AVFoundation - 捕捉设备: AVCaptureDevice

AVCaptureDevice是相机硬件的接口，用于配置底层硬件的属性，这些底层硬件包括前后置摄像头、麦克风、闪光灯等。

验证授权

1. 请求用户授权指定的媒体类型

为保护用户隐私，应用在使用相机或者麦克风时，总是需要用户授权才能正常使用。当应用第一次需要权限的媒体类型创建任何AVCaptureDeviceInput对象时，系统会自动显示一个alert以请求用户授权。在被授予任何访问权限之前，任何AVMediaType类型的AVCaptureDevice都将关闭静默音频样本或黑色视频帧。
调用下面方法，可以让应用直接获取用户授权，而不是需要等到创建AVCaptureDeviceInput对象时，系统自动显示一个alert以请求用户授权。

+ (void)requestAccessForMediaType:(AVMediaType)mediaType completionHandler:(void (^)(BOOL granted))handler

该方法有两个参数:

第一个参数mediaType: 媒体类型常量，可以是AVMediaTypeVideo和AVMediaTypeAudio，如果没有提供媒体类型或提供其他的媒体类型，都将抛出异常
第二个参数(void (^)(BOOL granted))handler: 获得用户相应后调用的块，如果用户授予使用硬件的权限，则granted返回YES,否则返回NO.注意块回调可能在任意线程，如果需要处理UI，需要切回主线程。
如果调用该方法之前，已经显示alert以请求用户授权，不管用户同意或者拒绝授权，该方法的回调都会立即放回用户曾经的授权结果，而不会再次显示一个alert请求用户授权。

应用程序必须在配置信息info.plist中提供使用NSCameraUsageDescription或NSMicrophoneUsageDescription信息的解释。iOS在最初请求用户许可时显示了这个解释，然后在设置应用程序中显示。在没有使用说明的情况下启动AVCaptureSession会引发异常。

2. 获取制定媒体类型的授权状态

为了获悉应用程序是否获取指定媒体类型的权限，应用可以调用下面的类方法获取授权状态:

+ (AVAuthorizationStatus)authorizationStatusForMediaType:(AVMediaType)mediaType;

该方法同步调用，会立即返回授权状态。如果此方法返回AVAuthorizationStatusNotDetermined，则可以调用+requestAccessForMediaType:completionHandler:以提示用户记录权限

授权状态AVAuthorizationStatus

AVAuthorizationStatusNotDetermined: 用户尚未授权
AVAuthorizationStatusRestricted:不允许用户访问媒体捕获设备，用户不能改变客户机的状态,可能由于活跃的限制,如家长控制，这个状态通常是看不到的,用于发现设备的类方法不会返回用户被限制访问的设备。
AVAuthorizationStatusDenied:用户已经明确拒绝了应用访问捕获设备
AVAuthorizationStatusAuthorized: 用户授予应用访问捕获设备的权限

媒体类型AVMediaType

AVMediaTypeVideo: 指定视频
AVMediaTypeAudio: 指定音频
AVMediaTypeText: 指定文本
AVMediaTypeClosedCaption: 指定闭路内容
AVMediaTypeSubtitle: 指定字幕
AVMediaTypeTimecode: 指定一个时间代码
AVMediaTypeMetadata: 指定元数据
AVMediaTypeMuxed: 指定混合媒体
AVMediaTypeMetadataObject
AVMediaTypeDepthData

通知

AVCaptureDeviceWasConnectedNotification
当新设备可用时发送一个通知，通知对象是AVCaptureDevice实例，表示已可用的设备。
AVCaptureDeviceWasDisconnectedNotification
当现有设备不可用时发送一个通知，通知对象是AVCaptureDevice实例，表示不可用的设备。

闪光灯

在光线不足的情况下，需要开启屏幕的闪光灯来进行补光，便于镜头可以捕捉更好的场景，拍摄出好的照片和视频

iOS 10之前闪光灯设置

   AVCaptureDevice *device = nil;
   NSArray *inputs = self.session.inputs;
   for (AVCaptureDeviceInput *input in inputs) {
       if ([device.deviceType isEqual:AVMediaTypeVideo]) {
           device = input.device;
       }
   }
   NSError *errorProperty = nil;
   if ([device hasFlash]) {
       if ([device isFlashAvailable]) {
           if ([device isFlashModeSupported:AVCaptureFlashModeOn]) {
               BOOL result = NO;
               result = [device lockForConfiguration:&errorProperty];
               if (result) {
                   [device setFlashMode:AVCaptureFlashModeOn];
               }else {
                   NSLog(@"ERROR : CONFIGURATION CAPTURE DEVICE FLASH FAILURE, ERROR CODE:%ld", (long)errorProperty.code);
               }
               [device unlockForConfiguration];
           }else{
               NSLog(@"ERROR : FLASH IS UNAVAILABLE BECAUSE THE DEVCICE OVERHEATS");
           }
       }else {
           NSLog(@"ERROR : SOFTWARE DEVICE HAVE NO FLASH");
       }
   }

iOS 10之后闪光灯设置

    NSArray *outputs = self.session.outputs;
    for (AVCaptureOutput *output in outputs) {
        if ([output isMemberOfClass:[AVCapturePhotoOutput class]]) {
            AVCapturePhotoOutput *photoOutput = (AVCapturePhotoOutput *)output;
            BOOL flashSupported = [[photoOutput supportedFlashModes] containsObject:@(AVCaptureFlashModeAuto)];
            if (flashSupported) {
                AVCapturePhotoSettings *photoSettings = photoOutput.photoSettingsForSceneMonitoring;
                photoSettings.flashMode = AVCaptureFlashModeAuto;
            }else {
                NSLog(@"ERROR : PHOTOOUTPUT CAN NOT SUPPORT AVCAPTUREMODE TYPE");
            }
        }
    }

闪光灯类型

    AVCaptureFlashModeOff  = 0,//闪光灯关闭
    AVCaptureFlashModeOn   = 1,//闪光灯开启
    AVCaptureFlashModeAuto = 2,//闪光灯自动

手电筒

在光线不是很暗的情况下我们可以用手机的LED灯当作手电筒使用。

    AVCaptureDevice *device = nil;
    NSArray *inputs = self.session.inputs;
    for (AVCaptureDeviceInput *input in inputs) {
        if ([device.deviceType isEqual:AVMediaTypeVideo]) {
            device = input.device;
        }
    }
    NSError *error = nil;
    if ([device hasTorch]) {
        if ([device isTorchAvailable]) {
            if ([device isTorchModeSupported:AVCaptureTorchModeOn]) {
                BOOL result = NO;
                result = [device lockForConfiguration:&error];
                if (result) {
                    [device setTorchMode:AVCaptureTorchModeOn];
                }else {
                    NSLog(@"ERROR : CONFIGURATION DEVICE TORCH FAIL AND ERROR CODE %ld", (long)error.code);
                }
                error = nil;
                // Torch light
                result = [device setTorchModeOnWithLevel:0.5 error:&error];
                if (!result) {
                    NSLog(@"ERROR : DEVICE SET TORCH FAILURE AND ERROR CODE %ld", error.code);
                }
                [device unlockForConfiguration];
            }else {
                NSLog(@"ERROR : DEVICE CAN NO SUPPORT TORCH");
            }
        }else {
            NSLog(@"ERROR : SOFTHARE DEVICE TORCH IS UNAVAILABLE BECAUSE OVERHEATS");
        }
    }else {
        NSLog(@"ERROR : SOFFHARE DEVICE HAS NO TORCH");
    }

手电筒模式类型

   AVCaptureTorchModeOff  = 0,//关闭
   AVCaptureTorchModeOn   = 1,//打开
   AVCaptureTorchModeAuto = 2,//自动

聚焦

- (void)focusAtPoint:(CGPoint)point {
    AVCaptureDevice *device = [self activeCamera];
    
    if (device.isFocusPointOfInterestSupported && [device isFocusModeSupported:AVCaptureFocusModeAutoFocus]) {
        NSError *error;
        // 锁定设备准备配置，如果获得了锁
        if ([device lockForConfiguration:&error]) {
            // 将focusPointOfInterest属性设置CGPoint
            device.focusPointOfInterest = point;
            
            device.focusMode = AVCaptureFocusModeAutoFocus;
            
            // 释放该锁定
            [device unlockForConfiguration];
        } else {
            if ([self.delegate respondsToSelector:@selector(deviceConfigurationFailedWithError:)]) {
                [self.delegate deviceConfigurationFailedWithError:error];
            }
        }
    }
}

聚焦类型

   AVCaptureFocusModeLocked              = 0,//锁定当前镜头位置
   AVCaptureFocusModeAutoFocus           = 1,//镜头自动调焦
   AVCaptureFocusModeContinuousAutoFocus = 2,//镜头连续自动调焦

曝光

- (void)exposeAtPoint:(CGPoint)point {
    AVCaptureDevice *device = [self activeCamera];
    
    if (device.isExposurePointOfInterestSupported && [device isExposureModeSupported:AVCaptureExposureModeContinuousAutoExposure]) {
        NSError *error;
        
        if ([device lockForConfiguration:&error]) {
            device.exposurePointOfInterest = point;
            device.exposureMode = AVCaptureExposureModeContinuousAutoExposure;
            
            [device unlockForConfiguration];
        } else {
            if ([self.delegate respondsToSelector:@selector(deviceConfigurationFailedWithError:)]) {
                [self.delegate deviceConfigurationFailedWithError:error];
            }
        }
    }
}

曝光设置类型

    AVCaptureExposureModeLocked                            = 0,//锁定
    AVCaptureExposureModeAutoExpose                        = 1,//自动对焦
    AVCaptureExposureModeContinuousAutoExposure            = 2,//实现连续自动对焦

白平衡

类型设置白平衡

    AVCaptureDevice *device = nil;
    NSArray *inputs = self.session.inputs;
    for (AVCaptureDeviceInput *input in inputs) {
        if ([device.deviceType isEqual:AVMediaTypeVideo]) {
            device = input.device;
        }
    }
    if ([device isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeAutoWhiteBalance]) {
        NSError *error;
        if ([device lockForConfiguration:&error]) {
            [device setWhiteBalanceMode:AVCaptureWhiteBalanceModeAutoWhiteBalance];
        }
        [device unlockForConfiguration];
    }

白平衡类型

    AVCaptureWhiteBalanceModeLocked                     = 0,
    AVCaptureWhiteBalanceModeAutoWhiteBalance           = 1,
    AVCaptureWhiteBalanceModeContinuousAutoWhiteBalance = 2,

RGB设置白平衡

    AVCaptureDevice *device = nil;
    NSArray *inputs = self.session.inputs;
    for (AVCaptureDeviceInput *input in inputs) {
        if ([device.deviceType isEqual:AVMediaTypeVideo]) {
            device = input.device;
        }
    }
    float maxWhiteBalance = device.maxWhiteBalanceGain;
    float redGain =  MIN(2.0, maxWhiteBalance);
    float greenGain = MIN(2.0, maxWhiteBalance);
    float blueGain = MIN(2.0, maxWhiteBalance);
    AVCaptureWhiteBalanceGains whiteBalanceGains = {
        redGain,
        greenGain,
        blueGain
    };
    
    [device setWhiteBalanceModeLockedWithDeviceWhiteBalanceGains:whiteBalanceGains completionHandler:nil];

AVFoundation - 捕捉设备: AVCaptureDevice

验证授权

1. 请求用户授权指定的媒体类型

2. 获取制定媒体类型的授权状态

通知

闪光灯

手电筒

聚焦

曝光

白平衡

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