objective-c - Correctly freeing a buffer from vImageBuffer_InitWithCVPixelBuffer

Question

I'm attempting to convert CVPixelBufferRefs from a video source to CGImageRefs using vImage convert libraries on 10.10. This for the most part works fine. However, each time I initialize a new vImage_Buffer from my CVPixelBufferRef, memory is gobbled up that is never returned.

Here is a simplified version of the conversion, that should ideally use no memory at the end of the day:

CVPixelBufferRef pixelBuffer = ...; // retained CVPixelBufferRef from somewhere else
vImage_Buffer buffer;
vImage_CGImageFormat format = {.bitsPerComponent = 8, .bitsPerPixel = 32, .colorSpace = NULL, .bitmapInfo = kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little, .version = 0, .decode = NULL, .renderingIntent = kCGRenderingIntentAbsoluteColorimetric};

vImage_Error imageError = vImageBuffer_InitWithCVPixelBuffer(&buffer, &format, pixelBuffer, NULL, NULL, kvImagePrintDiagnosticsToConsole);

// Do conversion here

free(buffer.data);

Commenting out the last two lines (the init and free) effectively uses no more memory than what I started with. With the two lines there, however, 6 MB are being consumed each time.

If I only comment out the free, even more memory is being consumed, so the free is definitely doing something, but I can only assume vImageBuffer_InitWithCVPixelBuffer is using more memory than it is supposed to. Has anyone else seen this?

For completion, here is the whole conversion method to go from CVPixelBufferRef to NSImage:

CVPixelBufferRef pixelBuffer = ...; // retained CVPixelBufferRef from somewhere else

NSImage *image = nil;

vImage_Buffer buffer;
vImage_CGImageFormat format = {.bitsPerComponent = 8, .bitsPerPixel = 32, .colorSpace = NULL, .bitmapInfo = kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little, .version = 0, .decode = NULL, .renderingIntent = kCGRenderingIntentAbsoluteColorimetric};

vImage_Error imageError = vImageBuffer_InitWithCVPixelBuffer(&buffer, &format, pixelBuffer, NULL, NULL, kvImagePrintDiagnosticsToConsole);

if (imageError != 0) {
    NSLog(@"vImageBuffer_InitWithCVPixelBuffer Error: %zd", imageError);
} else {
    CGImageRef imageRef = vImageCreateCGImageFromBuffer(&buffer, &format, NULL, NULL, kvImagePrintDiagnosticsToConsole|kvImageHighQualityResampling, &imageError);

    if (!imageRef) {
        NSLog(@"vImageCreateCGImageFromBuffer Error: %zd", imageError);
    } else {
        image = [[NSImage alloc] initWithCGImage:imageRef size:NSMakeSize(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef))];

        CGImageRelease(imageRef);

        NSAssert(image != nil, @"Creating the image failed!");
    }
}

free(buffer.data);