ITU-T Recommendations

Audiovisual content (such as video) often contain text, which cannot be easily accessed by a wide section of the audience. While captions/subtitles provide text alternatives to audio elements in audiovisual content, other on-screen text may have various functions. It can be part of the story (as a message written on a piece of paper by one of the characters) or it can provide additional information (such as graphs, emergency alerts or superimposed titles). Complementarily, audio description provides a description of audiovisual content auditorily, including captions/subtitles and other on-screen text if present and are of particular benefit to persons who, for different reasons, cannot access on-screen text. However, some users may only require captions/subtitles and other on-screen text to be made accessible as audio because they already have access to other visual content such as the images.
Recommendation ITU-T T.701.25 provides guidance for audiovisual content producers, distributors and exhibitors on the audio presentation of captions/subtitles and other on-screen text. It acknowledges the relationship with existing access services such as audio description. While considering current implementations, as well as future possibilities suggested by research, and bearing in mind possible trade-offs between quantity and quality, this document positions itself for situations in which various access services coexist and users are given the choice to select those best suited to their needs.
Recommendation ITU-T T.701.25 is twin with the published ISO/IEC TS 20071-25:2017 "Information Technology – User interface component accessibility – Part 25: Guidance on the audio presentation of text in videos, including captions, subtitles and other on-screen text" developed by ISO/IEC JTC1 SC35.