AVCaptureDevice.h，主要用来获取iphone一些关于相机设备的属性。

AVCaptureDevice.h，必须要引入AVFoundation.framework包。

1. 前置和后置摄像头
enum {
    AVCaptureDevicePositionBack = 1,
    AVCaptureDevicePositionFront = 2
};
typedef NSInteger AVCaptureDevicePosition;

2. 闪光灯开关
enum {
    AVCaptureFlashModeOff = 0,
    AVCaptureFlashModeOn = 1,
    AVCaptureFlashModeAuto = 2
};
typedef NSInteger AVCaptureFlashMode;

3. 手电筒开关
enum {
    AVCaptureTorchModelOff = 0,
    AVCaptureTorchModelOn = 1,
    AVCaptureTorchModeAuto = 2
};
typedef NSInteger AVCaptureTorchMode;

4. 焦距调整
enum {
    AVCaptureFocusModelLocked = 0,
    AVCaptureFocusModeAutoFocus = 1,
    AVCaptureFocusModeContinousAutoFocus = 2
};
typedef NSInteger AVCaptureFocusMode;

5. 曝光量调节
enum {
    AVCaptureExposureModeLocked = 0,
    AVCaptureExposureModeAutoExpose = 1,
    AVCaptureExposureModeContinuousAutoExposure = 2
};
typedef NSInteger AVCaptureExposureMode;

6. 白平衡
enum {
    AVCaptureWhiteBalanceModeLocked = 0,
    AVCaptureWhiteBalanceModeAutoWhiteBalance = 1,
    AVCaptureWhiteBalanceModeContinuousAutoWhiteBalance = 2
};
typedef NSInteger AVCaptureWhiteBalanceMode;