iOS AVFoundation之自定義相機AVCaptureSession(曝光和聚集控制)

轉自:https://www.jianshu.com/p/58790d70b08f

要自定義一個相機,涉及的類有很多, 這也是AVFounation的重要學習內容之一, 音視頻的捕獲方面的知識更是重中之重,大概涉及的類有AVCaptureSession、AVCaptureConnection、AVCaptureDevice、AVCaptureDeviceInput、AVCapturePhotoOutput、AVCaptureMovieFileOutput等，下面來一一介紹

AVCaptureSession

這個就是充當會話者的角色，我們可以理解爲平時生活中的插線板，有輸入，有輸出。其中AVCaptureDeviceInput爲輸入， AVCapturePhotoOutput、AVCaptureMovieFileOutput等爲輸出它們之間的關係我們可以看一下下面這幅圖

輸入，輸出與會話者之間的關係

這裏的AVCaptureStillImageOutPut和AVCapturePhotoOutput是類似的， iOS10之前用AVCaptureStillImageOutPut， iOS10之後用AVCapturePhotoOutput

其中輸入源有：AVCaptureDeviceInput（video）、 AVCaptureDeviceInput（audio）
輸出源有：AVCaptureVideoDataOutput, AVCaptureAudioDataOutput, AVCaptureMovieFileOutput, AVCaptureStillImageOutput(AVCapturePhotoOutput), AVCaptureMetadataOutput,

簡單的創建一個會話者

AVCaptureSession *session = [[AVCaptureSession alloc] init];

// 添加輸入與輸出

[session startRunning];

AVCaptureSession可以擁有一個或多個輸入源，當你想獲取一張圖片的時候你只需要AVCaptureDeviceInput（video）也就是圖像的輸入源就可以了，當你想獲取一段有聲的視頻時，則需要兩個輸入源AVCaptureDeviceInput（video）和AVCaptureDeviceInput（audio），你還可以只獲取聲音數據的時候，只要AVCaptureDeviceInput（audio）就可以了。
在創建AVCaptureSession時我們一般會設定一個預設來獲取不同規格的數據：

NSString *const AVCaptureSessionPresetPhoto; //一般在獲取靜態圖片的時候用
NSString *const AVCaptureSessionPresetHigh; 
NSString *const AVCaptureSessionPresetMedium;
NSString *const AVCaptureSessionPresetLow; 
NSString *const AVCaptureSessionPreset352x288;
NSString *const AVCaptureSessionPreset640x480;  //  VGA.
NSString *const AVCaptureSessionPreset1280x720;  // 720p HD.
NSString *const AVCaptureSessionPreset1920x1080;
NSString *const AVCaptureSessionPresetiFrame960x540;
NSString *const AVCaptureSessionPresetiFrame1280x720;
NSString *const AVCaptureSessionPresetInputPriority; //通過已連接的捕獲設備的 activeFormat 來反過來控制 capture session 的輸出質量等級

在配置AVCaptureSession, 需要注意的是：
1、在輸入輸出或配置它的時候，線程是阻塞的，所以最後是創建一條串行隊列異步執行。
2、在改變或配置輸入，輸出，預設（sessionPreset）的時候，在AVCaptureSession所在線程在修改或配置之前調用- (void)beginConfiguration; 修改完之後，或修改失敗之後調用- (void)commitConfiguration;，這樣可以提高流暢性等不必要的BUG。

AVCaptureConnection

在AVCaptureSession中，可能存在着很多的AVCaptureConnection， AVCaptureConnection代表着一條連接通道，例如：獲取一張圖片，輸入是AVCaptureDeviceInput（video） 輸出是 AVCaptureStillImageOutput(AVCapturePhotoOutput)，在輸入到輸出這個過程中，就有一個AVCaptureConnection對象去管理者這個流程。AVCaptureConnection可以有多個輸入和輸出，例如：獲取視視頻的時候，就有視頻和音頻的輸入，輸出也可以分視頻數據和音頻數據，還可以獲取圖片數據。一般這個對象在你AVCaptureSession中加入輸入輸出的時候就會自動的幫你創建了。

AVCaptureConnection與輸入輸出的關係

所以我們一般是去獲取使用：

AVCaptureConnection *connection = [movieFileOutput connectionWithMediaType:AVMediaTypeAudio];

我們一般用它來管理視頻或圖片輸出的方向格式等問題，還有音頻輸出的音量、聲道等，控制輸入或輸出

//圖片輸出朝向問題
       AVCaptureConnection *photoOutputConnection = [self.photoOutput connectionWithMediaType:AVMediaTypeVideo];
        photoOutputConnection.videoOrientation = videoPreviewLayerVideoOrientation;

其中朝向問題，這裏整理出來然大家有個很好的對比

[UIApplication sharedApplication].statusBarOrientation; 狀態欄的方向跟視頻的方向是一致的， 還有對比設備的朝向
typedef NS_ENUM(NSInteger, UIInterfaceOrientation) {
    UIInterfaceOrientationUnknown                                                           = UIDeviceOrientationUnknown, 
    UIInterfaceOrientationPortrait            =  AVCaptureVideoOrientationPortrait          = UIDeviceOrientationPortrait,              //home button on the bottom.
    UIInterfaceOrientationPortraitUpsideDown  = AVCaptureVideoOrientationPortraitUpsideDown = UIDeviceOrientationPortraitUpsideDown,    //home button on the top.
    UIInterfaceOrientationLandscapeLeft       = AVCaptureVideoOrientationLandscapeRight     = UIDeviceOrientationLandscapeRight,        //home button on the right.
    UIInterfaceOrientationLandscapeRight      = AVCaptureVideoOrientationLandscapeLeft      = UIDeviceOrientationLandscapeLeft          //home button on the left.  
} __TVOS_PROHIBITED;

AVCaptureDeviceInput

這個類代表着AVCaptureSession中的輸入，其中會根據AVCaptureDevice中的是視頻設備（攝像頭）還是音頻設備（麥克風），的不同而不同，創建出來之後充當輸入的角色添加到AVCaptureSession中

    //配置session輸入輸出, 或輸入輸出屬性, sessionPreset時,需要用到-beginConfiguration, -commitConfiguration
    [self.session beginConfiguration];
    self.session.sessionPreset = AVCaptureSessionPresetPhoto;
    //添加視頻輸入
    AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithDeviceType:AVCaptureDeviceTypeBuiltInWideAngleCamera mediaType:AVMediaTypeVideo position:AVCaptureDevicePositionUnspecified];
    AVCaptureDeviceInput *videoDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
    if (!videoDeviceInput) {
        NSLog(@"視頻設備輸出創建錯誤--%@", error);
        self.setupResult = AVCamManualSetupResultSessionConfigurationFailed;
        [self.session commitConfiguration];
        return;
    }
    if ([self.session canAddInput:videoDeviceInput]) {
        [self.session addInput:videoDeviceInput];
        self.videoDeviceInput = videoDeviceInput;
        self.videoDevice = videoDevice;
        dispatch_async(dispatch_get_main_queue(), ^{//調整視頻輸入方向
            UIInterfaceOrientation statusBarOriebtation = [UIApplication sharedApplication].statusBarOrientation;
            AVCaptureVideoOrientation initialVideoOrientation = AVCaptureVideoOrientationPortrait;
            if (statusBarOriebtation != UIInterfaceOrientationUnknown) {
                initialVideoOrientation = (AVCaptureVideoOrientation)statusBarOriebtation;
            }
            
            AVCaptureVideoPreviewLayer *previewLayer = (AVCaptureVideoPreviewLayer *)self.previewView.layer;
            previewLayer.connection.videoOrientation = initialVideoOrientation;
        });
    }else {
        NSLog(@"不能添加視頻輸入到session");
        self.setupResult = AVCamManualSetupResultSessionConfigurationFailed;
        [self.session commitConfiguration];
        return;
    
    }
    
    //添加音頻輸入
    AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
    AVCaptureDeviceInput *audioDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:&error];
    if (!audioDeviceInput) {
        NSLog(@"音頻設備輸出創建錯誤--%@", error);
        
    }
    
    if ([self.session canAddInput:audioDeviceInput]) {
        [self.session addInput:audioDeviceInput];
    }else {
     
        NSLog(@"不能添加音頻輸入到session");
    }

需要注意的是：
1、攝像頭的聚焦（AVCaptureFocusMode）、曝光（AVCaptureExposureMode）、白平衡（AVCaptureWhiteBalanceMode）和感光度（ISO）等等一些參數設置都是在AVCaptureDevice（video）裏面配置完成的。
2、AVCaptureDevice配置參數或修改參數的時候都要注意先調用 - (BOOL)lockForConfiguration:(NSError **)outError; 配置完成後調用 - (void)unlockForConfiguration;

下面是一下參數的配置：

//改變聚焦模式
- (IBAction)changeFocusMode:(id)sender
{
    UISegmentedControl *control = sender;
    AVCaptureFocusMode mode = (AVCaptureFocusMode)[self.focusModes[control.selectedSegmentIndex] intValue];
    NSError *error = nil;
    if ([self.videoDevice lockForConfiguration:&error]) {
        if ([self.videoDevice isFocusModeSupported:mode]) {
            self.videoDevice.focusMode = mode;
        }
        else {
           NSLog( @"Focus mode %@ is not supported. Focus mode is %@.", [self stringFromFocusMode:mode], [self stringFromFocusMode:self.videoDevice.focusMode] );
            self.focusModeControl.selectedSegmentIndex = [self.focusModes indexOfObject:@(self.videoDevice.focusMode)];
            [self.videoDevice unlockForConfiguration];
        }
       
    }
    else {
         NSLog( @"Could not lock device for configuration: %@", error );
    }
    
}

//手動模式下， 改變鏡頭聚焦位置
- (IBAction)changeLensPosition:(id)sender
{
    UISlider *control = sender;
    NSError *error = nil;
    if ([self.videoDevice lockForConfiguration:&error]) {
        [self.videoDevice setFocusModeLockedWithLensPosition:control.value completionHandler:nil];//手動聚焦
        [self.videoDevice unlockForConfiguration];
    }
    else {
        NSLog( @"Could not lock device for configuration: %@", error );
    }
}

//設置輸入設備的聚焦和曝光的模式和點
- (void)focusWithMode:(AVCaptureFocusMode)focusMode exposeWithMode:(AVCaptureExposureMode)exposureMode atDevicePoint:(CGPoint)point monitorSubjectAreaChange:(BOOL)monitorSubjectAreaChange
{
    dispatch_async(self.sessionQueue, ^{
        AVCaptureDevice *device = self.videoDevice;
        NSError *error = nil;
        if ([device lockForConfiguration:&error]) {
            if (focusMode != AVCaptureFocusModeLocked && device.isFocusPointOfInterestSupported && [device isFocusModeSupported:focusMode]) {
                device.focusPointOfInterest = point;
                device.focusMode = focusMode;
            }
            
            if (exposureMode != AVCaptureExposureModeCustom && device.isExposurePointOfInterestSupported && [device isExposureModeSupported:exposureMode]) {
                device.exposurePointOfInterest = point;
                device.exposureMode = exposureMode;
            }
            
            device.subjectAreaChangeMonitoringEnabled = monitorSubjectAreaChange;
            [device unlockForConfiguration];
        }else {
          NSLog( @"Could not lock device for configuration: %@", error );
        }
    });
}

//根據點擊的位置， 進行聚焦和曝光
- (IBAction)focusAndExposeTap:(UIGestureRecognizer *)gestureRecognizer
{
    CGPoint devicePoint = [(AVCaptureVideoPreviewLayer *)self.previewView.layer captureDevicePointOfInterestForPoint:[gestureRecognizer locationInView:[gestureRecognizer view]]];
    [self focusWithMode:self.videoDevice.focusMode exposeWithMode:self.videoDevice.exposureMode atDevicePoint:devicePoint monitorSubjectAreaChange:YES];
    
}

//改變曝光模式
- (IBAction)changeExposureMode:(id)sender
{
    UISegmentedControl *control = sender;
    AVCaptureExposureMode mode = (AVCaptureExposureMode)[self.exposureModes[control.selectedSegmentIndex] intValue];
    NSError *error = nil;
    if ([self.videoDevice lockForConfiguration:&error]) {
        if ([self.videoDevice isExposureModeSupported:mode]) {
            self.videoDevice.exposureMode = mode;
        }
        else {
          NSLog( @"Exposure mode %@ is not supported. Exposure mode is %@.", [self stringFromExposureMode:mode], [self stringFromExposureMode:self.videoDevice.exposureMode] );
            self.exposureModeControl.selectedSegmentIndex = [self.exposureModes indexOfObject:@(self.videoDevice.exposureMode)];
        }
        [self.videoDevice unlockForConfiguration];
    }
    else {
       NSLog( @"Could not lock device for configuration: %@", error );
    }
}

//手動模式下的設置曝光時間
- (IBAction)changeExposureDuration:(id)sender
{
    UISlider *control = sender;
    NSError *error = nil;
    
    double p = pow( control.value, kExposureDurationPower ); // Apply power function to expand slider's low-end range
    double minDurationSeconds = MAX( CMTimeGetSeconds( self.videoDevice.activeFormat.minExposureDuration ), kExposureMinimumDuration );
    double maxDurationSeconds = CMTimeGetSeconds( self.videoDevice.activeFormat.maxExposureDuration );
    double newDurationSeconds = p * ( maxDurationSeconds - minDurationSeconds ) + minDurationSeconds; // Scale from 0-1 slider range to actual duration
    if ([self.videoDevice lockForConfiguration:&error]) {
        [self.videoDevice setExposureModeCustomWithDuration:CMTimeMakeWithSeconds(newDurationSeconds, 1000*1000*1000) ISO:AVCaptureISOCurrent completionHandler:nil];
        [self.videoDevice unlockForConfiguration];
    }
    else {
    
      NSLog( @"Could not lock device for configuration: %@", error );
    }
}

AVCaptureOutput

一般是用他們的子類AVCaptureVideoDataOutput, AVCaptureAudioDataOutput, AVCaptureMovieFileOutput, AVCaptureStillImageOutput(AVCapturePhotoOutput), AVCaptureMetadataOutput, 他們都用相對應的代理，其中數據輸出都是通過代理來實現的，
下面的是視頻的數據輸出和存儲

- (IBAction)toggleMovieRecording:(id)sender
{
    self.recordButton.enabled = NO;
    self.cameraButton.enabled = NO;
    self.captureModeControl.enabled = NO;
    
    AVCaptureVideoPreviewLayer *previewLayer = (AVCaptureVideoPreviewLayer *)self.previewView.layer;
    AVCaptureVideoOrientation previewLayerVideoOrientation = previewLayer.connection.videoOrientation;
    dispatch_async(self.sessionQueue, ^{
        if (!self.movieFileOutput.isRecording) {
            
            if ([UIDevice currentDevice].isMultitaskingSupported) {
                self.backgroundRecordingID = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:nil];
            }
            AVCaptureConnection *moviceConnection = [self.movieFileOutput connectionWithMediaType:AVMediaTypeVideo];
            moviceConnection.videoOrientation = previewLayerVideoOrientation;
            //保存到相冊
            NSString *outputFileName = [NSProcessInfo processInfo].globallyUniqueString;
            NSString *outputFilePath = [NSTemporaryDirectory() stringByAppendingPathComponent:[outputFileName stringByAppendingPathExtension:@"mov"]];
            [self.movieFileOutput startRecordingToOutputFileURL:[NSURL fileURLWithPath:outputFilePath] recordingDelegate:self];
        }
        else {
            [self.movieFileOutput stopRecording];
        
        }
        
    });
}

- (void)captureOutput:(AVCaptureFileOutput *)captureOutput didStartRecordingToOutputFileAtURL:(NSURL *)fileURL fromConnections:(NSArray *)connections
{
    dispatch_async( dispatch_get_main_queue(), ^{
        self.recordButton.enabled = YES;
        [self.recordButton setTitle:NSLocalizedString( @"Stop", @"Recording button stop title" ) forState:UIControlStateNormal];
    });
}

- (void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error
{
    UIBackgroundTaskIdentifier  currentBackgroundRecordingID = self.backgroundRecordingID;
    self.backgroundRecordingID = UIBackgroundTaskInvalid;
    dispatch_block_t cleanup = ^{
        if ([[NSFileManager defaultManager] fileExistsAtPath:outputFileURL.path]) {
            [[NSFileManager defaultManager] removeItemAtPath:outputFileURL.path error:nil];
        }
        if (currentBackgroundRecordingID != UIBackgroundTaskInvalid) {
            [[UIApplication sharedApplication] endBackgroundTask:currentBackgroundRecordingID];
        }
    
    };
    BOOL success = YES;
    if (error) {
        NSLog( @"Error occurred while capturing movie: %@", error );
        success = [error.userInfo[AVErrorRecordingSuccessfullyFinishedKey] boolValue];
    }
    if (success) {
        [PHPhotoLibrary requestAuthorization:^(PHAuthorizationStatus status) {
            if (status == PHAuthorizationStatusAuthorized) {
                [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{
                    PHAssetResourceCreationOptions *options = [[PHAssetResourceCreationOptions alloc] init];
                    options.shouldMoveFile = YES;
                    PHAssetCreationRequest *changeRequest = [PHAssetCreationRequest creationRequestForAsset];
                    [changeRequest addResourceWithType:PHAssetResourceTypeVideo fileURL:outputFileURL options:options];
                } completionHandler:^(BOOL success, NSError * _Nullable error) {
                    if (!success) {
                        NSLog( @"Could not save movie to photo library: %@", error);
                    }
                    cleanup();
                }];
            }else {
                cleanup();
            }
        }];
    }
    else {
        cleanup();
    }
    dispatch_async(dispatch_get_main_queue(), ^{
        self.cameraButton.enabled = (self.videoDeviceDiscoverySession.devices.count > 1);
        self.recordButton.enabled = self.captureModeControl.selectedSegmentIndex == AVCamManualCaptureModeMovie;
        [self.recordButton setTitle:NSLocalizedString( @"Record", @"Recording button record title" ) forState:UIControlStateNormal];
        self.captureModeControl.enabled = YES;
    });
}

參考

文章代碼都是官方代碼DEMO
大家還可以參考另外一篇比較好的文章iOS-AVFoundation自定義相機詳解

作者：牀前明月_光
鏈接：https://www.jianshu.com/p/58790d70b08f
來源：簡書
著作權歸作者所有。商業轉載請聯繫作者獲得授權，非商業轉載請註明出處。

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