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POVideo filtering in iPhone is slow
 

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  1. POVideo filtering in iPhone is slow
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    <p>I am trying to filter video in iPhone. Here's my program structure and source code:</p> <pre><code>AppDelegate.h AppDelegate.m ViewController.h ViewController.m </code></pre> <p>The AppDelegate file is same as default. Here's my ViewController.</p> <pre><code>//ViewController.h #import &lt;UIKit/UIKit.h&gt; #import &lt;GLKit/GLKit.h&gt; #import &lt;AVFoundation/AVFoundation.h&gt; #import &lt;CoreMedia/CoreMedia.h&gt; #import &lt;CoreVideo/CoreVideo.h&gt; #import &lt;QuartzCore/QuartzCore.h&gt; #import &lt;CoreImage/CoreImage.h&gt; #import &lt;ImageIO/ImageIO.h&gt; @interface ViewController : GLKViewController &lt;AVCaptureVideoDataOutputSampleBufferDelegate&gt;{ 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, &amp;_renderBuffer); glBindRenderbuffer(GL_RENDERBUFFER, _renderBuffer); NSError *error; AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]; AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&amp;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); } </code></pre> <p>The sepia filter works, but the video is little slower. When I don't apply filter, the video is normal. Any idea on how I can improve the video and make it faster?</p> <p>Thanks.</p>
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    1. COPerhaps there is computational work you can offload to a separate thread. You might read up on `NSThread`, `NSOperation` and blocks.
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    2. COdoes it make any difference, as i am filtering and showing the video on the screen, delegating the filtering task to another thread and then getting filtered output from that thread, and showing it on the screen, wouldn't it be same as doing the whole thing in the same thread? Using a background thread would be helpful if it wasn't real time I guess. Please suggest. Thanks.
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    3. COThreading would probably help on dual core devices. Do computation on a background thread, and UI updates on the main thread. Profile with a smaller version of your app, maybe.
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