There some known case on when introducing the internal OpenMP threading, it may increase the CPU usage. More discussion on this problem could be found here:
If one CPU core is enough to decoding the video, and you are using the threading the high level, I suggest you disabling the internal threading in the H.264 decoder, and use the serial code to decode the video.
At first I thought taking that code out resulted in lower performance, but it turned out to be some code I had to work around another IPP 7 issue. Unlike IPP 6 when you hit the maximum number of frames and pass in the next frame it returns the first decoded frame, but does not read in any of the data. In IPP 6 samples it would return the first decoded frame AND queue up the new data. Our application needs to keep track of how many frames are buffered so our frame stepping is more accurate so this change is a little annoying.