Timed Text Markup Language (TTML), previously referred to as Distribution Format Exchange Profile (DFXP), is an

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. T ...

-based

W3C The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 and led by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working to ...

standard for

timed text Timed text is the presentation of text media in synchrony with other media, such as audio and video. Applications Typical applications of timed text are the real-time subtitling of foreign-language movies on the Web, captioning for people lack ...

in online media and was designed to be used for the purpose of authoring, transcoding or exchanging timed text information presently in use primarily for subtitling and captioning functions
TTML2
the second major revision of the language, was finalized on November 8, 2018. It has been adopted widely in the television industry, including by Society of Motion Picture and Television Engineers (SMPTE), European Broadcasting Union (EBU),

ATSC Advanced Television Systems Committee (ATSC) standards are an American set of standards for digital television transmission over terrestrial, cable and satellite networks. It is largely a replacement for the analog NTSC standard and, like that ...

DVB Digital Video Broadcasting (DVB) is a set of international open standards for digital television. DVB standards are maintained by the DVB Project, an international industry consortium, and are published by a Joint Technical Committee (JTC) o ...

HbbTV Hybrid Broadcast Broadband TV (HbbTV) is both an industry standard ( European Telecommunications Standards Institute (ETSI) TS 102 796) and promotional initiative for hybrid digital TV to harmonise the broadcast, Internet Protocol Television ( ...

and

MPEG CMAF The Moving Picture Experts Group (MPEG) is an alliance of working groups established jointly by ISO and IEC that sets standards for media coding, including compression coding of audio, video, graphics, and genomic data; and transmission and ...

and several profiles and extensions for the language exist nowadays. TTML Content may also be used directly as a distribution format and is widely supported in media players, with the exception of major web browsers, where WebVTT, the second

standard for

in online media, has better built-in support in connection with the

HTML5 HTML5 is a markup language used for structuring and presenting content on the World Wide Web. It is the fifth and final major HTML version that is a World Wide Web Consortium (W3C) recommendation. The current specification is known as the HTML ...

<track> element; many organisations nevertheless use TTML content on web video using their own player code.

History

The idea of adding timing information on the Web by extending HTML came very early on, out of the work done on the

Synchronized Multimedia Integration Language Synchronized Multimedia Integration Language (SMIL ()) is a World Wide Web Consortium recommended Extensible Markup Language (XML) markup language to describe multimedia presentations. It defines markup for timing, layout, animations, visual t ...

. Based on

, the work on TTML started in 2003 and an early draft was released in November 2004 as Timed Text (TT) Authoring Format 1.0 – Distribution Format Exchange Profile (DFXP). The first version of TTML
TTML1
was finalized in November 2010. In 2010, after discussions about its adoption in HTML5,

WHATWG The Web Hypertext Application Technology Working Group (WHATWG) is a community of people interested in evolving HTML and related technologies. The WHATWG was founded by individuals from Apple Inc., the Mozilla Foundation and Opera Software, lea ...

opted for a new but more lightweight standard based on the popular SRT format, now named WebVTT. In February 2012 the

FCC The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdictio ...

declared the

SMPTE The Society of Motion Picture and Television Engineers (SMPTE) (, rarely ), founded in 1916 as the Society of Motion Picture Engineers or SMPE, is a global professional association of engineers, technologists, and executives working in the m ...

closed-captioning standard for online video content, a superset of TTML, as a "safe harbor interchange, delivery format". In 2015,

Netflix Netflix, Inc. is an American subscription video on-demand over-the-top streaming service and production company based in Los Gatos, California. Founded in 1997 by Reed Hastings and Marc Randolph in Scotts Valley, California, it offers a fil ...

, Home Box Office (

HBO Home Box Office (HBO) is an American premium television network, which is the flagship property of namesake parent subsidiary Home Box Office, Inc., itself a unit owned by Warner Bros. Discovery. The overall Home Box Office business unit is ba ...

Telestream Telestream, Inc. is an American privately held computer software company. History The company, founded in 1998, is headquartered in Nevada City, California with personnel in France, Germany, Sweden, Poland, Canada and the UK. Telestream prov ...

, and

received a

Technology & Engineering Emmy Award The Technology and Engineering Emmy Awards, or Technology and Engineering Emmys, are one of two sets of Emmy Awards that are presented for outstanding achievement in engineering development in the television industry. The Technology and Engineer ...

for the category “Standardization and Pioneering Development of Non-Live Broadband Captioning,” for their work on TTML.
TTML2
the second version of TTML started in February 2015, was finalized in November 2018, along with a new revision o
TTML1

Profiles

The TTML standard specifies a wide range of features, of which a smaller set are sometimes necessary, depending on the specific application. For this reason, the standard developed the concept of profiles, which are subsets of required features from the full specification
TTML1
defines three standard profiles: DFXP Transformation, DFXP Presentation and DFXP Full. Many profiles of TTML were developed by

and other organizations over the years to subset or extend the features of TTML. Th
Timed Text Working Group
maintains
registry
used to identify TTML profiles.

DFXP Transformation

This profile defines the minimum feature requirements that a transformation processor (e.g. caption converter) needs to support in order to be considered TTML compliant.

DFXP Presentation

This profile defines the minimum feature requirements that a presentation processor (e.g. video player) needs to support in order to be considered TTML compliant.

DFXP Full

This profile requires the support of all the feature defined by TTML specification.

SMPTE-TT

This profile extends TTML with three SMPTE-specific elements aimed at legacy formats. Interoperability with pre-existing and regionally-specific formats (such as CEA-708, CEA-608, DVB Subtitles, and WST (World System Teletext)) is provided by means of tunneling data or bit map images and adding necessary metadata. * #data –

Base64 In computer programming, Base64 is a group of binary-to-text encoding schemes that represent binary data (more specifically, a sequence of 8-bit bytes) in sequences of 24 bits that can be represented by four 6-bit Base64 digits. Common to all bina ...

encoded

binary data Binary data is data whose unit can take on only two possible states. These are often labelled as 0 and 1 in accordance with the binary numeral system and Boolean algebra. Binary data occurs in many different technical and scientific fields, wher ...

stream * #image –

encoded transparent PNG images * #information – Metadata The U.S Federal Communications Commission (FCC) has declared SMPTE-TT to be a safe harbor interchange and delivery format in February 2012.

EBU-TT

EBU defined several related profiles. EBU-TT Part 1 (Tech3350) uses a subset o
TTML1
constraining the features to make it more suitable for archive, exchange and use with broadcast video and web video applications. EBU-TT Part 3 (Tech3370) extends and constrains Part 1 further, in particular adding functionality to support live streaming of subtitles from the subtitle author to a distribution encoder. EBU-TT-D (Tech3380) is highly constrained profile of TTML1 intended specifically for distribution to players, and has been adopted by HbbTV, DVB and Freeview Play for example.

IMSC

TTML Profiles for Internet Media Subtitles and Captions
specifies two profiles, a text-only profile and an image-only profile, intended to be used across subtitle and caption delivery applications worldwide, thereby simplifying interoperability, consistent rendering and conversion to other subtitling and captioning formats. It incorporate extensions from SMPTE-TT and EBU-TT.

Adoption

ATSC

ATSC A/343
requires subtitle and caption content essence to be either IMSC 1 Text or Image Profile conformant.

DVB

ETSI EN 303 560 v1.1.1 (May 2018)
is the DVB TTML Subtitling Systems specification. It defines a default conformance point that is the common intersection of conformance between EBU-TT-D and IMSC 1 Text Profile, and allows for subtitle and caption documents conformant to EBU-TT-D, IMSC1 Text Profile or other profiles of TTML to be sent and signalled within DVB MPEG-2 transport streams, and includes the ability to embed fonts for subtitle presentation, also within the transport stream.

HbbTV 2

ETSI TS 102 796 V1.5.1 (2018-09)
is the HbbTV 2.0.2 specification. It specifies that conformant players must be able to play back EBU-TT-D subtitles delivered online for example in ISO BMFF via MPEG DASH, as well as allowing for other existing broadcast subtitle formats.

HLS

A
WWDC 2017
Apple announced support for IMSC 1 Text Profile in HLS, and shortly after shipped systems that include presentation support, including

iOS iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, including the iPhone; the term also includes ...

and

tvOS tvOS (formerly known as Apple TV Software) is an operating system developed by Apple Inc. for the Apple TV, a digital media player. In the first-generation Apple TV, Apple TV Software was based on Mac OS X. Starting with the second-generation ...

Freeview Play

Freeview Play — Technical Specification 2018 Profile Version: 3.0.9 (14/07/2017)
defines the application requirements for the

Freeview (UK) Freeview is the United Kingdom's sole digital terrestrial television platform. It is operated by Digital UK Ltd and DTV Services Ltd, a joint venture between the BBC, ITV, Channel 4, Channel 5 and Sky. It was launched on 30 October 2002, t ...

hybrid IPTV and Broadcast device for the UK market, conforming to the HbbTV specification, requiring support for "DASH streaming technology with integrated EBU-TT-D subtitles".

MPEG CMAF

CMAF is the Common Media Application Format published by MPEG as part 19 of

MPEG-A MPEG-A is a group of standards for composing MPEG systems formally known as ''ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a ...

, also published a
ISO/IEC 23000-19:2018 Information technology -- Multimedia application format (MPEG-A) -- Part 19: Common media application format (CMAF) for segmented media
The format specifies CMFHD presentation profiles in which subtitle tracks shall include at least one "switching set" for each language and role in the IMSC 1 Text profile, while also allowing for other representations of subtitles in WebVTT.

References

{{reflist Subtitling Subtitle file formats