AVFoundationで背面カメラと前面カメラの切り替えをする

環境

• Xcode 8.1
• えるたそ (OS X El Capitan 10.11.6)
• Swift 3.0.1
• iOS 10.1 (iPhoneSE)

画面構成

正方形の previewView (UIView)が配置されていて、
changeUseCamera: アクションボタンと pushShutter: アクションボタンが設置されています。

サンプルソースコード

ViewController.swift

import UIKit
import AVFoundation

class ViewController: UIViewController {

	@IBOutlet weak var previewView: UIView!
	
	var isBackCamera: Bool = true
	var captureSession: AVCaptureSession!
	var cameraDevices: AVCaptureDevice!
	var imageOutput: AVCaptureStillImageOutput!
	
	// MARK: - Life Cycle
	override func viewWillAppear(_ animated: Bool) {
		super.viewWillAppear(animated)
		self.setupCamera(isBack: self.isBackCamera)
	}

	// MARK: - Private Method
	fileprivate func setupCamera(isBack: Bool) {
		guard let devices = AVCaptureDevice.devices() else {
			return
		}
		for device in devices {
			// isBack == True  -> Back Camera
			// iSBack == False -> Front Camera
			let devicePosition: AVCaptureDevicePosition = isBack ? .back : .front
			if (device as AnyObject).position == devicePosition {
				self.cameraDevices = device as! AVCaptureDevice
			}
		}

		let videoInput: AVCaptureInput!
		do {
			videoInput = try AVCaptureDeviceInput.init(device: self.cameraDevices)
		} catch {
			videoInput = nil
		}

		self.captureSession = AVCaptureSession()
		self.captureSession.addInput(videoInput)

		self.imageOutput = AVCaptureStillImageOutput()
		self.captureSession.addOutput(self.imageOutput)

		let captureVideoLayer = AVCaptureVideoPreviewLayer.init(session: self.captureSession)
		let layerRect = CGRect(x: self.previewView.frame.origin.x,
						       y: 0,
						       width: UIScreen.main.bounds.size.width,
						       height: UIScreen.main.bounds.size.width)

		captureVideoLayer?.frame = layerRect
		captureVideoLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill

		guard let videoLayer = captureVideoLayer else {
			return
		}
		self.previewView.layer.addSublayer(videoLayer)

		// 開始
		self.captureSession.startRunning()
	}
	
	// MARK: - IBAction
	
	// Change Camera
	@IBAction func changeUseCamera(_ sender: Any) {
		self.isBackCamera = !self.isBackCamera
		setupCamera(isBack: self.isBackCamera)
	}

	// Save taken photo
	@IBAction func pushShutter(_ sender: Any) {
		let captureVideoConnection = imageOutput.connection(withMediaType: AVMediaTypeVideo)

		self.imageOutput.captureStillImageAsynchronously(from: captureVideoConnection) { [weak self] (imageDataBuffer, error) -> Void in

			let capturedImageData: Data = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(imageDataBuffer) as Data

			guard let image = UIImage(data: capturedImageData),
					let wself = self else {
				return
			}

			UIImageWriteToSavedPhotosAlbum(image, wself, nil, nil)
		}
	}
}

補足

このままだと、一度アプリから離脱をしてしまうとカメラのセッションが切れてしまうので AppDelegate.swift の applicationDidBecomeActive: 等のメソッドを使って通知してセッションを再始動しないとダメなようです。