想要实时地，获取前置摄像头正在拍的每一帧，然后用来做人脸检测，成功的就存下来，失败的就丢掉，但是搜了很久没有找到一个好的实现方法，最好的一个方法（http://www.open-open.com/lib/view/open1438438855910.html）已经试过，这篇博客讲得很详细，但是不知道是不是swift的版本更新了的原因，还是失败。
大家讲道理2017-04-17 17:39:18
Apple iOS 9 and later has built-in face detection, which is in timed metadata. It is also possible to obtain each frame of pictures, it has nothing to do with the front camera. These are available in Apple’s official demo.
