Crop a sample buffer to a view and return a pixel buffer

crop_samplebuffer.m

+ (CVPixelBufferRef)croppedPixelBufferFromSampleBuffer:(CMSampleBufferRef)buffer frame:(CGRect)frame {
    if (buffer == nil) return nil;
    
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(buffer);
    if (imageBuffer == nil) return nil;
    
    CIImage *ciImage = [CIImage imageWithCVPixelBuffer:imageBuffer];
    ciImage = [ciImage imageByCroppingToRect:frame];
    
    CFDictionaryRef empty; // empty value for attr IOSurface
    empty = CFDictionaryCreate(kCFAllocatorDefault, NULL, NULL, 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
    CFMutableDictionaryRef attrs = CFDictionaryCreateMutable(kCFAllocatorDefault, 1, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
    CFDictionarySetValue(attrs, kCVPixelBufferIOSurfacePropertiesKey, empty);
    
    CVPixelBufferRef pixelBuffer;
    CVPixelBufferCreate(kCFAllocatorSystemDefault, frame.size.width, frame.size.height, kCVPixelFormatType_32BGRA, attrs, &pixelBuffer);
    CVPixelBufferLockBaseAddress(pixelBuffer, 0);
    CIContext *ciContext = [CIContext contextWithOptions: nil];
    [ciContext render:ciImage toCVPixelBuffer:pixelBuffer];
    CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);
    
    CFRelease(attrs);
    CFRelease(empty);
    
    return pixelBuffer;
}