Sustainability of Digital Formats: Planning for Library of Congress Collections
Sustainability of Digital Formats: Planning for Library of Congress Collections |
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| Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact | |
| Full name | Timed Text Markup Language Version 2 (TTML2) |
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| Description |
Timed Text Markup Language Version 2 (TTML2) is an XML-based format for the interchange of timed text media, but also can be used as an authoring and distribution format. TTML2 is defined by the World Wide Web Consortium (W3C) and is specified in the Timed Text Markup Language (TTML2) (2nd Edition) W3C Recommendation Snapshot 09 March 2021 (referenced throughout this document). TTML2 is the second version specification of the Timed Text Markup Language (TTML) W3C Recommendation standard, previously referred to as Distribution Format Exchange Profile (DFXP). TTML2 was specified by the Timed Text Working Group (TTWG) and the TTML2 W3C Recommendation First Edition was released in November 2018. See History for more information. According to W3C Press Release, World Wide Web Consortium (W3C) to Receive Emmy ® Award for Standards Work on Accessible Video Captioning and Subtitles, January 2016, “TTML2 is the next version of TTML, published as a first public working draft in February 2015. In addition to the features introduced in IMSC1 and generally refining TTML1 features, it adds support for East Asian languages, enables stereoscopic 3D, and details the mapping to HTML and CSS.” System Model Per specification, TTML timed text files are designed to be used as a bidirectional interchange format for authoring systems and as a unidirectional interchange format for distribution formats. Two classes of processor are described:
TTML2 Document Instance: A Timed Text Document Instance is a defined TTML document, per specification, “a concrete realization of a TTML document, where the concrete form is specific to the context of reference.” Example Fragment from specification: Consisting of a tt (root) document element containing:
TTML2 adds new definitions, profiles, elements, attributes, as well as describing forward and backward compatibility with conforming TTML1 content/processors. The TTML2 specification defines the TTML Abstract Document Types (set of constraints that defines a class of XML Information Sets):
TTML2 specification defines the XML namespaces, profiles, and vocabulary (element/attribute catalog). Added namespaces defined in the TTML2 specification include TT Audio, TT Intermediate Synchronic Document, and TT Resource. TTML2 Profiles: The specification describes TTML’s profiling sub-system and the applied requirements. Profiles have two functions: declare constraints on what and how vocabulary is used and declare content processor conditions.
The TTML2 specification defines the following Standard Designators:
The specification defines TTML2 vocabulary, divided into two catalogs, core and extension. The core catalog defines the baseline vocabulary of TTML, in particular TTML Content. The extension catalog is a placeholder for vocabulary extensions defined by TTML. The core catalog baseline vocabulary includes Profile, Parameter, Content, Embedded Content, Styling, Layout, Timing, Animation, and Metadata. Added defined TTML2 elements include animate, animation, audio, chunk, data, resources, source, font, image, ttm:item, and initial. Profile is information expressing requirements or optionality for authoring or processing. Parameter is either essential or of significant importance for interpreting TTML Content. Content specifies the structure and principal content. Embedded Content is arbitrary content data or external reference embedded, audio, data, font, or image. Styling has an extended library of visual styling attributes, additional audio styling attributes and Ruby styling. Uses of TTML2: W3C’s Draft Community Group Report, Proposal for an Exchange Format to Support Audio Description, May 2022, defines TTML2 as “A Markup Language designed for the storage and delivery of Timed Text, as defined in [TTML2] primarily used in the television industry. TTML is used for authoring, transcoding and exchanging timed text information and for delivering captions, subtitles, and other metadata for television material repurposed for the Web or, more generally, the Internet.” |
| Production phase | Primarily middle state for the delivery of captions and subtitles online, but also developed for the purpose of authoring, transcoding, and exchanging time text information. |
| Relationship to other formats | |
| Defined via | XML, Extensible Markup Language (XML) |
| May contain | CSS,
Cascading Style Sheet (CSS) Markup. CSS style specification syntax is mapped to XML by use of attributes defined in the TT Style Namespace. Vocabulary Derivation - TTML element vocabulary items are based on the syntactic and/or semantic model defined by the reference CSS2, CSS3. |
| May contain | XHTML 1.0,
Extensible HyperText Markup Language (XHTML). Vocabulary Derivation - TTML element vocabulary items are based on the syntactic and/or semantic model defined by the reference XHTML 1.0. |
| May contain | SVG 1.1,
Scalable Vector Graphics (SVG) File Format Family. Vocabulary Derivation - TTML element vocabulary items are based on the syntactic and/or semantic model defined by the reference SVG 1.1. |
| May contain | MPEG 7-5,
Multimedia Content Description Interface (MPEG 7-5). Not described separately on this website at this time. Vocabulary Derivation - TTML element vocabulary items are based on the syntactic and/or semantic model defined by the reference MPEG 7-5. |
| May contain | XSL 1.1,
Extensible Stylesheet Language (XSL) Version 1.1. Not described separately on this website at this time. Vocabulary Derivation - TTML element vocabulary items are based on the syntactic and/or semantic model defined by the reference XSL 1.1. |
| Has earlier version | TTML1,
Timed Text Markup Language (TTML), Version 2 (TTML2). The Timed Text Markup Language (TTML) Version 1, also referred to as TTML1. Vocabulary Derivation TTML element vocabulary items are based on the syntactic and/or semantic model defined by the reference TTML1. |
| Component of | DVB-SUB, Digital Video Broadcasting; Subtitling systems (DVB-SUB). Per standard, the document "specifies the transport of TTML subtitle streams in DVB MPEG-2 transport streams, based on the MPEG-2 system described in ISO/IEC 13818-1...The present document provides syntax for delivery of TTML subtitle streams over MPEG-2 transport stream, and is based on EBU-TT-D compatible with the IMSC1 Text Profile of W3C TTML." See TTML1 for more information on the W3C's IMSC1 Text Profile. |
| LC experience or existing holdings | Likely exists in LC collections but not separately documented. |
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| LC preference | The Library of Congress has not defined format preferences for caption or subtitle files for moving image works in the Recommended Formats Statement. |
| Disclosure | Open standard and fully documented. Timed Text Markup Language 2 (TTML2) is a W3C Recommendation which is considered Web standard. |
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| Documentation | Timed Text Markup Language 2 (TTML2) (2nd Edition) | W3C Candidate Recommendation Snapshot 09 March 2021, is the most current specification and is maintained by the W3C’s Timed Text Working Group (TTWG). The mission of TTWG is “to develop W3C Recommendations for media online captioning by developing and maintaining new versions of the Timed Text Markup Language (TTML).” |
| Adoption |
According to Richard Lane in TTML – The XML Standard Adopted by Top Media Brands, November 2022, “TTML2, the second major revision of the language, was finalised 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), Advanced Television Systems Committee (ATSC), Digital Video Broadcasting (DVB), Hybrid Broadcast Broadband TV (HbbTV) and Moving Picture Experts Group (MPEG). Several profiles and extensions of the language have been developed since the standard was published." See TTML1 |
| Licensing and patents |
See TTML1 |
| Transparency |
See TTML1 |
| Self-documentation |
According to the TTML2 documentation, “This specification does not define any presentation semantics for metadata; therefore, a conformant presentation processor may ignore all metadata matter... Note: Although this specification does not ascribe any presentation semantics to metadata, a superset profile of this specification may do so, in which case any metadata dependent presentation semantics defined by such a profile is considered outside the scope of this specification.” See TTML1 |
| External dependencies |
See TTML1 |
| Technical protection considerations |
TTML2 specification Security and Privacy Considerations: “When [XML 1.0] is used as the concrete encoding of a timed text document instance, the security considerations specified by [XML Media Types] and [XML Guidelines] apply.” See TTML1 |
| Text | |
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| Normal rendering |
See TTML1 |
| Integrity of document structure |
See TTML1 |
| Integrity of layout and display |
TTML2 specification defines the added element font and the font resource that contains font information, such as glyph mapping data, glyph metrics, and/or other mapping/rendering process data. Font styling attributes includes family, kerning, selection strategy, shear, size, style, variant, weight, letter spacing, ruby styling, and more. Per TTML2, “Note: Authors are advised to use subset fonts wherever possible. A subset font is a syntactically valid font resource that removes unreferenced glyphs and unreferenced glyph metrics. In general, a subset font is tied to a specific document, since it may have been generated based on the actual character content of that document.” See TTML1. |
| Support for mathematics, formulae, etc. |
See TTML1. |
| Functionality beyond normal rendering |
TTML2 specification defines two new animation elements, animate and animation, along with TTML1 set element. “The animate element expresses a series of changes (animations) to be applied (targeted) to one or more style property attributes of associated elements...The animation element is a container element used to group out-of-line animation (must specify an xml:id attribute) matter, including metadata that apples to animation matter...Semantics for the set and animate elements are based upon that defined by SVG 1.1, which, in turn, is based upon SMIL 3.0.” TTML2 specification defines a new audio element and an audio resource containing coded and unencoded audio samples, as well as editable attributes gain, pan, pitch, and speak. TTML2’s #speech feature supports an optional speech synthesis component of content processors, which synthesizes audio speech rendered from text content. See TTML1. |
| Tag | Value | Note |
|---|---|---|
| Filename extension | ttml |
Per specification. See https://www.w3.org/TR/ttml1/#media-types-registration. |
| Filename extension | dfxp |
Per specification, previous drafts referred to TTML as DFXP (Distribution Format Exchange Profile), the term is retained for historical reasons in certain contexts, such as profiles and designators.See https://www.w3.org/TR/ttml1/#media-types-registration. TTML's Wikipedia page lists this as an extension. According to Rudolf Boogerman in How to Create Captions/Subtitles for Video and Audio in WebVTT, SRT, DFXP Format, Updated March 2019, users can “save the file with an .dfxp extension, like mycaption.dfxp, but you also may use mycaption.xml since this basically is a XML file.” See Notes for more file extension information found. Comments welcome. |
| Filename extension | xml |
TTML's Wikipedia page lists this as an extension. According to Rudolf Boogerman in How to Create Captions/Subtitles for Video and Audio in WebVTT, SRT, DFXP Format, Updated March 2019, users can “save the file with an .dfxp extension, like mycaption.dfxp, but you also may use mycaption.xml since this basically is a XML file.” See Notes for more file extension information found. Comments welcome. |
| Internet Media Type | See note. | The mediatype was removed from the TTML2 specification, https://www.w3.org/TR/ttml1/#media-types-registration. See TTML1. Comments welcome. |
| Mac OS file type | See related format. | See TTML1 |
| Pronom PUID | See note. | PRONOM has no corresponding entry as of April 2023. |
| Wikidata Title ID | Q25339304 |
Wikidata entry for Timed Text Markup Language. See https://www.wikidata.org/wiki/Q25339304. Wikidata does not specify a version of TTML. |
| General |
Per the specification, MediaType Registration appendix has been removed from the TTML2 specification. W3C TTML2 GitHub Issues Forum, user Plehegar commented on November 4, 2015, “When Issue-351 has been completed, add a Media Type Registration Annex to TTML2 that reflects the updated registration, similar to what’s in Annex C of TTML1.” User Skynavga replied October 29, 2016, “It has been decided that the registration annex will not be included in TTML2.” No other Media Type Registration information was found at this time. - Timed Text Working Group website lists a “TTML3” under Recommendation Track Specification Repositories with a link to W3C’s GitHub page, but the README.md (February 2022) states, “IMPORTANT: Development of Timed Text Markup Language 3 (TTML3) is currently suspended.” |
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| History |
TTML2 is the second version of the Timed Text Markup Language, having its first working draft published in 2015 and its first W3C Candidate Recommendation specification released in March of 2018. Timed Text Markup Language 2 (TTML2) (2nd Edition) | W3C Candidate Recommendation Snapshot 09 March 2021, is the most current specification and is maintained by the W3C’s Timed Text Working Group (TTWG). - TTML specification states, “In previous drafts of this specification, TTML was referred to as DFXP (Distribution Format Exchange Profile). This latter term is retained for historical reasons in certain contexts, such as profile names and designators.” - Participating Organizations of the Timed Text Working Group (TTWG) include: Adobe, Apple Inc., Brightcove, British Broadcasting Corporation, ERICSSON, Google LLC, Igalia, Kodansha, Publishers, Ltd., MovieLabs, Mux, and Netflix. |
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