// 采集
- (void)setupCaputureVideo {
 // 1.創(chuàng)建捕獲對話，必須要強引用，否則會釋放
 _captureSession = [[AVCaptureSession alloc] init];
 // 2.捕獲攝像頭設備，默認前置攝像頭
 AVCaptureDevice *videoDevice = [self getVideoDevice:AVCaptureDevicePositionFront];
 // 3.獲取聲音設備
 AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
 // 4.創(chuàng)建對應視頻設備輸入對象
 _currentVideoDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:nil];
 // 5.創(chuàng)建對應音頻設備輸入對象
 AVCaptureDeviceInput *audioDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:nil];
 // 6.添加到會話中 注意：最好要判斷是否能添加輸入，會話不能添加空的
 // 6.1 添加視頻
 if ([_captureSession canAddInput:_currentVideoDeviceInput]) {
 [_captureSession addInput:_currentVideoDeviceInput];
 }
 // 6.2 添加音頻
 if ([_captureSession canAddInput:audioDeviceInput]) {
 [_captureSession addInput:audioDeviceInput];
 }
 // 7.捕獲視頻數據輸出設備
 AVCaptureVideoDataOutput *videoOutput = [[AVCaptureVideoDataOutput alloc] init];
 //7.1 設置代理， 捕獲視頻樣品數據
 dispatch_queue_t videoQueue = dispatch_queue_create("Video Capure Queue", DISPATCH_QUEUE_SERIAL);
 [videoOutput setSampleBufferDelegate: self queue:videoQueue];
 // 8.設置音頻數據輸出設備
 AVCaptureAudioDataOutput *audioOutput = [[AVCaptureAudioDataOutput alloc] init];
 // 8.1 設置代理，捕獲音頻樣品數據 注意：必須是串行隊列才能捕獲到數據,而且不能為空
 dispatch_queue_t audioQueue = dispatch_queue_create("Audio Capure Queue", DISPATCH_QUEUE_SERIAL);
 [audioOutput setSampleBufferDelegate:self queue:audioQueue];
 // 9.添加到會話中 注意：最好要判斷是否能添加輸入，會話不能添加空的
 if ([_captureSession canAddOutput:videoOutput]) {
 [_captureSession addOutput:videoOutput];
 }
 if ([_captureSession canAddOutput:audioOutput]) {
 [_captureSession addOutput:audioOutput];
 }
 // 10.獲取視屏輸入與輸出連接，用于分辨音視頻數據
 _videoConnection = [videoOutput connectionWithMediaType:AVMediaTypeVideo];
 // 11.添加視屏預覽圖層
 _previewdLayer = [AVCaptureVideoPreviewLayer layerWithSession:_captureSession];
 _previewdLayer.frame = [UIScreen mainScreen].bounds;
 [self.view.layer insertSublayer:_previewdLayer atIndex:0];
 // 12.開啟會話
 [_captureSession startRunning];
}
// 根據攝像頭方向獲取攝像頭
- (AVCaptureDevice *)getVideoDevice: (AVCaptureDevicePosition)position {
 NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
 for (AVCaptureDevice *device in devices) {
 if (device.position == position) {
 return device;
 }
 }
 return nil;
}

AVCaptureDevicePositionUnspecified，那么是不能調用攝像頭的。
typedef NS_ENUM(NSInteger, AVCaptureDevicePosition) {
 AVCaptureDevicePositionUnspecified = 0, // 不指定
 AVCaptureDevicePositionBack = 1, //后置
 AVCaptureDevicePositionFront = 2 // 前置
}

// 獲取輸出設備數據，有可能是音頻，有可能是視頻
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
 if (_videoConnection == connection) {
 NSLog(@"采集到視屏數據");
 }else {
 NSLog(@"采集到音頻數據");
 }
}

#pragma mark - 切換攝像頭
- (IBAction)toggleCapture:(id)sender {
 // 1.獲取當前設備方向
 AVCaptureDevicePosition cureentPosition = _currentVideoDeviceInput.device.position;
 // 2.獲取需要改變的方向
 AVCaptureDevicePosition togglePosition = (cureentPosition == AVCaptureDevicePositionFront ? AVCaptureDevicePositionBack : AVCaptureDevicePositionFront);
 // 3.獲取需要改變的攝像頭設備
 AVCaptureDevice *toggleDevice = [self getVideoDevice:togglePosition];
 // 4.獲取需要改變的攝像頭輸入設備
 AVCaptureDeviceInput *toggleDeviceInput = [[AVCaptureDeviceInput alloc] initWithDevice:toggleDevice error:nil];
 // 5.停止會話，否則會有一瞬間的白屏
 [_captureSession stopRunning];
 // 6.移除之前的攝像頭輸入設備,否則會崩潰，因為會話里只能有一個攝像頭設備
 [_captureSession removeInput:_currentVideoDeviceInput];
 // 7.添加新的攝像頭輸入設備
 [_captureSession addInput:toggleDeviceInput];
 // 8.重新開始會話
 [_captureSession startRunning];
 // 記錄當前攝像頭輸入設備
 //9.重新開始
 _currentVideoDeviceInput = toggleDeviceInput;
}