如何用CIFilter改变视频的UISlider值？

Question

我正试图将CIFilters添加到视频中。但是我使用UISliders更改值，因为AVPlayer需要时间来播放过滤器添加的视频。我搜索这个问题，UISlider值不断变化，它也采用浮点值。因为每次过滤添加到视频和播放。当滑块值不断变化时，我想知道如何改变CIFilter的值，而不延迟改变AVPlayer的值。

float value = sender.value;
CIFilter *filter = [CIFilter filterWithName:@"CIColorControls"];
AVVideoComposition *composition = [AVVideoComposition videoCompositionWithAsset:tempAVAsset applyingCIFiltersWithHandler:
                                   ^(AVAsynchronousCIImageFilteringRequest *request){
                                       NSError *err = nil;
                                       CIImage *filtered = [request.sourceImage imageByClampingToExtent];
                                       [filter setDefaults];
                                       [filter setValue:filtered forKey:kCIInputImageKey];

                                       [filter setValue:[NSNumber numberWithFloat:0.00] forKey:@"inputSaturation"];
                                       [filter setValue:[NSNumber numberWithFloat:0.00] forKey:@"inputBrightness"];
                                       [filter setValue:[NSNumber numberWithFloat:value] forKey:@"inputContrast"];

                                       CIImage *output = [filter.outputImage imageByCroppingToRect:request.sourceImage.extent];
                                       if (filtered)
                                           [request finishWithImage:output context:nil];
                                       else
                                           [request finishWithError:err];

                                   }];

Answer 1

当滑块值发生变化时，只需在组合块外部更改筛选器参数，并且不要在块内重新设置它。所以就这么做吧

[adjustFilter setValue:[NSNumber numberWithFloat:sender.value] forKey:@"inputContrast"];

在valueChanged回调中，而不是在组合块中。这样，过滤器总是得到最当前的值，并将它用于下一个视频帧。

编辑：

以下是视图控制器中可能实现的一些部分：

@interface DemoViewController ()

@property (strong, nonatomic) CIFilter *filter;
@property (strong, nonatomic) AVPlayer *player;
@property (strong, nonatomic) AVAsset *tempAVAsset;

@end

@implementation DemoViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    // setup filter
    self.filter = [CIFilter filterWithName:@"CIColorControls"];
    [self.filter setDefaults];
    [self.filter setValue:[NSNumber numberWithFloat:0.00] forKey:@"inputSaturation"];
    [self.filter setValue:[NSNumber numberWithFloat:0.00] forKey:@"inputBrightness"];

    AVVideoComposition *composition = [AVVideoComposition videoCompositionWithAsset:self.tempAVAsset applyingCIFiltersWithHandler:
        ^(AVAsynchronousCIImageFilteringRequest *request){
            NSError *err = nil;
            CIImage *filtered = [request.sourceImage imageByClampingToExtent];

            [self.filter setValue:filtered forKey:kCIInputImageKey];
            CIImage *output = [self.filter.outputImage imageByCroppingToRect:request.sourceImage.extent];
            if (filtered)
               [request finishWithImage:output context:nil];
            else
               [request finishWithError:err];
        }
    ];

    // setup player with composition
    // ...
}


- (IBAction)sliderValueChanged:(UISlider*)sender
{
    // get the new slider value and assign it to the filter
    [self.filter setValue:[NSNumber numberWithFloat:sender.value] forKey:@"inputContrast"];
}

@end