileURL, audioUrl: soundFileURL!, shouldFlipHorizontally: true, completion: {(err, url) in DispatchQueue.main.async {
                self.videoWithAudioURL = url
                if (err != nil){
                    print(err?.localizedDescription ?? "Error in merging video and audio")
                }
                self.isFirstTouch = true
                }
            })
    }
    }
}

[king8314700]

不懂什麼意思？