For R3, the maximum supported resolution for H264 encode and decode is 4096x2304, which covers many of the most common 4k formats/aspect ratios. By "true 4k", do you mean 4k Ultra High Definition (4096x2560) or something higher?
The link Intel gave me a few days ago to download IMSDK for Linux Servers points to R2 (Version 4.0.1602356.62938). And in the Release Notes document, I can read that h264 decoder/encoder maximum supported resolution is 1920x1088.
I guess that I'll have to upgrade to R3 to encode/decode 4K (4096x2304 is fine). So.. How do I do that ?