Hello everyone, I'm also new here. :-)
@shuzhiyu I'm also interested in getting optical flow data. I don't think it can be generated by unrealcv at this point, but hopefully others will correct me if I'm wrong.
In the MPI Sintel dataset the authors "modified
Blender’s internal motion blur pipeline to give us accurate motion vectors at
each pixel" [http://files.is.tue.mpg.de/black/papers/ButlerECCV2012-corrected.pdf]
Doing something similar might be possible in UE4 as well.