Cache-hit ratio is the percentage of viewer requests answered directly from the CDN edge cache rather than fetched from the origin. A high ratio (often 95%+ for popular VOD) means the origin barely sees traffic, keeping both latency and expensive origin egress low; a low ratio means the origin is doing work the CDN should absorb.
It is driven by cache-key design (identical requests must map to the same object), content popularity, and TTL tuning - and easily wrecked by personalization or per-user tokens that fragment objects. Because delivery cost scales with origin pulls, improving cache-hit ratio is one of the cheapest, highest-impact levers in OTT cost engineering.
