你好：
我下载了intel iOS 4.1的sdk，现有问题如下，请帮忙解答下，谢谢！
1、demo里面的本地流预览功能缺失，无法展示本地流预览；
2、如何切换iOS设备的前后摄像头，找不到对应的方法；
3、开启/关闭音频、开启/关闭视频没有对应API；
----------------------------------------------------
hi：
I downloaded the SDK of Intel iOS 4.1. The existing questions are as follows. Please help to answer them. Thank you.
1. The local stream preview function in demo is missing, so it can't display the local stream preview.
2. How to switch the front and rear cameras of iOS devices can not find the corresponding method;
3. There is no corresponding API to turn on/off audio and turn on/off video.
