Captioning rhymes with:
optioning, airconditioning, apportioning, auctioning, auditioning, cautioning, commissioning, conditioning, cushioning, decommissioning, fashioning, freshening, functioning, malfunctioning, mentioning, motioning, optioning, partitioning, petitioning, positioning, rationing, reconditioning, repositioning, sanctioning, sectioning, stationing, transitioning, vacationing
Captioning sounds like:
caftans, captain's, captaining, captains, captions, chieftain's, chieftains, cohabiting