I see the comments in nvEncodeAPI.h but I am not entirely certain what they are still.
This document should shed some light.
Thanks - that was helpful!
// Holds the interval between frames that trigger a new intra refresh cycle
// and this cycle lasts for intraRefreshCnt frames.
encodeConfig.encodeCodecConfig.h264Config.intraRefreshPeriod = this->fps * 10;
// Holds the number of frames over which intra refresh will happen
encodeConfig.encodeCodecConfig.h264Config.intraRefreshCnt = this->fps