[AVAssetWriter startWriting] Cannot call method when status is 1

self.videoOutput = [[AVCaptureVideoDataOutput alloc]init];
AVCaptureConnection *captureConnection = [_videoOutput connectionWithMediaType:AVMediaTypeVideo];
captureConnection.videoOrientation = [_captureVideoPreviewLayer connection].videoOrientation;
如果有后面这两行代码,删了,试试.