The STU, Subtitle Transmission Unit, can playout multiple formats simultaneously, interfacing to several transmission output devices. The common standard formats for transmission of subtitles are:
- In–vision subtitles – Meaning subtitles are keyed on to the video prior to or during the transmission. This can be done for analogue as well as digital SD and HD signals.
- EBU Teletext – This has long been the standard format for hard of hearing subtitling and multi-lingual subtitling in Europe. More correct name is; CCIR Teletext System B. Current standard name is; Enhanced Teletext specification ETS 300 706.
- WST. In some countries they refer to WST (World System Teletext), it's the same as EBU Teletext, see above.
- DVB Teletext – This is the standard for wrapping EBU teletext into a DVB signal. An IRD can decode and display this data or re-insert into VBI for the TV to decode. Today it is the most common method for multi-lingual subtitling in DVB transmissions in Europe.
- DVB Subtitling – This is a subtitle bitmap image that is compressed and sent as a DVB transport stream along with the DVB video and audio and decoded and displayed in the IRD. The latest specification also includes HD bitmap support. This gives the broadcaster full control of the appearance of the subtitles, as well as full support for all languages.
- Line 21 Closed Captions – EIA-608 has been the standard in the Americas for hard of hearing subtitling and to some extent also used for translated subtitling. EIA-708 – The new standard for HD subtitling for ATSC. It is also backwards compatible with EIA-608.
Read more about subtitling technology and Cavena interfaces to external systems