Copyright © 2016 W3C® (MIT, ERCIM, Keio, Beihang). W3C liability, trademark and document use rules apply.
This document specifies two profiles of [TTML1]: a text-only profile and an image-only profile. These profiles are intended to be used across subtitle and caption delivery applications worldwide, thereby simplifying interoperability, consistent rendering and conversion to other subtitling and captioning formats.
It is feasible to create documents that simultaneously conform to both [ttml10-sdp-us] and the text-only profile.
The document defines extensions to [TTML1], as well as incorporates extensions specified in [ST2052-1] and [EBU-TT-D].
Both profiles are based on [SUBM].
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
This document was published by the Timed Text Working Group as a Superseded Recommendation. A newer specification exists that is recommended for new adoption in place of this specification.
No change were done to this document since its previous publication.
This document has been reviewed by W3C Members, by software developers, and by other W3C groups and interested parties, and is endorsed by the Director as a W3C Recommendation.
This specification has been superseded by IMSC 1.0.1. For purposes of the W3C Patent Policy this Superseded Recommendation has the same status as an active Recommendation; it retains licensing commitments and remains available as a reference for old implementations. IMSC 1.0.1 is recommended for new adoption.
This document is governed by the 1 September 2015 W3C Process Document.
This document specifies two profiles of [TTML1]: a text-only profile and an image-only profile. These profiles are intended for subtitle and caption delivery worldwide, including dialog language translation, content description, captions for deaf and hard of hearing, etc.
The text profile is a syntactic superset of [ttml10-sdp-us], and a document can simultaneously conform to both [ttml10-sdp-us] and the text-only profile.
The document defines extensions to [TTML1], as well as incorporates extensions specified in [ST2052-1] and [EBU-TT-D].
This specification uses the same conventions as [TTML1] for the specification of parameter attributes, styling attributes and metadata elements. In particular, Section 2.3 of [TTML1] specifies conventions used in the XML representation of elements.
All content of this specification that is not explicitly marked as non-normative is considered to be normative. If a section or appendix header contains the expression "non-normative", then the entirety of the section or appendix is considered non-normative.
This specification uses Feature and Extension designations as defined in Appendices D.1 and E.1 at [TTML1]:
If the name of an element referenced in this specification is not namespace qualified, then the TT namespace applies (see 6.3 Namespaces.)
Default Region. See Section 9.3.1 at [TTML1].
Document Instance. See Section 2.2 at [TTML1].
Extension. See Section 2.2 at [TTML1].
Feature. See Section 2.2 at [TTML1].
Intermediate Synchronic Document. See Section 9.3.2 at [TTML1].
Document Interchange Context. See Section 2.2 at [TTML1].
Document Processing Context. See Section 2.2 at [TTML1].
Processor. Either a Presentation processor or a Transformation processor.
Presentation processor. See Section 2.2 at [TTML1].
Transformation processor. See Section 2.2 at [TTML1].
Related Media Object. See Section 2.2 at [TTML1].
Related Video Object. A Related Media Object that consists of a sequence of image frames, each a rectangular array of pixels.
Text Alternative. As defined in [WCAG20].
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 are to be interpreted as described in [RFC2119].
A Document Instance that conforms to a profile defined herein:
A Document Instance, by definition, satisfies the requirements of Section 3.1 at [TTML1], 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 a profile defined in this specification:
A transformation processor that conforms to a profile defined in this specification:
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 [TTML1]. 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).
This specification does not specify presentation processor or transformation processor behavior when processing or transforming a non-conformant Document Instance.
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.
Notwithstanding special cases, e.g. a Document Instance that contains no p
, span
, br
element and no smpte:backgroundImage
attribute, it is generally not possible to construct a Document Instance that conforms to the Text Profile and Image Profile simultaneously, and it is not possible to construct a Document Instance that results in the presentation of both text data and image data.
In applications that require subtitle/caption content in image form to be simultaneously available in text form, two distinct Document Instances, one conforming to the Text Profile and the other conforming to the Image Profile, SHOULD be offered. In addition, the Text Profile Document Instance SHOULD be associated with the Image Profile Document Instance such that, when image content is encountered, assistive technologies have access to its corresponding text form. The method by which this association is made is left to each application.
The ittm:altText
element specified 6.7.4 ittm:altText also allows text equivalent
string to be associated with an image, e.g. to support indexation of the content and also facilitate quality checking of the
document during authoring.
Annex D. WCAG Considerations specifically discusses this specification in the context of the [WCAG20] guidelines.
The Text Profile consists of Sections 6. Common Constraints and 7. Text Profile Constraints.
The Image Profile consists of Sections 6. Common Constraints and 8. Image Profile Constraints.
For the purpose of content processing, the determination of the resolved profile SHOULD take into account both the signaled profile, as defined in 6.9 Profile Signaling, and profile metadata, as designated by either (or both) the Document Interchange Context or (and) the Document Processing Context, which MAY entail inspecting document content.
If the resolved profile is not a profile supported by the Processor but is feasibly interoperable with the Text Profile, then the resolved profile is the Text Profile; otherwise, if the resolved profile is not a profile supported by the Processor but is feasibly interoperable with the Image Profile, then the resolved profile is the Image Profile.
If the resolved profile is a profile supported by the Processor, then the Processor SHOULD process the Document Instance according to the resolved profile. If the resolved profile is neither Text Profile nor Image Profile, processing is outside the scope of this specification.
If the resolved profile is undetermined or not supported by the Processor, then the Processor SHOULD nevertheless process the Document Instance using one of its supported profiles, with a preference for the Text Profile over the Image Profile; otherwise, processing MAY be aborted.
A Document Instance SHALL use UTF-8 character encoding as specified in [UNICODE].
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.
Document Instances remain subject to the structural requirements of [TTML1].
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 |
[TTML1] |
TT Parameter | ttp |
http://www.w3.org/ns/ttml#parameter |
[TTML1] |
TT Styling | tts |
http://www.w3.org/ns/ttml#styling |
[TTML1] |
TT Feature | none | http://www.w3.org/ns/ttml/feature/ |
[TTML1] |
SMPTE-TT Extension | smpte |
http://www.smpte-ra.org/schemas/2052-1/2010/smpte-tt |
[ST2052-1] |
EBU-TT Styling | ebutts |
urn:ebu:tt:style |
[EBU-TT-D] |
EBU-TT Metadata | ebuttm |
urn:ebu:tt:metadata |
[EBU-TT-D] |
IMSC 1.0 Styling | itts |
http://www.w3.org/ns/ttml/profile/imsc1#styling |
This specification |
IMSC 1.0 Parameter | ittp |
http://www.w3.org/ns/ttml/profile/imsc1#parameter |
This specification |
IMSC 1.0 Metadata | ittm |
http://www.w3.org/ns/ttml/profile/imsc1#metadata |
This specification |
IMSC 1.0 Extension | none | http://www.w3.org/ns/ttml/profile/imsc1/extension/ |
This specification |
IMSC 1.0 Text Profile Designator | none | http://www.w3.org/ns/ttml/profile/imsc1/text |
This specification |
IMSC 1.0 Image Profile Designator | none | http://www.w3.org/ns/ttml/profile/imsc1/image |
This specification |
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.
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.
As specified in [TTML1], tts:overflow
has no effect on the extent of the region, and hence
the total normalized drawing area S(En) at 9.3 Paint Regions.
Each intermediate synchronic document of the Document Instance is intended to be displayed on a specific frame and removed on a specific frame of the Related Video Object.
When mapping a media time expression M to a frame F of a Related Video Object, e.g. for the purpose of rendering a Document Instance onto the Related Video Object, the presentation processor SHALL map M to the frame F with the presentation time that is the closest to, but not less, than M.
In typical scenario, the same video program (the Related Video Object) will be used for Document Instance authoring, delivery and user playback. The mapping from media time expression to Related Video Object above allows the author to precisely associate subtitle video content with video frames, e.g. around scene transitions. In circumstances where the video program is downsampled during delivery, the application can specify that, at playback, the relative video object be considered the delivered video program upsampled to is original rate, thereby allowing subtitle content to be rendered at the same temporal locations it was authored.
The ittp:aspectRatio
attributes allows authorial control of the mapping of the root container 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>+ |
The root container of a Document Instance SHALL be mapped to each image frame of the Related Video Object according to the following:
If ittp:aspectRatio
is present, the root container SHALL be mapped to a rectangular area within the
image frame such that:
ittp:aspectRatio
,Otherwise, the root container of a Document Instance SHALL be mapped to the image frame in its entirety.
An ittp:aspectRatio
attribute is considered to be significant only when specified on the tt
element.
The ittp:aspectRatio
parameter effectively defines the intended display aspect ratio (DAR) of the root container, while
the tts:extent
style property on the root element effectively defines the intended storage aspect ratio (SAR) of the root container.
ttp:aspectRatio="4 3"
, allowing the combination
to be displayed on both 4:3 and 16:9 display devices while preserving both caption/subtitles content and the relative position
of caption/subtitles with video elements.
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:
head
element;p
element that lexically precedes any p
element that B includes;
p
; andIf 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.
<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>
[TTML1] specifies explicitly referencing of elements identified using xml:id
in the following
circumstances:
body
referencing region
elements. In this case, Requirement 4 above is
always satisfied.body
referencing style
elements. In this case, Requirement 4 above is
always satisfied.region
element referencing style
elements. In this case, Requirement 4 above is always
satisfied.style
element referencing other style
elements. In this case, Requirement 4 provides an
optimization of style
element ordering within the head
element.ttm:actor
element referencing a ttm:agent
element. In this case, Requirement 4 provides
optimization of metadata elements ordering within the document.ttm:agent
elements using the ttm:agent
attribute. In this
case, Requirement 4 provides optimization of metadata elements ordering within the document.itts:forcedDisplay
can be used to hide content whose computed value of tts:visibility
is "visible"
when the processor has been configured to do so via the application parameter displayForcedOnlyMode
.
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, but still affect layout, regardless of the computed
value of tts:visibility
.
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 |
Annex C. Forced content (non-normative) 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 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.
... <head> ... <region xml:id="r1" tts:origin="10% 2%" tts:extent="80% 10%" tts:color="white" itts:forcedDisplay="true" tts:backgroundColor="black"/> <region xml:id="r2" tts:origin="10% 80%" tts:extent="80% 88%" tts:color="white" tts:backgroundColor="black"/> ... </head> ... <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> ...
As specified in [TTML1], 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
.
Although itts:forcedDisplay
, like all the TTML style attributes, has no defined semantics on a
br
content element, itts:forcedDisplay
will apply to a br
content element if it is
either defined on an ancestor content element of the br
content element or it is applied to a region element
corresponding to a region that the br
content element is being flowed into.
It is expected that the functionality of itts:forcedDisplay
will be mapped to a conditional
style construct in a future revision of this specification.
The presentation semantics associated with itts:forcedDisplay
are intended to be
compatible with those associated with the forcedDisplayMode
attribute defined in [CFF].
ittm:altText
allows an author to provide a text string equivalent for an element, typically an image. This
text equivalent MAY be used to support indexing of the content and also facilitate quality checking of the document during
authoring.
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 1.0 namespace}> Content: #PCDATA </ittm:altText> |
The ittm:altText
element SHALL be a child of the metadata
element.
8. Image Profile Constraints specifies the use of the ittm:altText
element with images.
... <div region="r1" begin="1s" end="6s" smpte:backgroundImage="1.png"> <metadata> <ittm:altText>Nous étions inscrits au même lycée.</ttm:title> </metadata> </div> ...
In contrast to the common use of alt
attributes in [HTML5], 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
attribute content can however be read and used by assistive technologies.
A presented region is a temporally active region that satisfies the following conditions:
tts:opacity
is not equal to "0.0"
; andtts:display
is not "none"
; andtts:visibility
is not "hidden"
; andtts:showBackground
is equal
to "always"
and the computed value of tts:backgroundColor
has non-transparent alpha.All regions SHALL NOT extend beyond the root container, i.e. the intersection of the sets of coordinates belonging to a region and the sets of coordinates belonging to the root container is the set of coordinates belonging to the 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.
The number of presented regions in a given intermediate synchronic document SHALL NOT be greater than 4.
The ttp:profile
attribute SHOULD be present on the tt
element and equal to the designator of the IMSC1 profile to which the Document Instance conforms, and the ttp:profile
element SHOULD NOT be present, unless:
ttp:profile
attribute
and the ttp:profile
element SHOULD NOT be present, and instead the designator of the IMSC1 profile to which the Document Instance conforms and
the URI "urn:ebu:tt:distribution:2014-01"
SHOULD each be carried in an ebuttm:conformsToStandard
element as specified in
[EBU-TT-D]; or
ttp:profile
attribute SHOULD NOT be present. [ttml10-sdp-us] requires that the ttp:profile
element be present and that its use
attribute be set to a specified value.
The ttp:profile
and ebuttm:conformsToStandard
elements SHALL NOT signal conformance to both Image Profile and Text Profile in a given Document Instance.
It SHALL be possible to apply the Hypothetical Render Model specified in Section 9. Hypothetical Render Model to any sequence of consecutive intermediate synchronic documents without error as defined in Section 9.2 General.
See 4. Conformance for a definition of permitted and prohibited.
Feature | Disposition | Additional provision |
---|---|---|
Relative to the TT Feature namespace | ||
#animation |
permitted | |
#backgroundColor-block |
permitted | |
#backgroundColor-region |
permitted | |
#cellResolution |
permitted | If the Document Instance includes any length value that uses the c expression,
ttp:cellResolution SHOULD be present on the tt element. |
#clockMode |
prohibited | |
#clockMode-gps |
prohibited | |
#clockMode-local |
prohibited | |
#clockMode-utc |
prohibited | |
#core |
permitted | |
#display-block |
permitted | |
#display-inline |
permitted | |
#display-region |
permitted | |
#display |
permitted | |
#dropMode |
prohibited | |
#dropMode-dropNTSC |
prohibited | |
#dropMode-dropPAL |
prohibited | |
#dropMode-nonDrop |
prohibited | |
#extent-root |
permitted | If the Document Instance includes any length value that uses the px expression,
tts:extent SHALL be present on the tt element. |
#extent |
permitted | |
#frameRate |
permitted | 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. |
#frameRateMultiplier |
permitted | |
#layout |
permitted | |
#length-cell |
permitted | c units SHALL NOT be present outside of the value of ebutts:linePadding . |
#length-integer |
permitted | |
#length-negative |
prohibited | |
#length-percentage |
permitted | |
#length-pixel |
permitted | |
#length-positive |
permitted | |
#length-real |
permitted | |
#length |
permitted | |
#markerMode |
prohibited | |
#markerMode-continuous |
prohibited | |
#markerMode-discontinuous |
prohibited | |
#metadata |
permitted | |
#opacity |
permitted | |
#origin |
permitted | |
#overflow |
permitted | |
#overflow-visible |
permitted | |
#pixelAspectRatio |
prohibited | |
#presentation |
permitted | See constraints applied to #profile. |
#profile |
permitted | See 6.9 Profile Signaling. |
#showBackground |
permitted | |
#structure |
permitted | |
#styling-chained |
permitted | |
#styling-inheritance-content |
permitted | |
#styling-inheritance-region |
permitted | |
#styling-inline |
permitted | |
#styling-nested |
permitted | |
#styling-referential |
permitted | |
#styling |
permitted | |
#subFrameRate |
prohibited | |
#tickRate |
permitted | ttp:tickRate SHALL be present on the tt element if the
document contains any time expression that uses the t metric. |
#timeBase-clock |
prohibited | |
#timeBase-media |
permitted | NOTE: [TTML1] specifies that the default timebase is |
#timeBase-smpte |
prohibited | |
#time-clock-with-frames |
permitted | |
#time-clock |
permitted | |
#time-offset-with-frames |
permitted | |
#time-offset-with-ticks |
permitted | |
#time-offset |
permitted | |
#timeContainer |
permitted | |
#timing |
permitted |
|
#transformation |
permitted | See constraints at #profile. |
#visibility-block |
permitted | |
#visibility-region |
permitted | |
#writingMode-horizontal-lr |
permitted | |
#writingMode-horizontal-rl |
permitted | |
#writingMode-horizontal |
permitted | |
#zIndex |
permitted | |
Extension | Disposition | Provisions |
Relative to the IMSC 1.0 Extension namespace | ||
#aspectRatio |
permitted | |
#forcedDisplay |
permitted | |
#progressivelyDecodable |
permitted | |
#altText |
permitted |
As specified in [TTML1], a #time-offset-with-frames
expression is translated to a media time
M according to M = 3600 · hours + 60 · minutes + seconds + (frames ÷ (ttp:frameRateMultiplier
·
ttp:frameRate
)).
This profile is associated with the following profile designator:
Profile Name | Profile Designator |
---|---|
IMSC 1.0 Text | http://www.w3.org/ns/ttml/profile/imsc1/text |
As specified in 6.11 Features and Extensions, the presence of the ttp:profile
attribute is
not required by this profile. The profile designator specified above is intended to be generally used to signal conformance
of a Document Instance to the profile. The details of such signaling depends on the application, and can, for instance, use
metadata structures out-of-band of the Document Instance.
A Document Instance SHOULD be authored using characters selected from the sets specified in B. Recommended Character Sets.
The flow of text within a region depends the dimensions and spacing (kerning) between individual glyphs. The following allows, for instance, region extents to be set such that text flows without clipping.
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.
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.
See 4. Conformance for a definition of permitted and prohibited.
Feature | Disposition | Additional provisions |
---|---|---|
Relative to the TT Feature namespace | ||
#backgroundColor-inline |
permitted | |
#backgroundColor |
permitted | |
#bidi |
permitted | |
#content |
permitted | |
#color |
permitted | The initial value of NOTE: This is consistent with [ST2052-1]. |
#direction |
permitted | |
#displayAlign |
permitted | |
#extent-region |
permitted | The tts:extent attribute SHALL be present on all region elements, where it
SHALL use either px units or "percentage" syntax. |
#fontFamily-generic |
permitted | 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
If the computed value of NOTE: The term used value is defined in CSS 2.1, as normatively referenced by [TTML1]. |
#fontFamily-non-generic |
permitted | |
#fontFamily |
permitted | |
#fontSize-anamorphic |
prohibited | |
#fontSize-isomorphic |
permitted | |
#fontSize |
See individual disposition of #fontSize-anamorphic and #fontSize-isomorphic . |
|
#fontStyle-italic |
permitted | |
#fontStyle-oblique |
permitted | |
#fontStyle |
permitted | |
#fontWeight-bold |
permitted | |
#fontWeight |
permitted | |
#length-em |
permitted | |
#lineBreak-uax14 |
The processor SHALL implement the #lineBreak-uax14 feature defined in the TT Feature namespace. |
|
#lineHeight |
permitted | As implementation of the "normal" value is not uniform at the time of this writing, tts:lineHeight SHOULD NOT be set to "normal" and SHOULD be explicitly specified such that the specified style set of each p element contains a tts:lineHeight property whose value is not assigned by initial value fallback. |
#nested-div |
permitted | |
#nested-span |
permitted | |
#origin |
permitted | The tts:origin attribute SHALL use px units or "percentage" representation, and SHALL NOT
use em units. |
#padding-1 |
permitted | |
#padding-2 |
permitted | |
#padding-3 |
permitted | |
#padding-4 |
permitted | |
#padding |
permitted | |
#textAlign-absolute |
permitted | |
#textAlign-relative |
permitted | |
#textAlign |
permitted | |
#textDecoration-over |
permitted | |
#textDecoration-through |
permitted | |
#textDecoration-under |
permitted | |
#textDecoration |
permitted | |
#textOutline-blurred |
prohibited | |
#textOutline-unblurred |
permitted | |
#textOutline |
permitted | The computed value of tts:textOutline on a span element
SHALL be 10% or less than the computed value of tts:fontSize on the same element. |
#unicodeBidi |
permitted | |
#visibility |
permitted | |
#visibility-inline |
permitted | |
#wrapOption |
permitted | |
#writingMode |
permitted | |
#writingMode-vertical |
permitted | |
Extension | Disposition | Provisions |
Relative to the SMPTE-TT Extension Namespace | ||
#image |
prohibited | |
Relative to the IMSC 1.0 Extension namespace | ||
#linePadding |
permitted |
If used, the attribute The processor:
NOTE: The |
#multiRowAlign |
permitted |
If used, the attribute The processor:
|
In contrast to this specification, [EBU-TT-D] specifies that the attributes ebutts:linePadding
and ebutts:multiRowAlign
are allowed only on the style
element.
This profile is associated with the following profile designator:
Profile Name | Profile Designator |
---|---|
IMSC 1.0 Image | http://www.w3.org/ns/ttml/profile/imsc1/image |
As specified in 6.11 Features and Extensions, the presence of the ttp:profile
attribute is
not required by this profile. The profile designator specified above is intended to be generally used to signal conformance
of a Document Instance to the profile. The details of such signaling depends on the application, and can, for instance, use
metadata structures out-of-band of the Document Instance.
A presented image is a div
element with a smpte:backgroundImage
attribute that flows into a presented region.
In a given intermediate synchronic document, each presented region SHALL contain at most one div
element, which SHALL be a presented image.
For the purposes of constructing an intermediate synchronic document, a div
element with a smpte:backgroundImage
attribute SHALL NOT be considered empty.
If a smpte:backgroundImage
attribute is applied to a div
element:
smpte:backgroundImage
SHALL be equal
to the width and height (as specified by the tts:extent
attribute using px
units) of the region in which the
div
element is presented;div
element SHOULD contain a metadata
element containing an ittm:altText
element that is a Text Alternative of the image referenced by the smpte:backgroundImage
attribute; andsmpte:backgroundImage
attribute SHALL reference a PNG datastream as specified in [PNG]. If a pHYs chunk is present, it SHALL indicate square pixels. Note that if no pixel aspect ratio is carried, the default of square pixels is assumed.In [TTML1], tts:extent
and tts:origin
do not apply to div
elements. In order to individually position multiple div
elements, each div
can be associated with a distinct region
with the desired tts:extent
and tts:origin
.
See 4. Conformance for a definition of permitted and prohibited.
Feature | Disposition | Additional provisions |
---|---|---|
Relative to the TT Feature namespace | ||
#backgroundColor-inline |
prohibited | |
#backgroundColor |
See individual disposition of #backgroundColor-inline , #backgroundColor-region and #backgroundColor-block . |
|
#bidi |
See individual disposition of #direction , #unicodeBidi and #writingMode-horizontal . |
|
#color |
prohibited | |
#content |
permitted | The p , span and br elements SHALL NOT be present. See Section 8.2.2 Constraints for constraints on div elements. |
#direction |
prohibited | |
#displayAlign |
prohibited | |
#extent-region |
permitted | The tts:extent attribute SHALL be present on all region elements, where it
SHALL use px units. |
#fontFamily |
prohibited | |
#fontFamily-generic |
prohibited | |
#fontFamily-non-generic |
prohibited | |
#fontSize |
prohibited | |
#fontSize-anamorphic |
prohibited | |
#fontSize-isomorphic |
prohibited | |
#fontStyle |
prohibited | |
#fontStyle-italic |
prohibited | |
#fontStyle-oblique |
prohibited | |
#fontWeight |
prohibited | |
#fontWeight-bold |
prohibited | |
#length-em |
prohibited | |
#lineBreak-uax14 |
No processor requirement is specified. | |
#lineHeight |
prohibited | |
#nested-div |
prohibited | |
#nested-span |
prohibited | NOTE: The prohibition of |
#padding |
prohibited | |
#padding-1 |
prohibited | |
#padding-2 |
prohibited | |
#padding-3 |
prohibited | |
#padding-4 |
prohibited | |
#textAlign |
prohibited | |
#textAlign-absolute |
prohibited | |
#textAlign-relative |
prohibited | |
#textDecoration |
prohibited | |
#textDecoration-over |
prohibited | |
#textDecoration-through |
prohibited | |
#textDecoration-under |
prohibited | |
#textOutline |
prohibited | |
#textOutline-blurred |
prohibited | |
#textOutline-unblurred |
prohibited | |
#unicodeBidi |
prohibited | |
#visibility |
See individual disposition of #visibility-inline ,
#visibility-region and #visibility-block . |
|
#visibility-inline |
prohibited | |
#wrapOption |
prohibited | |
#writingMode |
See individual disposition of #writingMode-vertical and
#writingMode-horizontal . |
|
#writingMode-vertical |
prohibited | |
Extension | Disposition | Provisions |
Relative to the SMPTE-TT Extension namespace | ||
#image |
permitted |
|
This Section specifies the Hypothetical Render Model illustrated in Fig. 1 Hypothetical Render Model .
The purpose of the model is to limit Document Instance complexity. It is not intended as a specification of the processing requirements for implementations. For instance, while the model defines a glyph buffer for the purpose of limiting the number of glyphs displayed at any given point in time, it neither requires the implementation of such a buffer, nor models the sub-pixel character positioning and anti-aliased glyph rendering that can be used to produce text output.
The model operates on successive intermediate synchronic documents obtained from an input Document Instance, and uses a simple double buffering model: while an intermediate synchronic document En is being painted into Presentation Buffer Pn (the "front buffer" of the model), the previous intermediate synchronic document En-1 is available for display in Presentation Buffer Pn-1 (the "back buffer" of the model).
The model specifies an (hypothetical) time required for completely painting an intermediate synchronic document as a proxy for complexity. Painting includes drawing region backgrounds, rendering and copying glyphs, and decoding and copying images. Complexity is then limited by requiring that painting of intermediate synchronic document En completes before the end of intermediate synchronic document En-1.
Whenever applicable, constraints are specified relative to root container dimensions, allowing subtitle sequences to be authored independently of Related Video Object resolution.
To enable scenarios where the same glyphs are used in multiple successive intermediate synchronic documents, e.g. to convey a CEA-608/708-style roll-up (see [CEA-608] and [CEA-708]), the Glyph Buffers Gn and Gn-1 store rendered glyphs across intermediate synchronic documents, allowing glyphs to be copied into the Presentation Buffer instead of rendered, a more costly operation.
Similarly, Decoded Image Buffers Dn and Dn-1 store decoded images across intermediate synchronic documents, allowing images to be copied into the Presentation Buffer instead of decoded.
The Presentation Compositor SHALL render in Presentation Buffer Pn each successive intermediate synchronic document En using the following steps in order:
The Presentation Compositor SHALL start rendering En:
The duration DUR(En) for painting an intermediate synchronic document En in the Presentation Buffer Pn SHALL be:
DUR(En) = S(En) / BDraw + DURT(En) + DURI(En)
where
The contents of the Presentation Buffer Pn SHALL be transferred instantaneously to Presentation Buffer Pn-1 at the presentation time of intermediate synchronic document En, making the latter available for display.
It is possible for the contents of Presentation Buffer Pn-1 to never be displayed. This can happen if Presentation Buffer Pn is copied twice to Presentation Buffer Pn-1 between two consecutive video frame boundaries of the Related Video Object.
It SHALL be an error for the Presentation Compositor to fail to complete painting pixels for En before the presentation time of En.
Unless specified otherwise, the following table SHALL specify values for IPD and BDraw.
Parameter | Initial value |
---|---|
Initial Painting Delay (IPD) | 1 s |
Normalized background drawing performance factor (BDraw) | 12 s-1 |
BDraw effectively sets a limit on fillings regions - for example, assuming that the root container is ultimately rendered at 1920×1080 resolution, a BDraw of 12 s-1 would correspond to a fill rate of 1920×1080×12/s=23.7×220pixels s-1.
IPD effectively sets a limit on the complexity of any given intermediate synchronic document.
The total normalized drawing area S(En) for intermediate synchronic document En SHALL be
S(En) = CLEAR(En) + PAINT(En )
where CLEAR(E0) = 0 and CLEAR(En | n > 0) = 1, i.e. the root container in its entirety.
To ensure consistency of the Presentation Buffer, a new intermediate synchronic document requires clearing of the root container.
PAINT(En) SHALL be the normalized area to be painted for all regions that are used in intermediate synchronic document En according to:
PAINT(En) = ∑Ri∈Rp NSIZE(Ri) ∙ NBG(Ri)
where R_p SHALL be the set of presented regions in the intermediate synchronic document En.
NSIZE(Ri) SHALL be given by:
NSIZE(Ri) = (width of Ri ∙ height of Ri ) ÷ (root container height ∙ root container width)
NBG(Ri) SHALL be the total number of tts:backgroundColor
attributes associated with the given
region Ri in the intermediate synchronic document. A tts:backgroundColor
attribute is
associated with a region when it is explicitly specified (either as an attribute in the element, or by reference to a
declared style) in the following circumstances:
region
layout element that defines the region; ordiv
, p
, span
or br
content element that is
to be flowed into the region for presentation in the intermediate synchronic document (see [TTML1] for more
details on when a content element is followed into a region); or
set
animation element that is to be applied to content elements that are to be
flowed into the region for presentation in the intermediate synchronic document (see [TTML1] for more details
on when a set
animation element is applied to content elements).
Even if a specified tts:backgroundColor
is the same as specified on the nearest ancestor content element or
animation element, specifying any tts:backgroundColor
SHALL require an additional fill operation for all
region pixels.
The Presentation Compositor SHALL paint into the Presentation Buffer Pn all visible pixels of presented images of intermediate synchronic document En.
For each presented image, the Presentation Compositor SHALL either:
Two images SHALL be identical if and only if they reference the same encoded image source.
The duration DURI(En) for painting images of an intermediate synchronic document En in the Presentation Buffer SHALL be as follows:
DURI(En) = ∑Ii ∈ Ic NRGA(Ii) / ICpy + ∑Ij ∈ Id NSIZ(Ij) / IDec
where
NRGA(Ii) is the Normalized Image Area of presented image Ii and SHALL be equal to:
NRGA(Ii)= (width of Ii ∙ height of Ii ) ÷ ( root container height ∙ root container width )
NSIZ(Ii) SHALL be the number of pixels of presented image Ii.
The contents of the Decoded Image Buffer Dn SHALL be transferred instantaneously to Decoded Image Buffer Dn-1 at the presentation time of intermediate synchronic document En.
The total size occupied by images stored in Decoded Image Buffers Dn or Dn-1 SHALL be the sum of their Normalized Image Area.
The size of Decoded Image Buffers Dn or Dn-1 SHALL be the Normalized Decoded Image Buffer Size (NDIBS).
Unless specified otherwise, the following table SHALL specify ICpy, IDec, and NDBIS.
Parameter | Initial value |
---|---|
Normalized image copy performance factor (ICpy) | 6 |
Image Decoding rate (IDec) | 1 × 220 pixels s-1 |
Normalized Decoded Image Buffer Size (NDIBS) | 0.9885 |
In the context of this section, a glyph is a tuple consisting of (i) one character and (ii) the computed values of the following style properties:
tts:color
tts:fontFamily
tts:fontSize
tts:fontStyle
tts:fontWeight
tts:textDecoration
tts:textOutline
While one-to-one mapping between characters and typographical glyphs is generally the rule in some scripts, e.g. latin script, it is the exception in others. For instance, in arabic script, a character can yield multiple glyphs depending on its position in a word. The Hypothetical Render Model always assumes a one-to-one mapping, but reduces the performance of the glyph buffer for scripts where one-to-one mapping is not the general rule (see GCpy below).
For each glyph associated with a character in a presented region of intermediate synchronic document En, the Presentation Compositor SHALL:
The duration DURT(En) for rendering the text of an intermediate synchronic document En in the Presentation Buffer is as follows:
DURT(En) = ∑gi ∈ Γr NRGA(gi) / Ren(gi) + ∑gj ∈ Γc NRGA(gj) / GCpy
where
The Normalized Rendered Glyph Area NRGA(gi) of a glyph gi SHALL be equal to:
NRGA(gi) = (fontSize of gi as percentage of root container height)2
NRGA(Gi) does not take into account decorations (e.g. underline), effects (e.g. outline) or actual typographical glyph aspect ratio. An implementation can determine an actual buffer size needs based on worst-case glyph size complexity.
The contents of the Glyph Buffer Gn SHALL be copied instantaneously to Glyph Buffer Gn-1 at the presentation time of intermediate synchronic document En.
It SHALL be an error for the sum of NRGA(gi) over all glyphs Glyph Buffer Gn to be larger than the Normalized Glyph Buffer Size (NGBS).
Unless specified otherwise, the following table specifies values of GCpy, Ren and NGBS.
Normalized glyph copy performance factor (GCpy) | |
---|---|
Script property (see Standard Annex #24 at [UNICODE]) for the character of gi | GCpy |
latin, greek, cyrillic, hebrew or common | 12 |
any other value | 3 |
Text rendering performance factor Ren(Gi) | |
Block property (see [UNICODE]) for the character of gi | Ren(Gi) |
CJK Unified Ideograph | 0.6 |
any other value | 1.2 |
Normalized Glyph Buffer Size (NGBS) | |
1 |
The choice of font by the presentation processor can increase rendering complexity. For instance, a cursive font can generally result in a given character yielding different typographical glyphs depending on context, even if latin script is used.
Computed Font Family | Code Points | Reference Font |
---|---|---|
monospaceSerif |
All code points specified in B. Recommended Character Sets | Courier New or Liberation Mono |
proportionalSansSerif |
All code points specified in B. Recommended Character Sets, excluding the code points defined for Hebrew and Arabic scripts. | Arial or Helvetica or Liberation Sans |
When authoring textual content, authors are encouraged to select from sets of characters based on the language indicated
using xml:lang
. The idea is to increase the confidence that the text will be presented correctly by
implementations targeting specific locales.
Specifically, for a given language, an author SHOULD choose characters from the set resulting from the union of the following sets:
Some of these sets overlap.
Table 1 captures the set of characters intended to be available to authors across all languages. The terms used in the table are defined in [UNICODE].
(Basic Latin) |
---|
U+0020 - U+007E |
(Latin-1 Supplement) |
U+00A0 - U+00FF |
(Latin Extended-A) |
U+0152 : LATIN CAPITAL LIGATURE OE |
U+0153 : LATIN SMALL LIGATURE OE |
U+0160 : LATIN CAPITAL LETTER S WITH CARON |
U+0161 : LATIN SMALL LETTER S WITH CARON |
U+0178 : LATIN CAPITAL LETTER Y WITH DIAERESIS |
U+017D : LATIN CAPITAL LETTER Z WITH CARON |
U+017E : LATIN SMALL LETTER Z WITH CARON |
(Latin Extended-B) |
U+0192 : LATIN SMALL LETTER F WITH HOOK |
(Spacing Modifier Letters) |
U+02DC : SMALL TILDE |
(Combining Diacritical Marks) |
U+0301 : COMBINING ACUTE ACCENT |
(General Punctuation) |
U+2010 - U+2015 : Dashes |
U+2016 - U+2027 : General punctuation |
U+2030 - U+203A : General punctuation |
(Currency symbols) |
U+20AC : EURO SIGN |
(Letterlike Symbols) |
U+2103 : DEGREES CELSIUS |
U+2109 : DEGREES FAHRENHEIT |
U+2120 : SERVICE MARK SIGN |
U+2122 : TRADE MARK SIGN |
(Number Forms) |
U+2153 - U+215F : Fractions |
(Mathematical Operators) |
U+2212 : MINUS SIGN |
U+221E : INFINITY |
(Box Drawing) |
U+2500 : BOX DRAWINGS LIGHT HORIZONTAL |
U+2502 : BOX DRAWINGS LIGHT VERTICAL |
U+250C : BOX DRAWINGS LIGHT DOWN AND RIGHT |
U+2510 : BOX DRAWINGS LIGHT DOWN AND LEFT |
U+2514 : BOX DRAWINGS LIGHT UP AND RIGHT |
U+2518 : BOX DRAWINGS LIGHT UP AND LEFT |
(Block Elements) |
U+2588 : FULL BLOCK |
(Geometric Shapes) |
U+25A1 : WHITE SQUARE |
(Musical Symbols) |
U+2669 : QUARTER NOTE |
U+266A : EIGHTH NOTE |
U+266B : BEAMED EIGHTH NOTES |
Table 2 specifies supplementary character set that have proven useful in captioning and subtitling applications for a number of selected languages. Table 2 is non-exhaustive, and will be extended as needs arise.
Primary language subtag | Characters |
---|---|
sq, fi, da, nl, en, de, is, no, sv, ca, fr, it | no supplementary characters |
lv, lt, et, tr, hr, cs, pl, sl, sk | (Latin Extended-A) U+0100 - U+017F |
ro | (Latin Extended-A) U+0100 - U+017F (Latin Extended-B) U+0218 - U+0219 U+021A - U+021B |
el | (Combining Diacritical Marks) U+0308 (Greek and Coptic) U+0386 - U+038A U+038C U+038E - U+03A1 U+03A3 - U+03CE |
pt, es | (Currency symbols) U+20A1 - U+20A2 U+20B3 |
ar | (Arabic) U+0609 U+060C - U+060D U+061B U+061E - U+061F U+0621 - U+063A U+0640 - U+0652 U+0660 - U+066D U+0670 |
he | (Hebrew) U+05B0 - U+05C3 U+05D0 - U+05EA U+05F3 - U+05F4 |
bs, bg, mk, ru, sr, uk | (Latin Extended-A) U+0100 - U+017F (Spacing Modifier Letters) U+02BC (Cyrillic) U+0400 - U+045F U+048A - U+04F9 (Letterlike Symbols) U+2116 |
kk | (Latin Extended-A) U+0100 - U+017F (Cyrillic) U+0400 - U+045F U+048A - U+04F9 |
hu | (Latin Extended-A) U+0100 - U+017F (General Punctuation) U+2052 (Miscellaneous Mathematical Symbols-A) U+27E8–U+27E9 |
Fig. 3
Illustration of the use of itts:forcedDisplay
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.
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.
In order to meet the guidelines in [WCAG20], the following considerations apply.
Guideline 1.1 of [WCAG20] recommends that an implementation provide Text Alternatives for all non-text content. In the context of this specification, this Text Alternative is intended primarily to support users of the subtitles who cannot see images. Since the images of an Image Profile Document Instance usually represent subtitle or caption text, the guidelines for authoring text equivalent strings given at Images of text of [HTML5] are appropriate.
Thus, for each subtitle in an Image Profile Document Instance, a text equivalent content in a Text Profile Document Instance SHOULD be written so that it conveys all essential content and fulfills the same function as the corresponding subtitle image. In the context of subtitling and captioning, this content will be (as a minimum) the verbatim equivalent of the image without précis or summarization. However, the author MAY include extra information to the text equivalent string in cases where styling is applied to the text image with a deliberate connotation, as a functional replacement for the applied style.
For instance, in subtitling and captioning, italics can be used to indicate an off screen speaker context (for example a voice from a radio). An author can choose to include this functional information in the text equivalent; for example, by including the word "Radio: " before the image equivalent text. Note that images in an Image Profile Document Instance that are intended for use as captions, i.e. intended for a hard of hearing audience, might already include this functional information in the rendered text.
Guideline 1.1 of [WCAG20] also recommends that accessible Text Alternatives must be "programmatically determinable." This means that the text must be able to be read and used by the assistive technologies (and the accessibility features in browsers) that people with disabilities use. It also means that the user must be able to use their assistive technology to find the alternative text (that they can use) when they land on the non-text content (that they can't use).
The following sample Document Instances conforms to the Text Profile and Image Profile, respectively. These samples are for illustration only, and are neither intended to capture current or future practice, nor exercise all normative prose contained in this specification.
<?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:aspectRatio="4 3" ttp:profile="http://www.w3.org/ns/ttml/profile/imsc1/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 sit amet.</p> </div> </body> </tt>
<?xml version="1.0" encoding="UTF-8"?> <tt xml:lang="fr" 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:smpte="http://www.smpte-ra.org/schemas/2052-1/2010/smpte-tt" xmlns:itts="http://www.w3.org/ns/ttml/profile/imsc1#styling" tts:extent="640px 480px" ttp:frameRate="25" ttp:profile="http://www.w3.org/ns/ttml/profile/imsc1/image"> <head> <layout> <region xml:id="region1" tts:origin="120px 410px" tts:extent="240px 40px" tts:showBackground="whenActive"/> <region xml:id="region2" tts:origin="120px 20px" tts:extent="240px 40px" tts:showBackground="whenActive"/> </layout> </head> <body> <div region="region1" begin="00:00:01:00" end="00:00:02:00" smpte:backgroundImage="1.png"/> <div region="region1" begin="00:00:03:20" end="00:00:04:12" smpte:backgroundImage="2.png"/> <div region="region2" itts:forcedDisplay="true" begin="00:00:03:20" end="00:00:04:12" smpte:backgroundImage="3.png"/> </body> </tt>
The following sections define extension designations, expressed as relative URIs (fragment identifiers) relative to the IMSC 1.0 Extension Namespace base URI.
A transformation processor supports the #progressivelyDecodable
feature if it recognizes and is
capable of transforming values of the ittp:progressivelyDecodable
.
A presentation processor supports the #progressivelyDecodable
feature if it implements presentation
semantic support for values of the ittp:progressivelyDecodable
attribute.
A transformation processor supports the #aspectRatio
feature if it recognizes and is capable of
transforming values of the ittp:aspectRatio
.
A presentation processor supports the #aspectRatio
feature if it implements presentation semantic
support for values of the ittp:aspectRatio
attribute.
A transformation processor supports the #forcedDisplay
feature if it recognizes and is capable of
transforming values of the itts:forcedDisplay
.
A presentation processor supports the #forcedDisplay
feature if it implements presentation semantic
support for values of the itts:forcedDisplay
attribute.
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.
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].
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].
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.
This section documents extensibility objectives for this specification.
This specification is intended to allow:
This specification is designed to be compatible with [ST2052-1], [EBU-TT-D] and [ttml10-sdp-us]. Specifically, it is possible to create a document that:
This specification is also intended to allow straightforward conversion of a document that conforms to the text or image profiles of [CFF] to the Text Profile or Image Profile, respectively.
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:
Note that the ttp:profile
attribute is not allowed by [EBU-TT-D], and the ebuttm:conformsToStandard
element is used instead to signal Text Profile, as specified in 6.9 Profile Signaling.
It is not possible for a document that conforms to [EBU-TT-D] to also conform to Image Profile, and vice-versa, notwithstanding the special case where the document also conforms to Text Profile as noted at 5. Profiles.
The following is an example of a document that conforms to both Text Profile and [EBU-TT-D]. Note the presence of two ebuttm:conformsToStandard
elements, one of which equals the Text Profile designator:
<?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:documentMetadata> <ebuttm:conformsToStandard>urn:ebu:tt:distribution:2014-01</ebuttm:conformsToStandard> <ebuttm:conformsToStandard>http://www.w3.org/ns/ttml/profile/imsc1/text</ebuttm:conformsToStandard> </ebuttm:documentMetadata> </metadata> <styling> <style xml:id="baseStyle" tts:color="#FFFFFF" tts:lineHeight="100%"/> <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"/> <region xml:id="area2" tts:origin="15% 70%" tts:extent="70% 20%" style="blackBackground" tts:displayAlign="center"/> </layout> </head> <body> <div style="baseStyle"> <p xml:id="s1" region="area1" style="startEnd" 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 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:
[ttml10-sdp-us] requires a specific value of the use
attribute of the ttp:profile
. As a result, Text Profile is
not signaled using the ttp:profile
attribute. Instead, as
specified in 5.4 Profile Resolution Semantics, the Text Profile can be
signaled by the Document Interchange Context and/or the Document
Processing Context. Alternatively, a processor can choose to process a
document as a Text Profile document if the ttp:profile
element signals [ttml10-sdp-us], since [ttml10-sdp-us] is feasibly
interoperable with Text Profile.
It is not possible for a document that conforms to [ttml10-sdp-us] to also conform to Image Profile, and vice-versa, notwithstanding the special case where the document also conforms to Text Profile as noted at 5. Profiles.
As an illustration, Example 3 at [ttml10-sdp-us] conforms to both Text Profile and [ttml10-sdp-us].
[ST2052-1] specifies the use of the DFXP Full Profile (see Appendix F.3 at [TTML1]) supplemented by a number of extensions, including http://www.smpte-ra.org/schemas/2052-1/2010/smpte-tt#image
.
This specification defines practical constraints on [ST2052-1], supplemented by a few extensions defined at F. Extensions. These constraints and extensions are intended to reflect industry practice.
As a result, particular care is required when creating a document intended to be processed according to both [ST2052-1] and Text Profile or Image Profile. In particular:
smpte:backgroundImage
attributes and any of p
, span
, or br
elements;http://www.smpte-ra.org/schemas/2052-1/2010/smpte-tt#image
extension;#aspectRatio
, #forcedDisplay
,
#linePadding
and #multiRowAlign
extensions that impact presentation; and"http://www.smpte-ra.org/schemas/2052-1/2010/profiles/smpte-tt-full"
is used as a value for ttp:profile
element or attribute (see Section 5.8 at [ST2052-1]), Text Profile or Image Profile is signaled by the Document Interchange Context and/or the Document Processing Context.The following is an example of a document that conforms to both Text Profile and [ST2052-1]:
<?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>
This specification was derived from the text and image profiles specified in Section 6 at [CFF], and is intended to be a superset in terms of capabilities. Additional processing is however generally necessary to convert a document from [CFF] to this specification. In particular:
progressivelyDecodable
attribute is different;forcedDisplayMode
attribute in [CFF] is renamed to
forcedDisplay
in this specification;ttp:frameRate
is not subject to the requirements specified at 6.11 Features and Extensions; andttp:profile
element, whereas this
specification recommends the use of the ttp:profile
attribute.