Crop CMSampleBufferRef

Question

I am trying to crop image in CMSampleBufferRef to a specific size. I am making 5 steps - 1. Getting PixelBuffer from SampleBuffer 2. Converting PixelBuffer to CIImage 3. Cropping CIImage 4. Rendering CIImage back to PixelBuffer 5. Attaching PixelBuffer to SampleBuffer. So far I am having trouble with step 4 - rendering image back to PixelBuffer (can not check beyond this point) nothing is rendered to buffer (I check it using same CIImage imageWithCVPixelBuffer and get NULL as a return). Would greatly appreciate any tip or help.

CGRect cropRect = CGRectMake(0, 0, 640, 480);

CIImage *ciImage = [CIImage imageWithCVPixelBuffer:(CVPixelBufferRef)CMSampleBufferGetImageBuffer(sampleBuffer)]; //options: [NSDictionary dictionaryWithObjectsAndKeys:[NSNull null], kCIImageColorSpace, nil]];
ciImage = [ciImage imageByCroppingToRect:cropRect];    

CVPixelBufferRef pixelBuffer;
CVPixelBufferCreate(kCFAllocatorSystemDefault, 640, 480, kCVPixelFormatType_32BGRA, NULL, &pixelBuffer);

CVPixelBufferLockBaseAddress( pixelBuffer, 0 );

CIContext * ciContext = [CIContext contextWithOptions: nil];
[ciContext render:ciImage toCVPixelBuffer:pixelBuffer];
CVPixelBufferUnlockBaseAddress( pixelBuffer, 0 );

CMSampleTimingInfo sampleTime = {
    .duration = CMSampleBufferGetDuration(sampleBuffer),
    .presentationTimeStamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer),
    .decodeTimeStamp = CMSampleBufferGetDecodeTimeStamp(sampleBuffer)
};

CMVideoFormatDescriptionRef videoInfo = NULL;
CMVideoFormatDescriptionCreateForImageBuffer(kCFAllocatorDefault, pixelBuffer, &videoInfo);

CMSampleBufferRef oBuf;
CMSampleBufferCreateForImageBuffer(kCFAllocatorDefault, pixelBuffer, true, NULL, NULL, videoInfo, &sampleTime, &oBuf);

Answer 1

So I found the reason why I was having problem. Apparently I have to add kCVPixelBufferIOSurfacePropertiesKey key when initializing pixel buffer, by creating dictionary and passing it to initializer. Here's a code if anyone stumbles upon this problem:

CFDictionaryRef empty; // empty value for attr value.
CFMutableDictionaryRef attrs;
empty = CFDictionaryCreate(kCFAllocatorDefault, // our empty IOSurface properties dictionary
                           NULL,
                           NULL,
                           0,
                           &kCFTypeDictionaryKeyCallBacks,
                           &kCFTypeDictionaryValueCallBacks);
attrs = CFDictionaryCreateMutable(kCFAllocatorDefault,
                                  1,
                                  &kCFTypeDictionaryKeyCallBacks,
                                  &kCFTypeDictionaryValueCallBacks);

CFDictionarySetValue(attrs,
                     kCVPixelBufferIOSurfacePropertiesKey,
                     empty);

Then you just have to pass this dictionary as an argument to CVPixelBufferCreate

I found this solution here: http://allmybrain.com/2011/12/08/rendering-to-a-texture-with-ios-5-texture-cache-api/