Video start failure (VSF), also written video startup failure, is a session that attempted playback but terminated with a fatal error before any frame appeared. It is the bluntest QoE signal of all, because a failed start is a viewer who got nothing, and it is among the failure metrics defined by CTA-2066 alongside exits before video start and mid-stream playback failures. It is measured as a share of play attempts from player events, the error firing before the first playing event, and is distinct from a viewer voluntarily abandoning during the wait, which is exit-before-video-start. Its catch is the survivorship trap it exposes: because a session that never starts has no startup time to average, a service can report a tidy median startup while a tenth of sessions silently fail, so VSF must always be read beside startup time. A failure also poisons the next visit, cutting the chance a viewer returns within a week.
