[AVAssetWriter startWriting] Cannot call method when status is 1

self.videoOutput = [[AVCaptureVideoDataOutput alloc]init];
AVCaptureConnection *captureConnection = [_videoOutput connectionWithMediaType:AVMediaTypeVideo];
captureConnection.videoOrientation = [_captureVideoPreviewLayer connection].videoOrientation;
若是有後面這兩行代碼,刪了,試試.