Need help with resizing video frame

I'm capture a YUY2 640x480 video frame from camera in DirectShow. I have a transform filter and all I want to do is downsize the 640x480 frame to 320x240 frame. I have no clue what functions I should use for malloc and the actual downsize. Here's the functions I AM using and am not getting the desired results:

IppiSize roiInputSize = { 640, 480};

IppiSize roiOutputSize = { 320, 240 };

IppiRect roi = {0, 0, 640, 480};

ImageYUY2 = ippiMalloc_8u_C2( roiOutputSize.width, roiOutputSize.height, &stepYUY2 );