splitvr 2.0 had a unwarp/rewarp feature that i actually never got to work (think some scipt or exe was missing). i think it used ffmpeg filters to unmorph frames and later revert the morphing with the same settings. the plan was to make the faces look "normal" prior to extraction and training.
personally i stick to scenes with the target face in the center of the frames, usually the face being near the frame boarders and close-ups causes distortions.
edit: i was also looking for methods to convert vr to normal vids (other than screen capturing a vr player), this could be a workaround if you're interested in the scenes (soooo much good pov stuff) and not particularly care for vr