iOS視頻采集實(shí)戰(zhàn)(AVCaptureSession)

需求：使用AVFoundation中的AVCaptureSession實(shí)現(xiàn)設(shè)置相機(jī)的分辨率，幀率(包括高幀率), 切換前后置攝像頭，對焦，屏幕旋轉(zhuǎn)，調(diào)節(jié)曝光度...

閱讀前提:

GitHub地址(附代碼) : iOS視頻采集實(shí)戰(zhàn)(AVCaptureSession)

簡書地址 : iOS視頻采集實(shí)戰(zhàn)(AVCaptureSession)

博客地址 : iOS視頻采集實(shí)戰(zhàn)(AVCaptureSession)

掘金地址 : iOS視頻采集實(shí)戰(zhàn)(AVCaptureSession)

1. 設(shè)置分辨率與幀率

1.1. 低幀率模式(fps <= 30)

在要求幀率小于等于30幀的情況下,相機(jī)設(shè)置分辨率與幀率的方法是單獨(dú)的,即設(shè)置幀率是幀率的方法,設(shè)置分辨率是分辨率的方法,兩者沒有綁定.

  • 設(shè)置分辨率

    使用此方法可以設(shè)置相機(jī)分辨率,可以設(shè)置的類型可以直接跳轉(zhuǎn)進(jìn)API文檔處自行選擇,目前支持最大的是3840*2160,如果不要求相機(jī)幀率大于30幀,此方法可以適用于你.

- (void)setCameraResolutionByPresetWithHeight:(int)height session:(AVCaptureSession *)session {
    /*
     Note: the method only support your frame rate <= 30 because we must use `activeFormat` when frame rate > 30, the `activeFormat` and `sessionPreset` are exclusive
     */
    AVCaptureSessionPreset preset = [self getSessionPresetByResolutionHeight:height];
    if ([session.sessionPreset isEqualToString:preset]) {
        NSLog(@"Needn't to set camera resolution repeatly !");
        return;
    }
    
    if (![session canSetSessionPreset:preset]) {
        NSLog(@"Can't set the sessionPreset !");
        return;
    }
    
    [session beginConfiguration];
    session.sessionPreset = preset;
    [session commitConfiguration];
}

  • 設(shè)置幀率

    使用此方法可以設(shè)置相機(jī)幀率,僅支持幀率小于等于30幀.

- (void)setCameraForLFRWithFrameRate:(int)frameRate {
    // Only for frame rate <= 30
    AVCaptureDevice *captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    [captureDevice lockForConfiguration:NULL];
    [captureDevice setActiveVideoMinFrameDuration:CMTimeMake(1, frameRate)];
    [captureDevice setActiveVideoMaxFrameDuration:CMTimeMake(1, frameRate)];
    [captureDevice unlockForConfiguration];
}
1.2. 高幀率模式(fps > 30)

如果需要對某一分辨率支持高幀率的設(shè)置,如50幀,60幀,120幀...,原先setActiveVideoMinFrameDuration與setActiveVideoMaxFrameDuration是無法做到的,Apple規(guī)定我們需要使用新的方法設(shè)置幀率setActiveVideoMinFrameDuration與setActiveVideoMaxFrameDuration,并且該方法必須配合新的設(shè)置分辨率activeFormat的方法一起使用.

新的設(shè)置分辨率的方法activeFormat與sessionPreset是互斥的，如果使用了一個, 另一個會失效,建議直接使用高幀率的設(shè)置方法，廢棄低幀率下設(shè)置方法，避免產(chǎn)生兼容問題。

Apple在更新方法后將原先分離的分辨率與幀率的設(shè)置方法合二為一,原先是單獨(dú)設(shè)置相機(jī)分辨率與幀率,而現(xiàn)在則需要一起設(shè)置,即每個分辨率有其對應(yīng)支持的幀率范圍,每個幀率也有其支持的分辨率,需要我們遍歷來查詢,所以原先統(tǒng)一的單獨(dú)的設(shè)置分辨率與幀率的方法在高幀率模式下相當(dāng)于棄用,可以根據(jù)項(xiàng)目需求選擇,如果確定項(xiàng)目不會支持高幀率(fps>30),可以使用以前的方法,簡單且有效.

注意: 使用activeFormat方法后,之前使用sessionPreset方法設(shè)置的分辨率將自動變?yōu)?code>AVCaptureSessionPresetInputPriority,所以如果項(xiàng)目之前有用canSetSessionPreset比較的if語句也都將失效,建議如果項(xiàng)目必須支持高幀率則徹底啟用sessionPreset方法.

+ (BOOL)setCameraFrameRateAndResolutionWithFrameRate:(int)frameRate andResolutionHeight:(CGFloat)resolutionHeight bySession:(AVCaptureSession *)session position:(AVCaptureDevicePosition)position videoFormat:(OSType)videoFormat {
    AVCaptureDevice *captureDevice = [self getCaptureDevicePosition:position];
    
    BOOL isSuccess = NO;
    for(AVCaptureDeviceFormat *vFormat in [captureDevice formats]) {
        CMFormatDescriptionRef description = vFormat.formatDescription;
        float maxRate = ((AVFrameRateRange*) [vFormat.videoSupportedFrameRateRanges objectAtIndex:0]).maxFrameRate;
        if (maxRate >= frameRate && CMFormatDescriptionGetMediaSubType(description) == videoFormat) {
            if ([captureDevice lockForConfiguration:NULL] == YES) {
                // 對比鏡頭支持的分辨率和當(dāng)前設(shè)置的分辨率
                CMVideoDimensions dims = CMVideoFormatDescriptionGetDimensions(description);
                if (dims.height == resolutionHeight && dims.width == [self getResolutionWidthByHeight:resolutionHeight]) {
                    [session beginConfiguration];
                    if ([captureDevice lockForConfiguration:NULL]){
                        captureDevice.activeFormat = vFormat;
                        [captureDevice setActiveVideoMinFrameDuration:CMTimeMake(1, frameRate)];
                        [captureDevice setActiveVideoMaxFrameDuration:CMTimeMake(1, frameRate)];
                        [captureDevice unlockForConfiguration];
                    }
                    [session commitConfiguration];
                    
                    return YES;
                }
            }else {
                NSLog(@"%s: lock failed!",__func__);
            }
        }
    }
    
    NSLog(@"Set camera frame is success : %d, frame rate is %lu, resolution height = %f",isSuccess,(unsigned long)frameRate,resolutionHeight);
    return NO;
}

+ (AVCaptureDevice *)getCaptureDevicePosition:(AVCaptureDevicePosition)position {
    NSArray *devices = nil;
    
    if (@available(iOS 10.0, *)) {
        AVCaptureDeviceDiscoverySession *deviceDiscoverySession =  [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:@[AVCaptureDeviceTypeBuiltInWideAngleCamera] mediaType:AVMediaTypeVideo position:position];
        devices = deviceDiscoverySession.devices;
    } else {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
        devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
#pragma clang diagnostic pop
    }
    
    for (AVCaptureDevice *device in devices) {
        if (position == device.position) {
            return device;
        }
    }
    return NULL;
}

2. 前后置攝像頭切換

切換前后置攝像頭，看似簡單，實(shí)際應(yīng)用中會產(chǎn)生很多問題，因?yàn)橥徊吭O(shè)備前后置攝像頭支持的分辨率幀率的值是不同的，所以如果從支持切向不支持就會產(chǎn)生問題,具體案例如下

比如iPhoneX, 后置攝像頭最大支持(4K,60fps),前置攝像頭最大支持(2K,30fps),當(dāng)使用(4K,60fps)后置攝像頭切到前置攝像頭如果不做處理則無法切換,程序錯亂.

注意

下面代碼中我們這行代碼session.sessionPreset = AVCaptureSessionPresetLow;,因?yàn)閺暮笾们械角爸梦覀冃枰匦掠嬎惝?dāng)前輸入設(shè)備支持最大的分辨率與幀率,而輸入設(shè)備如果不先添加上去我們無法計算,所以在這里先隨便設(shè)置一個可接受的分辨率以使我們可以把輸入設(shè)備添加,之后在求出當(dāng)前設(shè)備最大支持的分辨率與幀率后再重新設(shè)置分辨率與幀率.

- (void)setCameraPosition:(AVCaptureDevicePosition)position session:(AVCaptureSession *)session input:(AVCaptureDeviceInput *)input videoFormat:(OSType)videoFormat resolutionHeight:(CGFloat)resolutionHeight frameRate:(int)frameRate {
    if (input) {
        [session beginConfiguration];
        [session removeInput:input];
        
        AVCaptureDevice *device = [self.class getCaptureDevicePosition:position];
        
        NSError *error = nil;
        AVCaptureDeviceInput *newInput = [AVCaptureDeviceInput deviceInputWithDevice:device
                                                                               error:&error];
        
        if (error != noErr) {
            NSLog(@"%s: error:%@",__func__, error.localizedDescription);
            return;
        }
        
        // 比如: 后置是4K, 前置最多支持2K,此時切換需要降級, 而如果不先把Input添加到session中,我們無法計算當(dāng)前攝像頭支持的最大分辨率
        session.sessionPreset = AVCaptureSessionPresetLow;
        if ([session canAddInput:newInput])  {
            self.input = newInput;
            [session addInput:newInput];
        }else {
            NSLog(@"%s: add input failed.",__func__);
            return;
        }
        
        int maxResolutionHeight = [self getMaxSupportResolutionByPreset];
        if (resolutionHeight > maxResolutionHeight) {
            resolutionHeight = maxResolutionHeight;
            self.cameraModel.resolutionHeight = resolutionHeight;
            NSLog(@"%s: Current support max resolution height = %d", __func__, maxResolutionHeight);
        }
        
        int maxFrameRate = [self getMaxFrameRateByCurrentResolution];
        if (frameRate > maxFrameRate) {
            frameRate = maxFrameRate;
            self.cameraModel.frameRate = frameRate;
            NSLog(@"%s: Current support max frame rate = %d",__func__, maxFrameRate);
        }

        BOOL isSuccess = [self.class setCameraFrameRateAndResolutionWithFrameRate:frameRate
                                                              andResolutionHeight:resolutionHeight
                                                                        bySession:session
                                                                         position:position
                                                                      videoFormat:videoFormat];
        
        if (!isSuccess) {
            NSLog(@"%s: Set resolution and frame rate failed.",__func__);
        }
        
        [session commitConfiguration];
    }
}

3.屏幕視頻方向切換

我們在這里首先要區(qū)分下屏幕方向與視頻方向的概念,一個是用來表示設(shè)備方向(UIDeviceOrientation),一個是用來表示視頻方向(AVCaptureVideoOrientation). 我們使用的AVCaptureSession,如果要支持屏幕旋轉(zhuǎn),需要在屏幕旋轉(zhuǎn)的同時將我們的視頻畫面也進(jìn)行旋轉(zhuǎn).

屏幕方向的旋轉(zhuǎn)可以通過通知UIDeviceOrientationDidChangeNotification接收,這里不做過多說明.

- (void)adjustVideoOrientationByScreenOrientation:(UIDeviceOrientation)orientation previewFrame:(CGRect)previewFrame previewLayer:(AVCaptureVideoPreviewLayer *)previewLayer videoOutput:(AVCaptureVideoDataOutput *)videoOutput {
    [previewLayer setFrame:previewFrame];
    
    switch (orientation) {
        case UIInterfaceOrientationPortrait:
            [self adjustAVOutputDataOrientation:AVCaptureVideoOrientationPortrait
                                    videoOutput:videoOutput];
            break;
        case UIInterfaceOrientationPortraitUpsideDown:
            [self adjustAVOutputDataOrientation:AVCaptureVideoOrientationPortraitUpsideDown
                                    videoOutput:videoOutput];
            break;
        case UIInterfaceOrientationLandscapeLeft:
            [[previewLayer connection] setVideoOrientation:AVCaptureVideoOrientationLandscapeLeft];
            [self adjustAVOutputDataOrientation:AVCaptureVideoOrientationLandscapeLeft
                                    videoOutput:videoOutput];
            break;
        case UIInterfaceOrientationLandscapeRight:
            [[previewLayer connection] setVideoOrientation:AVCaptureVideoOrientationLandscapeRight];
            [self adjustAVOutputDataOrientation:AVCaptureVideoOrientationLandscapeRight
                                    videoOutput:videoOutput];
            break;
            
        default:
            break;
            
    }
}

-(void)adjustAVOutputDataOrientation:(AVCaptureVideoOrientation)orientation videoOutput:(AVCaptureVideoDataOutput *)videoOutput {
    for(AVCaptureConnection *connection in videoOutput.connections) {
        for(AVCaptureInputPort *port in [connection inputPorts]) {
            if([[port mediaType] isEqual:AVMediaTypeVideo]) {
                if([connection isVideoOrientationSupported]) {
                    [connection setVideoOrientation:orientation];
                }
            }
        }
    }
}

4.對焦調(diào)節(jié)

關(guān)于對焦,我們需要特別說明手動設(shè)置對焦點(diǎn)進(jìn)行對焦,因?yàn)閷狗椒▋H接受以左上角為(0,0),右下角為(1,1)的坐標(biāo)系,所以我們需要對UIView的坐標(biāo)系進(jìn)行轉(zhuǎn)換,但是轉(zhuǎn)換需要分為多種情況,如下

  • 視頻是否以鏡像模式輸出: 如前置攝像頭可能會開啟鏡像模式(x,y坐標(biāo)是反的)
  • 屏幕方向是以Home在右還是在左: 在右的話是以左上角為原點(diǎn),在左的話則是以右下角為原點(diǎn).
  • 視頻渲染方式: 是保持分辨率比例,還是填充模式,因?yàn)槭謾C(jī)型號不同,所以可能是填充黑邊,可能超出屏幕,需要重新計算對焦點(diǎn).

如果我們是直接使用AVCaptureSession的AVCaptureVideoPreviewLayer做渲染,我們可以使用captureDevicePointOfInterestForPoint方法自動計算,此結(jié)果會考慮上面所有情況.但如果我們是自己對屏幕做渲染,則需要自己計算對焦點(diǎn),上面的情況都需要考慮. 下面提供自動與手動計算兩種方法.

- (void)autoFocusAtPoint:(CGPoint)point {
    AVCaptureDevice *device = self.input.device;
    if ([device isFocusPointOfInterestSupported] && [device isFocusModeSupported:AVCaptureFocusModeAutoFocus]) {
        NSError *error;
        if ([device lockForConfiguration:&error]) {
            [device setExposurePointOfInterest:point];
            [device setExposureMode:AVCaptureExposureModeContinuousAutoExposure];
            [device setFocusPointOfInterest:point];
            [device setFocusMode:AVCaptureFocusModeAutoFocus];
            [device unlockForConfiguration];
        }
    }
}
4.1. 自動計算對焦點(diǎn)
- (CGPoint)convertToPointOfInterestFromViewCoordinates:(CGPoint)viewCoordinates captureVideoPreviewLayer:(AVCaptureVideoPreviewLayer *)captureVideoPreviewLayer {
    CGPoint pointOfInterest = CGPointMake(.5f, .5f);
    CGSize frameSize = [captureVideoPreviewLayer frame].size;
    
    if ([captureVideoPreviewLayer.connection isVideoMirrored]) {
        viewCoordinates.x = frameSize.width - viewCoordinates.x;
    }

    // Convert UIKit coordinate to Focus Point(0.0~1.1)
    pointOfInterest = [captureVideoPreviewLayer captureDevicePointOfInterestForPoint:viewCoordinates];
    
    // NSLog(@"Focus - Auto test: %@",NSStringFromCGPoint(pointOfInterest));
    
    return pointOfInterest;
}
4.2. 手動計算對焦點(diǎn)
  • 如果手機(jī)屏幕尺寸與分辨率比例完全吻合,則直接將坐標(biāo)系轉(zhuǎn)為(0,0)到(1,1)即可
  • 如果屏幕尺寸比例與分辨率比例不同,需要進(jìn)一步分析視頻渲染方式來計算,如果是保持分辨率,則肯定會留下黑邊,我們在計算對焦點(diǎn)時需要減去黑邊長度,如果是以分辨率比例填充屏幕則會犧牲一部分像素,我們在計算對焦點(diǎn)時同樣需要加上犧牲的像素.
- (CGPoint)manualConvertFocusPoint:(CGPoint)point frameSize:(CGSize)frameSize captureVideoPreviewLayer:(AVCaptureVideoPreviewLayer *)captureVideoPreviewLayer position:(AVCaptureDevicePosition)position videoDataOutput:(AVCaptureVideoDataOutput *)videoDataOutput input:(AVCaptureDeviceInput *)input {
    CGPoint pointOfInterest = CGPointMake(.5f, .5f);
    
    if ([[videoDataOutput connectionWithMediaType:AVMediaTypeVideo] isVideoMirrored]) {
        point.x = frameSize.width - point.x;
    }
    
    for (AVCaptureInputPort *port in [input ports]) {
        if ([port mediaType] == AVMediaTypeVideo) {
            CGRect cleanAperture = CMVideoFormatDescriptionGetCleanAperture([port formatDescription], YES);
            CGSize resolutionSize = cleanAperture.size;
            
            CGFloat resolutionRatio = resolutionSize.width / resolutionSize.height;
            CGFloat screenSizeRatio = frameSize.width / frameSize.height;
            CGFloat xc = .5f;
            CGFloat yc = .5f;
        
            if (resolutionRatio == screenSizeRatio) {
                xc = point.x / frameSize.width;
                yc = point.y / frameSize.height;
            }else if (resolutionRatio > screenSizeRatio) {
                if ([[captureVideoPreviewLayer videoGravity] isEqualToString:AVLayerVideoGravityResizeAspectFill]) {
                    CGFloat needScreenWidth = resolutionRatio * frameSize.height;
                    CGFloat cropWidth = (needScreenWidth - frameSize.width) / 2;
                    xc = (cropWidth + point.x) / needScreenWidth;
                    yc = point.y / frameSize.height;
                }else if ([[captureVideoPreviewLayer videoGravity] isEqualToString:AVLayerVideoGravityResizeAspect]){
                    CGFloat needScreenHeight = frameSize.width * (1/resolutionRatio);
                    CGFloat blackBarLength   = (frameSize.height - needScreenHeight) / 2;
                    xc = point.x / frameSize.width;
                    yc = (point.y - blackBarLength) / needScreenHeight;
                }else if ([[captureVideoPreviewLayer videoGravity] isEqualToString:AVLayerVideoGravityResize]) {
                    xc = point.x / frameSize.width;
                    yc = point.y / frameSize.height;
                }
            }else {
                if ([[captureVideoPreviewLayer videoGravity] isEqualToString:AVLayerVideoGravityResizeAspectFill]) {
                    CGFloat needScreenHeight = (1/resolutionRatio) * frameSize.width;
                    CGFloat cropHeight = (needScreenHeight - frameSize.height) / 2;
                    xc = point.x / frameSize.width;
                    yc = (cropHeight + point.y) / needScreenHeight;
                }else if ([[captureVideoPreviewLayer videoGravity] isEqualToString:AVLayerVideoGravityResizeAspect]){
                    CGFloat needScreenWidth = frameSize.height * resolutionRatio;
                    CGFloat blackBarLength   = (frameSize.width - needScreenWidth) / 2;
                    xc = (point.x - blackBarLength) / needScreenWidth;
                    yc = point.y / frameSize.height;
                }else if ([[captureVideoPreviewLayer videoGravity] isEqualToString:AVLayerVideoGravityResize]) {
                    xc = point.x / frameSize.width;
                    yc = point.y / frameSize.height;
                }
            }
            pointOfInterest = CGPointMake(xc, yc);
        }
    }
    
    if (position == AVCaptureDevicePositionBack) {
        if (captureVideoPreviewLayer.connection.videoOrientation == AVCaptureVideoOrientationLandscapeLeft) {
            pointOfInterest = CGPointMake(1-pointOfInterest.x, 1-pointOfInterest.y);
        }
    }else {
        pointOfInterest = CGPointMake(pointOfInterest.x, 1-pointOfInterest.y);
    }
    
    //NSLog(@"Focus - manu test: %@",NSStringFromCGPoint(pointOfInterest));
    return pointOfInterest;
}

5.曝光調(diào)節(jié)

如果我們是以UISlider作為調(diào)節(jié)控件,最簡單的做法可以將其范圍設(shè)置的與曝光度值的范圍相同,即(-8~8),這樣無需轉(zhuǎn)換值,直接傳入即可,如果是手勢或是其他控件可根據(jù)需求自行調(diào)整.較為簡單,不再敘述.

- (void)setExposureWithNewValue:(CGFloat)newExposureValue device:(AVCaptureDevice *)device {
    NSError *error;
    if ([device lockForConfiguration:&error]) {
        [device setExposureTargetBias:newExposureValue completionHandler:nil];
        [device unlockForConfiguration];
    }
}

6.手電筒模式

  • AVCaptureTorchModeAuto: 自動
  • AVCaptureTorchModeOn: 打開
  • AVCaptureTorchModeOff: 關(guān)閉
- (void)setTorchState:(BOOL)isOpen device:(AVCaptureDevice *)device {
    if ([device hasTorch]) {
        NSError *error;
        [device lockForConfiguration:&error];
        device.torchMode = isOpen ? AVCaptureTorchModeOn : AVCaptureTorchModeOff;
        [device unlockForConfiguration];
    }else {
        NSLog(@"The device not support torch!");
    }
}

7.視頻穩(wěn)定性調(diào)節(jié)

注意: 部分機(jī)型,部分分辨率使用此屬性渲染可能會出現(xiàn)問題 (iphone xs, 自己渲染)

-(void)adjustVideoStabilizationWithOutput:(AVCaptureVideoDataOutput *)output {
    NSArray *devices = nil;
    
    if (@available(iOS 10.0, *)) {
        AVCaptureDeviceDiscoverySession *deviceDiscoverySession =  [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:@[AVCaptureDeviceTypeBuiltInWideAngleCamera] mediaType:AVMediaTypeVideo position:self.cameraModel.position];
        devices = deviceDiscoverySession.devices;
    } else {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
        devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
#pragma clang diagnostic pop
    }
    
    for(AVCaptureDevice *device in devices){
        if([device hasMediaType:AVMediaTypeVideo]){
            if([device.activeFormat isVideoStabilizationModeSupported:AVCaptureVideoStabilizationModeAuto]) {
                for(AVCaptureConnection *connection in output.connections) {
                    for(AVCaptureInputPort *port in [connection inputPorts]) {
                        if([[port mediaType] isEqual:AVMediaTypeVideo]) {
                            if(connection.supportsVideoStabilization) {
                                connection.preferredVideoStabilizationMode = AVCaptureVideoStabilizationModeStandard;
                                NSLog(@"activeVideoStabilizationMode = %ld",(long)connection.activeVideoStabilizationMode);
                            }else {
                                NSLog(@"connection don't support video stabilization");
                            }
                        }
                    }
                }
            }else{
                NSLog(@"device don't support video stablization");
            }
        }
    }
}

8.白平衡調(diào)節(jié)

  • temperature: 通過華氏溫度調(diào)節(jié) (-150-~250)
  • tint: 通過色調(diào)調(diào)節(jié) (-150-~150)

注意在使用setWhiteBalanceModeLockedWithDeviceWhiteBalanceGains方法時必須比較當(dāng)前的AVCaptureWhiteBalanceGains值是否在有效范圍.

-(AVCaptureWhiteBalanceGains)clampGains:(AVCaptureWhiteBalanceGains)gains toMinVal:(CGFloat)minVal andMaxVal:(CGFloat)maxVal {
    AVCaptureWhiteBalanceGains tmpGains = gains;
    tmpGains.blueGain   = MAX(MIN(tmpGains.blueGain , maxVal), minVal);
    tmpGains.redGain    = MAX(MIN(tmpGains.redGain  , maxVal), minVal);
    tmpGains.greenGain  = MAX(MIN(tmpGains.greenGain, maxVal), minVal);
    
    return tmpGains;
}

-(void)setWhiteBlanceValueByTemperature:(CGFloat)temperature device:(AVCaptureDevice *)device {
    if ([device isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeLocked]) {
        [device lockForConfiguration:nil];
        AVCaptureWhiteBalanceGains currentGains = device.deviceWhiteBalanceGains;
        CGFloat currentTint = [device temperatureAndTintValuesForDeviceWhiteBalanceGains:currentGains].tint;
        AVCaptureWhiteBalanceTemperatureAndTintValues tempAndTintValues = {
            .temperature = temperature,
            .tint        = currentTint,
        };
        
        AVCaptureWhiteBalanceGains deviceGains = [device deviceWhiteBalanceGainsForTemperatureAndTintValues:tempAndTintValues];
        CGFloat maxWhiteBalanceGain = device.maxWhiteBalanceGain;
        deviceGains = [self clampGains:deviceGains toMinVal:1 andMaxVal:maxWhiteBalanceGain];
        
        [device setWhiteBalanceModeLockedWithDeviceWhiteBalanceGains:deviceGains completionHandler:nil];
        [device unlockForConfiguration];
    }
}

-(void)setWhiteBlanceValueByTint:(CGFloat)tint device:(AVCaptureDevice *)device {
    if ([device isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeLocked]) {
        [device lockForConfiguration:nil];
        CGFloat maxWhiteBalaceGain = device.maxWhiteBalanceGain;
        AVCaptureWhiteBalanceGains currentGains = device.deviceWhiteBalanceGains;
        currentGains = [self clampGains:currentGains toMinVal:1 andMaxVal:maxWhiteBalaceGain];
        CGFloat currentTemperature = [device temperatureAndTintValuesForDeviceWhiteBalanceGains:currentGains].temperature;
        AVCaptureWhiteBalanceTemperatureAndTintValues tempAndTintValues = {
            .temperature = currentTemperature,
            .tint        = tint,
        };
        
        AVCaptureWhiteBalanceGains deviceGains = [device deviceWhiteBalanceGainsForTemperatureAndTintValues:tempAndTintValues];
        deviceGains = [self clampGains:deviceGains toMinVal:1 andMaxVal:maxWhiteBalaceGain];
        
        [device setWhiteBalanceModeLockedWithDeviceWhiteBalanceGains:deviceGains completionHandler:nil];
        [device unlockForConfiguration];
    }
}

9.屏幕填充方式

  • AVLayerVideoGravityResizeAspect: 保持分辨率比例,如果屏幕分辨率與視頻分辨率不一致會留下黑邊.
  • AVLayerVideoGravityResizeAspectFill: 保持分辨率比例去填充屏幕,即以較小的邊來準(zhǔn)填充屏幕,會犧牲掉一些像素,因?yàn)槌銎聊?
  • AVLayerVideoGravityResize:以拉伸的方式來填充屏幕,不會犧牲像素,但是畫面會被拉伸.
- (void)setVideoGravity:(AVLayerVideoGravity)videoGravity previewLayer:(AVCaptureVideoPreviewLayer *)previewLayer session:(AVCaptureSession *)session {
    [session beginConfiguration];
    [previewLayer setVideoGravity:videoGravity];
    [session commitConfiguration];
}
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