[karl_lillevold]

MaxBFrames is just the max number of B frames to use for the whole clip. Each scene is then independently decided by the NumBFrames setting for that scene, as given in the analysis file. If you see NumBFrames = 3, and would like to use 1 B frame instead, which is good for less than full framerate animation, then edit the analysis file before re-encoding 2nd pass, or even simpler: just use the patternAdaptivity setting to always force 1 B frame. If you decide to use patternAdaptivity=1, you have to re-run both passes for this particular encode.

RPRSize is used only for very low bitrates, where pictures are resampled and encoded at a lower resolution. Not recommeded. QP_Hat is ignored, but it is the 1st pass estimate of what QP value should be used to encode the clip at a constant quality, and reach the target filesize. It is a very rough estimate. The actual QPs used will vary between the limits given by MaxSuggestedQP and MinSuggestedQP for each scene.