How did you build Intel IPP sample, do you use static library or dynamic library from version 5.1?
I would recommend to get the latest version to check this issue again:
In both versions mentioned above, threaded static libraries have been added, so you could use threaded static libraires for multi-core systems.
When you recheck this issue with newer version, please ensure upgrade both libraires and sample.
additionally, there were a lot improvements on umc manual since version 5.1 , you may check this new manual located in directory ipp-samplesaudio-video-codecsdoc.You can check the part of vidoe encoding and see how these parameters are set up..
Please let us know how it works with new version.