TTML profiles and features

TTML is large, and most players support only part of it. A profile names the part a document uses, or the part a player must support. Each feature of the language has a designator, a URI such as http://www.w3.org/ns/ttml/feature/#textOutline, and a profile is a list of features, each required, optional or prohibited.

Designators

Kind	Base URI
Profile	`http://www.w3.org/ns/ttml/profile/`
Feature	`http://www.w3.org/ns/ttml/feature/`
Extension	`http://www.w3.org/ns/ttml/extension/`
Resource (TTML2)	`http://www.w3.org/ns/ttml/resource/`

Profile	Designator, after the profile base	Defined by
DFXP Transformation	`dfxp-transformation`	TTML1: what a program that converts TTML must understand
DFXP Presentation	`dfxp-presentation`	TTML1: what a player must support
DFXP Full	`dfxp-full`	TTML1: every feature
SDP US	`sdp-us`	TTML1: Simple Delivery Profile for US closed captions
TTML2 Transformation	`ttml2-transformation`	TTML2
TTML2 Presentation	`ttml2-presentation`	TTML2
TTML2 Full	`ttml2-full`	TTML2
IMSC 1.2 Text	`imsc1.2/text`	W3C IMSC 1.2
IMSC Image	`imsc1/image`	W3C IMSC

Profile elements

Element	Attributes	Content	Meaning
`ttp:profile`	`use` (a designator), `xml:id`; in TTML2 also `type` (`processor`, the default, or `content`), `designator`, `combine` (`replace`, the default, `leastRestrictive`, `mostRestrictive`), `xml:base`	metadata, then `ttp:features` and `ttp:extensions`, or (TTML2) `ttp:profile`	A profile, in `head` or as the root of a separate profile document. `use` starts from a known profile, which the children then change.
`ttp:features`	`xml:base` (default the feature base URI), `xml:id`	metadata, `ttp:feature`	A group of features.
`ttp:feature`	`value`, `xml:id`; in TTML2 also `extends` or `restricts`	a designator, relative to the base	One feature and whether it is needed.
`ttp:extensions`	`xml:base` (default the extension base URI), `xml:id`	metadata, `ttp:extension`	A group of extensions.
`ttp:extension`	as `ttp:feature`	a designator	One extension: a feature defined outside TTML.

`value`	Meaning
`required`	Must be supported. The default in a processor profile.
`optional`	May be supported. The default in a content profile.
`prohibited`	TTML2: must not be used.
`use`	TTML1’s word for required; deprecated in TTML2 and read as `required`.

Profile attributes

Written on tt. TTML1 has only ttp:profile; the rest are TTML2.

Attribute	Values	Default	Meaning
`ttp:profile`	one designator	none	The profile a processor needs. TTML2 prefers the next two.
`ttp:contentProfiles`	designators, or `all(…)`	none	The profiles the document conforms to.
`ttp:processorProfiles`	designators, or `all(…)` or `any(…)`	none	The profiles a processor must support: all of them, or any one.
`ttp:contentProfileCombination`	`leastRestrictive`, `mostRestrictive`, `replace`, `ignore`	`ignore`	How several content profiles combine: where they disagree about a feature, the least or most restrictive value wins, or a later one replaces an earlier one.
`ttp:processorProfileCombination`	as above	`ignore`	How several processor profiles combine.
`ttp:inferProcessorProfileMethod`	`loose`, `strict`	`loose`	How strictly a processor profile is worked out from the content profile when none is given.
`ttp:inferProcessorProfileSource`	`combined`, `first`	`first`	Whether to infer it from all content profiles or the first.
`ttp:permitFeatureNarrowing`	`true`, `false`	`false`	Whether a feature or extension may be satisfied by a more narrowly defined one, related to it through `extends` or `restricts`.
`ttp:permitFeatureWidening`	`true`, `false`	`false`	Whether a feature or extension may be satisfied by a more widely defined one, where its definition has a `restricts` attribute.
`ttp:validation`	`required`, `optional`, `prohibited`	`optional`	Whether the document must be validated before use.
`ttp:validationAction`	`abort`, `warn`, `ignore`	follows `ttp:validation`: `abort`, `warn`, `ignore`	What to do when validation fails.

TTML1 features

Each is written after # on the feature base URI. TTML2 keeps these and adds a feature for each new element, attribute and value.

Area	Features
Groups	`#core`, `#content`, `#structure`, `#styling`, `#layout`, `#timing`, `#animation`, `#metadata`, `#profile`, `#presentation`, `#transformation`
Structure	`#nested-div`, `#nested-span`, `#lineBreak-uax14`, `#bidi`
Styling methods	`#styling-chained`, `#styling-inheritance-content`, `#styling-inheritance-region`, `#styling-inline`, `#styling-nested`, `#styling-referential`
Styles	`#backgroundColor` (`-block`, `-inline`, `-region`), `#color`, `#direction`, `#display` (`-block`, `-inline`, `-region`), `#displayAlign`, `#extent` (`-region`, `-root`), `#fontFamily` (`-generic`, `-non-generic`), `#fontSize` (`-anamorphic`, `-isomorphic`), `#fontStyle` (`-italic`, `-oblique`), `#fontWeight` (`-bold`), `#lineHeight`, `#opacity`, `#origin`, `#overflow` (`-visible`), `#padding` (`-1` to `-4`), `#showBackground`, `#textAlign` (`-absolute`, `-relative`), `#textDecoration` (`-over`, `-through`, `-under`), `#textOutline` (`-blurred`, `-unblurred`), `#unicodeBidi`, `#visibility` (`-block`, `-inline`, `-region`), `#wrapOption`, `#writingMode` (`-horizontal`, `-horizontal-lr`, `-horizontal-rl`, `-vertical`), `#zIndex`
Lengths	`#length`, `#length-cell`, `#length-em`, `#length-integer`, `#length-negative`, `#length-percentage`, `#length-pixel`, `#length-positive`, `#length-real`
Parameters	`#cellResolution`, `#clockMode` (`-gps`, `-local`, `-utc`), `#dropMode` (`-dropNTSC`, `-dropPAL`, `-nonDrop`), `#frameRate`, `#frameRateMultiplier`, `#markerMode` (`-continuous`, `-discontinuous`), `#pixelAspectRatio`, `#subFrameRate`, `#tickRate`, `#timeBase-clock`, `#timeBase-media`, `#timeBase-smpte`
Timing	`#timeContainer`, `#time-clock`, `#time-clock-with-frames`, `#time-offset`, `#time-offset-with-frames`, `#time-offset-with-ticks`

IMSC

IMSC (Internet Media Subtitles and Captions) is the W3C’s TTML profile for online video, used in DASH, HLS and CMAF streams. Its Text profile carries styled text and its Image profile carries pictures of subtitles. It limits a document to at most four regions shown at once, which must not overlap or leave the root container, and adds a few attributes of its own:

Attribute	On	Values	Meaning
`itts:forcedDisplay`	body, div, p, region, span	`true`, `false` (default)	Shown even when the player shows forced subtitles only. Inherited.
`itts:fillLineGap`	p	`true`, `false` (default)	Fill the background between lines. Inherited.
`ittp:activeArea`	tt	four percentages: left, top, width, height	The part of the root container the subtitles use.
`ittp:aspectRatio`	tt	`numerator denominator`	Deprecated; replaced by `ttp:displayAspectRatio`.
`ittp:progressivelyDecodable`	tt	`true`, `false` (default)	Deprecated: the document can be shown before it has all arrived.
`ittm:altText`	in `metadata`	text	Deprecated; replaced by the `altText` metadata item.

The namespaces are http://www.w3.org/ns/ttml/profile/imsc1#styling (itts:), …#parameter (ittp:) and …#metadata (ittm:).

Worked example

<tt xmlns="http://www.w3.org/ns/ttml" xmlns:ttp="http://www.w3.org/ns/ttml#parameter"
    xml:lang="en"
    ttp:contentProfiles="http://www.w3.org/ns/ttml/profile/imsc1.2/text">
  <head>
    <ttp:profile use="ttml2-presentation">
      <ttp:features>
        <ttp:feature value="required">#textShadow</ttp:feature>
        <ttp:feature value="optional">#animation</ttp:feature>
      </ttp:features>
    </ttp:profile>
  </head>
  …

The document says it conforms to IMSC 1.2 Text, and that a player needs the TTML2 presentation profile with text shadows required and animation optional.

Not confirmed

TTML2’s own feature and extension lists, which name a feature for every TTML2 addition, are not reproduced here. Drafts of TTML2 had a ttp:version parameter, but it is not among the parameters of the published Recommendation as read for this page. The exact working of loose and strict inference, and of the ignore combination method, is defined in tables of the specification not covered here.

.TTML File Format – Profiles and features