The latest EBU contribution to the subtitling domain is EBU-TT Live (Tech 3370). It specifies how to carry live subtitles from authoring stations to play-out, encoding and distribution facilities. Up to now this has typically been addressed by using proprietary protocols in undocumented ways or by carrying subtitles as teletext in video data. By publishing EBU-TT Live, the EBU aims to provide a smarter way to handle (live) subtitles in production facilities and to improve interoperability.
EBU-TT live specifies three things:
- A system model;
- A content profile (= what data to use, based on EBU-TT part 1);
- A mechanism to improve synchronization.
Enabling better subtitling
An interesting application of the new format will be the use of modular ‘improvers’ that can increase the quality of the live subtitles on the fly. Think of speech correctors or timing re-aligners that transform a stream of subtitles at their input into an even better one at their output. The EBU-TT Live format supports such scenarios by allowing detailed timing parameters to be retained from the authoring station.
Of course EBU-TT Live can also handle non-live subtitles. The difference is merely a workflow question. You can imagine sending prepared subtitles out ‘as live’ using the same infrastructure as used for ‘live subtitling’. Mixed-mode operation (e.g. cueing prepared subtitles, complemented with partly live subtitled content) is a common use case for many broadcasters.
Part of a family
EBU-TT Live is part of a wider family of EBU subtitle standards:
- EBU-TT part 1 (Tech 3350), the core spec for production, archiving and exchange;
- EBU-TT part 2 (Tech 3360), which gives guidance for converting STL into EBU-TT part 1;
- EBU-TT part 3 (Tech 3370), the new Live specification
- EBU-TT-D (Tech 3380), the distribution version of EBU-TT part 1 (used for e.g. HbbTV, online players, etc.)
EBU-TT Live is published as a v0.8 draft version to allow implementers and users to provide feedback (before September 2015).
More on EBU-TT subtitling will be presented at the EBU booth during IBC 2015. On IBC Friday, Saturday and Sunday every day a different aspect of EBU-TT subtitles will be presented on. Additionally, the EBU is again organizing a vendors tour (on IBC Friday & Saturday) to meet with subtitling product / service providers and discuss the latest developments in this domain. Pre-registration is open via firstname.lastname@example.org.