IMSC Text Profile 1.3

W3C Editor's Draft

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https://w3c.github.io/imsc/imsc1/spec/ttml-ww-profiles.html
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Copyright © 2026 World Wide Web Consortium . W3C ® liability , trademark and document use rules apply.

Abstract

This specification defines a text-only profile of [ ttml2 ] intended for subtitle and caption delivery applications worldwide.

It improves over the Text Profile specified at at [ ttml-imsc1.2 ], with the improvements summarized at L. Summary of substantive changes .

Status of This Document

This is a preview

Do not attempt to implement this version of the specification. Do not reference this version as authoritative in any way. Instead, see https://w3c.github.io/imsc/imsc1/spec/ttml-ww-profiles.html for the Editor's draft.

This section describes the status of this document at the time of its publication. A list of current W3C publications and the latest revision of this technical report can be found in the W3C standards and drafts index .

This document was published by the Timed Text Working Group as an Editor's Draft.

Publication as an Editor's Draft does not imply endorsement by W3C and its Members.

This is a draft document and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to cite this document as other than a work in progress.

This document was produced by a group operating under the W3C Patent Policy . W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent that the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy .

This document is governed by the 18 August 2025 W3C Process Document .

1. Scope

This specification defines a text-only profile of [ ttml2 ], which is intended for subtitle and caption delivery worldwide, including dialog language translation, content description, captions for deaf and hard of hearing, etc.

The specification is designed such that:

2. Introduction

This section is non-normative.

2.1 Overview

This specification defines a document exchange format and associated validation and presentation requirements for subtitle and caption delivery worldwide, including dialog language translation, content description, captions for deaf and hard of hearing, etc.

The format is a profile of [ ttml2 ], called the Text Profile , consisting of a subset of the features of [ ttml2 ] alongside additional features specified in [ EBU-TT-D ], e.g., F.8 #multiRowAlign , and defines new features, e.g., F.5 #fillLineGap . The Text Profile is text-only: the timed text that comprise the subtitles and captions is expressed exclusively using code points defined in The Unicode Standard .

As detailed in 6.3 Profile Resolution Semantics and I. Compatibility with other TTML-based specifications , this specification is designed to be compatible with other text-only profiles of TTML, including [ ttml-imsc1 ], [ ttml-imsc1.0.1 ], [ ttml-imsc1.1 ], [ ttml-imsc1.2 ], [ SMPTE2052-1 ], [ EBU-TT-D ], [ ttml10-sdp-us ] and [ CFF ].

Earlier versions of this specification specify an image-only profile, called the Image Profile, which is no longer specified herein. I.6 Previous versions of IMSC discusses the relationship between this and earlier versions of the specification.

To improve rendering fidelity, A. Reference Fonts defines reference fonts and requires Processors to support one or more fonts with similar font metrics as these reference fonts. Similarly, in order to increase the confidence that text will be presented correctly by Processors targeting specific languages, B. Common Character Sets defines common character sets that authors are encouraged to use.

An Hypothetical Render Model is specified separately at [ imsc-hrm ]. The Hypothetical Render Model allows subtitle and caption authors and providers to verify that the Text Profile documents they supply do not exceed defined complexity levels, so that playback systems can render the content synchronized with the author-specified display times.

This specification was initially based on [ SUBM ].

2.2 Example Document

The following example demonstrates a syntactically valid Text Profile and [ EBU-TT-D ] document instance and how it would be rendered. It is not intended to be used as a template for a subtitle file.

The example is arranged such that there is no white space added to the text within the p element; such white space can cause unexpected formatting, if present.

Example 1 
<?xml version="1.0" encoding="UTF-8"?>
<tt xmlns="http://www.w3.org/ns/ttml"
    xmlns:ttm="http://www.w3.org/ns/ttml#metadata"
    xmlns:ttp="http://www.w3.org/ns/ttml#parameter"
    xmlns:tts="http://www.w3.org/ns/ttml#styling" 
    xmlns:ebutts="urn:ebu:tt:style"
    xmlns:ebuttm="urn:ebu:tt:metadata"
    xmlns:itts="http://www.w3.org/ns/ttml/profile/imsc1#styling"
    ttp:timeBase="media"
    ttp:cellResolution="32 15"
    xml:lang="en" >
    <head>
        <metadata>
            <ebuttm:documentMetadata>
                <!-- EBU-TT-D defines its own conformance signalling mechanism,
                     since, being based on TTML1, the ttp:contentProfiles parameter
                     is not available; it was introduced in TTML2. -->
                <ebuttm:conformsToStandard>urn:ebu:tt:distribution:2018-04</ebuttm:conformsToStandard>
                <ebuttm:conformsToStandard>http://www.w3.org/ns/ttml/profile/imsc1/text</ebuttm:conformsToStandard>
                <ebuttm:conformsToStandard>http://www.w3.org/ns/ttml/profile/imsc1.2/text</ebuttm:conformsToStandard>
                <ebuttm:conformsToStandard>http://www.w3.org/ns/ttml/profile/imsc1.3/text</ebuttm:conformsToStandard>
            </ebuttm:documentMetadata>
        </metadata>
        <!-- 
          The styling element defines the styles that will be applied to <p> and <span> tags. 
          EBU-TT-D uses referenced styles only - inline styles are not supported. 
        -->
        <styling>
            <style xml:id="paragraphStyle"
                tts:fontFamily="ReithSans, Arial, Roboto, proportionalSansSerif, default"
                tts:fontSize="100%" 
                tts:lineHeight="120%"
                tts:textAlign="center"
                tts:wrapOption="noWrap"
                ebutts:multiRowAlign="center"
                ebutts:linePadding="0.5c"
                itts:fillLineGap="true"/>
            <style xml:id="spanStyle"
                tts:color="#FFFFFF"
                tts:backgroundColor="#000000"/>
            <style xml:id="yellowStyle"
                tts:color="#FFFF00"
                tts:backgroundColor="#000000"/>
        </styling>
          <!-- 
            The layout element defines the regions where subtitle text is displayed.
            Here, a top and a bottom region are defined, with a clearance of 2 lines of
            text from the top and bottom. 
            With a cell resolution of 32 by 15, a font height of 100% (of cell height) equals
            6.66% (100/15). A line height of 120% of the font size equals 8% of the height of the 
            active video (1.2 x 6.66). Each region accommodates 3 lines of text: 3 x 8% = 24%.
            The width of the regions is set at 70% to take into account 3:4 display and 1c 
            of line padding (2 x 0.5c). 
          -->
        <layout>
            <region xml:id="topRegion"
                tts:origin="15% 16%"
                tts:extent="70% 24%"
                tts:displayAlign="before"
                tts:writingMode="lrtb"
                tts:overflow="visible"/>
            <region xml:id="bottomRegion"
                tts:origin="15% 60%"
                tts:extent="70% 24%"
                tts:displayAlign="after"
                tts:writingMode="lrtb"
                tts:overflow="visible"/>
        </layout>
    </head>
    <body>
        <!-- 
          The intended use of DIVs is to hold semantic information, for example sections
          within a programme. DIVs are not intended to be used for presentation, although 
          style applied to them would cascade to descendent elements. 
        -->
        <div>
            <!-- 
              A paragraph holds a single subtitle of one or more lines, with a 
              time range and region allocation. 
            -->
            <p xml:id="subtitle1" region="bottomRegion" style="paragraphStyle"
                begin="00:00:10.000" end="00:00:20.000"><!-- 
                  A span is used to apply style to the text, by reference. 
             --><span style="spanStyle">Beware the Jubjub bird, and shun</span><br/><span style="spanStyle">The frumious Bandersnatch!</span></p>
            <p xml:id="subtitle2" region="topRegion" style="paragraphStyle"
                begin="00:00:30.000" end="00:00:31.000"
                ><span style="spanStyle">This subtitle is in the top region.</span><br
                /><span style="spanStyle">it contains one word in </span><span style="yellowStyle">yellow </span><span style="spanStyle">colour.</span></p>
        </div>
    </body>
</tt>

The illustrative renders below show how the document above is interpreted (only the subtitle text and the black background will be displayed). Note that the underlying grid is virtual and that elements don't necessarily align to it; it is a graphical representation of the ttp:cellResolution parameter.

Image showing rendering of example, with text 'Beware the Jubjub bird' etc in lower region of image, on a 32x15 cell grid.
Figure 1 Displayed between 00:00:10 and 00:00:20
Image showing rendering of example, with text 'This subtitle is in the top region' etc in upper region of image, on a 32x15 cell grid. The word 'yellow' is coloured yellow; the other words are white.
Figure 2 Displayed between 00:00:30 and 00:00:31

This example is based on [ BBC-SUB ].

3. Documentation Conventions

This specification uses the same conventions as [ ttml2 ] for the specification of parameter attributes, styling attributes and metadata elements. In particular:

This specification uses Feature and Extension designations as defined in Appendices E.1 and F.1 at [ ttml2 ]:

If the name of an element referenced in this specification is not namespace qualified, then the TT namespace applies (see 8.8 Namespaces .)

4. Terms and Definitions

Character Information Item . See Section 2.2 at [ ttml2 ].

Document Instance . See Section 2.2 at [ ttml2 ].

Default Processor Profile . As defined in [ ttml2 ].

Default Region . See Section 9.3.1 at [ ttml2 ].

Extension . See Section 2.2 at [ ttml2 ].

External Data Resource . See Section 2.2 at [ ttml2 ].

Feature . See Section 2.2 at [ ttml2 ].

Intermediate Synchronic Document . See Section 9.3.2 at [ ttml2 ].

Document Interchange Context . See Section 2.2 at [ ttml2 ].

Document Processing Context . As defined in [ ttml2 ].

Effective Processor Profile . As defined in [ ttml2 ].

Font Resource . As defined in [ ttml2 ].

Linear White-Space . See Section 2.3 at [ ttml2 ].

Override Content Profile . As defined in [ ttml2 ].

Processor . Either a Presentation processor or a Transformation processor .

Presentation processor . See Section 2.2 at [ ttml2 ].

Specified Value . As defined in [ ttml2 ].

Transformation processor . See Section 2.2 at [ ttml2 ].

Processor Profile . As defined in [ ttml2 ].

Related Media Object . See Section 2.2 at [ ttml2 ].

Related Video Object . A Related Media Object that consists of a sequence of image frames, each a rectangular array of pixels.

Root Container Region . See Section 2.2 at [ ttml2 ].

Text Profile transformation processor . A transformation processor that conforms to the Text Profile .

Text Profile presentation processor . A presentation processor that conforms to the Text Profile .

5. Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key words MAY , SHALL , SHALL NOT , SHOULD , and SHOULD NOT in this document are to be interpreted as described in BCP 14 [ RFC2119 ] [ RFC8174 ] when, and only when, they appear in all capitals, as shown here.

A Document Instance that conforms to the Text Profile :

Note

A Document Instance , by definition, satisfies the requirements of Section 3.1 at [ ttml2 ], and hence a Document Instance that conforms to a profile defined herein is also a conforming TTML1 Document Instance.

A presentation processor that conforms to the Text Profile :

A transformation processor that conforms to the Text Profile :

A Feature or Extension currently designated permitted-deprecated is intended to be designated as optional or prohibited in future versions of this specification.

A Feature or Extension designated as partially supported is neither completely prohibited nor completely permitted . Instead, the disposition of each of its subset Feature or Extension is specified individually.

Note

[ ttml2 ] makes a distinction between a presentation processor , whose purpose is to present a Document Instance , and transformation processor , whose purpose is to process a Document Instance without presenting it. A renderer embedded in the media pipeline of a mobile device is an example of a presentation processor , whereas a validator is an example of a transformation processor .

Note

A processor that conforms to the Text Profile is not required to conform to any other profile. For convenience, and for consistency with previous versions of this specification, the terms Text Profile transformation processor and Text Profile presentation processor are defined.

Note

The use of the term presentation processor ( transformation processor ) within this specification does not imply conformance to the DFXP Presentation Profile (DFXP Transformation Profile) specified in [ ttml2 ]. In other words, it is not considered an error for a presentation processor ( transformation processor ) to conform to a profile defined in this specification without also conforming to the DFXP Presentation Profile (DFXP Transformation Profile).

Note

This specification does not specify presentation processor or transformation processor behavior when processing or transforming a non-conformant Document Instance .

Note

The permitted and prohibited dispositions do not refer to the specification of a ttp:feature or ttp:extension element as being permitted or prohibited within a ttp:profile element.

6. Text Profile

6.1 General

The Text Profile consists of Sections 7. Supported Features and Extensions and 8. Additional Provisions .

6.2 Designator

This Text Profile is associated with the following profile designator:

Profile Name Profile Designator
IMSC 1.3 Text http://www.w3.org/ns/ttml/profile/imsc1.3/text

6.3 Profile Resolution Semantics

6.3.1 General

The Profile Semantics specified in [ ttml2 ] apply.

Note

The default value of prohibited attributes, e.g. ttp:contentProfileCombination , applies.

The Text Profile processor profile includes all of the features required by each of the following processor profiles :

Note

Authors can use TTML content verification tools to detect and warn about overly constrained uses of content and processor profile attribute vocabulary, e.g. warn if (a) a document simultaneously (i) specifies conformance to content profile X and (ii) requires use of processor profile Y, and (b) profiles X and Y are semantically incompatible.

6.3.2 Override

If one or more ebuttm:conformsToStandard elements, as specified in [ EBU-TT-M ], are set to any of the following designators, then the override content profile SHALL be set to the profile associated with any one of the matching designators:

7. Supported Features and Extensions

See 5. Conformance for a definition of permitted , prohibited , optional and permitted-deprecated .

Feature or Extension Text Profile Disposition
Relative to the TT Feature namespace
All features specified in [ ttml2 ] are prohibited unless specified otherwise below
#animation permitted
#animation-version-2 Partially supported via #animation .
#background Partially supported via #backgroundColor .
#backgroundColor permitted
#backgroundColor-block permitted
#backgroundColor-inline permitted
#backgroundColor-region permitted
#base permitted
#base-version-2 Partially supported via #base .
#bidi permitted
#bidi-version-2 Partially supported via #bidi and #unicodeBidi-version-2 .
#cellResolution permitted
#color permitted
Section 8.1.4 #color specifies additional constraints.
#content permitted
#contentProfiles permitted
#core permitted
#direction permitted
#disparity permitted
#display permitted
#display-block permitted
#display-inline permitted
#display-region permitted
#display-version-2 Partially supported via #display , #display-block , #display-inline , and #display-region .
#displayAlign permitted
#displayAlign-region permitted
#displayAlign-relative permitted
#displayAlign-version-2 Partially supported via #displayAlign-region , and #displayAlign-relative .
#displayAspectRatio permitted
Section 8.1.5 #displayAspectRatio specifies additional constraints.
#embedded-audio prohibited
#embedded-data is however partially supported .
#embedded-content Partially supported via #embedded-font .
#embedded-data Partially supported via #resources and #source .
#embedded-font Partially supported via #embedded-data and #font .
#embedded-image prohibited
#embedded-data is however partially supported .
#extent permitted
#extent-full-version-2 Partially supported via #extent-version-2 .
#extent-length permitted
#extent-length-version-2 permitted
#extent-region Partially supported via #extent-length .
Section 8.1.7 #extent-region specifies additional constraints.
#extent-region-version-2 Partially supported via #extent-region .
#extent-root Partially supported via #extent-length .
Section 8.1.6 #extent-root specifies additional constraints.
#extent-root-version-2 Partially supported via #extent-root .
#extent-version-2 Partially supported via #extent and #extent-region-version-2 .
#font permitted
Section 8.1.8 #font and #source specifies additional constraints.
#fontFamily permitted
Section 8.1.10 #fontFamily specifies additional constraints.
#fontFamily-generic permitted
Section 8.1.9 #fontFamily-generic specifies additional constraints.
#fontFamily-non-generic permitted
#fontSize Partially supported via #fontSize-isomorphic .
#fontSize-isomorphic permitted
#fontStyle permitted
#fontStyle-italic permitted
Section 8.1.23 Slanted Japanese-language text provides additional information.
#fontStyle-oblique permitted
Section 8.1.23 Slanted Japanese-language text provides additional information.
#fontVariant permitted
Section 8.1.11 #fontVariant specifies additional constraints.
#fontWeight permitted
#fontWeight-bold permitted
#frameRate permitted
Section 8.1.12 #frameRate specifies additional constraints.
#frameRateMultiplier permitted
#initial permitted
#layout permitted
Section 8.13 Regions specifies additional constraints.
#length permitted
#length-cell permitted
Section 8.1.13 #length-cell specifies additional constraints.
#length-em permitted
#length-integer permitted
#length-negative permitted
Section 8.1.14 #length-negative specifies additional constraints.
#length-percentage permitted
#length-pixel permitted
#length-positive permitted
#length-real permitted
#length-root-container-relative permitted
Section 8.1.15 #length-root-container-relative specifies additional constraints.
#length-version-2 permitted
#lineBreak-uax14

The processor SHALL implement the #lineBreak-uax14 feature.

#lineHeight permitted
Section 8.1.16 #lineHeight specifies additional constraints.
#luminanceGain permitted
#metadata permitted
#metadata-item permitted
Section 8.1.1 altText named metadata item specifies additional constraints.
#metadata-version-2 permitted
#nested-div permitted
#nested-span permitted
#opacity permitted
#opacity-region permitted
#opacity-version-2 Partially supported via #opacity .
#origin permitted
Section 8.1.19 #origin specifies additional constraints.
#overflow permitted
#overflow-visible permitted
#padding permitted
#padding-1 permitted
#padding-2 permitted
#padding-3 permitted
#padding-4 permitted
#padding-region permitted
#padding-version-2 Partially supported via #padding , #padding-1 , #padding-2 , #padding-3 , #padding-4 , and #padding-region
#position permitted
Section 8.1.20 #position specify additional constraints.
#presentation permitted
#presentation-version-2 Partially supported via #presentation and #profile-version-2
#profile permitted
#profile-full-version-2 Partially supported via #contentProfiles , #profile , and #profile-version-2 .
#profile-version-2 Partially supported via #contentProfiles , and #profile .
#region-timing permitted
#resources permitted
Section 8.1.21 #resources specify additional constraints.
#ruby permitted
#ruby-full Partially supported via #ruby , #rubyAlign , #rubyPosition , and #rubyReserve .
#rubyAlign Partially supported via #rubyAlign-minimal .
#rubyAlign-minimal permitted
Section 8.1.22 #rubyAlign specifies additional constraints.
#rubyPosition permitted
#rubyReserve permitted
#set permitted
#shear permitted
Section 8.1.23 Slanted Japanese-language text provides additional information.
#showBackground permitted
#source permitted
Section 8.1.8 #font and #source specify additional constraints.
#structure permitted
#styling permitted
#styling-chained permitted
#styling-inheritance-content permitted
#styling-inheritance-region permitted
#styling-inline permitted
#styling-nested permitted
#styling-referential permitted
#textAlign permitted
#textAlign-absolute permitted
#textAlign-relative permitted
#textAlign-version-2 Partially supported via #textAlign , #textAlign-relative , and #textAlign-absolute .
#textCombine permitted
#textDecoration permitted
#textDecoration-over permitted
#textDecoration-through permitted
#textDecoration-under permitted
#textEmphasis Partially supported via #textEmphasis-minimal .
#textEmphasis-minimal permitted
#textOutline Partially supported via #textOutline-unblurred .
#textOutline-unblurred permitted
Section 8.1.24 #textOutline-unblurred specifies additional constraints.
#textShadow permitted
Section 8.1.25 #textShadow specifies additional constraints.
#tickRate permitted
Section 8.1.26 #tickRate specifies additional constraints.
#timeBase-media permitted
#timeContainer permitted
#time-clock permitted
#time-clock-with-frames permitted
#time-offset permitted
#time-offset-with-frames permitted
#time-offset-with-ticks permitted
#timing permitted
Section 8.1.29 #timing specifies additional constraints.
#transformation permitted
#transformation-version-2 Partially supported via #transformation and #profile-version-2 .
#unicodeBidi permitted
#unicodeBidi-version-2 Partially supported via #unicodeBidi .
#visibility permitted
#visibility-block permitted
#visibility-inline permitted
#visibility-region permitted
#visibility-version-2 Partially supported via #visibility .
#wrapOption permitted
#writingMode permitted
#writingMode-horizontal permitted
#writingMode-horizontal-lr permitted
#writingMode-horizontal-rl permitted
#writingMode-vertical permitted
#zIndex permitted-deprecated
Relative to the IMSC Extension namespace
#activeArea permitted
#altText permitted-deprecated
#aspectRatio permitted-deprecated
Section 8.1.3 #aspectRatio specifies additional constraints.
#fillLineGap permitted
#forcedDisplay permitted
#linePadding permitted
Section 8.1.17 ebutts:linePadding specifies additional constraints.
#multiRowAlign permitted
Section 8.1.18 ebutts:multiRowAlign specifies additional constraints.
#progressivelyDecodable permitted-deprecated
CSS Snapshot 2026

8. Additional Provisions

8.1 Constraints on Features and Extensions

8.1.1 altText named metadata item

The altText named metadata item SHOULD NOT be present since no image-based timed text information is used in a Text Profile Document Instance .

A altText named metadata item SHALL NOT be present in a Document Instance if any ittm:altText element is also present.

8.1.2 #altText

The ittm:altText element SHOULD NOT be present since no image-based timed text information is used in a Text Profile Document Instance .

A ittm:altText element SHALL NOT be present in a Document Instance if any altText named metadata item element is also present.

8.1.3 #aspectRatio

The ittp:aspectRatio attribute SHOULD NOT be present in a Document Instance unless compatibility with [ ttml-imsc1.0.1 ] processors is desired.

The ittp:aspectRatio attribute SHALL not be present in a Document Instance if any ttp:displayAspectRatio attribute is also present.

8.1.4 #color

The initial value of tts:color SHALL be "white" .

Note

This is consistent with [ SMPTE2052-1 ].

Note

The named color green defined in [ ttml2 ] is equivalent to the RGB color triple #008000 and is not full luminance. For full luminance green, an author can specify the RGB color triple #00ff00 or the named color lime .

8.1.5 #displayAspectRatio

The ttp:displayAspectRatio attribute SHALL not be present in a Document Instance if any ittp:aspectRatio attribute is also present.

8.1.6 #extent-root

If the Document Instance includes any length value that uses the px unit, tts:extent SHALL be present on the tt element.

8.1.7 #extent-region

For each region element defined in the Document Instance , the specified value of the tts:extent style property SHALL consist of two length expressions that use pixel (px), percentage (%), or root container relative units.

Note

If no region element is defined in the Document Instance , then content flows into the default region ; conversely, if one or more region elements are defined in the Document Instance , the default region is not used.

Note

The requirement above requires the author to explicitly specify the value of tts:extent in the Document Instance , e.g. by specifying the tts:extent attribute for each region element.

8.1.8 #font and #source

A font element in the Document Instance SHALL not specify a src attribute.

All source elements that are children of a font element SHALL reference an external data resource .

Note
Note

A Processor MAY use the [ css-fonts-3 ] §5 font matching algorithm for associating a font with a run of text.

Note

8.1.9 #fontFamily-generic

In absence of specific instructions on the choice of font families, and in order to enhance reproducibility of line fitting, authors are encouraged to use the monospaceSerif or proportionalSansSerif generic font families, for which reference font metrics are defined at A. Reference Fonts .

If the computed value of tts:fontFamily is "default" , then the used value of tts:fontFamily SHALL be "monospaceSerif" .

Note

The term used value is defined in CSS 2.1, as normatively referenced by [ ttml2 ].

8.1.10 #fontFamily

Linear white-space SHOULD NOT appear between components of the specified value of tts:fontFamily .

8.1.11 #fontVariant

The computed value of the tts:fontVariant attribute SHALL be one of the following:

  • normal ;
  • sub ; or
  • super .

8.1.12 #frameRate

If the Document Instance includes any clock time expression that uses the frames term or any offset time expression that uses the f metric, the ttp:frameRate attribute SHALL be present on the tt element.

8.1.13 #length-cell

c units SHALL NOT be present outside of the value of ebutts:linePadding .

8.1.14 #length-negative

Strictly negative length expressions SHALL NOT be used with attributes other than:

  • tts:disparity ; and
  • tts:textShadow .
Note

8.1.15 #length-root-container-relative

When specified on a tts:extent or tts:position attribute:

  • rh units SHALL NOT be used for horizontal length components; and
  • rw units SHALL NOT be used for vertical length components.
Note

8.1.16 #lineHeight

The specified value of the tts:lineHeight attribute SHOULD be such that specified style set of each p element contains a tts:lineHeight property whose value is not normal .

Note

Implementation of the normal value is not uniform at the time of this writing.

8.1.17 ebutts:linePadding

In addition to the style element, the attribute ebutts:linePadding MAY be specified on the following elements:

  • region
  • body
  • div
  • p
  • initial

The processor :

  • SHALL apply ebutts:linePadding to p only; and
  • SHALL treat ebutts:linePadding as inheritable.
Note

The ebutts:linePadding attribute only supports c length units.

Note

In contrast to this specification, [ EBU-TT-D ] specifies that the attribute ebutts:linePadding is allowed only on the style element.

8.1.18 ebutts:multiRowAlign

In addition to the style element, the attribute ebutts:multiRowAlign MAY be specified on the following elements:

  • region
  • body
  • div
  • p
  • initial

The processor :

  • SHALL apply ebutts:multiRowAlign to p only; and
  • SHALL treat ebutts:multiRowAlign as inheritable.
Note

In contrast to this specification, [ EBU-TT-D ] specifies that the attribute ebutts:multiRowAlign is allowed only on the style element.

8.1.19 #origin

The value of the tts:origin attribute SHALL consist of two length expressions that use pixel (px) or percentage (%) units.

If the tts:position attribute is specified anywhere in a Document Instance , then the tts:origin attribute SHALL NOT be specified anywhere in that Document Instance .

8.1.20 #position

All length components of the value of a tts:position attribute SHALL use pixel (px), percentage (%) or root container relative units.

If the tts:origin attribute is specified anywhere in a Document Instance , then the tts:position attribute SHALL NOT be specified anywhere in that Document Instance .

8.1.21 #resources

The resources element SHALL not contain any of the following children elements:

  • audio ;
  • data ; and
  • image .

8.1.22 #rubyAlign

The specified value of the tts:rubyAlign attribute SHALL be such that its computed value is center or spaceAround .

8.1.23 Slanted Japanese-language text

This section is non-normative.

Since (a) Japanese-language fonts typically do not include italic or oblique faces, and (b) Japanese-language slanted vertical text consists of characters slanted in the vertical direction (and not in the horizontal direction), it is recommended that tts:shear be specified to slant Japanese-language text – instead of specifying tts:fontStyle="italic" or tts:fontStyle="oblique" .

8.1.24 #textOutline-unblurred

The specified value of the tts:textOutline attribute SHALL be such that its computed value on any span element is 10% or less than the computed value of tts:fontSize attribute on the same element.

8.1.25 #textShadow

The specified value of the tts:textShadow attribute SHALL NOT have more than 4 <shadow> values.

8.1.26 #tickRate

ttp:tickRate SHALL be present on the tt element if the document contains any time expression that uses the t metric.

8.1.27 #timeBase-media

This section is non-normative.

[ ttml2 ] specifies that the default timebase is "media" if ttp:timeBase is not specified on tt .

8.1.28 #time-clock-with-frames

This section is non-normative.

As specified in [ ttml2 ], a #time-clock-with-frames expression is translated to a media time M according to M = 3600 · hours + 60 · minutes + seconds + (frames ÷ ( ttp:frameRateMultiplier · ttp:frameRate )).

8.1.29 #timing

For any content element that contains br elements or text nodes, both the begin attribute and one of either the end or dur attributes SHOULD be specified on the content element or at least one of its ancestors.

8.1.30 usesForced named metadata item

This section is non-normative.

The usesForced named metadata item does not apply since the condition attribute is prohibited.

The itts:forcedDisplay attribute is used to specify forced content semantics.

8.1.31 #zIndex

This section is non-normative.

This feature has no effect since, as specified at 8.13.2 Dimensions and Position , presented regions do not overlap in a Document Instance .

8.2 Document Complexity

A Text Profile document SHOULD conform to the Hypothetical Render Model specified at [ imsc-hrm ].

Note

This limits the complexity of the Text Profile document, so that playback systems can render the content synchronized with the author-specified display times.

8.3 Document Encoding

A Document Instance SHALL be concretely encoded as a well-formed XML 1.0 [ xml ] document using the UTF-8 character encoding as specified in [ UNICODE ].

The resulting [ xml ] document SHOULD NOT contain any of the following physical structures:

Note

These physical structures are intended to be prohibited in future versions of this specification.

Note

The resulting [ xml ] document can contain character references , and entity references to predefined entities .

8.4 Extension Vocabulary

8.4.1 ittp:activeArea

The Active Area of a Document Instance is the area within the Root Container Region that the author intends to be minimally visible to the viewer. This area typically fully contains all of the referenced regions within the Document Instance .

Note

Under normal circumstances, the entirety of the Root Container Region is presented. However, under special circumstances, such as when the related video object is cropped, a system can, for instance, use the ittp:activeArea parameter to avoid cropping areas of the Root Container Region that are intended to be visible to the viewer. The specific behavior of the system is however left undefined intentionally: the system can select a presentation mode appropriate to the display shape, user preferences, etc. The ittp:activeArea is analogous to the Active Format Description (AFD) metadata commonly used in broadcast applications.

The Active Area is specified using the ittp:activeArea attribute.

If present, the ittp:activeArea attribute SHALL conform to the following syntax: 

ittp:activeArea
  : leftOffset topOffset width height
leftOffset | topOffset | width | height
:
<percentage>
//
where
<percentage>
is
non-negative
and
not
greater
than
100%.

The width percentage value is relative to the width of the Root Container Region .

The height percentage value is relative to the height of the Root Container Region .

The width and height percentage values are the width and height of the Active Area .

The leftOffset and topOffset percentage values specify an alignment point between the Root Container Region and the Active Area .

The origin top left {x, y} percentage coordinates of the Active Area SHALL be calculated as follows: 

x = leftOffset * (1 - width/100)
y
=
topOffset
*
(1
-
height/100)
Note

The use of left and top offset positions is co-incident with the [ css3-background ] background-position property where a two percentage value position is used.

Note

The syntax of the ittp:activeArea parameter is such that the Active Area cannot extend outside the Root Container Region in any dimension.

The ittp:activeArea attribute is considered to be significant only when specified on the tt element.

If the ittp:activeArea attribute is not specified, the Active Area SHALL be the Root Container Region .

Example 4 
<?xml version="1.0" encoding="UTF-8"?>
<tt xml:lang="en"
    xmlns="http://www.w3.org/ns/ttml"
    xmlns:ttm="http://www.w3.org/ns/ttml#metadata" 
    xmlns:tts="http://www.w3.org/ns/ttml#styling"
    xmlns:ttp="http://www.w3.org/ns/ttml#parameter" 
    xmlns:ittp="http://www.w3.org/ns/ttml/profile/imsc1#parameter"
    ittp:activeArea="50% 50% 80% 80%"
    tts:extent="640px 480px"
    ttp:contentProfiles="http://www.w3.org/ns/ttml/profile/imsc1.3/text">
    
    <head>
        <layout>
            <region xml:id="area1" tts:origin="10% 10%" tts:extent="80% 10%" tts:backgroundColor="blue" tts:displayAlign="center" tts:textAlign="center" tts:color="white" tts:fontSize="24px"/>
            <region xml:id="area2" tts:origin="10% 80%" tts:extent="80% 10%" tts:backgroundColor="blue" tts:displayAlign="center" tts:textAlign="center" tts:color="white" tts:fontSize="24px"/>
            <region xml:id="area3" tts:origin="10% 92%" tts:extent="80% 6%" tts:backgroundColor="red" tts:displayAlign="center" tts:textAlign="center" tts:color="yellow" tts:fontSize="24px"/>
        </layout>
    </head>
    <body>
        <div>
            <p region="area1" begin="0s" end="6s">This region is within the editorial area.</p>
            <p region="area2" begin="0s" end="6s">This region is within the editorial area.</p>
            <p region="area3" begin="0s" end="6s">This region is not.</p>
        </div>
    </body>
</tt>

8.4.2 ittm:altText

The #altText feature is designated as permitted-deprecated in the profiles defined by this specification. The altText named metadata item provides equivalent semantics.

ittm:altText allows an author to provide a text string equivalent for an element, which MAY be used to support indexing of the content, or facilitate quality checking of the document. It can also be used by assistive technologies.

Note

The #altText feature is primarily useful in providing a text alternative to image-based subtitles and captions, which are not supported by the Text Profile .

Note

In contrast to the common use of alt attributes in [ HTML ], the ittm:altText attribute content is not intended to be displayed in place of the element if the element is not loaded.

The ittm:altText element SHALL conform to the following syntax: 

<ittm:altText
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute not in the default namespace, any TT namespace or any IMSC namespace}>
  Content: #PCDATA
</ittm:altText>

The ittm:altText element SHALL be a child of the metadata element.

8.4.3 ittp:aspectRatio

The #aspectRatio feature is designated as permitted-deprecated in the profiles defined by this specification. The #displayAspectRatio feature provides equivalent semantics.

The ittp:aspectRatio attributes allows authorial control of the mapping of the Root Container Region of a Document Instance to each image frame of the Related Video Object .

If present, the ittp:aspectRatio attribute SHALL conform to the following syntax: 

ittp:aspectRatio
  : numerator denominator          // with int(numerator) != 0 and int(denominator) != 0
                                   // where int(s) parses string s as a decimal integer.
numerator | denominator
  : <digit>+                       // no linear white-space is implied or permitted
//
between
each
<digit>
token

An ittp:aspectRatio attribute is considered to be significant only when specified on the tt element.

If specified on the tt element, the ittp:aspectRatio attribute specifies the display aspect ratio of the Root Container Region . If not specified, then the display aspect ratio of the Root Container Region is determined according to Appendix H of [ ttml2 ].

8.4.4 itts:fillLineGap

The itts:fillLineGap attribute allows the author to control the application of background between successive line areas.

If itts:fillLineGap="true" then the background of each inline area generated by descendant spans of the p element SHALL extend to the before-edge and after-edge of its containing line area ( before-edge and after-edge are defined at Section 4.2.3 of [ XSL11 ]).

The itts:fillLineGap attribute SHALL conform to the following:

Values: false | true
Initial: false
Applies to: p
Inherited: yes
Percentages: N/A
Animatable: discrete

In the following example, the p specifies itts:fillLineGap="true" , and, as a result, no gap exists between its lines.

Example 5 
<?xml version="1.0" encoding="UTF-8"?>
<tt xmlns="http://www.w3.org/ns/ttml"
    xmlns:ttp="http://www.w3.org/ns/ttml#parameter"
    xmlns:tts="http://www.w3.org/ns/ttml#styling"
    xmlns:itts="http://www.w3.org/ns/ttml/profile/imsc1#styling"
    ttp:timeBase="media"
    xml:lang="en"
    ttp:cellResolution="50 30"
    ttp:contentProfiles="http://www.w3.org/ns/ttml/profile/imsc1.3/text">
  <head>
    <styling>
      <style xml:id="spanStyle" tts:color="#ffffff" tts:backgroundColor="#000000" />
      <style xml:id="spanStyleSmall" tts:color="#000000" tts:backgroundColor="#dfbb02" tts:fontSize="50%"/>
      <style xml:id="spanStyleBig" tts:color="#ffffff" tts:backgroundColor="#b75800" tts:fontSize="150%"/>
      <style xml:id="paragraphStyle" tts:fontFamily="monospaceSerif" tts:textAlign="center"
              tts:fontSize="200%" tts:lineHeight="165%"  itts:fillLineGap="true"/>
    </styling>
    <layout>
      <region xml:id="bottom" tts:origin="10% 10%" tts:extent="80% 80%" tts:displayAlign="after" />
    </layout>
  </head>
  <body>
    <div>
      <p xml:id="subtitle1" region="bottom" begin="00:00:00.000" end="00:00:30.000" style="paragraphStyle">
        <span style="spanStyle">##Line gaps##</span>
        <br/>
        <span style="spanStyle">The quick </span>
        <span style="spanStyleBig">brown</span>
        <span style="spanStyle"> fox</span>
        <br/>
        <span style="spanStyle">jumps over the </span>
        <span style="spanStyleSmall">lazy</span>
        <span style="spanStyle"> dog</span>
        <br/>
        <span style="spanStyle">##Line gaps##</span>
      </p>
    </div>
  </body>
</tt>
itts:fillLineGap rendering example 1
Figure 3 Illustrative rendition of the example immediately above with itts:fillLineGap="true" removed (left) or preserved (right). Blue lines have been added to show the before-edge and after-edge of each line area, which are coincident for successive line areas.

Also, as illustrated in the following example, because the line areas of successive p elements are contiguous, no gap exists between two successive p elements where itts:fillLineGap="true" .

Example 6 
<?xml version="1.0" encoding="UTF-8"?>
<tt xmlns="http://www.w3.org/ns/ttml"
    xmlns:ttp="http://www.w3.org/ns/ttml#parameter"
    xmlns:tts="http://www.w3.org/ns/ttml#styling"
    xmlns:itts="http://www.w3.org/ns/ttml/profile/imsc1#styling"
    ttp:timeBase="media"
    xml:lang="en"
    ttp:cellResolution="50 30"
    ttp:contentProfiles="http://www.w3.org/ns/ttml/profile/imsc1.3/text">
  <head>
    <styling>
      <style xml:id="spanStyle" tts:color="#ffffff" tts:backgroundColor="#000000" />
      <style xml:id="paragraphStyleNoGap" tts:fontFamily="monospaceSerif" tts:textAlign="center" tts:fontSize="200%"
          tts:lineHeight="165%" itts:fillLineGap="true"/>
      <style xml:id="paragraphStyle" tts:fontFamily="monospaceSerif" tts:textAlign="center" tts:fontSize="200%"
          tts:lineHeight="165%" itts:fillLineGap="false"/>
    </styling>
    <layout>
      <region xml:id="bottom" tts:origin="10% 10%" tts:extent="80% 80%" tts:displayAlign="after" />
      <region xml:id="top" tts:origin="10% 10%" tts:extent="80% 80%" tts:displayAlign="before" />
    </layout>
  </head>
  <body>
    <div region="bottom" begin="00:00:00.000" end="00:00:30.000">
      <p xml:id="subtitle1" style="paragraphStyle">
        <span style="spanStyle">Paragraph 1</span>
      </p>
      <p xml:id="subtitle1" style="paragraphStyle">
        <span style="spanStyle">Paragraph 2</span>
      </p>
    </div>
    <div region="top" begin="00:00:00.000" end="00:00:30.000">
      <p xml:id="subtitle1" style="paragraphStyleNoGap">
        <span style="spanStyle">Paragraph 1</span>
      </p>
      <p xml:id="subtitle1" style="paragraphStyleNoGap">
        <span style="spanStyle">Paragraph 2</span>
      </p>
    </div>
  </body>
</tt>
itts:fillLineGap rendering example 2
Figure 4 Illustrative rendition of the example immediately above, where itts:fillLineGap="true" on the two paragraphs of the top region, itts:fillLineGap="false" on the two paragraphs of the bottom region.

8.4.5 itts:forcedDisplay

The itts:forcedDisplay attribute can be used to hide content when the processor has been configured to do so via the application parameter displayForcedOnlyMode .

Annex C. Forced content illustrates the use of itts:forcedDisplay in an application in which a single document contains both hard of hearing captions and translated foreign language subtitles, using itts:forcedDisplay to display translation subtitles always, independently of whether the hard of hearing captions are displayed or hidden.

The itts:forcedDisplay attribute SHALL conform to the following:

Values: false | true
Initial: false
Applies to: body , div , p , region , span
Inherited: yes
Percentages: N/A
Animatable: discrete

If and only if the value of displayForcedOnlyMode is "true" , a content element with a itts:forcedDisplay computed value of "false" SHALL NOT produce any visible rendering, regardless of the computed value of tts:visibility .

The itts:forcedDisplay attribute has no effect on content layout or composition, but merely determines whether composed content is visible or not.

The presentation processor SHALL accept an optional boolean parameter called displayForcedOnlyMode , whose value MAY be set by a context external to the presentation processor . If not set, the value of displayForcedOnlyMode SHALL be assumed to be equal to "false" .

The algorithm for setting the displayForcedOnlyMode parameter based on the circumstances under which the Document Instance is presented is left to the application.

Example 7 
<?xml version="1.0" encoding="UTF-8"?>
<tt xml:lang="en"
    xmlns="http://www.w3.org/ns/ttml"
    xmlns:ttm="http://www.w3.org/ns/ttml#metadata" 
    xmlns:tts="http://www.w3.org/ns/ttml#styling"
    xmlns:ttp="http://www.w3.org/ns/ttml#parameter" 
    xmlns:itts="http://www.w3.org/ns/ttml/profile/imsc1#styling"
    ttp:displayAspectRatio="16 9"
    ttp:contentProfiles="http://www.w3.org/ns/ttml/profile/imsc1.3/text">
    
    <head>
        <layout>
            <region xml:id="r1" itts:forcedDisplay="true" tts:origin="10% 2%" tts:extent="80% 10%" tts:color="white" tts:backgroundColor="black" tts:showBackground="whenActive"/>
            <region xml:id="r2" tts:origin="10% 80%" tts:extent="80% 10%" tts:color="white" tts:backgroundColor="black" tts:showBackground="whenActive"/>
        </layout>
    </head>
    <body>
        <div>
            <p region="r1" begin="1s" end="6s">Lycée</p>
            <!-- the following will not appear if displayForcedOnlyMode='true' -->
            <p region="r2" begin="4s" end="6s">Nous étions inscrits au même lycée.</p>
        </div>
    </body>
</tt>
Note

As specified in [ ttml2 ], the background of a region can be visible even if the computed value of tts:visibility equals "hidden" for all active content within. The background of a region for which itts:forcedDisplay equals "true" can therefore remain visible even if itts:forcedDisplay equals "false" for all active content elements within the region and displayForcedOnlyMode equals "true" . Authors can avoid this situation, for instance, by ensuring that content elements and the regions that they are flowed into always have the same value of itts:forcedDisplay .

Note

It is expected that the functionality of itts:forcedDisplay will be mapped to a conditional style construct in a future revision of this specification.

Note

The presentation semantics associated with itts:forcedDisplay are intended to be compatible with those associated with the forcedDisplayMode attribute defined in [ CFF ].

8.4.6 ittp:progressivelyDecodable

The #progressivelyDecodable feature is designated as permitted-deprecated in the profiles defined by this specification.

A progressively decodable Document Instance is structured to facilitate presentation before the document is received in its entirety, and can be identified using ittp:progressivelyDecodable attribute.

A progressively decodable Document Instance is a Document Instance that conforms to the following:

  1. no attribute or element of the TTML timing vocabulary is present within the head element;
  2. given two intermediate synchronic documents A and B of the Document Instance , with start times TA and TB , respectively, TA is not greater than TB if A includes a p element that lexically precedes any p element that B includes;
  3. no attribute of the TTML timing vocabulary is present on a descendant element of p ; and
  4. no element E1 explicitly references another element E2 where the opening tag of E2 is lexically subsequent to the opening tag of E1 .

If present, the ittp:progressivelyDecodable attribute SHALL conform to the following syntax: 

ittp:progressivelyDecodable
  : "true"
|
"false"

An ittp:progressivelyDecodable attribute is considered to be significant only when specified on the tt element.

If not specified, the value of ittp:progressivelyDecodable SHALL be considered to be equal to "false" .

A Document Instance for which the computed value of ittp:progressivelyDecodable is "true" SHALL be a progressively decodable Document Instance .

A Document Instance for which the computed value of ittp:progressivelyDecodable is "false" is neither asserted to be a progressively decodable Document Instance nor asserted not to be a progressively decodable Document Instance .

Example 8 
<tt
  xmlns="http://www.w3.org/ns/ttml"
  xmlns:ttm="http://www.w3.org/ns/ttml#metadata"
  xmlns:tts="http://www.w3.org/ns/ttml#styling"
  xmlns:ttp="http://www.w3.org/ns/ttml#parameter"
  xmlns:ittp="http://www.w3.org/ns/ttml/profile/imsc1#parameter"
  ittp:progressivelyDecodable="true"
  ttp:profile="..."
 >
 ...
</tt>
Note

[ ttml2 ] specifies explicitly referencing of elements identified using xml:id in the following circumstances:

  • an element in body referencing region elements. In this case, Requirement 4 above is always satisfied.
  • an element in body referencing style elements. In this case, Requirement 4 above is always satisfied.
  • a region element referencing style elements. In this case, Requirement 4 above is always satisfied.
  • a style element referencing other style elements. In this case, Requirement 4 provides an optimization of style element ordering within the head element.
  • a ttm:actor element referencing a ttm:agent element. In this case, Requirement 4 provides optimization of metadata elements ordering within the document.
  • a content element referencing ttm:agent elements using the ttm:agent attribute. In this case, Requirement 4 provides optimization of metadata elements ordering within the document.

8.5 Font Resources

A Presentation Processor SHALL support font resources of the following media types, as defined in [ IANA-MEDIA-TYPES ]:

Note

[ IANA-MEDIA-TYPES ] specifies that the media type font/otf includes file extensions .ttf and .otf .

8.6 Foreign Element and Attributes

A Document Instance MAY contain elements and attributes that are neither specifically permitted nor forbidden by a profile.

A transformation processor SHOULD preserve such elements or attributes whenever possible.

Note

Document Instances remain subject to the content conformance requirements specified at Section 3.1 of [ ttml2 ]. In particular, a Document Instance can contain elements and attributes not in any TT namespace, i.e. in foreign namespaces, since such elements and attributes are pruned by the algorithm at Section 4 of [ ttml2 ] prior to evaluating content conformance.

Note
For validation purposes it is good practice to define and use a content specification for all foreign namespace elements and attributes used within a Document Instance .

8.8 Namespaces

The following namespaces (see [ xml-names ]) are used in this specification:

Name Prefix Value Defining Specification
XML xml http://www.w3.org/XML/1998/namespace [ xml-names ]
TT tt http://www.w3.org/ns/ttml [ ttml2 ]
TT Parameter ttp http://www.w3.org/ns/ttml#parameter [ ttml2 ]
TT Styling tts http://www.w3.org/ns/ttml#styling [ ttml2 ]
TT Feature none http://www.w3.org/ns/ttml/feature/ [ ttml2 ]
EBU-TT Styling ebutts urn:ebu:tt:style [ EBU-TT-D ]
EBU-TT Metadata ebuttm urn:ebu:tt:metadata [ EBU-TT-D ]
IMSC Styling itts http://www.w3.org/ns/ttml/profile/imsc1#styling This specification
IMSC Parameter ittp http://www.w3.org/ns/ttml/profile/imsc1#parameter This specification
IMSC Metadata ittm http://www.w3.org/ns/ttml/profile/imsc1#metadata This specification
IMSC Extension none http://www.w3.org/ns/ttml/profile/imsc1/extension/ This specification
IMSC 1.3 Text Profile Designator none See Section 6.2 Designator

The namespace prefix values defined above are for convenience and Document Instances MAY use any prefix value that conforms to [ xml-names ].

The namespaces defined by this specification are mutable [ namespaceState ]; all undefined names in these namespaces are reserved for future standardization by the W3C .

8.9 Overflow

A Document Instance SHOULD be authored assuming strict clipping of content that falls out of region areas, regardless of the computed value of tts:overflow for the region.

8.10 Profile Signaling

8.10.1 General

The ttp:contentProfiles attribute SHOULD be present on the tt element, with exactly one of its values equal to the designator Text Profile .

Note

The ttp:contentProfiles attribute is prohibited in some profiles, e.g. [ EBU-TT-D ] as discussed in I.2 EBU-TT-D .

Note

To minimize the risk of incompatibility, the use of the ttp:contentProfiles attribute and other syntax introduced in [ ttml2 ] is not recommended in documents intended to conform to profiles that are based on [ TTML1 ], e.g. [ SMPTE2052-1 ], [ ttml-imsc1 ] , [ ttml-imsc1.0.1 ] , or [ ttml10-sdp-us ].

Note

The ttp:contentProfiles attribute can include additional designators, beyond those specified herein, including designators for other versions of this specification.

Note

6.3 Profile Resolution Semantics specifies the process by which the effective processor profile associated with the Document Instance is determined.

8.10.2 Signaling conformance using EBU-TT metadata

When using the ebuttm:conformsToStandard element specified in [ EBU-TT-M ], the designators of the Text Profile SHALL be used when indicating conformance to the corresponding profile.

Note

See I.2 EBU-TT-D for a sample Document Instance that follows the recommendations of this section.

8.12 Reference Fonts

When rendering codepoints matching one of the combinations of computed font family and codepoints listed in A. Reference Fonts , a processor SHALL use a font that generates a glyph sequence whose dimension is substantially identical to the glyph sequence that would have been generated by one of the specified reference fonts.

Note

This clause only applies to codepoints supported by the processor. See 8.11 Recommended Character Sets for codepoints that a processor is likely to encounter for various languages.

Note

When a content author sets a bounding box for a subtitle, they want to maximize the likelihood that the text will fit within it when displayed by the processor. If the processor doesn't use the specific font the content author had in mind, the font actually used might cause the text to grow in size so that it no longer fits in the bounding box. This is further compounded by differences in the way text wraps when a font has bigger glyphs, which might increase the number of lines used, and increased line spacing, which might also push some of the text outside the bounding box.
To help ensure that things such as text size, line breaking, and line height behave as expected relative to the size of the bounding box set by the content author, the author can use one of the reference fonts defined by this specification. This specification requires processors to support one or more fonts with similar font metrics as reference fonts. Note that, however, the reference fonts as currently defined only cover characters used for a few writing systems – in particular, a subset of those based on Latin, Greek, Cyrillic, Hebrew, and Arabic scripts.

Note

Implementations can use fonts other than those specified in A. Reference Fonts . Two fonts with equal metrics can have a different appearance, but flow identically.

8.13 Regions

8.13.1 Presented Region

A presented region is a temporally active region that satisfies the following conditions:

  1. the computed value of tts:opacity is not equal to "0.0" ; and
  2. the computed value of tts:display is not "none" ; and
  3. the computed value of tts:visibility is not "hidden" ; and
  4. either (a) content is selected into the region or (b) the computed value of tts:showBackground is equal to "always" and the computed value of tts:backgroundColor has non-transparent alpha.

8.13.2 Dimensions and Position

All regions SHALL NOT extend beyond the Root Container Region , i.e. every coordinate in the set of coordinates of each region is also in the set of coordinates of the Root Container Region .

No two presented regions in a given intermediate synchronic document SHALL overlap, i.e. the intersection of the sets of coordinates within each presented region is empty.

Note

8.13.3 Maximum number

The number of presented regions in a given intermediate synchronic document SHALL NOT be greater than 4.

8.15 Style Resolution

The following style properties SHALL be subject to the Style Resolution procedures specified at Section 10.4 of [ ttml2 ]:

Note

The style properties above can be specified as attributes of the initial element specified at Section 10.1.1 of [ ttml2 ].

A. Reference Fonts

Computed Font Family Code Points Reference Font
monospaceSerif All code points specified in B. Common Character Sets Courier New or Liberation Mono
proportionalSansSerif All code points specified in B. Common Character Sets , excluding the code points defined for Hebrew and Arabic scripts. Arial or Helvetica or Liberation Sans

C. Forced content

This section is non-normative.

Figure 5 below illustrates the use of forced content, i.e. itts:forcedDisplay and displayForcedOnlyMode . The content with itts:forcedDisplay="true" is the French translation of the "High School" sign. The content with itts:forcedDisplay="false" are French subtitles capturing a voiceover.

Illustration of the use of itts:forcedDisplay
Figure 5 Illustration of the use of itts:forcedDisplay

When the user selects French as the playback language but does not select French subtitles, displayForcedOnlyMode is set to "true" , causing the display of the sign translation, which is useful to any French speaker, but hiding the voiceover subtitles as the voiceover is heard in French.

If the user selects French as the playback language and also selects French subtitles, e.g. if the user is hard-of-hearing, displayForcedOnlyMode is set to "false" , causing the display of both the sign translation and the voiceover subtitles.

The algorithm for setting the displayForcedOnlyMode parameter and selecting the appropriate combination of subtitle and audio tracks depends on the application.

D. Accessibility Considerations

D.1 WCAG Considerations

D.1.1 Success Criterion 1.4.3 Contrast (Minimum)

Success Criterion 1.4.3 at [ WCAG22 ] specifies that, with some exceptions, the visual presentation of text and images of text has a contrast ratio of at least 4.5:1.

In the context of Text Profile , this is achieved by specifying appropriate foreground and background colors.

D.1.2 Success Criterion 1.4.12 Text Spacing

Success Criterion 1.4.12 at [ WCAG22 ] specifies that no loss of content or functionality occur when spacing of lines, letters, words and paragraphs is modified by a specified amount.

In the context of this specification, this is achieved by specifying an appropriate combination of style properties to achieve the desired line height, font size, region extent, etc.

D.1.3 Success Criteria 3.1.1 Language of Page and 3.1.2 Language of Parts

Success Criteria 3.1.1 and 3.1.2 at [ WCAG22 ] specify that the human language of each passage or phrase in the content can be programmatically determined.

In the context of this specification, this is achieved by specifying xml:lang .

D.1.4 Success Criterion 1.3.1 Info and Relationships

This section is non-normative.

Success Criterion 1.3.1 at [ WCAG22 ] is intended to ensure that information and relationships that are implied by visual or auditory formatting are preserved when the presentation format changes.

As an example in the context of this specification, implementations should, when rendering a Document Instance to [ HTML ] with [ CSS ] styling, ensure that the resultant [ HTML ] document can be understood by assistive technologies even when a user style sheet is substituted for the style sheet provided by the author. For instance, when rendering tts:fontVariant , the use of CSS vertical-align property alone might not be sufficient for assistive technology to identify that the glyphs concerned are superscript or subscript.

D.2 MAUR Considerations

This section is non-normative.

Authors and implementers are encouraged to consult [ media-accessibility-reqs ], which presents accessibility requirements users with disabilities have with respect to audio and video on the web.

Note

E. Sample Document Instance

This section is non-normative.

The following sample Document Instances conforms to the Text Profile . This sample are for illustration only, and are neither intended to capture current or future practice, nor exercise all normative prose contained in this specification.

Example 11 
<?xml version="1.0" encoding="UTF-8"?>
<tt xml:lang="en"
    xmlns="http://www.w3.org/ns/ttml"
    xmlns:ttm="http://www.w3.org/ns/ttml#metadata" 
    xmlns:tts="http://www.w3.org/ns/ttml#styling"
    xmlns:ttp="http://www.w3.org/ns/ttml#parameter" 
    ttp:displayAspectRatio="4 3"
    ttp:contentProfiles="http://www.w3.org/ns/ttml/profile/imsc1.3/text">
    
    <head>
        <layout>
            <region xml:id="area1" tts:origin="10% 10%" tts:extent="80% 10%" tts:backgroundColor="black" tts:displayAlign="center" tts:color="red"/>
        </layout>
    </head>
    <body>
        <div>
            <p region="area1" begin="0s" end="6s">Lorem ipsum dolor.</p>
        </div>
    </body>
</tt>

The above sample specifies two Intermediate Synchronic Documents , one from 0 seconds to 6 seconds, that renders as Figure 6 , and the other from 6 seconds onwards, that renders as Figure 7 .

Text Profile example rendering 1, 0s to 6s
Figure 6 Illustrative rendition of the example immediately above, for the period between 0s and 6s.

Figure 6 shows a black rectangular region positioned so that its upper left corner is 10% down from the top of the rendering area and 10% right of the left edge of the rendering area, and whose width is 80% of the rendering area and whose height is 10% of the rendering area. The region contains the text "Lorem ipsum dolor." in red using the default font, at the default size; that size is 1/15th the height of the rendering area, and is computed from the default values of the ttp:cellResolution parameter ( "32 15" ) and the ttp:fontSize ( "100%" ) style attribute, which are used because both are omitted from this document.

Text Profile example rendering 1, 6s onwards
Figure 7 Illustrative rendition of the example immediately above, for the period from 6s onwards.

Figure 7 shows the same black rectangular region in the same position. The region is empty aside from the black background, which is nevertheless visible because the tts:showBackground attribute is missing from the region element, so its default value always applies.

F. Extensions

F.1 General

The following sections define extension designations, expressed as relative URIs (fragment identifiers) relative to the IMSC Extension Namespace base URI.

F.2 #activeArea

A transformation processor supports the #activeArea feature if it recognizes and is capable of transforming values of the ittp:activeArea attribute.

A presentation processor supports the #activeArea feature if it implements presentation semantic support for values of the ittp:activeArea attribute.

F.3 #altText

The #altText feature is designated as permitted-deprecated in the profiles defined by this specification. The altText named metadata item provides equivalent semantics.

A transformation processor supports the #altText feature if it recognizes and is capable of transforming values of the ittm:altText element.

A presentation processor supports the #altText feature if it implements presentation semantic support for values of the ittm:altText element.

F.4 #aspectRatio

The #aspectRatio feature is designated as permitted-deprecated in the profiles defined by this specification. The #displayAspectRatio feature provides equivalent semantics.

A transformation processor supports the #aspectRatio feature if it recognizes and is capable of transforming values of the ittp:aspectRatio attribute.

A presentation processor supports the #aspectRatio feature if it implements presentation semantic support for values of the ittp:aspectRatio attribute.

F.5 #fillLineGap

A transformation processor supports the #fillLineGap feature if it recognizes and is capable of transforming values of the itts:fillLineGap attribute.

A presentation processor supports the #fillLineGap feature if it implements presentation semantic support for values of the itts:fillLineGap attribute.

F.6 #forcedDisplay

A transformation processor supports the #forcedDisplay feature if it recognizes and is capable of transforming values of the itts:forcedDisplay attribute.

A presentation processor supports the #forcedDisplay feature if it implements presentation semantic support for values of the itts:forcedDisplay attribute.

F.7 #linePadding

A transformation processor supports the #linePadding feature if it recognizes and is capable of transforming values of the ebutts:linePadding attribute specified in [ EBU-TT-D ].

A presentation processor supports the #linePadding feature if it implements presentation semantic support for values of the ebutts:linePadding attribute specified in [ EBU-TT-D ].

F.8 #multiRowAlign

A transformation processor supports the #multiRowAlign feature if it recognizes and is capable of transforming values of the ebutts:multiRowAlign attribute specified in [ EBU-TT-D ].

A presentation processor supports the #multiRowAlign feature if it implements presentation semantic support for values of the ebutts:multiRowAlign attribute specified in [ EBU-TT-D ].

F.9 #progressivelyDecodable

The #progressivelyDecodable feature is designated as permitted-deprecated in the profiles defined by this specification.

A transformation processor supports the #progressivelyDecodable feature if it recognizes and is capable of transforming values of the ittp:progressivelyDecodable attribute.

A presentation processor supports the #progressivelyDecodable feature if it implements presentation semantic support for values of the ittp:progressivelyDecodable attribute.

G. XML Schema Definitions

This section is non-normative.

XML Schema definitions (see [ xmlschema-1 ]) for extension vocabulary defined by this specification are provided here for convenience.

These definitions are non-normative and are not sufficient to validate conformance of a Document Instance .

In any case where a definition specified by this appendix diverge from the prose of the specification, then the latter takes precedence.

H. Extensibility Objectives

This section is non-normative.

This section documents extensibility objectives for this specification.

This specification is intended to allow:

I. Compatibility with other TTML-based specifications

This section is non-normative.

I.1 Overview

This specification is designed to be compatible with [ ttml-imsc1 ], [ ttml-imsc1.0.1 ], [ ttml-imsc1.1 ], [ ttml-imsc1.2 ], [ SMPTE2052-1 ], [ EBU-TT-D ] and [ ttml10-sdp-us ]. Specifically, by selecting a subset of the features and extensions defined in this specification, it is possible to create a document that:conforms to one or more of [ ttml-imsc1 ], [ ttml-imsc1.0.1 ], [ ttml-imsc1.1 ], [ ttml-imsc1.2 ], [ SMPTE2052-1 ], [ EBU-TT-D ] or [ ttml10-sdp-us ], and also conforms to Text Profile .

This specification is also intended to allow straightforward conversion of a document that conforms to the text profile of [ CFF ] to the Text Profile .

I.2 EBU-TT-D

The Text Profile is a strict syntactic superset of [ EBU-TT-D ].

A document that conforms to [ EBU-TT-D ] therefore generally also conforms to the Text Profile , with a few exceptions, including:

The profile vocabulary defined in [ ttml2 ] is prohibited by [ EBU-TT-D ]. Instead, as specified in [ EBU-TT-M ], multiple ebuttm:conformsToStandard elements are optionally present in the metadata element of the head element, with each ebuttm:conformsToStandard indicating conformance to a specification, including other versions of this specification.

Note

Conformance to a [ ttml-imsc1.0.1 ] profile can be indicated as defined in [ ttml-imsc1.0.1 ], by including an additional ebuttm:conformsToStandard element whose value is equal to the designator of the [ ttml-imsc1.0.1 ] profile to which the Document Instance conforms.

The following is an example of a document that conforms to Text Profile , [ ttml-imsc1.0.1 ] Text Profile and [ EBU-TT-D ]. Note the presence of multiple ebuttm:conformsToStandard elements, one of which equals the Text Profile designator:

Example 12 
<?xml version="1.0" encoding="UTF-8"?>
<tt xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://www.w3.org/ns/ttml" xmlns:ttp="http://www.w3.org/ns/ttml#parameter"
    xmlns:tts="http://www.w3.org/ns/ttml#styling" xmlns:ttm="http://www.w3.org/ns/ttml#metadata"
    xmlns:ebutts="urn:ebu:tt:style" xml:lang="en" ttp:timeBase="media" xmlns:ebuttm="urn:ebu:tt:metadata" >
    <head>
        <metadata>
            <ebuttm:conformsToStandard>urn:ebu:tt:distribution:2014-01</ebuttm:conformsToStandard>
            <ebuttm:conformsToStandard>http://www.w3.org/ns/ttml/profile/imsc1/text</ebuttm:conformsToStandard>
            <ebuttm:conformsToStandard>http://www.w3.org/ns/ttml/profile/imsc1.1/text</ebuttm:conformsToStandard>
            <ebuttm:conformsToStandard>http://www.w3.org/ns/ttml/profile/imsc1.2/text</ebuttm:conformsToStandard>
            <ebuttm:conformsToStandard>http://www.w3.org/ns/ttml/profile/imsc1.3/text</ebuttm:conformsToStandard>
        </metadata>
        <styling>
            <style xml:id="baseStyle" tts:color="#FFFFFF" tts:lineHeight="100%" tts:fontFamily="sansSerif" ebutts:linePadding="0.5c"/>
            <style xml:id="black" tts:color="#000000"/>
            <style xml:id="blackBackground" tts:backgroundColor="#000000"/>
            <style xml:id="greenBackground" tts:backgroundColor="#00FF00"/>
            <style xml:id="startEnd" tts:textAlign="start" ebutts:multiRowAlign="end"/>
            <style xml:id="centerStart" tts:textAlign="center" ebutts:multiRowAlign="start"/>
        </styling>
        <layout>
            <region xml:id="area1" tts:origin="15% 10%" tts:extent="70% 20%" style="greenBackground" tts:displayAlign="center" tts:showBackground="whenActive"/>
            <region xml:id="area2" tts:origin="15% 70%" tts:extent="70% 20%" style="blackBackground" tts:displayAlign="center" tts:showBackground="whenActive"/>
        </layout>
    </head>
    <body>
        <div style="baseStyle">
            <p xml:id="s1" region="area1" style="startEnd black" begin="00:00:01" end="00:00:09">
                multiRowAlign="end"<br/>textAlign="start"
            </p>
            <p xml:id="s2" region="area2" style="centerStart" begin="00:00:01" end="00:00:09">
                multiRowAlign="start"<br/>textAlign="center"
            </p>
        </div>
    </body>
</tt>

The above sample results in three Intermediate Synchronic Documents , one from 0 seconds to 1 second, that renders as Figure 8 , the next from 1 second to 9 seconds, that renders as Figure 9 , and the last from 9 seconds onwards, that renders as Figure 10 .

Text Profile and EBU-TT-D example rendering 1, 0s to 1s
Figure 8 Illustrative rendition of the example immediately above, for period 0s to 1s.

Figure 8 shows no pixels being generated from the document in the period 0s to 1s.

Text Profile and EBU-TT-D example rendering 2, 1s to 9s
Figure 9 Illustrative rendition of the example immediately above, for the period 1s to 9s.

Figure 9 shows a lime green and a black rectangular region. The green region is positioned in the upper part of the rendering area and the black region is positioned in the lower part, according to the tts:origin and tts:extent attribute values. The text is black in the green region and white in the black region. In both cases it is in a generic sans-serif font, and the text is vertically centred within the region, according to the tts:displayAlign attribute value specified on each region. The horizontal alignment of each line of text demonstrates the combined application of the ebutts:multiRowAlign and tts:textAlign attributes. The start (left, in this case) aligned text in the green region is offset slightly from the region edge due to the application of the ebutts:linePadding style attribute on the div element.

Text Profile and EBU-TT-D example rendering 3, 9s onwards
Figure 10 Illustrative rendition of the example immediately above, for the period from 9s onwards.

Figure 10 shows no pixels being generated from the document in the period from 9s onwards.

I.3 SDP-US

The Text Profile is a strict syntactic superset of [ ttml10-sdp-us ].

A document that conforms to [ ttml10-sdp-us ] therefore also generally conforms to the Text Profile , with a few exceptions, including:

As an illustration, Example 3 at [ ttml10-sdp-us ] conforms to both Text Profile and [ ttml10-sdp-us ].

I.4 SMPTE-TT (SMPTE ST 2052-1)

[ SMPTE2052-1 ] specifies the use of the DFXP Full Profile (see Appendix F.3 at [ ttml2 ]) supplemented by a number of extensions, including http://www.smpte-ra.org/schemas/2052-1/2010/smpte-tt#image .

The Text Profile applies a set of practical constraints and extensions to [ SMPTE2052-1 ] for text-only subtitles and captions. These constraints and extensions reflect industry practice and experience.

Care is required when creating a document intended to be processed according to [ SMPTE2052-1 ], and Text Profile presentation processor . In particular:

The following is an example of a document that conforms to both Text Profile and [ SMPTE2052-1 ]:

Example 13 
<?xml version="1.0" encoding="UTF-8"?>
<tt xml:lang="en"
    xmlns="http://www.w3.org/ns/ttml"
    xmlns:ttm="http://www.w3.org/ns/ttml#metadata" 
    xmlns:ttp="http://www.w3.org/ns/ttml#parameter"
    ttp:profile="http://www.smpte-ra.org/schemas/2052-1/2010/profiles/smpte-tt-full"
    xmlns:tts="http://www.w3.org/ns/ttml#styling"
    ttp:frameRate="24">
    <head>
        <layout>
            <region xml:id="area1" tts:origin="10% 70%" tts:extent="80% 20%" tts:showBackground="whenActive" tts:backgroundColor="red" tts:displayAlign="center" tts:color="white"/>
        </layout>
    </head>
    <body tts:lineHeight="100%">
        <div>
            <p region="area1" begin="00:00:01.01" end="00:00:03">This should appear on frame 25.</p>
            <p region="area1" begin="00:00:04" end="00:00:06">This should appear on frame 96.</p>
            <p region="area1" begin="00:00:07.33" end="00:00:09">This should appear on frame 176.</p>
        </div>
    </body>
</tt>

I.5 CFF-TT

This specification was derived from the text profile specified in Section 6 at [ CFF ], and is intended to be a superset of it in terms of capabilities. Additional processing is however generally necessary to convert a [ CFF ] Text Profile document to a Document Instance that conforms to the Text Profile specification. In particular:

It is not possible to transform a [ CFF ] Image Profile document to a document that conforms to the Text Profile specification without additional complex processing such as extracting text content from images.

I.6 Previous versions of IMSC

A document that conforms to [ ttml-imsc1 ] or [ ttml-imsc1.0.1 ] or [ ttml-imsc1.1 ] or [ ttml-imsc1.2 ] Text Profile also conforms to this specification.

A number of features that are previously permitted in previous versions of IMSC Text Profile are designated as permitted-deprecated in the Text Profile . Documents that use such features are therefore susceptible to being incompatible with future versions of this specification.

Earlier versions of this specification specify an image-only profile, called the Image Profile, which is no longer specified herein. Applications that require such an image-only profile can consider referencing [ ttml-imsc1.2 ].

J. Acknowledgements

This section is non-normative.

The editor acknowledges the current and former members of the Timed Text Working Group, the members of other W3C Working Groups, and industry experts in other forums who have contributed directly or indirectly to the process or content of this document.

The editor wishes to especially acknowledge the following contributions by members: Glenn Adams, Skynav; John Birch, Invited expert; Mike Dolan, Invited expert; Nigel Megitt, British Broadcasting Corporation; Thierry Michel, W3C ; Andreas Tai, Institut für Rundfunktechnik; Stefan Pöschel, Institut für Rundfunktechnik.

The editor also wishes to acknowledge Digital Entertainment Content Ecosystem (DECE) for contributing to the initial document for the Member Submission.

K. Privacy and Security Considerations

This section is non-normative.

With the exception of the following, the security and privacy considerations of [ ttml2 ] apply:

L. Summary of substantive changes

This section is non-normative.

L.1 Overview

This appendix summarizes changes made from [ ttml-imsc1.2 ].

L.2 Changes

L.2.1 Japanese character set

Added Japanese ( ja ) set to the Supplementary Character Sets at B. Common Character Sets .

L.2.2 Hypothetical Render Model

The definition of the Hypothetical Render Model is removed from this document and replaced with a reference to [ imsc-hrm ].

L.2.3 Image Profile

The Image Profile specified in earlier versions of this specification is removed.

L.2.4 Added Features

Added support (partial or complete) for the following features.

Relative to the TT Feature namespace
#fontVariant

L.2.5 Deprecated Features

None

M. References

M.1 Normative references

[ARIB-STD-B62]
STD-B62, Multimedia Coding Specification For Digital Broadcasting (Second Generation), Version 2.2 (Fascicle 1) . ARIB. URL: https://www.arib.or.jp/english/std_tr/broadcasting/std-b62.html
[CLDR]
Unicode Common Locale Data Repository . Unicode Consortium. URL: https://cldr.unicode.org/
[CSS]
CSS Snapshot 2026 . Chris Lilley; Elika Etemad; Tab Atkins Jr.; Florian Rivoal; Sebastian Zartner. W3C. 26 February 2026. W3C Working Group Note. URL: https://www.w3.org/TR/css-2026/
[css-fonts-3]
CSS Fonts Module Level 3 . John Daggett; Myles Maxfield; Chris Lilley. W3C. 20 September 2018. W3C Recommendation. URL: https://www.w3.org/TR/css-fonts-3/
[EBU-TT-D]
Tech 3380, EBU-TT-D Subtitling Distribution Format Version 1.0.1 . European Broadcasting Union (EBU). URL: https://tech.ebu.ch/docs/tech/tech3380v1_0_1.pdf
[EBU-TT-M]
Tech 3390, EBU-TT-M Metadata Definitions 1.0 . European Broadcasting Union (EBU). URL: https://tech.ebu.ch/docs/tech/tech3390v1_0.pdf
[IANA-MEDIA-TYPES]
Media Types . IANA. URL: https://www.iana.org/assignments/media-types/
[imsc-hrm]
IMSC Hypothetical Render Model . Pierre-Anthony Lemieux. W3C. 25 April 2024. W3C Recommendation. URL: https://www.w3.org/TR/imsc-hrm/
[ISO10646]
ISO/IEC 10646:2020 Information technology — Universal coded character set (UCS)/ (UCS) . International Organization for Standardization. URL: https://www.iso.org/standard/76835.html
[namespaceState]
The Disposition of Names in an XML Namespace . Norman Walsh. W3C. 29 March 2006. W3C Working Draft. URL: https://www.w3.org/TR/2006/WD-namespaceState-20060329/
[RFC2119]
Key words for use in RFCs to Indicate Requirement Levels . S. Bradner. IETF. March 1997. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc2119
[RFC8174]
Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words . B. Leiba. IETF. May 2017. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc8174
[ttml-imsc1.0.1]
TTML Profiles for Internet Media Subtitles and Captions 1.0.1 (IMSC1) . Pierre-Anthony Lemieux. W3C. 24 April 2018. W3C Recommendation. URL: https://www.w3.org/TR/2018/REC-ttml-imsc1.0.1-20180424/
[ttml-imsc1.1]
TTML Profiles for Internet Media Subtitles and Captions 1.1 . Pierre-Anthony Lemieux. W3C. 8 November 2018. W3C Recommendation. URL: https://www.w3.org/TR/ttml-imsc1.1/
[ttml-imsc1.2]
TTML Profiles for Internet Media Subtitles and Captions 1.2 . Pierre-Anthony Lemieux. W3C. 4 August 2020. W3C Recommendation. URL: https://www.w3.org/TR/ttml-imsc1.2/
[ttml10-sdp-us]
TTML Simple Delivery Profile for Closed Captions (US) . Glenn Adams; Monica Martin; Sean Hayes. W3C. 5 February 2013. W3C Working Group Note. URL: https://www.w3.org/TR/2013/NOTE-ttml10-sdp-us-20130205/
[ttml2]
Timed Text Markup Language 2 (ttml2) (2nd Edition) . W3C. 9 March 2021. Candidate Recommendation Snapshot. URL: https://www.w3.org/TR/2021/CR-ttml2-20210309
[UNICODE]
The Unicode Standard . Unicode Consortium. URL: https://www.unicode.org/versions/latest/
[WCAG22]
Web Content Accessibility Guidelines (WCAG) 2.2 . Michael Cooper; Andrew Kirkpatrick; Alastair Campbell; Rachael Bradley Montgomery; Charles Adams. W3C. 12 December 2024. W3C Recommendation. URL: https://www.w3.org/TR/2024/REC-WCAG22-20241212/
[xml]
Extensible Markup Language (XML) 1.0 (Fifth Edition) . Tim Bray; Jean Paoli; Michael Sperberg-McQueen; Eve Maler; François Yergeau et al. W3C. 26 November 2008. W3C Recommendation. URL: https://www.w3.org/TR/2008/REC-xml-20081126/
[xml-names]
Namespaces in XML 1.0 (Third Edition) . Tim Bray; Dave Hollander; Andrew Layman; Richard Tobin; Henry Thompson et al. W3C. 8 December 2009. W3C Recommendation. URL: https://www.w3.org/TR/2009/REC-xml-names-20091208/
[XSL11]
Extensible Stylesheet Language (XSL) Version 1.1 . Anders Berglund. W3C. 5 December 2006. W3C Recommendation. URL: https://www.w3.org/TR/2006/REC-xsl11-20061205/

M.2 Informative references

[ARIB-TR-B39]
TR-B39, Operational Guidelines for Advanced Digital Satellite Broadcasting, Version 2.11 (Fascicle 2) (English translation) . ARIB. URL: https://www.arib.or.jp/english/std_tr/broadcasting/tr-b39.html
[BBC-SUB]
BBC Subtitle Guidelines . BBC. URL: https://www.bbc.co.uk/accessibility/forproducts/guides/subtitles/
[CFF]
Common File Format & Media Formats Specification (CFF) Version 2.2 . Digital Entertainment Content Ecosystem (DECE). URL: https://www.uvcentral.com
[css3-background]
CSS Backgrounds and Borders Module Level 3 . Elika Etemad; Brad Kemper. W3C. 11 March 2024. CRD. URL: https://www.w3.org/TR/css-backgrounds-3/
[HTML]
HTML Standard . Anne van Kesteren; Domenic Denicola; Dominic Farolino; Ian Hickson; Philip Jägenstedt; Simon Pieters. WHATWG. Living Standard. URL: https://html.spec.whatwg.org/multipage/
[media-accessibility-reqs]
Media Accessibility User Requirements . Shane McCarron; Michael Cooper; Mark Sadecki. W3C. 3 December 2015. W3C Working Group Note. URL: https://www.w3.org/TR/2015/NOTE-media-accessibility-reqs-20151203/
[MPEGDASH]
Information technology — Dynamic adaptive streaming over HTTP (DASH) — Part 1: Media presentation description and segment formats . ISO/IEC. Under development. URL: https://www.iso.org/standard/89027.html
[SMPTE2052-1]
SMPTE ST 2052-1:2010 "Timed Text Format (SMPTE-TT)" . SMPTE. URL: https://doi.org/10.5594/SMPTE.ST2052-1.2010
[SUBM]
TTML Text and Image Profiles for Internet Media Subtitles and Captions (Member Submission, 07 June 2013) . World Wide Web Consortium (W3C). URL: https://www.w3.org/Submission/2013/SUBM-ttml-ww-profiles-20130607/
[ttml-imsc1]
TTML Profiles for Internet Media Subtitles and Captions 1.0 (IMSC1) . Pierre-Anthony Lemieux. W3C. 26 June 2018. W3C Recommendation. URL: https://www.w3.org/TR/2018/SPSD-ttml-imsc1-20180626/
[ttml-profile-registry]
TTML Media Type Definition and Profile Registry . Mike Dolan; Nigel Megitt; Glenn Adams. W3C. 19 November 2020. W3C Working Group Note. URL: https://www.w3.org/TR/ttml-profile-registry/
[TTML1]
Timed Text Markup Language 1 (TTML1) (Third Edition) . Glenn Adams; Pierre-Anthony Lemieux. W3C. 8 November 2018. W3C Recommendation. URL: https://www.w3.org/TR/2018/REC-ttml1-20181108/
[xmlschema-1]
XML Schema Part 1: Structures Second Edition . Henry Thompson; David Beech; Murray Maloney; Noah Mendelsohn et al. W3C. 28 October 2004. W3C Recommendation. URL: https://www.w3.org/TR/2004/REC-xmlschema-1-20041028/