I've run aboard an issue with rvio and OCIO not playing nicely together. Despite $OCIO being set, it appears rvio does not support OCIO? I also cannot find any documentation on the subject.
With OCIO enabled and set, exporting annotated frames using File > Export > Annotated Frames will fail as rvio_hw gives this :
ERROR: OCIOIPNode: Config::GetProcessor failed. Destination colorspace is null.
Additionally, I am curious, when rvio writes out images from an Rv session (.rv) file, where is it getting the user drawing (annotated) data from? For example, if I scribble in the view, then export an annotated frame, I see Rv saves a text-based session file and feeds that to rvio. But I cannot see any painting or binary information in the session file representing the drawings...