I found out that dynamic frame rate changes are not supported by the codec, but I am able to get it to work correctly by setting param->maxFrameRate to my desired frame rate and then manually dropping frames in the capture thread. This allows the codec to correctly report bit rate.
I think I have also found another issue that arises when setting intraFrameInterval = 0. The problem is that when encoding in this mode, I loose control over the bit rate. Is there a workaround for this? (Note: this is not an issue with H264 encoder codec).
Thank you!