Closed captions present spoken dialogue plus relevant non-speech audio - sound effects, speaker IDs, music cues - as on-screen text that viewers can turn on or off. Unlike translation subtitles, captions (and SDH, subtitles for the deaf and hard of hearing) are designed for accessibility and convey more than just the words.
Technically they ride as a selectable text track (WebVTT, TTML/IMSC) referenced from the manifest and rendered by the player with styling controls. Captions are legally required for much content in many markets, so correct authoring, carriage, and rendering across every device is a compliance obligation - and, given how many viewers use captions by choice, a mainstream usability feature too.
The handbook · 7 volumes
Fora Soft Video Engineering Handbook
Closed captions must stay in sync, readable, and selectable on every device, or deaf and hard-of-hearing viewers lose the story. We wrote seven volumes on the video stack; for closed captions start with Volume 4 on accessibility and subtitles, then Volume 3 on subtitle rendering in players and Volume 2 on caption tracks in HLS and DASH. Written by Nikolay Sapunov, CEO at Fora Soft.
Closed captions out of sync or missing on some of your OTT devices?
We will test your caption pipeline across devices and send fixes for timing, formats, and player support. 250+ video products shipped since 2005.
