What is ad request timeout in CTV and how does it affect fill rate?

Ad request timeout is the maximum time (in milliseconds) a CTV app or ad server waits for a bid response before abandoning the auction and either moving to the next demand source or showing a house ad. In CTV, the timeout covers the full round-trip: the app sends a bid request, the SSP forwards it to connected DSPs, DSPs respond, the SSP selects a winner, and the VAST tag is returned to the app. CTV timeouts are longer than display (which runs at 100–200 ms) because CTV auctions involve heavier payloads and network conditions vary. Typical CTV auction timeout: 300–800 ms. Add another 1–3 seconds for video buffering after the VAST tag is returned — the total ad break initiation time in India CTV is typically 2–5 seconds.

Shorter timeouts improve the viewer experience (less buffering) but reduce fill rate — fewer DSPs can respond within the window, so more auctions end with no winner. Longer timeouts allow more DSPs to participate and increase fill, but extend the delay before the ad plays. In India, network latency adds 50–150 ms compared to US or European benchmarks, so a 300 ms timeout that works for a US CTV publisher may cut off many valid Indian DSP responses. India CTV publishers typically set timeouts of 400–600 ms for the initial bid and allow a second request (passback) if the first auction does not fill. If a DSP’s win rate suddenly drops on an India CTV publisher, check whether the publisher reduced its timeout — this is a common source of unexplained fill drops.

A VAST 301 or 302 error code indicates a wrapper timeout — the CTV player fetched a VAST wrapper tag but the next level in the chain did not respond within the allowed time. This is different from the auction timeout (which happens before the VAST tag is selected) — a VAST timeout happens during VAST chain resolution after the winning bid is selected. Common causes in India CTV: long wrapper chains (3+ levels) combined with India CDN latency; video creative hosted on a CDN with no India Points of Presence (PoPs); slow ad verification vendor response. Fixes: reduce wrapper chain depth to 2–3 levels; ensure video creative CDN has India PoPs; check verification vendor SLA for India. VAST error logs in your DSP or ad server will show exactly which wrapper level timed out.