iPhone 中的视频过滤速度很慢

我正在尝试在 iPhone 中过滤视频。这是我的程序结构和源代码：

AppDelegate.h
AppDelegate.m
ViewController.h
ViewController.m

AppDelegate 文件与默认文件相同。这是我的视图控制器。

//ViewController.h

#import <UIKit/UIKit.h>
#import <GLKit/GLKit.h>
#import <AVFoundation/AVFoundation.h>
#import <CoreMedia/CoreMedia.h>
#import <CoreVideo/CoreVideo.h>
#import <QuartzCore/QuartzCore.h>
#import <CoreImage/CoreImage.h>
#import <ImageIO/ImageIO.h>

@interface ViewController : GLKViewController <AVCaptureVideoDataOutputSampleBufferDelegate>{
    AVCaptureSession *avCaptureSession;
    CIContext *coreImageContext;
    CIImage *maskImage;
    CGSize screenSize;
    CGContextRef cgContext;
    GLuint _renderBuffer;
    float scale;
}

@property (strong, nonatomic) EAGLContext *context;

-(void)setupCGContext;

@end

// ViewController.m
#import "ViewController.h"

@implementation ViewController

@synthesize context;

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
    if (!self.context) {
        NSLog(@"Failed to create ES context");
    }

    GLKView *view = (GLKView *)self.view;
    view.context = self.context;
    view.drawableDepthFormat = GLKViewDrawableDepthFormat24;

    coreImageContext = [CIContext contextWithEAGLContext:self.context];

    glGenRenderbuffers(1, &_renderBuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, _renderBuffer);

    NSError *error;
    AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
    AVCaptureVideoDataOutput *dataOutput = [[AVCaptureVideoDataOutput alloc] init];

    [dataOutput setAlwaysDiscardsLateVideoFrames:YES]; 
    [dataOutput setVideoSettings:[NSDictionary  dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] 
                                                              forKey:(id)kCVPixelBufferPixelFormatTypeKey]];
    [dataOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()];

    avCaptureSession = [[AVCaptureSession alloc] init];
    [avCaptureSession beginConfiguration];
    [avCaptureSession setSessionPreset:AVCaptureSessionPreset1280x720];
    [avCaptureSession addInput:input];
    [avCaptureSession addOutput:dataOutput];
    [avCaptureSession commitConfiguration];
    [avCaptureSession startRunning];

    [self setupCGContext];
    CGImageRef cgImg = CGBitmapContextCreateImage(cgContext);
    maskImage = [CIImage imageWithCGImage:cgImg];
    CGImageRelease(cgImg);
}

-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {

    CVPixelBufferRef pixelBuffer = (CVPixelBufferRef)CMSampleBufferGetImageBuffer(sampleBuffer);
    CIImage *image = [CIImage imageWithCVPixelBuffer:pixelBuffer];
    image = [CIFilter   filterWithName:@"CISepiaTone" keysAndValues:kCIInputImageKey, 
                        image, @"inputIntensity", 
                        [NSNumber numberWithFloat:0.8], 
                        nil].outputImage;

    [coreImageContext drawImage:image atPoint:CGPointZero fromRect:[image extent] ];

    [self.context presentRenderbuffer:GL_RENDERBUFFER];
}

-(void)setupCGContext {
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    NSUInteger bytesPerPixel = 4;
    NSUInteger bytesPerRow = bytesPerPixel * screenSize.width;
    NSUInteger bitsPerComponent = 8;
    cgContext = CGBitmapContextCreate(NULL, screenSize.width, screenSize.height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast);

    CGColorSpaceRelease(colorSpace);
}

棕褐色滤镜有效，但视频速度稍慢。当我不应用滤镜时，视频是正常的。关于如何改进视频并使其速度更快有什么想法吗？

Thanks.

正如我所描述的here https://stackoverflow.com/a/6628208/19679，Core Image 中的棕褐色滤镜不太能够实时运行，但其他滤镜可能可以。这取决于目标设备的硬件功能以及 iOS 版本（Core Image 的性能较过去几个 iOS 版本有了显着提高）。

但是，如果我可以再次插入我的开源框架，GPUImage https://github.com/BradLarson/GPUImage让您更快地完成这项工作。它可以在 iPhone 4 上在 2.5 毫秒内对 640x480 帧的视频应用棕褐色调滤镜，这对于来自该相机的 30 FPS 视频来说已经足够快了。

以下代码将对 iOS 设备上后置摄像头的视频进行实时过滤，并在纵向视图中显示该视频：

videoCamera = [[GPUImageVideoCamera alloc] initWithSessionPreset:AVCaptureSessionPreset640x480 cameraPosition:AVCaptureDevicePositionBack];

sepiaFilter = [[GPUImageSepiaFilter alloc] init];
GPUImageRotationFilter *rotationFilter = [[GPUImageRotationFilter alloc] initWithRotation:kGPUImageRotateRight];

[videoCamera addTarget:rotationFilter];
[rotationFilter addTarget:sepiaFilter];
filterView = [[GPUImageView alloc] initWithFrame:self.view.bounds];
[self.view addSubview:filterView];
[sepiaFilter addTarget:filterView];

[videoCamera startCameraCapture];