照片、视频捕捉，小视频、直播都会用到AVFoundation框架
捕捉回话
- 捕捉回话：AVCaptureSession
- 捕捉设备：AVCaptureDevice
- 捕捉设备输入：AVCaptureDeviceInput
- 捕捉连接：AVCaptureConnection
- 捕捉预览：AVCaptureVideoPreviewLayer
- 捕捉设备输出：AVCaptureOutput(抽象类)
- AVCaptureStillImageOutput
- AVCaputureMovieFileOutput
- AVCaputureAudioDataOutput
- AVCaputureVideoDataOutput
