Yes, seeing from IPP manual, there are some format conversion function which support interlace. but it seems no onecandothefunctionality you need.
And yes, use 2x srcStep should be ok to jusmp over rows. but no function to make the four pixel groupings.
(not related, butquery about four pixel groupings, YCbCr 422 C2 will be YCbYCr.. 2 pixel a group, total 32bit. If 4 Cb, 4Y, 4Cr, the format 422 haven't so much Cb and Cr?)
Converts interlaced 4:2:2 CbYCr image to 4:2:0 YCbCr image.