Dubbing and Audio description Profiles of TTML2

This specification defines DAPT, a TTML-based file format for the exchange of timed text content in dubbing and audio description workflows.

This document incorporates a registry section and defines registry tables, as defined in the [[w3c-process]] requirements for w3c registries. Updates to the document that only change registry tables can be made without meeting other requirements for Recommendation track updates, as set out in Updating Registry Tables; requirements for updating those registry tables are normatively specified within .

A list of the substantive changes applied since the initial Working Draft is found at substantive-changes-summary.txt.

The Working Group has identified the following at risk features:

At risk features may be be removed before advancement to Proposed Recommendation.

Scope

This specification defines a text-based profile of the Timed Text Markup Language version 2.0 [[TTML2]] intended to support dubbing and audio description workflows worldwide, to meet the requirements defined in [[?DAPT-REQS]], and to permit usage of visual presentation features within [[TTML2]] and its profiles, for example those in [[TTML-IMSC1.2]].

Introduction

Transcripts and Scripts

In general usage, one meaning of the word script is the written text of a film, television programme, play etc. A script can be either a record of the completed production, also known as a transcript, or as a plan for a yet to be created production. In this document, we use domain-specific terms, and define more specifically that:

The term DAPT script is used generically to refer to both transcripts and scripts, and is a point of conformance to the formal requirements of this specification. DAPT Scripts consist of timed text and associated metadata, such as the character speaking.

In dubbing workflows, a transcript is generated and translated to create a script. In audio description workflows, a transcript describes the video image, and is then used directly as a script for recording an audio equivalent.

DAPT is a TTML-based format for the exchange of transcripts and scripts (i.e. DAPT Scripts) among authoring, prompting and playback tools in the localization and audio description pipelines. A DAPT document is a serializable form of a DAPT Script designed to carry pertinent information for dubbing or audio description such as type of DAPT script, dialogue, descriptions, timing, metadata, original language transcribed text, translated text, language information, and audio mixing instructions, and to be extensible to allow user-defined annotations or additional future features.

This specification defines the data model for DAPT scripts and its representation as a [[TTML2]] document (see [[[#data-model]]]) with some constraints and restrictions (see [[[#profile-constraints]]]).

A DAPT script is expected to be used to make audio visual media accessible or localized for users who cannot understand it in its original form, and to be used as part of the solution for meeting user needs involving transcripts, including accessibility needs described in [[media-accessibility-reqs]], as well as supporting users who need dialogue translated into a different language via dubbing.

Every part of the DAPT script content is required to be marked up with some indication of what it represents in the related media, via the Represents property; likewise the DAPT Script as a whole is required to list all the types of content that it represents, for example if it represents audio content or visual content, and if visual, then if it represents text or non-text etc. A registry of hierarchical content descriptors is provided.

The authoring workflow for both dubbing and audio description involves similar stages, that share common requirements as described in [[DAPT-REQS]]. In both cases, the author reviews the content and writes down what is happening, either in the dialogue or in the video image, alongside the time when it happens. Further transformation processes can change the text to a different language and adjust the wording to fit precise timing constraints. Then there is a stage in which an audio rendering of the script is generated, for eventual mixing into the programme audio. That mixing can occur prior to distribution, or in the player directly.

Dubbing scripts

The dubbing process which consists in creating a dubbing script is a complex, multi-step process involving:

  • Transcribing and timing the dialogue in its own language from a completed programme to create a transcript;
  • Notating dialogue with character information and other annotations;
  • Generating localization notes to guide further adaptation;
  • Translating the dialogue to a target language script;
  • Adapting the translation to the dubbing; for example matching the actor’s lip movements in the case of dubs.

A dubbing script is a transcript or script (depending on workflow stage) used for recording translated dialogue to be mixed with the non-dialogue programme audio, to generate a localized version of the programme in a different language, known as a dubbed version, or dub for short.

Dubbing scripts can be useful as a starting point for creation of subtitles or closed captions in alternate languages. This specification is designed to facilitate the addition of, and conversion to, subtitle and caption documents in other profiles of TTML, such as [[TTML-IMSC1.2]], for example by permitting subtitle styling syntax to be carried in DAPT documents. Alternatively, styling can be applied to assist voice artists when recording scripted dialogue.

Audio Description scripts

Creating audio description content is also a multi-stage process. An audio description, also known as video description or in [[media-accessibility-reqs]] as described video, is an audio service to assist viewers who can not fully see a visual presentation to understand the content. It is the result of mixing the main programme audio with the audio rendition of each description, authored to be timed when it does not clash with dialogue, to deliver an audio description mixed audio track. Main programme audio refers to the audio associated with the programme prior to any further mixing. A description is a set of words that describes an aspect of the programme presentation, suitable for rendering into audio by means of vocalisation and recording or used as a text alternative source for text to speech translation, as defined in [[WCAG22]]. More information about what audio description is and how it works can be found at [[BBC-WHP051]].

Writing the audio description script typically involves:

  • watching the video content of the programme, or series of programmes,
  • identifying the key moments during which there is an opportunity to speak descriptions,
  • writing the description text to explain the important visible parts of the programme at that time,
  • creating an audio version of the descriptions, either by recording a human actor or using text to speech,
  • defining mixing instructions (applied using [[TTML2]] audio styling) for combining the audio with the programme audio.

The audio mixing can occur prior to distribution of the media, or in the client. If the audio description script is delivered to the player, the text can be used to provide an alternative rendering, for example on a Braille display, or using the user's configured screen reader.

Other uses

DAPT Scripts can be useful in other workflows and scenarios. For example, Original language transcripts could be used as:

  • the output format of a speech to text system, even if not intended for translation, or for the production of subtitles or captions;
  • a document known in the broadcasting industry as a "post production script", used primarily for preview, editorial review and sales purposes;

Both Original language transcripts and Translated transcripts could be used as:

  • an accessible transcript presented alongside audio or video in a web page or application; in this usage, the timings could be retained and used for synchronisation with, or navigation within, the media or discarded to present a plain text version of the entire timeline.

Example documents

Basic document structure

The top level structure of a document is as follows:

The structure is applicable to all types of DAPT scripts, dubbing or audio description.

        

The following examples correspond to the timed text transcripts and scripts produced at each stage of the workflow described in [[DAPT-REQS]].

The first example shows an early stage transcript in which timed opportunities for descriptions or transcriptions have been identified but no text has been written; the daptm:represents attribute present on the <body> element here is inherited by the <div> elements since they do not specify a different value:

        

The following examples will demonstrate different uses in dubbing and audio description workflows.

Audio Description Examples

When descriptions are added this becomes a Pre-Recording Script. Note that in this case, to reflect that most of the audio description content transcribes the video image where there is no inherent language, the Text Language Source, represented by the daptm:langSrc attribute, is set to the empty string at the top level of the document. It would be semantically equivalent to omit the attribute altogether, since the default value is the empty string:

        

Audio description content often includes text present in the visual image, for example if the image contains a written sign, a location, etc. The following example demonstrates such a case: Script Represents is extended to show that the script's contents represent textual visual information in addition to non-textual visual information. Here a more precise value of Represents is specified on the Script Event to reflect that the text is in fact a location, which is allowed because the more precise value is a sub-type of the new value in Script Represents. Finally, since the text has an inherent language, the Text Language Source is set to reflect that language.

        

After creating audio recordings, if not using text to speech, instructions for playback mixing can be inserted. For example, The gain of "received" audio can be changed before mixing in the audio played from inside the <span> element, smoothly animating the value on the way in and returning it on the way out:

        

At the document level, the daptm:scriptRepresents attribute indicates that the document represents both visual text and visual non-text content in the related media. It is possible that there are no Script Events that actually represent visual text, for example because there is no text in the video image.

In the above example, the <div> element's begin attribute defines the time that is the "syncbase" for its child, so the times on the <animate> and <span> elements are relative to 25s here. The first <animate> element drops the gain from 1 to 0.39 over 0.3s, freezing that value after it ends, and the second one raises it back in the final 0.3s of this description. Then the <span> element is timed to begin only after the first audio dip has finished.

If the audio recording is long and just a snippet needs to be played, that can be done using clipBegin and clipEnd. If we just want to play the part of the audio from file from 5s to 8s it would look like:

        

Or audio attributes can be added to trigger the text to be spoken:

        

It is also possible to embed the audio directly, so that a single document contains the script and recorded audio together:

        

Dubbing Examples

From the basic structure of , transcribing the audio produces an original language dubbing transcript, which can look as follows. No specific style or layout is defined, and here the focus is on the transcription of the dialogue. Characters are identified within the <metadata> element. Note that the language and the text language source are defined using xml:lang and daptm:langSrc attributes respectively, which have the same value because the transcript is not translated.

        

After translating the text, the document is modified. It includes translation text, and in this case the original text is preserved. The main document's default language is changed to indicate that the focus is on the translated language. The combination of the xml:lang and daptm:langSrc attributes are used to mark the text as being original or translated. In this case, they are present on both the <tt> and <p> elements to make the example easier to read, but it would also be possible to omit them in some cases, making use of the inheritance model:

        

The process of adaptation, before recording, could adjust the wording and/or add further timing to assist in the recording. The daptm:scriptType attribute is also modified, as in the following example:

        

Documentation Conventions

This document uses the following conventions:

DAPT Data Model and corresponding TTML syntax

This section specifies the data model for DAPT and its corresponding TTML syntax. In the model, there are objects which can have properties and be associated with other objects. In the TTML syntax, these objects and properties are expressed as elements and attributes, though it is not always the case that objects are expressed as elements and properties as attributes.

illustrates the DAPT data model, hyperlinking every object and property to its corresponding section in this document. Shared properties are shown in italics. All other conventions in the diagram are as per [[?uml]].

(Informative) Class diagram showing main entities in the DAPT data model.

DAPT Script

A DAPT Script is a transcript or script that corresponds to a document processed within an authoring workflow or processed by a client, and conforms to the constraints of this specification. It has properties and objects defined in the following sections: Script Represents, Script Type, Default Language, Text Language Source, Script Events and, for Dubbing Scripts, Characters.

A DAPT Document is a [[TTML2]] timed text content document instance representing a DAPT Script. A DAPT Document has the structure and constraints defined in this and the following sections.

A [[TTML2]] timed text content document instance has a root <tt> element in the TT namespace.

Script Represents

The Script Represents property is a mandatory property of a DAPT Script which indicates which components of the related media object the contents of the document represent. The contents of the document could be used as part of a mechanism to provide an accessible alternative for those components.

Script Events have a related property, Represents, and there are constraints about the permitted values of that property that are dependent on the values of Script Represents.

To represent this property, the daptm:scriptRepresents attribute MUST be present on the <tt> element, with a value conforming to the following syntax:

  daptm:scriptRepresents
  : <content-descriptor> ( <lwsp>+ <content-descriptor>)*

  <lwsp>                # as TTML2
            

Default Language

The Default Language is a mandatory property of a DAPT Script which represents the default language for the Text content of Script Events. This language may be one of the original languages or a Translation language. When it represents a Translation language, it may be the final language for which a dubbing or audio description script is being prepared, called the Target Recording Language or it may be an intermediate, or pivot, language used in the workflow.

The Default Language is represented in a DAPT Document by the following structure and constraints:

  • the xml:lang attribute MUST be present on the <tt> element and its value MUST NOT be empty.

All text content in a DAPT Script has a specified language. When multiple languages are used, the Default Language can correspond to the language of the majority of Script Events, to the language being spoken for the longest duration, or to a language arbitrarily chosen by the author.

Script Type

The Script Type property is a mandatory property of a DAPT Script which describes the type of documents used in Dubbing and Audio Description workflows, among the following: Original Language Transcript, Translated Transcript, Pre-recording Script, As-recorded Script.

To represent this property, the daptm:scriptType attribute MUST be present on the <tt> element:

  daptm:scriptType
    : "originalTranscript"
    | "translatedTranscript"
    | "preRecording"
    | "asRecorded"
            

The definitions of the types of documents and the corresponding daptm:scriptType attribute values are:

The following example is orphaned - move to the top of the section, before the enumerated script types?

<tt daptm:scriptType="originalTranscript">
...
</tt>
          

Script Events

A DAPT Script MAY contain zero or more Script Event objects, each corresponding to dialogue, on screen text, or descriptions for a given time interval.

If any Script Events are present, the DAPT Document MUST have one <body> element child of the <tt> element.

Characters

A DAPT Script MAY contain zero or more Character objects, each describing a character that can be referenced by a Script Event.

If any Character objects are present, the DAPT Document MUST have one <head> element child of the <tt> element, and that <head> element MUST have at least one <metadata> element child.

recommends that all the Character objects be located within a single <metadata> element parent, and in the case that there are more than one <metadata> element children of the <head> element, that the Character objects are located in the first such child.

Shared properties and Value Sets

Some of the properties in the DAPT data model are common within more than one object type, and carry the same semantic everywhere they occur. These shared properties are listed in this section.

Some of the value sets in DAPT are reused across more than one property, and have the same constraints everywhere they occur. These shared value sets are also listed in this section.

Would it be better to make a "Timed Object" class and subclass Script Event, Mixing Instruction and Audio Recording from it?

Timing Properties

The following timing properties define when the entities that contain them are active:

  • The Begin property defines when an object becomes active, and is relative to the active begin time of the parent object. DAPT Scripts begin at time zero on the media timeline.
  • The End property defines when an object stops being active, and is relative to the active begin time of the parent object.
  • The Duration property defines the maximum duration of an object.

    If both an End and a Duration property are present, the end time is the earlier of End and Begin + Duration, as defined by [[TTML2]].

If any of the timing properties is omitted, the following rules apply, paraphrasing the timing semantics defined in [[TTML2]]:
  • The default value for Begin is zero, i.e. the same as the begin time of the parent object.
  • The default value for End is indefinite, i.e. it resolves to the same as the end time of the parent timed object, if there is one.
  • The default value for Duration is indefinite, i.e. the end time resolves to the same as the end time of the parent object.

The end time of a DAPT Script is for practical purposes the end of the Related Media Object.

<content-descriptor> values

The values permitted in the Script Represents and Represents properties depend on the <content-descriptor> syntactic definition and its associated registry table.

<content-descriptor> has a value conforming to the following syntax:

    <content-descriptor>  # see registry table below
    : <descriptor-token> ( <descriptor-delimiter> <descriptor-token> )*
  
    <descriptor-token>
    : (descriptorTokenChar)+

    descriptorTokenChar  # xsd:NMtoken without the "."
    : NameStartChar | "-" | [0-9] | #xB7 | [#x0300-#x036F] | [#x203F-#x2040]

    <descriptor-delimiter>
    : "."  # FULL STOP U+002E
              

<content-descriptor> has values that are delimiter separated ordered lists of tokens.

A <content-descriptor> value B is a content descriptor sub-type of another <content-descriptor> value A if A's ordered list of descriptor-tokens is present at the beginning of B's ordered list of descriptor-tokens.

The permitted values for <content-descriptor> are either those listed in the following registry table, or can be user-defined.

Valid user-defined values MUST begin with x- or be sub-types of values in the content-descriptor registry table, where the first additional <descriptor-token> component begins with x-.

Registry table for the <content-descriptor> component whose Registry Definition is at
<content-descriptor> Status Description Example usage
audio Provisional Indicates that the DAPT content represents any part of the audio programme. Dubbing, translation and hard of hearing subtitles and captions, pre- and post- production scripts
audio.dialogue Provisional Indicates that the DAPT content represents verbal communication in the audio programme, for example, a spoken conversation. Dubbing, translation and hard of hearing subtitles and captions, pre- and post- production scripts
audio.nonDialogueSounds Provisional Indicates that the DAPT content represents a part of the audio programme corresponding to sounds that are not verbal communication, for example, significant sounds, such as a door being slammed in anger. Translation and hard of hearing subtitles and captions, pre- and post- production scripts
visual Provisional Indicates that the DAPT content represents any part of the visual image of the programme. Audio Description
visual.dialogue Provisional Indicates that the DAPT content represents verbal communication, within the visual image of the programme, for example, a signed conversation. Dubbing or Audio Description, translation and hard of hearing subtitles and captions, pre- and post- production scripts
visual.nonText Provisional Indicates that the DAPT content represents non-textual parts of the visual image of the programme, for example, a significant object in the scene. Audio Description
visual.text Provisional Indicates that the DAPT content represents textual content in the visual image of the programme, for example, a signpost, a clock, a newspaper headline, an instant message etc. Audio Description
visual.text.title Provisional A sub-type of visual.text where the text is the title of the related media. Audio Description
visual.text.credit Provisional A sub-type of visual.text where the text is a credit, e.g. the name of an actor. Audio Description
visual.text.location Provisional A sub-type of visual.text where the text indicates the location where the content is occurring. Audio Description
Unique identifiers

Some entities in the data model include unique identifiers. A Unique Identifier has the following requirements:

  • it is unique within the DAPT Script, i.e. the value of a Unique Identifier can only be used one time within the document, regardless of which specific kind of identifier it is.

    If a Character Identifier has the value "abc" and a Script Event Identifier in the same document has the same value, that is an error.

  • its value has to conform to the requirements of Name as defined by [[XML]]

    It cannot begin with a digit, a combining diacritical mark (an accent), or any of the following characters:

        .
        -
        ·  // #xB7
        ‿  // #x203F
        ⁀  // #x2040

    but those characters can be used elsewhere.

A Unique Identifier for an entity is expressed in a DAPT Document by an xml:id attribute on the corresponding element.

The formal requirements for the semantics and processing of xml:id are defined in [[xml-id]].

Character

This section is mainly relevant to Dubbing workflows.

A character in the programme can be described using a Character object which has the following properties:

A Character is represented in a DAPT Document by the following structure and constraints:

Script Event

A Script Event object represents dialogue, on screen text or audio descriptions to be spoken and has the following properties:

A Script Event is represented in a DAPT Document at the path /tt/head/body//div, with the following structure and constraints:

Text

The Text object contains text content typically in a single language. This language may be the Original language or a Translation language.

Text is defined as Original if it is any of:

  1. the same language as the dialogue that it represents in the original programme audio;
  2. a transcription of text visible in the programme video, in the same language as that text;
  3. an untranslated representative of non-dialogue sound;
  4. an untranslated description of the scene in the programme video.

Text is defined as Translation if it is a representation of an Original Text object in a different language.

Text can be identified as being Original or Translation by inspecting its language and its Text Language Source together, according to the semantics defined in Text Language Source.

The source language of Translation Text objects and, where applicable, Original Text objects is indicated using the Text Language Source property.

A Text object may be styled.

Zero or more Mixing Instruction objects used to modify the programme audio during the Text MAY be present.

A Text object is represented in a DAPT Document by a <p> element at the path /tt/head/body//div/p, with the following constraints:

Text Language Source

The Text Language Source property is an annotation indicating the source language of a Text object, if applicable, or that the source content had no inherent language:

Text Language Source is an inheritable property.

The Text Language Source property is represented in a DAPT Document by a daptm:langSrc attribute with the following syntax, constraints and semantics:

daptm:langSrc
: <empty-string> | <language-identifier>

<empty-string>
: ""                    # default

<language-identifier>   # valid BCP-47 language tag
            

An example of the usage of Text Language Source in a document is present in the Text section.

On Screen

The On Screen property is an annotation indicating the position in the scene relating to the subject of a Script Event, for example of the character speaking:

If omitted, the default value is "ON".

The On Screen property is represented in a DAPT Document by a daptm:onScreen attribute on the <div> element, with the following constraints:

Represents

The Represents property indicates which component of the related media object the Script Event represents.

The Represents property is represented in a DAPT Document by a daptm:represents attribute, whose value MUST be a single <content-descriptor>.

The Represents property is inheritable. If it is absent from an element then its computed value is the computed value of the Represents property on its parent element, or, if it has no parent element, it is the empty string. If it is present on an element then its computed value is the value specified.

Since there is no empty <content-descriptor>, this implies that an empty computed Represents property can never be valid; one way to construct a valid DAPT Document is to specify a Represents property on the DAPT Script so that it is inherited by all descendants that do not have a Represents property.

It is an error for a Represents property value not to be a content descriptor sub-type of at least one of the values in the Script Represents property.

Script Event Description

The Script Event Description object is an annotation providing a human-readable description of some aspect of the content of a Script Event. Script Event Descriptions can themselves be classified with a Description Type.

A Script Event Description object is represented in a DAPT Document by a <ttm:desc> element at the <div> element level.

Zero or more <ttm:desc> elements MAY be present.

Script Event Descriptions SHOULD NOT be empty.

The Script Event Description does not need to be unique, i.e. it does not need to have a different value for each Script Event. For example a particular value could be re-used to identify in a human-readable way one or more Script Events that are intended to be processed together, e.g. in a batch recording.

The <ttm:desc> element MAY specify its language using the xml:lang attribute.

          

Each Script Event Description can be annotated with one or more Description Types to categorise further the purpose of the Script Event Description.

Each Description Type is represented in a DAPT Document by a daptm:descType attribute on the <ttm:desc> element.

The <ttm:desc> element MAY have zero or one daptm:descType attributes. The daptm:descType attribute is defined below.

daptm:descType : string
            

The permitted values for daptm:descType are either those listed in the following registry table, or can be user-defined:

Registry table for the daptm:descType attribute whose Registry Definition is at
daptm:descType Status Description Notes
pronunciationNote Provisional Notes for how to pronounce the content.
scene Provisional Contains a scene identifier
plotSignificance Provisional Defines a measure of how significant the content is to the plot. Contents are undefined and may be low, medium or high, or a numerical scale.

Valid user-defined values MUST begin with x-.

          

Amongst a sibling group of <ttm:desc> elements there are no constraints on the uniqueness of the daptm:descType attribute, however it may be useful as a distinguisher as shown in the following example.

          

Audio

An Audio object is used to specify an audio rendering of a Text. The audio rendering can either be a recorded audio resource, as an Audio Recording object, or a directive to synthesize a rendering of the text via a text to speech engine, which is a Synthesized Audio object. Both are types of Audio object.

It is an error for an Audio not to be in the same language as its Text.

A presentation processor that supports audio plays or inserts the Audio at the specified time on the related media object's timeline.

The Audio object is "abstract": it only can exist as one of its sub-types, Audio Recording or Synthesized Audio.

Audio Recording

An Audio Recording is an Audio object that references an audio resource. It has the following properties:

  • One or more alternative Sources, each of which is either 1) a link to an external audio resource or 2) an embedded audio recording;
  • For each Source, one mandatory Type that specifies the type ([[MIME-TYPES]]) of the audio resource, for example audio/basic;
  • An optional Begin property and an optional End and an optional Duration property that together define the Audio Recording's time interval in the programme timeline, in relation to the parent element's time interval;
  • An optional In Time and an optional Out Time property that together define a temporal subsection of the audio resource;

    The default In Time is the beginning of the audio resource.

    The default Out Time is the end of the audio resource.

    If the temporal subsection of the audio resource is longer than the duration of the Audio Recording's time interval, then playback MUST be truncated to end when the Audio Recording's time interval ends.

    If the temporal subsection of the audio resource is shorter than the duration of the Audio Recording's time interval, then the audio resource plays once.

  • Zero or more Mixing Instructions that modify the playback characteristics of the Audio Recording.

When a list of Sources is provided, a presentation processor MUST play no more than one of the Sources for each Audio Recording.

This feature may contribute to browser fingerprintability. Implementations can use the Type, and if present, any relevant additional formatting information, to decide which Source to play. For example, given two Sources, one being a WAV file, and the other an MP3, an implementation that can play only one of those formats, or is configured to have a preference for one or the other, would select the playable or preferred version.

An Audio Recording is represented in a DAPT Document by an <audio> element child of a <p> or <span> element corresponding to the Text to which it applies. The following constraints apply to the <audio> element:

  • The begin, end and dur attributes represent respectively the Begin, End and Duration properties;
  • The clipBegin and clipEnd attributes represent respectively the In Time and Out Time properties, as illustrated by ;
  • For each Source, if it is a link to an external audio resource, the Source and Type properties are represented by exactly one of:
    1. A src attribute that is not a fragment identifier, and a type attribute respectively;

      This mechanism cannot be used if there is more than one Source.

                        
    2. A <source> child element with a src attribute that is not a fragment identifier and a type attribute respectively;
                        

    A src attribute that is not a fragment identifier is a URL that references an external audio resource, i.e. one that is not embedded within the DAPT Script. No validation that the resource can be located is specified in DAPT.

    Do we need both mechanisms here? It's not clear what semantic advantage the child <source> element carries in this case. Consider marking use of that child <source> element as "at risk"?

  • If the Source is an embedded audio resource, the Source and Type properties are represented together by exactly one of:
    1. A src attribute that is a fragment identifier that references either an <audio> element or a <data> element, where the referenced element is a child of /tt/head/resources and specifies a type attribute and the xml:id attribute used to reference it;

      This mechanism cannot be used if there is more than one Source.

                        
    2. A <source> child element with a src attribute that is a fragment identifier that references either an <audio> element or a <data> element, where the referenced element is a child of /tt/head/resources and specifies a type attribute and the xml:id attribute used to reference it;
                        
    3. A <source> child element with a <data> element child that specifies a type attribute and contains the audio recording data.
                        

    In each of the cases above the type attribute represents the Type property.

    A src attribute that is a fragment identifier is a pointer to an audio resource that is embedded within the DAPT Script

    If <data> elements are defined, each one MUST contain either #PCDATA or <chunk> child elements and MUST NOT contain any <source> child elements.

    <data> and <source> elements MAY contain a format attribute whose value implementations MAY use in addition to the type attribute value when selecting an appropriate audio resource.

    Do we need all 3 mechanisms here? Do we need any? There may be a use case for embedding audio data, since it makes the single document a portable (though large) entity that can be exchanged and transferred with no concern for missing resources, and no need for e.g. manifest files. If we do not need to support referenced embedded audio then only the last option is needed, and is probably the simplest to implement. One case for referenced embedded audio is that it more easily allows reuse of the same audio in different document locations, though that seems like an unlikely requirement in this use case. Another is that it means that all embedded audio is in an easily located part of the document in tt/head/resources, which potentially could carry an implementation benefit? Consider marking the embedded data features as "at risk"?

  • Mixing Instructions MAY be applied as specified in their TTML representation;
  • The computed value of the xml:lang attribute MUST be identical to the computed value of the xml:lang attribute of the parent element and any child <source> elements and any referenced embedded <data> elements.

Synthesized Audio

A Synthesized Audio is an Audio object that represents a machine generated audio rendering of the parent Text content. It has the following properties:

  • A mandatory Rate that specifies the rate of speech, being normal, fast or slow;
  • An optional Pitch that allows adjustment of the pitch of the speech.

A Synthesized Audio is represented in a DAPT Document by the application of a tta:speak style attribute on the element representing the Text object to be spoken, where the computed value of the attribute is normal, fast or slow. This attribute also represents the Rate Property.

The tta:pitch style attribute represents the Pitch property.

The TTML representation of a Synthesized Audio is illustrated by .

A tta:pitch attribute on an element whose computed value of the tta:rate attribute is none has no effect. Such an element is not considered to have an associated Synthesized Audio.

The semantics of the Synthesized Audio vocabulary of DAPT are derived from equivalent features in [[SSML]] as indicated in [[TTML2]]. This version of the specification does not specify how other features of [[SSML]] can be either generated from DAPT or embedded into DAPT documents. The option to extend [[SSML]] support in future versions of this specification is deliberately left open.

Mixing Instruction

A Mixing Instruction object is a static or animated adjustment of the audio relating to the containing object. It has the following properties:

A Mixing Instruction is represented by applying audio style attributes to the element that corresponds to the relevant object, either inline, by reference to a <style> element, or in a child (inline) <animate> element:

If the Mixing Instruction is animated, that is, if the adjustment properties change during the containing object's active time interval, then it is represented by one or more child <animate> elements. This representation is required if more than one Gain or Pan property is needed, or if any timing properties are needed.

The <animate> element(s) MUST be children of the element corresponding to the containing object, and have the following constraints:

The TTML representation of animated Mixing Instructions is illustrated by .

See also .

Constraints

Document Encoding

A DAPT Document MUST be serialised as a well-formed XML 1.0 [[!xml]] document encoded using the UTF-8 character encoding as specified in [[UNICODE]].

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

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

The predefined entities are (including the leading ampersand and trailing semicolon):

  • &amp; for an ampersand & (unicode code point U+0026)
  • &apos; for an apostrophe ' (unicode code point U+0027)
  • &gt; for a greater than sign > (unicode code point U+003E)
  • &lt; for a less than sign < (unicode code point U+003C)
  • &quot; for a quote symbol " (unicode code point U+0022)

A DAPT Document can also be used as an in-memory model for processing, in which case the serialisation requirements do not apply.

Processing of unrecognised or foreign elements and attributes

The requirements in this section are intended to facilitate forwards and backwards compatibility, specifically to permit:

A DAPT document that conforms to more than one version of the specification could specify conformance to multiple DAPT content profiles.

Unrecognised vocabulary

Unrecognised vocabulary is the set of elements and attributes that are not associated with features that the processor supports.

A transformation processor MUST prune unrecognised vocabulary that is neither an attribute nor a descendant of a <metadata> element.

A transformation processor SHOULD preserve unrecognised vocabulary that is either an attribute or a descendant of a <metadata> element.

See also which prohibits the signalling of profile conformance to profiles that the transformation processor does not support.

After attribute value computation, a presentation processor SHOULD ignore unrecognised vocabulary.

The above constraint is specified as being after attribute value computation because it is possible that an implementation recognises and supports attributes present only on particular elements, for example those corresponding to the DAPT data model. As described in it is important that processor implementations do not ignore such attributes when present on other elements.

Special considerations for foreign vocabulary

Foreign vocabulary is the subset of unrecognised vocabulary that consists of those elements and attributes whose namespace is not one of the namespaces listed in and those attributes whose namespace has no value that are not otherwise defined in DAPT or in [[TTML2]].

A DAPT Document MAY contain foreign vocabulary that is neither specifically permitted nor forbidden by the profiles signalled in ttp:contentProfiles.

For validation purposes it is good practice to define and use a specification for all foreign vocabulary used within a DAPT Document, for example a content profile.

Proprietary Metadata and Foreign Vocabulary

Many dubbing and audio description workflows permit annotation of Script Events or documents with proprietary metadata. Metadata vocabulary defined in this specification or in [[TTML2]] MAY be included. Foreign vocabulary MAY also be included, either as attributes of <metadata> elements or as descendant elements of <metadata> elements.

It is possible to add information such as the title of the programme using [[TTML2]] constructs.

            

It is possible to add workflow-specific information using a foreign namespace. In the following example, a fictitious namespace vendorm from an "example vendor" is used to provide document-level information not defined by DAPT.

            
It is strongly recommended not to place data whose semantics depend on the contents of the document within <metadata> elements.

Such data can be invalidated by transformation processors that modify the contents of the document but preserve metadata while being unaware of their semantics.

Defining and using foreign vocabulary that is not metadata

If foreign vocabulary is included in locations other than <metadata> elements it will be pruned by transformation processors that do not support features associated with that vocabulary, as required in .

A mechanism is provided to prevent such pruning, and to define semantics for such foreign vocabulary, allowing it to be located outside a <metadata> element without being pruned, and to indicate content and processor conformance:

  1. Define a profile including a feature definition for that semantic and vocabulary, with a profile designator.
  2. Signal document conformance to that profile using the

This allows processors that support the feature to process the vocabulary in whatever way is appropriate, to avoid pruning it, and allows processors that do not support the feature to take appropriate action, for example warning users that some functionality may be lost.

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 Audio Style tta http://www.w3.org/ns/ttml#audio [[TTML2]]
TT Metadata ttm http://www.w3.org/ns/ttml#metadata [[TTML2]]
TT Feature none http://www.w3.org/ns/ttml/feature/ [[TTML2]]
DAPT Metadata daptm http://www.w3.org/ns/ttml/profile/dapt#metadata This specification
DAPT Extension none http://www.w3.org/ns/ttml/profile/dapt/extension/ This specification
EBU-TT Metadata ebuttm urn:ebu:tt:metadata [[EBU-TT-3390]]

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

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

Related Media Object

Within DAPT, the common language terms audio and video are used in the context of a programme. The audio and video are each a part of what is defined in [[TTML2]] as the Related Media Object that provides the media timeline and is the source of the main programme audio, and any visual timing references needed when adjusting timings relevant to the video image, such as for lip synchronization.

A DAPT document can identify the programme acting as the Related Media Object using metadata. For example, it is possible to use the <ebuttm:sourceMediaIdentifier> element defined in [[EBU-TT-3390]].


        

Synchronization

If the DAPT Document is intended to be used as the basis for producing an [[TTML-IMSC1.2]] document, the synchronization provisions of [[TTML-IMSC1.2]] apply in relation to the video.

Timed content within the DAPT Document is intended to be rendered starting and ending on specific audio samples.

In the context of this specification rendering could be visual presentation of text, for example to show an actor what words to speak, or could be audible playback of an audio resource, or could be physical or haptic, such as a Braille display.

In constrained applications, such as real-time audio mixing and playback, if accurate synchronization to the audio sample cannot be achieved in the rendered output, the combined effects of authoring and playback inaccuracies in timed changes in presentation SHOULD meet the synchronization requirements of [[EBU-R37]], i.e. audio changes are not to precede image changes by more than 40ms, and are not to follow them by more than 60ms.

Likewise, authoring applications SHOULD allow authors to meet the requirements of [[EBU-R37]] by defining times with an accuracy such that changes to audio are less than 15ms after any associated change in the video image, and less than 5ms before any associated change in the video image.

Taken together, the above two constraints on overall presentation and on DAPT documents intended for real-time playback mean that content processors SHOULD complete audio presentation changes no more than 35ms before the time specified in the DAPT document and no more than 45ms after the time specified.

Profile Signaling

This section defines how a TTML Document Instance signals that it is a DAPT Document and how it signals any processing requirements that apply. See also , which defines how to establish that a DAPT Document conforms to this specification.

Profile Designators

This profile is associated with the following profile designators:

Profile Name Profile type Profile Designator
DAPT 1.0 Content Profile content profile http://www.w3.org/ns/ttml/profile/dapt1.0/content
DAPT 1.0 Processor Profile processor profile http://www.w3.org/ns/ttml/profile/dapt1.0/processor

ttp:contentProfiles

The ttp:contentProfiles attribute is used to declare the [[TTML2]] profiles to which the document conforms.

DAPT Documents MUST specify a ttp:contentProfiles attribute on the <tt> element including at least one value equal to a content profile designator specified at . Other values MAY be present to declare conformance to other profiles of [[TTML2]], and MAY include profile designators in proprietary namespaces.

It is an error for a DAPT Document to signal conformance to a content profile to which it does not conform.

Transformation processors MUST NOT include values within the ttp:contentProfiles attribute associated with profiles that they (the processors) do not support; by definition they cannot verify conformance of the content to those profiles.

ttp:profile

The ttp:profile attribute is a mechanism within [[?TTML1]] for declaring the processing requirements for a Document Instance. It has effectively been superceded in [[TTML2]] by ttp:processorProfiles.

DAPT Documents MUST NOT specify a ttp:profile attribute on the <tt> element.

ttp:processorProfiles

The ttp:processorProfiles attribute is used to declare the processing requirements for a Document Instance.

DAPT Documents MAY specify a ttp:processorProfiles attribute on the <tt> element. If present, the ttp:processorProfiles attribute MUST include at least one value equal to a processor profile designator specified at . Other values MAY be present to declare additional processing constraints, and MAY include profile designators in proprietary namespaces.

The ttp:processorProfiles attribute can be used to signal that features and extensions in additional profiles need to be supported to process the Document Instance successfully. For example, a local workflow might introduce particular metadata requirements, and signal that the processor needs to support those by using an additional processor profile designator.

If the content author does not need to signal that additional processor requirements than those defined by DAPT are needed to process the DAPT document then the ttp:processorProfiles attribute is not expected to be present.

Other TTML2 Profile Vocabulary

[[TTML2]] specifies a vocabulary and semantics that can be used to define the set of features that a document instance can make use of, or that a processor needs to support, known as a Profile.

Except where specified, it is not a requirement of DAPT that this profile vocabulary is supported by processors; nevertheless such support is permitted.

The majority of this profile vocabulary is used to indicate how a processor can compute the set of features that it needs to support in order to process the Document Instance successfully. The vocabulary is itself defined in terms of TTML2 features. Those profile-related features are listed within as being optional. They MAY be implemented in processors and their associated vocabulary MAY be present in DAPT Documents.

Unless processor support for these features and vocabulary has been arranged (using an out-of-band protocol), the vocabulary is not expected to be present.

The additional profile-related vocabulary for which processor support is not required (but is permitted) in DAPT is:

Timing constraints

Within a DAPT Script, the following constraints apply in relation to time attributes and time expressions:

ttp:timeBase

The only permitted ttp:timeBase attribute value is media, since prohibits all timeBase features other than #timeBase-media.

This means that the beginning of the document timeline, i.e. time "zero", is the beginning of the Related Media Object.

timeContainer

The only permitted value of the timeContainer attribute is the default value, par.

Documents SHOULD omit the timeContainer attribute on all elements.

Documents MUST NOT set the timeContainer attribute to any value other than par on any element.

This means that the begin attribute value for every timed element is relative to the computed begin time of its parent element, or for the <body> element, to time zero.

ttp:frameRate

If the document contains any time expression that uses the f metric, or any time expression that contains a frames component, the ttp:frameRate attribute MUST be present on the <tt> element.

ttp:tickRate

If the document contains any time expression that uses the t metric, the ttp:tickRate attribute MUST be present on the <tt> element.

Time expressions

All time expressions within a document SHOULD use the same syntax, either clock-time or offset-time as defined in [[TTML2]], with DAPT constraints applied.

A DAPT clock-time has one of the forms:

  • hh:mm:ss.sss
  • hh:mm:ss

where hh is hours, mm is minutes, ss is seconds, and ss.sss is seconds with a decimal fraction of seconds (any precision).

Clock time expressions that use frame components, which look similar to "time code", are prohibited due to the semantic confusion that has been observed elsewhere when they are used, particularly with non-integer frame rates, "drop modes" and sub-frame rates.

An offset-time has one of the forms:

  • nn metric
  • nn.nn metric

where nn is an integer, nn.nn is a number with a decimal fraction (any precision), and metric is one of:

  • h for hours,
  • m for minutes,
  • s for seconds,
  • ms for milliseconds,
  • f for frames, and
  • t for ticks.

When mapping a media time expression M to a frame F of the video, e.g. for the purpose of accurately timing lip synchronization, the content processor SHOULD map M to the frame F with the presentation time that is the closest to, but not less, than M.

A media time expression of 00:00:05.1 corresponds to frame ceiling( 5.1 × ( 1000 / 1001 × 30) ) = 153 of a video that has a frame rate of 1000 / 1001 × 30 ≈ 29.97.

Layout and styles

This specification does not put additional constraints on the layout and rendering features defined in [[!TTML-IMSC1.2]].

Layout of the paragraphs may rely on the default TTML region (i.e. if no <layout> element is used in the <head> element) or may be explicit by the use of the region attribute, to refer to a <region> element present at /tt/head/layout/region.

Style references or inline styles MAY be used, using any combination of style attributes, <style> elements and inline style attributes as defined in [TTML2] or [TTML-IMSC1.2].

Bidirectional text

The following metadata elements are permitted in DAPT and specified in [[TTML2]] as containing #PCDATA, i.e. text data only with no element content. Where bidirectional text is required within the character content within such an element, Unicode control characters can be used to define the base direction within arbitrary ranges of text.

More guidance about usage of this mechanism is available at .

The <p> and <span> content elements permit the direction of text to be specified using the tts:direction and tts:unicodeBidi attributes. Document authors should use this more robust mechanism rather than using Unicode control characters.

The following example taken from [[TTML2]] demonstrates the syntax for bidirectional text markup within the <p> and <span> elements.


          

An example rendering of the above fragment is shown below.

Example rendition of direction example showing from left to right The title of the book is W3C and then from right to left the applicable Arabic text

Mapping from TTML to the DAPT Data Model

defines how objects and properties of the DAPT data model are represented in [[TTML2]], i.e. in a DAPT Document. However, a DAPT data model instance can be represented by multiple [[TTML2]] document instances.

For example, does not mandate that a <div> element representing a Script Event be a direct child of the <body> element. That <div> element could be nested in another <div> element. Therefore, it is possible to serialize the objects and properties of a DAPT Script into various DAPT Documents. This section defines how to interoperably and unambiguously reconstruct a DAPT model instance from a DAPT Document.

DAPT does not define a complete serialization of the DAPT data model for extensibility reasons, to allow future versions to do so if needed. Additionally, a DAPT Document can contain elements or attributes that are not mentioned in the representations of DAPT objects or properties. This could be because it has been generated by a processor conformant to some future version of DAPT, or through a generic [[TTML2]] process, or because it uses optional features, for example to add styling or layout. This section defines how to process those elements or attributes.

It is also possible to process DAPT Documents using generic [[TTML2]] processors, which do not necessarily map the documents to the DAPT data model. For example a generic TTML2 presentation processor could render an audio mix based on a DAPT document without needing to model Script Events per se. In that case, this section can be ignored.

Early identification of non-conformant documents

Normative provisions relating to this section are defined in [[TTML2]].

Since it is a requirement of DAPT that DAPT Documents include a ttp:contentProfiles attribute on the root element, and that the attribute includes a DAPT content profile designator, as specified at , it follows that any TTML document that does not include such an attribute, or does not include such a profile designator, can be considered not to be a DAPT Document; therefore a processor requiring strict adherence to DAPT could stop processing such a document.

Not supporting features excluded by the content profile

A processor that takes as its input a DAPT document that contains vocabulary relating to features that it does support, but where support for those features is excluded from the content profiles to which the document claims conformance, SHOULD NOT implement those features in the context of that document.

Handling <div> and <p> elements

[[TTML2]] allows <div> elements to contain any combination of <div> elements and <p> elements. The DAPT data model describes how each Script Event is represented by a <div> element that contains zero or more <p> elements. It also permits other intermediate <div> elements in the path between the <body> element and those Script Event <div> elements. In addition, attributes not corresponding to properties in the DAPT data model are permitted.

This gives rise to possibilities such as:

The following processing rules resolve these cases.

Rules for identifying Script Events:

  1. A <div> element that has no <div> element children and includes the TTML representations of all the mandatory properties of a Script Event MUST be mapped to a Script Event, such as having a valid xml:id representing the Script Event Identifier, even if it also contains additional unrecognised vocabulary;
  2. A <div> element that contains any <div> element children MUST NOT be mapped to a Script Event; the processor instead MUST iterate through those <div> element children (recursively, in a depth-first traversal) and consider if each one meets the requirements of a Script Event;
  3. Any remaining unmapped <div> elements MUST NOT be mapped to a Script Event.

Rules for identifying Text objects:

  1. A <p> element that is a child of a <div> element that maps to a Script Event MUST be mapped to a Text object.
  2. A <p> element that is not a child of a <div> element that maps to a Script Event MUST NOT be mapped to a Text object.

Future versions of DAPT could include features that use these structural possibilities differently, and therefore define other processing rules that are mutually exclusive with the rules defined here.

Using computed attribute values

Some attributes have semantics for computing their value that depend on the computed value of the attribute on some other element. For example if the xml:lang attribute is not specified on an element then its computed value is the computed value of the same attribute on the element's parent.

Or, for another example, the computed times of an element in a DAPT document are relative to the begin time of the element's parent. If a <div> element specifies a begin attribute, then the computed times of its child <div> elements are relative to that parent <div> element's begin time, and so on down the hierarchy. It is important to include those "intermediate" <div> elements' times in the computation even if the processing target is an instance of the DAPT data model in which they have no direct equivalent; otherwise the Script Event Begin and End times would be wrong.

Considering this situation more generally, it is possible that, within a DAPT document, there can be TTML elements that do not directly correspond to objects in the DAPT data model, and those elements can specify attributes that affect the computation of attribute values that apply to elements that do correspond to objects in the DAPT data model.

The semantics defined by [[TTML2]] or, for vocabulary defined herein, this specification, take precedence in this scenario. Implementations MUST compute attribute values based on the contents of the document instance before applying those computed values to DAPT data model objects. For example a processor that supports TTML2 styling features would need to implement the TTML2 semantics for inheritance and computing relative values of attributes like tts:fontSize.

If an implementation internally creates DAPT data model objects, such as the Script Events shown in the example above, it is important for interoperability that they use the computed values.

Considerations for transformation and validation processors

Retaining unrecognised vocabulary

As per , implementers of DAPT processors are encouraged to maintain unrecognised vocabulary within <metadata> elements in DAPT Documents. In practice it is possible that an implementation which both inputs DAPT documents and outputs DAPT documents might modify the input document structure and contents, and while doing so, effectively prune those entities with unrecognised vocabulary from the output document.

Validation warnings and errors

Normative provisions relating to this section are defined in [[TTML2]].

[[TTML2]] defines a validation processor, a class of implementation whose purpose is to assess a document instance and decide if it is valid or not. Typically this would be used within a processing workflow to check that documents are acceptable for onward usage. A real world example would likely not return simply "good" or "bad", but also output informational, warning and error messages describing unusual, unexpected or problematic contents in the input document.

When implementing a validation processor for a DAPT document, strict [[TTML2]] validation processing rules can be applied. Doing this involves checking for the presence and semantic validity of syntax and content associated with required or optional features defined in the profile, and checking for the absence of syntax associated with prohibited features.

The [[TTML2]] mechanism for dealing with vocabulary in unrecognised namespaces is to prune it prior to validation. This approach can be used; additionally it could be reasonable for an implementation to report as information those attributes and elements that have been pruned.

The term "vocabulary" here refers to XML elements and attributes.

Validation warnings could be issued when unsupported or deprecated vocabulary in recognised namespaces is encountered after pruning, or when supported vocabulary contains unexpected but not invalid content, but in these scenarios errors are not expected.

Validation errors are expected when prohibited vocabulary is present, or when semantically invalid content within permitted vocabulary is encountered.

[[TTML2]] specifies a formal language for expressing document and processor requirements, within the Profiling sub-system. The normative requirements of this specification are defined using the conformance terminology described above, and are also defined using this TTML2 profile mechanism. Where TTML2 vocabulary is referenced, the syntactic and semantic requirements relating to that vocabulary as defined in [[TTML2]] apply.

Whilst there is no requirement for a DAPT processor to implement the TTML2 profile processing semantics in general, implementers can use the TTML2 profiles defined in as a means of verifying that their implementations meet the normative requirements of DAPT, for example as a checklist.

Conversely, a general purpose [[TTML2]] processor that does support the TTML2 profile processing semantics can use the TTML2 profiles defined in directly to determine if it is capable of processing a DAPT document.

Conformance of DAPT Documents

Conformant DAPT Documents are [[TTML2]] timed text content document instances that conform to the normative provisions of this specification. Those provisions are expressed using the profile vocabulary of [[TTML2]] in the content profile defined in .

DAPT Documents remain subject to the content conformance requirements specified at Section 3.1 of [[TTML2]]. In particular, a DAPT Document can contain foreign vocabulary, since such elements and attributes are pruned by the algorithm at Section 4 of [[TTML2]] prior to evaluating content conformance.

Conformance of DAPT Processors

Conformant DAPT Processors are [[TTML2]] content processors that conform to the normative provisions of this specification. Those provisions are expressed using the profile vocabulary of [[TTML2]] in the processor profile defined in .

Privacy Considerations

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

Personal Information

DAPT documents typically contain the names of characters or people who feature within the associated media, either fictional or real. In general this information would be present within the media itself or be public via other routes. If there is sensitivity associated with their being known to people with access to the DAPT documents in which their identity is contained, then such access should be managed with appropriate confidentiality. For example those documents could be available within a closed authoring environment and edited to remove the sensitive information prior to distribution to a wider audience. If this scenario arises, information security good practices within the closed environment should be applied, such as encryption of the document "at rest" and when being moved, access controlled by authentication platforms, etc.

Audio format preference

This feature may contribute to browser fingerprintability. DAPT documents can reference a set of alternate external audio resources for the same fragment of audio, where the processor is expected to select one of the alternatives based on features such as format support. If this pattern is used, it is possible that the processor's choice of audio resource, being exposed to the origin, reveals information about that processor, such as its preferred audio format.

Security Considerations

The security considerations of [[ttml2]] apply.

Timecode-related metadata

DAPT Documents express time as media time, which assumes that there is a reference start time (zero) on a media timeline, and a fixed playrate. An alternative scheme that is used in some other script formats is to synchronise media components using timecode, that match time stamps that are applied, for example to each frame of video.

Workflows that create DAPT documents from such timecode-based non-DAPT script formats need to map those timecode values onto the DAPT document's timeline.

If this mapping is not correct, presentation of the DAPT Document will not be synchronised with the related media object. A reference timecode that matches a known point on the DAPT document timeline can be used to achieve correct synchronisation, for example the timecode corresponding to the start of the programme, which should match DAPT time zero.

In this scenario, if such a reference point is not known, but timecodes corresponding to Script Events are known, it is still possible to construct a DAPT Document, albeit one whose synchronisation with the related media has not yet been resolved.

The optional DAPT Origin Timecode and Start of Programme Timecode properties can be used to identify when there is a possible synchronisation error, and to resynchronise the document when all the required information is known.

These properties are provided as metadata only and are not intended to be used to perform direct synchronisation offsets during presentation. In particular, when the related media object uses timecode, the presence of the timecode properties does not mean that the player needs to relate these timecode values with any timecode value embedded in the related media resource.

If either a DAPT Origin Timecode object or a Start of Programme Timecode object is present, the DAPT Document MUST have one <head> element child of the <tt> element, and that <head> element MUST have at least one <metadata> element child.

DAPT Origin Timecode

The optional DAPT Origin Timecode allows a timecode value to be declared that corresponds to the zero point of the DAPT document timeline, that is, the time of a hypothetical Script Event whose Begin is zero seconds.

The properties can be used to provide timecodes from the related media object or from any other script format used to produce the DAPT document, and are informational. However, when they are both provided and differ, it is an indication that the DAPT document is not synchronized with the related media object and that processing of the script event begins is needed. To achieve synchronization, the following needs to be done:

  1. The difference DAPT Origin Timecode minus the Start of Programme Timecode is computed as "delta". It may be positive or negative.
  2. Each Script Event's Begin and End value X shall be changed to X + delta.
  3. The DAPT Origin Timecode shall be removed or changed to the Start of Programme timecode value so that if this algorithm is run again it will result in delta that is zero.

A DAPT Script MAY contain zero or one DAPT Origin Timecode objects.

The DAPT Origin Timecode object is represented in a DAPT Document by a <daptm:daptOriginTimecode> element present at the path /tt/head/metadata/daptm:daptOriginTimecode, with the following constraints:

See also . No mechanism is defined here for declaring a different frame rate for the DAPT Origin Timecode than is used for other frame-based time expressions.

If the related media object contains a timecode for the video frame synchronized to the origin of the DAPT document timeline, the DAPT origin timecode is equal that timecode.

...
<head>
<metadata>
<daptm:daptOriginTimecode>10:01:20:12</daptm:daptOriginTimecode>
</metadata>
</head>
<body>
<div xml:id="se1" begin="0s" end="1.8s">
<!-- This script event was generated from a source whose begin timecode was 10:01:20:12 -->
</div>
</body>
...
      
Start of Programme Timecode

The optional Start of Programme Timecode allows a timecode value to be declared that corresponds to the beginning of the related media object's programme content.

In combination with DAPT Origin Timecode, the value of Start of Programme Timecode can be used to infer whether or not the media times in the DAPT Script are likely to be correctly synchronised with the Related Media Object.

If both DAPT Origin Timecode and Start of Programme Timecode are present, but their values are different, it is likely that the media times are not synchronised with the Related Media Object, since this implies that the equivalent time code to zero seconds in media time is not the start of the programme, which is the requirement for correctly synchronised media time.

A DAPT Script MAY contain zero or one Start of Programme Timecode objects.

The Start of Programme Timecode object is represented in a DAPT Document by a <ebuttm:documentStartOfProgramme> element present at the path /tt/head/metadata/ebuttm:documentStartOfProgramme, with the syntactic constraints as defined in [[EBU-TT-3390]].

...
<head>
<metadata>
<daptm:daptOriginTimecode>10:01:20:12</daptm:daptOriginTimecode>
<ebuttm:documentStartOfProgramme>10:00:00:00<ebuttm:documentStartOfProgramme>
<!-- It is likely that this document is 1 minute, 20 seconds and 12 frames too early,
  compared to the related media -->
</metadata>
</head>
<body>
<div xml:id="se1" begin="0s" end="1.8s">
<!-- This script event was generated from a source whose begin timecode was 10:01:20:12 -->
</div>
</body>
...
      

If the times of the Script Events are adjusted to bring the media time into synchronisation with the Related Media Object, as noted in DAPT Origin Timecode, the Start of Programme Timecode SHOULD NOT be changed, since it is an invariant feature of the Related Media Object, and does not describe the times in the DAPT Document.

Audio Mixing

Applying the Mixing Instructions can be implemented using [[webaudio]]. shows the flow of programme audio, and how, when audio-generating elements are active, the pan and gain (if set) on the Script Event are applied, then the output is passed to the Text, which mixes in the audio from any active Audio Recording, itself subject to its own Mixing Instructions, then the result has the Text's Mixing Instructions applied, prior to the output being mixed on to the master bus.

Example simple audio routing between objects

This example is shown as [[webaudio]] nodes in .

Web audio nodes representing the audio processing needed.

The above examples are simplified in at least two ways:

Profiles

This section defines a [[TTML2]] content profile and a processor profile by expressing dispositions against a set of features and extensions. The DAPT extensions are defined in .

The Profile Semantics specified in [[TTML2]] apply.

A TTML Profile specification is a document that lists all the features of TTML that are required / optional / prohibited within “document instances” (files) and “processors” (things that process the files), and any extensions or constraints.

A timed text content document instance that conforms to the content profile defined herein:

A timed text content document instance, by definition, satisfies the requirements of Section 3.1 at [[TTML2]], and hence a timed text content document instance that conforms to a profile defined herein is also a conforming TTML2 Document Instance.

A Presentation processor that conforms to the processor profile defined in this specification:

A Transformation processor that conforms to the processor profile defined in this specification:

The dispositions required, permitted, optional and prohibited as used in this specification map to the [[TTML2]] <ttp:feature> and <ttp:extension> elements' value attribute values as follows:

DAPT disposition <ttp:feature> or <ttp:extension> element value attribute value in
content profile processor profile
required required required
permitted optional required
optional optional optional
prohibited prohibited optional

The use of the terms presentation processor and transformation processor within this document does not imply conformance per se to any of the Standard Profiles defined in [[TTML2]]. In other words, it is not considered an error for a presentation processor or transformation processor to conform to the profile defined in this document without also conforming to the TTML2 Presentation Profile or the TTML2 Transformation Profile.

The use of the [[TTML2]] profiling sub-system to describe DAPT conformance within this specification is not intended imply that DAPT processors are required to support any features of that system other than those for which support is explicitly required by DAPT.

This document does not specify presentation processor or transformation processor behavior when processing or transforming a non-conformant timed text content 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.

Disposition of Features and Extensions

The features and extensions listed in this section express the minimal requirements for DAPT Documents, Presentation Processors, and Transformation Processors. DAPT Documents MAY additionally conform to other profiles, and include syntax not prohibited by the DAPT content profile. Presentation Processors and Transformation Processors MAY support additional syntax and semantics relating to other profiles.

For example, a DAPT Script can include syntax permitted by the IMSC ([[TTML-IMSC1.2]]) profiles of [[TTML2]] to enhance the presentation of scripts to actors recording audio, or to add styling important for later usage in subtitle or caption creation.

Editorial task: go through this list of features and check the disposition of each. There should be no prohibited features that are permitted in IMSC.

Feature or Extension Disposition Additional provision
Relative to the TT Feature namespace
#animate-fill permitted
#animate-minimal permitted
#animation-out-of-line prohibited See .
#audio permitted
#audio-description permitted
#audio-speech permitted
#bidi permitted
#bidi-version-2 permitted
#chunk permitted
#clockMode prohibited
#clockMode-gps prohibited
#clockMode-local prohibited
#clockMode-utc prohibited
#content permitted
#contentProfiles permitted See and .
#contentProfiles-combined optional See .
#core permitted
#data permitted
#direction permitted
#dropMode prohibited
#dropMode-dropNTSC prohibited
#dropMode-dropPAL prohibited
#dropMode-nonDrop prohibited
#embedded-audio permitted
#embedded-data permitted
#frameRate permitted See [[[#ttp-framerate]]].
#frameRateMultiplier permitted
#gain permitted
#markerMode prohibited
#markerMode-continuous prohibited
#markerMode-discontinuous prohibited
#metadata permitted
#metadata-item permitted
#metadata-version-2 permitted
#pan permitted
#permitFeatureNarrowing optional See .
#permitFeatureWidening optional See .
#pitch permitted
#presentation-audio permitted
#processorProfiles optional See .
#processorProfiles-combined optional See .
#profile partially permitted See .
#profile-full-version-2 partially permitted See .
#profile-version-2 partially permitted See .
#resources permitted
#set permitted
#set-fill permitted
#set-multiple-styles permitted
#source permitted
#speak permitted
#speech permitted
#structure required
#styling permitted
#styling-chained permitted
#styling-inheritance-content permitted
#styling-inline permitted
#styling-referential permitted
#subFrameRate prohibited
#tickRate permitted See [[[#ttp-tickrate]]].
#time-clock permitted
#time-clock-with-frames prohibited
#time-offset-with-frames permitted See [[[#ttp-framerate]]].
#time-offset-with-ticks permitted See [[[#ttp-tickrate]]].
#time-offset permitted
#time-wall-clock prohibited
#timeBase-clock prohibited
#timeBase-media required

See [[[#ttp-timebase]]].

NOTE: [[TTML1]] specifies that the default timebase is "media" if the ttp:timeBase attribute is not specified on the <tt> element.

#timeBase-smpte prohibited
#timeContainer prohibited See [[[#timecontainer]]].
#timing permitted See [[[#time-expressions]]].
#transformation permitted See constraints at #profile.
#unicodeBidi permitted
#unicodeBidi-isolate permitted
#unicodeBidi-version-2 permitted
#xlink permitted
Relative to the DAPT Extension namespace
#agent permitted This is the profile expression of .
#contentProfiles-root required This is the profile expression of .
#daptOriginTimecode permitted This is the profile expression of .
#descType permitted This is the profile expression of daptm:descType.
#onScreen permitted This is the profile expression of .
#profile-root prohibited This is the profile expression of the prohibition of the ttp:profile attribute on the <tt> element as specified in .
#represents required This is the profile expression of Represents as applied to Script Event.
#scriptEventGrouping permitted This is the profile expression of the permission to nest <div> elements described in .
#scriptEventMapping optional This is the profile expression of .
#scriptRepresents required This is the profile expression of Script Represents.
#scriptType-root required This is the profile expression of .
#serialization required This is the profile expression of .
#source-data prohibited This is the profile expression of the prohibition of <source> child elements of <data> elements as specified in .
#textLanguageSource permitted This is the profile expression of as required at .
#xmlId-div required This is the profile expression of .
#xmlLang-audio-nonMatching prohibited This is the profile expression of the prohibition of the xml:lang attribute on the <audio> element having a different computed value to the parent element and descendant or referenced <source> and <data> elements, as specified in .
#xmlLang-root required This is the profile expression of .

DAPT Content Profile

The DAPT Content Profile expresses the conformance requirements of DAPT Scripts using the profile mechanism of [[TTML2]]. It can be used by a validating processor that supports the DAPT Processor Profile to validate a DAPT Document.

There is no requirement to include the DAPT Content Profile within a DAPT Document.


      

DAPT Processor Profile

The DAPT Processor Profile expresses the processing requirements of DAPT Scripts using the profile mechanism of [[TTML2]]. A processor that supports the required features and extensions of the DAPT Processor Profile can, minimally, process all permitted features within a DAPT Document.

There is no requirement to include the DAPT Processor Profile within a DAPT Document.


    

Extensions

General

The following sections define extension designations, expressed as relative URIs (fragment identifiers) relative to the DAPT Extension Namespace base URI. These extension designations are used in to describe the normative provisions of DAPT that are not expressed by [[TTML2]] profile features.

#agent

A transformation processor supports the #agent extension if it recognizes and is capable of transforming values of the following elements and attributes on the <ttm:agent> element:

and if it recognizes and is capable of transforming each of the following value combinations:

A presentation processor supports the #agent extension if it implements presentation semantic support of the above listed elements, attributes and value combinations.

#contentProfiles-root

A transformation processor supports the #contentProfiles-root extension if it recognizes and is capable of transforming values of the ttp:contentProfiles attribute on the <tt> element.

A presentation processor supports the #contentProfiles-root extension if it implements presentation semantic support of the ttp:contentProfiles attribute on the <tt> element.

#daptOriginTimecode

A transformation processor supports the #daptOriginTimecode extension if it recognizes and is capable of transforming values of the <daptm:daptOriginTimecode> element.

No presentation processor behaviour is defined for the #daptOriginTimecode extension.

#descType

A transformation processor supports the #descType extension if it recognizes and is capable of transforming values of the daptm:descType attribute on the <ttm:desc> element.

A presentation processor supports the #descType extension if it implements presentation semantic support of the daptm:descType attribute on the <ttm:desc> element.

#onScreen

A transformation processor supports the #onScreen extension if it recognizes and is capable of transforming values of the daptm:onScreen attribute on the <div> element.

A presentation processor supports the #onScreen extension if it implements presentation semantic support of the daptm:onScreen attribute on the <div> element.

#profile-root

A transformation processor supports the #profile-root extension if it recognizes and is capable of transforming values of the ttp:profile attribute on the <tt> element.

A presentation processor supports the #profile-root extension if it implements presentation semantic support of the ttp:profile attribute on the <tt> element.

#represents

A transformation processor supports the #represents extension if it recognizes and is capable of transforming values of the daptm:represents attribute.

A presentation processor supports the #represents extension if it implements presentation semantic support of the daptm:represents attribute.

An example of a transformation processor that supports this extension is a validating processor that reports an error if the extension is permitted by a content profile but the timed text content document instance claiming conformance to that profile has a <div> element with a daptm:represents attribute whose value is not conformant with the requirements defined herein.

#scriptEventGrouping

A transformation processor supports the #scriptEventGrouping extension if it recognises and is capable of transforming <div> elements that contain <div> elements.

Support for the #scriptEventGrouping extension does not imply support for the #scriptEventMapping extension.

A presentation processor supports the #scriptEventGrouping extension if it implements presentation semantic support for <div> elements that contain <div> elements.

#scriptEventMapping

A transformation processor supports the #scriptEventMapping extension if, when mapping a DAPT document into an internal representation of the DAPT data model, it implements the processing requirements specified at .

No support for the #scriptEventMapping extension is required for presentation processors because there are no presentation semantics that either require, or depend upon, mapping a DAPT document into an internal representation of the DAPT data model. A presentation processor that does perform such a mapping can also be considered to be a transformation processor for the purpose of this extension.

#scriptRepresents

A transformation processor supports the #scriptRepresents extension if it recognizes and is capable of transforming values of the daptm:scriptRepresents attribute on the <tt> element.

A presentation processor supports the #scriptRepresents extension if it implements presentation semantic support of the daptm:scriptRepresents attribute on the <tt> element.

An example of a transformation processor that supports this extension is a validating processor that reports an error if the extension is required by a content profile but the timed text content document instance claiming conformance to that profile either does not have a daptm:scriptRepresents attribute on the <tt> element or has one whose value is not conformant with the requirements defined herein.

#scriptType-root

A transformation processor supports the #scriptType-root extension if it recognizes and is capable of transforming values of the daptm:scriptType attribute on the <tt> element.

A presentation processor supports the #scriptType-root extension if it implements presentation semantic support of the daptm:scriptType attribute on the <tt> element.

An example of a transformation processor that supports this extension is a validating processor that provides appropriate feedback, for example warnings, when the SHOULD requirements defined in for a DAPT Document's daptm:scriptType are not met, and that reports an error if the extension is required by a content profile but the timed text content document instance claiming conformance to that profile either does not have a daptm:scriptType attribute on the <tt> element or has one whose value is not defined herein.

#serialization

A serialized document that is valid with respect to the #serialization extension is an XML 1.0 [[xml]] document encoded using UTF-8 character encoding as specified in [[UNICODE]], that contains no entity declarations and no entity references other than to predefined entities.

A transformation processor or a presentation processor supports the #serialization extension if it can read a serialized document as defined above.

A transformation processor that writes documents supports the #serialization extension if it can write a serialized document as defined above.

#source-data

A transformation processor supports the #source-data extension if it recognizes and is capable of transforming values of the <source> element child of a <data> element.

A presentation processor supports the #source-data extension if it implements presentation semantic support of the <source> element child of a <data> element.

#textLanguageSource

A transformation processor supports the #textLanguageSource extension if it recognizes and is capable of transforming values of the daptm:langSrc attribute.

A presentation processor supports the #textLanguageSource extension if it implements presentation semantic support of the daptm:langSrc attribute.

#xmlId-div

A transformation processor supports the #xmlId-div extension if it recognizes and is capable of transforming values of the xml:id attribute on the <div> element.

A presentation processor supports the #xmlId-div extension if it implements presentation semantic support of the xml:id attribute on the <div> element.

#xmlLang-audio-nonMatching

A transformation processor supports the #xmlLang-audio-nonMatching extension if it recognizes and is capable of transforming values of the xml:lang attribute on the <audio> element that differ from the computed value of the same attribute of its parent element or any of its descendant or referenced <source> or <data> elements, known as non-matching values.

A presentation processor supports the #xmlLang-audio-nonMatching extension if it implements presentation semantic support of such non-matching xml:lang attribute values.

#xmlLang-root

A transformation processor supports the #xmlLang-root extension if it recognizes and is capable of transforming values of the xml:lang attribute on the <tt> element and the additional semantics specified in .

A presentation processor supports the #xmlLang-root extension if it implements presentation semantic support of the xml:lang attribute on the <tt> element and the additional semantics specified in .

Registry Section

Registry Definition

This section specifies the registry definition, consisting of the custodianship, change process and the core requirements of the registry tables defined in this document.

Custodianship

The custodian of this w3c registry is the Timed Text Working Group. If the TTWG is unable to fulfil the role of custodian, for example if it has been closed, the custodian in lieu is the W3C Team.

Change Process

Requesting a change

Changes to this W3C Registry MUST be requested (the change request) using any one of the following options:

The change request MUST include enough information for the custodian to be able to identify all of:

The proposer of the change MAY open a pull request (or equivalent) on the version control system, with that pull request containing the proposed changes. If a pull request is opened then a corresponding issue MUST also be opened and the pull request MUST be linked to that issue.

Change request assessment process

The process for assessing a change request depends on the custodian.

Custodian is TTWG

If the custodian is the TTWG:

  • If the change proposer did not open a pull request on the version control system, then assessment is paused until a TTWG member has opened such a pull request, which MUST represent the requested changes and MUST be linked to a related issue.
  • The TTWG follows its Decision Policy to review the proposal in the pull request.
  • At the end of the Decision Review Period if a TTWG Chair declares that there is consensus to approve, the change request is approved.
  • In the absence of consensus to approve the expectation is that a discussion will happen, to include the change requester. The result of this discussion can be any one of:
    1. the change request is abandoned;
    2. the change request is modified for another review;
    3. if the discussion resolves the objections, and a TTWG Chair declares consensus to approve, the change request can be approved.

An approved change request is enacted by merging its related pull request into the version control system and publishing the updated version of this document.

Custodian is the W3C Team

If the custodian is the W3C Team, the Team MUST seek wide review of the change request and offer a review period of at least 4 weeks, before assessing from the responses received if there is consensus amongst the respondents.

The Team MAY require a pull request on the version control system to be opened as the basis of the review.

If there is such consensus, the Team MUST make the proposed changes.

Registry Table Constraints

This section defines constraints on the registry tables defined in this document. Each registry table consists of a set of registry entries. Each registry table has an associated registry table definition in , which lists the fields present in each registry entry.

Registry Entries

Each registry entry has a status, a unique key, and if appropriate, other fields, for example any notes, a description, or a reference to some other defining entity.

The registry table definition MUST define the fields and the key to be used in each registry entry.

Status

The registry entry status field reflects the maturity of that entry. Permitted values are:

            Provisional
            Final
            Deprecated
          

No other values are permitted.

Provisional

Registry entries with a status of Provisional MAY be changed or deleted. Their status may be changed to Final or Deprecated.

Registry entry keys in Provisional entries that were later deleted MAY be reused.

Newly created registry entries SHOULD have status Provisional.

Final

Registry entries with a status of Final MUST NOT be deleted or changed. Their status MAY be changed to Deprecated.

Registry entry keys in Final entries MUST NOT be reused.

Newly created registry entries MAY have status Final.

Deprecated

Registry entries with a status of Deprecated MUST NOT be deleted or changed. Their status MAY be changed to Final unless that would result in a duplicate key within the set of entries whose status is either Provisional or Final.

Registry entry keys in Deprecated entries that were previously Provisional and never Final MAY be reused.

Registry entry keys in Deprecated entries that were previously Final MUST NOT be reused.

Newly created registry entries MUST NOT have status Deprecated.

Registry Table Definitions

This section defines registry tables and locates their registry entries.

daptm:descType registry table definition

The registry table for daptm:descType defines a set of values that can be used in the daptm:descType attribute.

The key is the "daptm:descType" field. The "description" field describes the intended purpose of each value.

The registry entries for this registry table are located in .

The key values for this registry table MUST NOT begin with x- which is reserved for user extensions.

<content-descriptor> registry table definition

The registry table for <content-descriptor> defines a set of values that can be used in the daptm:represents attribute.

The key is the "<content-descriptor>" field. The "Description" field describes the type of media content represented by each value. The "Example usage" field describes the type of script in which the content type described are commonly found.

The registry entries for this registry table are located in .

The key values for this registry table MUST NOT begin with x- which is reserved for user extensions.

Acknowledgments

The editors would like to thank XXX for their contributions to this specification.