ISO/IEC TS 20071-25:2017

ISO/IEC TS 20071-25:2017 provides recommendations on the audio presentation of captions/subtitles and other on-screen text for use in all type of videos regardless of the language and technology being used to transmit and present the recorded or live video.
ISO/IEC TS 20071-25:2017 applies to making captions/subtitles and other on-screen text accessible to users with various needs, including but not limited to people with learning and reading disabilities, people with cognitive disabilities, people who are blind or have low vision, older people, and non-native language speakers. It does not apply to captions/subtitles or other on-screen text whose content is already provided in the soundtrack in a language and a way users can access.
ISO/IEC TS 20071-25:2017 provides guidance on spoken captions/subtitles as a stand-alone access service but it also provides guidance on how to integrate spoken captions/subtitles, other spoken on-screen text and audio description, if needed, in different types of videos.
NOTE 1       Extensive guidance on audio description is provided in ISO/IEC/TS 20071-21.
ISO/IEC TS 20071-25:2017 does not consider the devices or transmission mechanisms used to deliver and play the content or the audio presentation of text in videos. These devices include, but are not limited to televisions, computers, wireless devices, projection equipment, DVD and home cinema equipment, cinema equipment and other forms of user interfaces technology. Therefore, this document does not consider transcoding files for the various video and audio outputs.
NOTE 2       Technical matters of transmission and distribution are covered by other documents (e.g. MPEG standards and other technical standards such as IEC 62731:2013).
ISO/IEC TS 20071-25:2017 acknowledges the various needs and preferences of users, as well as the different approaches to the audio presentation of text in videos.
It applies to audio presentations intended to be heard simultaneously along with the original video.