scope:

This International Standard specifies the coded representation of textual information for timed presentation on screens. The text may be streamed in association with video and audio, in which case the text may represent subtitles e.g. with translations of the associated audio in another language, or as an aid to the hard of hearing; another example is the text of a song in a Karaoke application. However, the text may also be streamed as a stand-alone application without any associated video and audio. The streaming text format is specified in a transport agnostic manner, so as to allow transport over a large variety of transport means, while providing a reasonable level of random access and error robustness.

The text streams are defined as byte streams that are capable of carrying text access units of a specified format, optionally interleaved with data needed for the decoding of the text stream. The format of text streams and text access units is specified, as well as signaling and decoding of text streams.