CMSampleBufferRef to vImage and resize

CMSampleBufferRef_to_vImage.m

CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
CVPixelBufferLockBaseAddress(imageBuffer,0);

size_t height = CVPixelBufferGetHeight(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);

void *sourceData = CVPixelBufferGetBaseAddress(imageBuffer);

// Set a bunch of variables we need. The "radius" for the blur kernel needs to be positive and odd. The permute map maps the BGRA channels of the buffer to the ARGB that vImage needs.
const NSUInteger bytesPerPixel = 4;

vImage_Buffer srcBuff = {sourceData, height, width, bytesPerRow};

// Create dest buffer
CGFloat aspectRatio = (CGFloat)width / (CGFloat)height;
CGSize fitSize = CGSizeMake(kMaximumSmallFrameHeight * aspectRatio, kMaximumSmallFrameHeight);
const NSUInteger scale = (NSUInteger)[[UIScreen mainScreen] scale];
const NSUInteger dstWidth = (NSUInteger)fitSize.width * scale;
const NSUInteger dstHeight = (NSUInteger)fitSize.height * scale;

const NSUInteger dstBytesPerRow = bytesPerPixel * dstWidth;
uint8_t* dstData = (uint8_t*)calloc(dstHeight * dstWidth * bytesPerPixel, sizeof(uint8_t));
vImage_Buffer dstBuffer = {
    .data = dstData,
    .height = dstHeight,
    .width = dstWidth,
    .rowBytes = dstBytesPerRow
};

// Scale
vImage_Error ret = vImageScale_ARGB8888(&srcBuff, &dstBuffer, NULL, kvImageHighQualityResampling);

if (ret != kvImageNoError)
{
    free(dstData);
}

// Create CGImage from vImage_Buffer

vImage_CGImageFormat format = {
    .bitsPerComponent = 8,
    .bitsPerPixel = 32,
    .colorSpace = NULL,
    .bitmapInfo = (CGBitmapInfo)kCGImageAlphaFirst,
    .version = 0,
    .decode = NULL,
    .renderingIntent = kCGRenderingIntentDefault,
};
CGImageRef destRef = vImageCreateCGImageFromBuffer(&dstBuffer, &format, NULL, NULL, kvImageNoFlags, &ret);
free(dstData);

// Create UIImage
UIImage* smallFrame = [[UIImage alloc] initWithCGImage:destRef];
// Free up the remaining memory
CGImageRelease(destRef);

CVPixelBufferUnlockBaseAddress(imageBuffer, 0);

Object-C

What "kMaximumSmallFrameHeight" stands for?

@nickdimiCiQ the height of the image to scale to, for instance, 640px