Errata for Timed Text Markup Language 1 (TTML1)

W3C Recommendation 29 October 2015

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About the TTML1 Recommendation

The TTML1 Recommendation was produced by the W3C Timed Text (TT) Working Group as part of the W3C Video in the Web Activity.

This document lists the known errata to the TTML1 Recommendation. Each entry has the following information:

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Added text marked thus. Removed text marked thus. Changed text marked thus.

Known errata as of 29 October 2015


Correction in TTML1 Section 2.2 Terminology (published 2014-07-31)


Add definitions of Temporally Active and Temporally Active Region.


Add following two definitions just prior to the definition of Timed Text:

Temporally Active

A syntactic or semantic feature, e.g., an element or the presentation of an element, is Temporally Active when the current time of selected time base intersects with the active time interval of the feature.

Temporally Active Region

A Region that is Temporally Active.

Correction in TTML1 Section 2.3 Document Conventions (published 2014-07-31)


Clarify meaning of expression {any attribute not in default or any TT namespace}.


Add following paragraph after the first paragraph (starting with "In an XML representation, ...") that follows the XML Representation — Element Information Item: example:

In an XML representation, the expression {any attribute not in default or any TT namespace} applies only to namespace qualified attributes; unqualified attributes are not permitted unless explicitly defined in this specification.

Correction in TTML1 Section 5.2 Profiles (published 2014-01-30)


Minor typographical error, in the third paragraph under Table 2.


Change "... and must not be appear ..."

to read "... and must not appear ...".

Correction in TTML1 Section 6.1.5 ttp:extension (published 2014-09-14)


Minor typographical error, in the second paragraph under XML Representation - Element Information Item ttp:extension.


Change "... of the ttp:feature element ..."

to read "... of the ttp:extension element ...".

Correction in TTML1 Section 8.2.7 - tts:extent attribute (published 2014-07-17)


Provide rationale for use of greater value when interpreting closest supported value..


Add a 2nd paragraph to Note as follows:

This rule for resolving closest supported value for the tts:extent attribute makes use of the nearest larger rather than nearest smaller supported distance. The rationale for this difference in treatment is that use of a larger extent ensures that the affected content will be contained in the region area without causing region overflow, while use of a smaller extent makes region overflow more likely.

Correction in TTML1 Section 8.2.15 - tts:overflow attribute (published 2014-09-17)


Clarify context in which oveflow semantics apply and constraints on those semantics when they do apply.


Add the following Note immediately after the paragraph starting with "If the value of this attribute is visible...":


This attribute has no impact on presentation processing when no overflow condition applies. An overflow condition applies when the bounding box of some descendant line area extends outside of the containing region's nominal content area extent in either or both 1) the inline and 2) the block progression dimensions, where the nominal content area extent in both dimensions is determined by the computed values of the tts:extent and tts:padding style properties of the containing region. Overflow in the inline progression dimension can occur only if tts:wrapOption is noWrap. Furthermore, when an overflow condition applies, it is not intended that the effective extent of the region be modified for the purpose of presentation processing. For example, the area painted with the region's background color is not extended in either dimension to enclose the overflowed content.

Note that, in particular, the normative text in the previous paragraph "region composition and layout must be performed as if the region's width and height were unconstrained" refers to the process of determining the effective extent and origin of descendant line areas produced in either (or both) of the two overflow contexts described here, and is not intended to imply that the region extent is altered for the purpose of determining the region's padding area insets or the extent of its background color. More specifically, the normative language above is not intended to override or contradict the semantics of [XSL 1.1], § 7.21.2, or of [CSS2], § 11.1.1, on which the former is based.

Correction in TTML1 Section 8.2.16 - tts:padding attribute (published 2014-07-17)


Interpret closest supported value as least (not greatest) padding on a per-edge basis in order to prevent content area overflow.


Change text of Note from:

"In this context, the phrase closest supported value means the value for which the Euclidean distance between the computed padding and the supported padding is minimized. If there are multiple closest supported values equally distant from the computed value, then the value most distant from 0, i.e., the greatest padding, is used."

to read:

"In this context, the phrase closest supported value means the value for which the one-dimensional Euclidean distance between the computed padding and the supported padding is minimized on a per-edge basis. If there are multiple closest supported values equally distant from the computed value for a given edge, then the value least distant from 0, i.e., the least padding, is used."

Correction in TTML1 Section 8.2.17 - tts:showBackground attribute (published 2014-07-31)


Clarify meaning of whenActive.


Add the following paragraph immediately prior to the paragraph starting with "If a computed value of the property ...":

A region satisfies the whenActive case if (1) it is a Temporally Active Region and (2) content is selected into the region, where that content is also Temporally Active.

Correction in TTML1 Section 10.2.3 - dur attribute (published 2014-07-17)


Add clarification about use of zero duration.


Add the following sentence to the last paragraph (that cites [SMIL 2.1] § 10.4.1):

In a deliberate divergence from [SMIL 2.1], § 10.4.1, the value of the dur attribute is permitted to be zero (0).

Correction in TTML1 Appendix C - Media Type Registration (published 2014-01-30)


Correction in the Media Type Registration wording:


Replace the body of Appendix C with the following:

This appendix is normative.

This appendix registers a new media type, "application/ttml+xml" in conformance with BCP 13 and W3CRegMedia. The information in this appendix is being submitted to the Internet Engineering Steering Group (IESG) for review, approval, and registration with the Internet Assigned Numbers Authority (IANA).

Type name:


Subtype name:


Required parameters:


Optional parameters:

If specified, the charset parameter must match the XML encoding declaration, or if absent, the actual encoding.


The document profile of a TTMLDocument Instance may be specified using an optional profile parameter, which, if specified, the value of which must adhere to the syntax and semantics of ttp:profile parameter defined by Section 6.2.8 ttp:profile of the published specification.

Encoding considerations:


Security considerations:

As with other XML types and as noted in [XML Media Types] (, Section 10, repeated expansion of maliciously constructed XML entities can be used to consume large amounts of memory, which may cause XML processors in constrained environments to fail.

In addition, because of the extensibility features for TTML and of XML in general, it is possible that "application/ttml+xml" may describe content that has security implications beyond those described here. However, TTML does not provide for any sort of active or executable content, and if the processor follows only the normative semantics of the published specification, this content will be outside TTML namespaces and may be ignored. Only in the case where the processor recognizes and processes the additional content, or where further processing of that content is dispatched to other processors, would security issues potentially arise. And in that case, they would fall outside the domain of this registration document.

Although not prohibited, there are no expectations that XML signatures or encryption would normally be employed.

Interoperability considerations:

The published specification describes processing semantics that dictate behavior that must be followed when dealing with, among other things, unrecognized elements and attributes, both in TTML namespaces and in other namespaces.

Because TTML is extensible, conformant "application/ttml+xml" processors may expect (and enforce) that content received is well-formed XML, but it cannot be guaranteed that the content is valid to a particular DTD or Schema or that the processor will recognize all of the elements and attributes in the document.

Published specification:

This media type registration is extracted from Appendix C Media Type Registration of the Timed Text Markup Language (TTML) 1.0 specification: Timed Text Markup Language 1 (TTML1).

Applications that use this media type:

TTML is used in the television industry for the purpose of 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.

There is partial and full support of TTML in components used by several Web browsers plugins, and in a number of caption authoring tools.

Additional information:
Magic number(s):
File extension(s):


Macintosh file type code(s):


Fragment identifiers:

For documents labeled as application/ttml+xml, the fragment identifier notation is intended to be used with xml:id attributes, as described in section 7.2.1 of the Timed Text Markup Language 1 (TTML1) specification.

Person & email address to contact for further information:

Timed Text Working Group (

Intended usage:


Restrictions on usage:



The published specification is a work product of the World Wide Web Consortium's Timed Text (TT) Working Group.

Change controller:

The W3C has change control over this specification.

Correction in TTML1 Appendix M - Concrete Encoding (published 2014-02-20)


Add standard XML named character entities unintentionally omitted from note.


Change "... only the following named character entities are defined: &, <, and >."

to read "... only the following named character entities are defined: &, ', <, >, and ".".

Correction in TTML1 Appendix N - Time Expression Semantics (Non-Normative) (published 2015-10-29)


Correction in the drop mode calculation:


In step (2), change

to read as

In step (3), change

to read as