iOS AVFoundation动态人脸识别功能

一、AVCaptureSession:设备输入数据管理对象

• 可以根据AVCaptureSession创建对应的AVCaptureDeviceInput、AVCaptureVideoDataOutput对象
• 创建出来的Input、Output对象会被添加到AVCaptureSession中管理，代表输入、输出数据对象，它配置抽象硬件设备的ports。

// 1.创建媒体管理会话
    AVCaptureSession *captureSession = [[AVCaptureSession alloc] init];
    self.session = captureSession;
    // 判断分辨率是否支持 640x480，支持就设置为：640x480
    if ([captureSession canSetSessionPreset:AVCaptureSessionPreset640x480]) {
        captureSession.sessionPreset = AVCaptureSessionPreset640x480;
    }

二、AVCaptureDevice：代表硬件设备

• 可以从这个类中获取手机硬件的照相机、声音传感器等
• 当我们在应用程序中需要改变一些硬件设备的属性（切换摄像头、闪光模式改变、相机聚焦改变）的时候必须要先为设备加锁，修改完成后解锁。
  （补充）

//4. 移除旧输入，添加新输入
//4.1 设备加锁
session.beginConfiguration()
//4.2. 移除旧设备
session.removeInput(deviceIn)
//4.3 添加新设备
session.addInput(newVideoInput)
//4.4 设备解锁
session.commitConfiguration()

// 2.获取前置摄像头
    AVCaptureDevice *captureDevice = nil;
    NSArray *cameras = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    for (AVCaptureDevice *camera in cameras) {
        if (camera.position == AVCaptureDevicePositionFront) {
            captureDevice = camera;
        }
    }
    if (!captureDevice) {
        [DLLoading DLToolTipInWindow:@"无前置摄像头！"];
        return;
    }

三、AVCaptureDeviceInput设备输入数据管理对象

• 可以根据AVCaptureDevice创建对应的AVCaptureDeviceInput对象
• 该对象将会被添加到AVCaptureSession中管理，代表输入设备，它配置抽象硬件设备的ports，常用的有麦克风、相机等

// 3.创建输入数据对象
    NSError *error = nil;
    AVCaptureDeviceInput *captureInput = [AVCaptureDeviceInput deviceInputWithDevice:captureDevice error:&error];
    if (error) {
        [DLLoading DLToolTipInWindow:@"创建输入数据对象错误"];
        return;
    }

四、AVCaptureOutput输出数据

• 输出的可以是图片(AVCaptureStillImageOutput)或者视频(AVCaptureMovieFileOutput)

// 4.创建输出数据对象
    AVCaptureVideoDataOutput *captureOutput = [[AVCaptureVideoDataOutput alloc] init];
    captureOutput.alwaysDiscardsLateVideoFrames = YES;
    [captureOutput setSampleBufferDelegate:self queue:dispatch_queue_create("cameraQueue", NULL)];
    
    NSDictionary *videoSettings = [NSDictionary dictionaryWithObject:[NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA] forKey:(NSString*)kCVPixelBufferPixelFormatTypeKey];
    [captureOutput setVideoSettings:videoSettings];

五、添加输入、输出数据对象到session中

// 5.添加【输入数据对象】和【输出数据对象】到会话中
    if ([captureSession canAddInput:captureInput]) {
        [captureSession addInput:captureInput];
    }
    if ([captureSession canAddOutput:captureOutput]) {
        [captureSession addOutput:captureOutput];
    }

六、AVCaptureVideoPreviewLayer创建实时预览图层

• 我们手机的照片以及视频是怎样显示在手机屏幕上的呢，就是通过把这个对象添加到UIView的layer上的。

// 6.创建实时预览图层
    AVCaptureVideoPreviewLayer *previewlayer = [AVCaptureVideoPreviewLayer layerWithSession:captureSession];
    [previewlayer connection].videoOrientation = (AVCaptureVideoOrientation)[[UIApplication sharedApplication] statusBarOrientation];
    self.view.layer.masksToBounds = YES;
    previewlayer.frame = CGRectMake((kMainScreenWidth-200)/2, 90, 200, 200);
    previewlayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    [self.scanView insertPreviewLayer:previewlayer];

人脸检测器

#pragma mark - 人脸检测器
- (CIDetector *)detector{
    if (_detector == nil){
        CIContext *context = [CIContext contextWithOptions:nil];
        NSDictionary *options = [NSDictionary dictionaryWithObject:CIDetectorAccuracyHigh forKey:CIDetectorAccuracy];
        _detector = [CIDetector detectorOfType:CIDetectorTypeFace context:context options:options];
    }
    return _detector;
}

检测人脸照片

#pragma mark - 检测人脸照片
- (UIImage *)getFaceImageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer{
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CIImage *ciImage = [CIImage imageWithCVPixelBuffer:imageBuffer];
    CIContext *temporaryContext = [CIContext contextWithOptions:nil];
    CGImageRef videoImage;
    if ([[UIApplication sharedApplication] statusBarOrientation] == UIInterfaceOrientationPortrait) {
        videoImage = [temporaryContext createCGImage:ciImage fromRect:CGRectMake(0, 80, 480, 480)];
    }else{
        videoImage = [temporaryContext createCGImage:ciImage fromRect:CGRectMake(80, 0, 480, 480)];
    }
    UIImage *resultImg = [[UIImage alloc] initWithCGImage:videoImage];
    CGImageRelease(videoImage);
    
    //人脸检测
    CIImage *resultCmg = [[CIImage alloc] initWithCGImage:resultImg.CGImage];
    CIFaceFeature * faceFeature = [self.detector featuresInImage:resultCmg].linq_firstOrNil;
    if (faceFeature && faceFeature.hasLeftEyePosition && faceFeature.hasRightEyePosition && faceFeature.hasMouthPosition) {
        return resultImg;
    }
    return nil;
}

代理方法

• 获取到outputSampleBuffer 后进行人脸识别操作。

#pragma mark - AVCaptureVideoDataOutputSampleBufferDelegate
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{
    if (!self.isDetecting) {
        self.isDetecting = YES;
        [connection setVideoOrientation:(AVCaptureVideoOrientation)[[UIApplication sharedApplication] statusBarOrientation]];
        UIImage *img = [self getFaceImageFromSampleBuffer:sampleBuffer];
        if (img && self.timeoutTime > 2) {
            dispatch_async(dispatch_get_main_queue(), ^{
                [self.session stopRunning];
                self.isDetecting = NO;
                self.timeoutTime = 0;
                [self.scanView startAnimating];
                [self.viewModel faceScanWithImg:img];
            });
        }else{
            self.isDetecting = NO;
        }
    }
}