func saveToCameraRoll(file: File, indexPath: NSIndexPath) {
        if UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(file.path) {
            UISaveVideoAtPathToSavedPhotosAlbum(file.path, self, "image:didFinishSavingWithError:contextInfo:", nil)
        } else {
            // save faild
        }
    }
    
    func image(image: UIImage, didFinishSavingWithError error: NSErrorPointer, contextInfo:UnsafePointer<Void>) {
        if error == nil {
            // save success
        } else {
            // save faild
        }
    }