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Timed Text Markup Language

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TTML
Filename extension
.ttml, .dfxp, .xml
Internet media type
application/ttml+xml
Developed byW3C
Initial release1 November 2004; 20 years ago (2004-11-01)[1]
Type of formatTimed text
Extended fromXML
StandardW3C TTML1
Free format?Yes

Timed Text Markup Language (TTML), previously referred to as Distribution Format Exchange Profile (DFXP), is an XML-based W3C standard for timed text in online media and was designed to be used for the purpose of transcoding or exchanging timed text information among legacy distribution content formats presently in use 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) and European Broadcasting Union (EBU), and several profiles and extensions for the language exist nowadays.

TTML Content may also be used directly as a distribution format and its support remains partial at best in media players. WebVTT, the second W3C standard for timed text in online media, has better built-in support in all major browsers in connection with the HTML5 <track> element.

History

The idea of adding timing information on the Web by extending HTML [2] came very early on, out of the work done on the Synchronized Multimedia Integration Language. Based on XML, the work on TTML started in 2003 [3] and an early draft was released in November 2004 as Timed Text (TT) Authoring Format 1.0 – Distribution Format Exchange Profile (DFXP) [4]. The first version of TTML, TTML1, was finalized in November 2010.

In 2010, after discussions about its adoption in HTML5, WHATWG opted for a new but more lightweight standard based on the popular SRT format, now named WebVTT.[5] Nonetheless, in February 2012 the FCC declared the SMPTE closed-captioning standard for online video content, a superset of TTML, as a "safe harbor interchange, delivery format".[6]

In 2015, Netflix, Home Box Office (HBO), Telestream, SMPTE, and W3C received a Technology & Engineering Emmy Award 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 of TTML1.

Profiles

The TTML standard specifies a wide range of features, many of which are not necessary for specific applications. 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 W3C and other organizations over the years to subset or extend the features of TTML. The Timed Text Working Group maintains a 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.[7]


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

This profile uses a subset of TTML1 constraining the features to make it more suitable for the use with broadcast video and web video applications.[8]

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.

References

  1. ^ "Timed Text (TT) Authoring Format 1.0 – Distribution Format Exchange Profile (DFXP)". Retrieved 2015-02-16.
  2. ^ "Timed Interactive Multimedia Extensions for HTML (HTML+TIME)". Retrieved 2019-08-09.
  3. ^ "W3C Launches Timed Text Working Group". Retrieved 2019-08-09.
  4. ^ "Timed Text (TT) Authoring Format 1.0 – Distribution Format Exchange Profile (DFXP)". Retrieved 2004-11-01.
  5. ^ "WebVTT versus TTML: XML considered harmful for web captions?". Retrieved 16 February 2015.
  6. ^ "FCC Declares SMPTE Closed-Captioning Standard For Online Video Content As Safe Harbor Interchange, Delivery Format". Retrieved 20 February 2015.
  7. ^ "SMPTE Timed Text Format (SMPTE ST 2052-1:2010)" (PDF). 3 December 2010.
  8. ^ "Part 1: EBU-TT Subtitling format definition (EBU Tech 3350)" (PDF). 6 May 2017.
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