DVB Steering Board approves new subtitling specification

DVB TTML Subtitling Joins UHD Family of Specifications Providing Commonality for the Delivery of Traditional Subtitling for IP-based Platforms.

At the most recent meeting of the DVB Steering Board, the new specification for DVB TTML subtitling systems was approved. The specification enables the delivery of next generation subtitles in transport streams for broadcast television services, based on W3C Timed Text Markup Language (TTML). The new specification complements the bitmap based subtitle solutions, which have been in use for over 20 years.

TTML subtitles are increasingly being adopted, including by standards bodies ARIB, ATSC, EBU, SMPTE, ISO/MPEG in the Common Media Application Format specification and many others including platform specifications such as HbbTV. TTML subtitles were initially chosen by DVB for internet delivery of services using the DVB profile of MPEG DASH (TS103 285). TTML subtitles provide a data rate efficient solution for SD, HD and even UHD resolutions.

This new TTML delivery specification will allow service providers to transition over time to a common TTML subtitle format for both broadcast and internet delivered services.

DVB Technical Module Chair, Kevin Murray, remarking on the new specification said “The approval of the transport stream carriage of the TTML specification adds a very important component to the DVB specifications, most notably providing support for UHD subtitles. This also provides a common subtitling mechanism between transport stream and DASH delivered content and, being a textual based format, opens up a range of new possibilities for enhancing accessibility of services.”

Commenting on the approval by the Steering Board, DVB Chairman, Peter MacAvock said “Access Services facilitated by DVB’s new specification are a cornerstone of media services. DVB’s existing bitmapped subtitling specification now has a complement that facilitates subtitling across different platforms and helps DVB addressing the ever increasing demand for accessible content across all platforms”.

The specification has been published as BlueBook A174 and has been forwarded to ETSI for standardization as an EN (European Norm). The elevated EN status is designed to ensure the TTML specification has a similar status to its bitmapped cousin (EN 300 743).