Timed Text Markup Language: Difference between revisions

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{{Short description|XML-based file format}}

{{Infobox file format

| name = TTML

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| extended_from = [[XML]]

| standard = [https://www.w3.org/TR/ttml1/ W3C TTML1]

| freeopen = 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 authoring, transcoding or exchanging timed text information among legacy distribution content formats presently in use primarily for [[Subtitle_Subtitle (captioning)|subtitling and captioning]] functions. [https://www.w3.org/TR/ttml2/ 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|Society of Motion Picture and Television Engineers (SMPTE)]] and, [[European Broadcasting Union|European Broadcasting Union (EBU)]], [[ATSC]], [[Digital Video Broadcasting|DVB]], [[HbbTV]] and [[MPEG CMAF]] and several profiles and extensions for the language exist nowadays.

TTML Content may also be used directly as a distribution format and itsis supportwidely remains partial at bestsupported in media players., with the exception of major web browsers, where [[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]] <code>&lt;track&gt;</code> 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 <ref>{{cite web |url=https://www.w3.org/TR/NOTE-HTMLplusTIME |title=Timed Interactive Multimedia Extensions for HTML (HTML+TIME)|accessdate=2019-08-09}}</ref> 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 <ref>{{cite web |url=https://www.w3.org/blog/news/archives/1571 |title=W3C Launches Timed Text Working Group|accessdate=2019-08-09}}</ref> and an early draft was released in November 2004 as '''Timed Text (TT) Authoring Format 1.0 – Distribution Format Exchange Profile (DFXP)'''.<ref>{{cite web |url=https://www.w3.org/TR/2004/WD-ttaf1-dfxp-20041101/ |title=Timed Text (TT) Authoring Format 1.0 – Distribution Format Exchange Profile (DFXP)|accessdate=2004-11-01}}</ref> The first version of TTML, [https://www.w3.org/TR/ttml1/ TTML1], was finalized in November 2010.

</ref> 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 <ref>{{cite web |url=https://www.w3.org/blog/news/archives/1571 |title=W3C Launches Timed Text Working Group|accessdate=2019-08-09}}</ref> and an early draft was released in November 2004 as '''Timed Text (TT) Authoring Format 1.0 – Distribution Format Exchange Profile (DFXP)''' <ref>{{cite web |url=https://www.w3.org/TR/2004/WD-ttaf1-dfxp-20041101/ |title=Timed Text (TT) Authoring Format 1.0 – Distribution Format Exchange Profile (DFXP)|accessdate=2004-11-01}}</ref>. The first version of TTML, [https://www.w3.org/TR/ttml1/ 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 [[SubRip|SRT]] format, now named [[WebVTT]].<ref>{{cite web

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|title=WebVTT versus TTML: XML considered harmful for web captions?

|accessdate=16 February 2015

}}</ref>

}}</ref> Nonetheless, in February 2012 the [[Federal Communications Commission|FCC]] declared the [[Society of Motion Picture and Television Engineers|SMPTE]] closed-captioning standard for online video content, a superset of TTML, as a "safe harbor interchange, delivery format".<ref>{{cite web |url=https://www.smpte.org/news-events/news-releases/fcc-declares-smpte-closed-captioning-standard-online-video-content-safe |title=FCC Declares SMPTE Closed-Captioning Standard For Online Video Content As Safe Harbor Interchange, Delivery Format |accessdate=20 February 2015}}</ref>

}}</ref> Nonetheless, inIn February 2012 the [[Federal Communications Commission|FCC]] declared the [[Society of Motion Picture and Television Engineers|SMPTE]] closed-captioning standard for online video content, a superset of TTML, as a "safe harbor interchange, delivery format".<ref>{{cite web |url=https://www.smpte.org/news-events/news-releases/fcc-declares-smpte-closed-captioning-standard-online-video-content-safe |title=FCC Declares SMPTE Closed-Captioning Standard For Online Video Content As Safe Harbor Interchange, Delivery Format |accessdate=20 February 2015}}</ref>

In 2015, [[Netflix]], Home Box Office ([[HBO]]), [[Telestream]], [[SMPTE]], and [[W3C]] received a [[Technology_%26_Engineering_Emmy_Award#2015_Awards|Technology & Engineering Emmy Award]] for the category “Standardization and Pioneering Development of Non-Live Broadband Captioning,” for their work on TTML.

In 2015, [[Netflix]], Home Box Office ([[HBO]]), [[Telestream]], [[SMPTE]], and [[W3C]] received a [[Technology_%26_Engineering_Emmy_AwardTechnology & Engineering Emmy Award#2015_Awards2015 Awards|Technology & Engineering Emmy Award]] for the category “Standardization and Pioneering Development of Non-Live Broadband Captioning,” for their work on TTML.

[https://www.w3.org/TR/ttml2/ TTML2], the second version of TTML started in February 2015, was finalized in November 2018, along with a new revision of [https://www.w3.org/TR/ttml1/ TTML1].

== Profiles ==

The TTML standard specifies a wide range of features, many of which a smaller set are notsometimes necessary, depending on forthe specific applicationsapplication. For this reason, the standard developed the concept of profiles, which are subsets of required features from the full specification. [https://www.w3.org/TR/ttml1/ 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 [https://www.w3.org/AudioVideo/TT/ Timed Text Working Group] maintains a [https://www.w3.org/TR/ttml-profile-registry/ registry] used to identify TTML profiles.

=== DFXP Transformation ===

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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 protocol|tunneling]] data or bit map images and adding necessary metadata.<ref>{{cite web | url=https://www.smpte.org/sites/default/files/st2052-1-2010.pdf |title=SMPTE Timed Text Format (SMPTE ST 2052-1:2010) |date=3 December 2010}}</ref>

* <code>#data</code> – [[Base64]] encoded [[binary large object|binary data]] stream

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=== EBU-TT ===

ThisThe profile[[European Broadcasting Union]] (EBU) defined several related profiles. EBU-TT Part 1 (Tech3350) uses a subset of [https://www.w3.org/TR/ttml1/ TTML1] constraining the features to make it more suitable for thearchive, exchange and use with broadcast video and web video applications.<ref>{{cite web | url=https://tech.ebu.ch/docs/techpublications/tech3350.pdf |title=Part 1: EBU-TT SubtitlingPart 1 - Subtitle format definition (EBU Tech 3350) |date=624 May 2017}}</ref> 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.<ref>{{cite web | url=https://tech.ebu.ch/publications/tech3370 |title=Part 1: EBU-TT Part 3 Live Subtitling (EBU Tech 3370) |date=24 May 2017}}</ref> 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.<ref>{{cite web | url=https://tech.ebu.ch/publications/tech3380 |title=EBU-TT-D Subtitling Distribution Format (Tech3380) |date=22 May 2018}}</ref>

=== IMSC ===

[[https://www.w3.org/TR/ttml-imsc1/| 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 ===

[https://www.atsc.org/wp-content/uploads/2016/12/A343-2018-Captions-and-Subtitles.pdf ATSC A/343] requires subtitle and caption content essence to be either IMSC 1 Text or Image Profile conformant.

=== DVB ===

[https://www.etsi.org/deliver/etsi_en/303500_303599/303560/01.01.01_60/en_303560v010101p.pdf 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 ===

[https://www.etsi.org/deliver/etsi_ts/102700_102799/102796/01.05.01_60/ts_102796v010501p.pdf 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 ===

At [https://developer.apple.com/videos/play/wwdc2017/504/# WWDC 2017] Apple announced support for IMSC 1 Text Profile in HLS, and shortly after shipped systems that include presentation support, including [[iOS]] and [[tvOS]].

=== Freeview Play ===

[http://www.digitaluk.co.uk/__data/assets/pdf_file/0004/93118/Freeview_Play_-_Technical_Specification_V3.0.9_2018.pdf Freeview Play — Technical Specification 2018 Profile Version: 3.0.9 (14/07/2017)] defines the application requirements for the [[Freeview (UK)]] 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]], also published as [https://www.iso.org/standard/71975.html 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 ==