Render Alpha image on CVImageBufferRef

Question

I am trying to achieve this effect . you can check this effect in musical.ly app (ripple effect)

https://drive.google.com/open?id=1uXExnmWQ7OfSGLFXdH7-5imay8tW87vO

Here is my approach.

I will render alpha and scaled image to pixel buffer I am showing all sample buffer using AVSampleBufferDisplayLayer . I want to show this animation for 3 sec - 5sec . Once user is done Then I will convert it to mp4 using AVAssetWriter .

I am unable to add alpha image to cvpixelbuffer

If there’s a better approach to make this animation . Please guide .

I get all the sample buffer using AVAssetReaderTrackOutput.

NSDictionary *readerOutputSettings = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA], kCVPixelBufferPixelFormatTypeKey, nil];
AVAssetReaderTrackOutput* readerOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:videoTrack
                                                                                    outputSettings:readerOutputSettings];
[reader addOutput:readerOutput];
[reader startReading];

  while ((sample = [readerOutput copyNextSampleBuffer]))
     {
        [samples addObject:(__bridge id)sample];
        CFRelease(sample);
     }

CVImageBufferRef pixelBuffer = CMSampleBufferGetImageBuffer((__bridge CMSampleBufferRef)[samples lastObject]);

CIImage *filteredImage = [CIImage imageWithCVPixelBuffer:pixelBuffer options:nil];

CIFilter* theFilter = [CIFilter filterWithName:@"CIColorMatrix"];

[theFilter setDefaults];

[theFilter setValue: filteredImage forKey: @"inputImage"];

CIVector *theRVector = [CIVector vectorWithX:1 Y:0 Z:0 W:0];
[theFilter setValue: theRVector forKey:@"inputRVector"];

CIVector *theGVector = [CIVector vectorWithX:0 Y:1 Z:0 W:0];
[theFilter setValue: theGVector forKey:@"inputGVector"];

CIVector *theBVector = [CIVector vectorWithX:0 Y:0 Z:1 W:0];
[theFilter setValue: theBVector forKey:@"inputBVector"];

CIVector *theAVector = [CIVector vectorWithX:0 Y:0 Z:0 W:0.5];
[theFilter setValue: theAVector forKey:@"inputAVector"];

CIVector *theBiasVector = [CIVector vectorWithX:0 Y:0 Z:0 W:0];
[theFilter setValue: theBiasVector forKey:@"inputBiasVector"];

CIImage* result = [theFilter valueForKey: @"outputImage"];

Then I have decrease the alpha of ciimage and render into first pixel buffer

EAGLContext *eaglContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES3];
    CIContext *cicontext =  [CIContext contextWithEAGLContext:eaglContext options:@{kCIContextWorkingColorSpace : [NSNull null]}];

 [cicontext render:result toCVPixelBuffer:CMSampleBufferGetImageBuffer((__bridge CMSampleBufferRef)[samplebuffers firstObject]) bounds:CGRectMake(0, 0, [result extent].size.width,[result extent].size.height) colorSpace:CGColorSpaceCreateDeviceRGB()];

I got this result .

Expected result

Thanks in advance

Answer 1

This image effect appears to be a fixed image with a zoom and a fade applied to a copy over the original. You should not need an animation library for this, just create a PNG and 2 layers to render it, then zoom one of the layers and fade it out as the zoom happens. Start with a 32 BPP image that contains alpha for the see through parts and you should be fine. If you want to capture the effect as .h264, that is a totally different problem.