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HTTP/2 200 date: Mon, 06 Oct 2025 20:58:08 GMT content-type: text/html; charset=utf-8 content-encoding: gzip content-location: Overview.html last-modified: Tue, 05 Sep 2023 12:33:37 GMT cache-control: max-age=21600 expires: Tue, 07 Oct 2025 02:58:08 GMT vary: Accept-Encoding x-backend: www-mirrors x-request-id: 98a81336396b8087 strict-transport-security: max-age=15552000; includeSubdomains; preload content-security-policy: frame-ancestors 'self' https://cms.w3.org/ https://cms-dev.w3.org/; upgrade-insecure-requests cf-cache-status: BYPASS set-cookie: __cf_bm=V_5UONjc6Y0FRMuEd7uC_ecczYWzKm5t2fB8LF2eWbI-1759784288-1.0.1.1-2kzI9Lx.9n7abt5Ds5QDv0CBDtGtK1GGILCeKSylsfU_9CN1aEMIdS2NXgV95_Zeocaad9loD5ioYrrLOg.kHwZhOyA2QbGgJHrkNAeaZPM; path=/; expires=Mon, 06-Oct-25 21:28:08 GMT; domain=.w3.org; HttpOnly; Secure; SameSite=None server: cloudflare cf-ray: 98a81336396b8087-BLR alt-svc: h3=":443"; ma=86400 TTML Text and Image Profiles for Internet Media Subtitles and Captions

TTML Text and Image Profiles for Internet Media Subtitles and Captions

W3C Member Submission 07 June 2013

This version:: https://www.w3.org/submissions/2013/SUBM-ttml-ww-profiles-20130607/
Latest published version:: https://www.w3.org/submissions/ttml-ww-profiles/
Previous version:
Editor:: Pierre Lemieux, pal@sandflow.com

Copyright © 2013 Motion Picture Laboratories, Inc. Derived from the Common File Format & Media Formats Specification 1.0.6 and Common File Format Timed Text XML Schemas 1.0.6 posted at https://www.uvvuwiki.com, © Digital Entertainment Content Ecosystem (DECE) LLC and used with permission.This document is available under the W3C Document License. See the W3C Intellectual Rights Notice and Legal Disclaimersfor additional information.

Abstract

This submission specifies two profiles of the Timed Text Markup Language (TTML) Version 2.0: a text-only profile and an image-only profile. These profiles are intended to be used across subtitle and caption delivery applications worldwide, thereby simplifying interoperability, consistent rendering and conversion to other subtitling and captioning formats.

Both profiles are based on the Common File Format & Media Formats Specification (CFF) developed by Digital Entertainment Content Ecosystem (DECE), and benefit from the technical consensus, conformance testing and implementation experience gathered there. The text profile is intended as a superset of SDP-US, which is a subset of CFF. The image profile extends a subset of TTML with SMPTE Timed Text (SMPTE-TT) image support.

DECE is an industry forum with more than 80 members across the content and consumer electronics communities.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications can be found in the W3C technical reports index at https://www.w3.org/TR/.

By publishing this document, W3C acknowledges that the Submitting Members have made a formal Submission request to W3C for discussion. Publication of this document by W3C indicates no endorsement of its content by W3C, nor that W3C has, is, or will be allocating any resources to the issues addressed by it. This document is not the product of a chartered W3C group, but is published as potential input to the W3C Process. A W3C Team Comment has been published in conjunction with this Member Submission. Publication of acknowledged Member Submissions at the W3C site is one of the benefits of W3C Membership. Please consult the requirements associated with Member Submissions of section 3.3 of the W3C Patent Policy. Please consult the complete list of acknowledged W3C Member Submissions.

1. Scope

This document specifies two profiles of [TTML2]: a text-only profile and an image-only profile. These profiles are intended for subtitle and caption delivery worldwide, including dialog language translation, content description, captions for deaf and hard of hearing, etc.

2. Conformance

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

The keywords MUST, MUST NOT, SHALL, SHALL NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this specification are to be interpreted as described in [RFC2119].

A subtitle document SHALL conform to a profile defined herein if it meets all normative provisions associated with the profile.

A TTML presentation processor SHALL conform to a profile if it is capable of presenting any subtitle document conforming to the profile, i.e. if it implements all features and provisions of the profile

3. Profiles

3.1 General

A subtitle document SHALL NOT conform to the Text and Image Profiles simultaneously.

3.2 Text Profile

A subtitle document conforming to the Text Profile SHALL conform to Sections 4. Common Constraints and 5. Text Profile Constraints.

3.3 Image Profile

A subtitle document conforming to the Image Profile SHALL conform to Sections 4. Common Constraints and 6. Image Profile Constraints.

4. Common Constraints

4.1 Document Encoding

A subtitle document SHALL use UTF-8 character encoding as specified in [UNICODE].

4.2 Related Video Object

4.2.1 General

A subtitle document MAY be associated with a related video object, which SHALL consist of a sequence of frames, each a rectangular array of pixels.

4.2.2 Root Container

Note

The following assumes the addition of a ttp:aspectRatio attribute to [TTML2].

The root container of a subtitle document SHALL be mapped to the related video object frame according to the following:

If ttp:aspectRatio is present, the root container SHALL be mapped to a rectangular area within the related video object such that:
1. the aspect ratio of the rectangular area is equal to ttp:aspectRatio,
2. the center of the rectangular area is colocated with the center of the related video object frame,
3. the rectangular area is entirely contained within the related video object frame and
4. the rectangular area has a height or width equal to that of the related video object frame.
Otherwise, the root container of a subtitle document SHALL be mapped to the related video object frame in its entirety. If tts:extent is present on the tt element, the extents of the root container SHALL be equal to the dimensions of the related video object frame.

ttp:aspectRatio SHALL NOT be present if tts:extent is present.

Note

As specified in Section 4.6 Features, tts:extent is present if the px length measure is used anywhere within the document.

Integer pixel positions on the related video object frame computed from real percentage length values SHALL use half-up rounding, i.e. round(x) = floor(x+0.5).

4.2.3 Synchronization

Each intermediate synchronic document of the subtitle document is intended to be displayed on a specific frame and removed on a specific frame of the related video object.

A media time expression M SHALL correspond to the frame of the related video object with the presentation time that is the closest to, but not less, than M.

If ttp:frameRate is specified, then the product of ttp:frameRate and ttp:frameRateMultiplier SHALL be the frame rate of the related video object.

4.3 Language

All instances of the xml:lang attribute within a subtitle document SHALL have identical values.

Note

xml:lang can have a value of "carview.php?tsp=".

4.4 Region

4.4.1 Presented Region

A region, as defined in [TTML2], SHALL be considered presented in a given intermediate synchronic document if both of the following conditions are true:

tts:opacity is not equal to "0.0" for the region; and
content is selected into the region or tts:showBackground is equal to "always" for the region.

Note

As specified in [TTML2], the initial value of tts:opacity is "1.0" and the default value of tts:showBackground is "always".

4.4.2 Dimensions and Position

All regions SHALL be entirely contained within the root container.

No two regions presented in a given intermediate synchronic document SHALL overlap

4.4.3 Maximum number

The number of presented regions in a given intermediate synchronic document SHALL be smaller than or equal to 4.

4.5 Hypothetical Render Model

Any sequence of consecutive intermediate synchronic documents SHALL be reproducible without error by the Hypothetical Render Model specified in Section 4.5 Hypothetical Render Model.

4.6 Features

Feature	Provisions
`#animation`	MAY be used.
`#cellResolution`	SHALL NOT be used.
`#clockMode`	SHALL NOT be used.
`#content`	MAY be used.
`#core`	MAY be used.
`#display-block`	MAY be used.
`#display-inline`	MAY be used.
`#display-region`	MAY be used.
`#display`	MAY be used.
`#dropMode`	SHALL NOT be used.
`#extent-region`	MAY be used. The `tts:extent` attribute SHALL be present on all `region` elements.
`#extent-root`	MAY be used. If the document includes any length value that uses the `px` expression, `tts:extent` SHALL be present on the `tt` element.
`#extent`	MAY be used.
`#frameRate`	If the document includes any time expression that uses the frame field, the `ttp:frameRate` attribute SHALL be present on the `tt` element.
`#frameRateMultiplier`	MAY be used.
`#layout`	MAY be used.
`#length-cell`	SHALL NOT be used.
`#length-integer`	MAY be used.
`#length-negative`	SHALL NOT be used.
`#length-percentage`	MAY be used.
`#length-pixel`	MAY be used.
`#length-positive`	MAY be used.
`#length-real`	MAY be used.
`#length`	MAY be used.
`#markerMode`	SHALL NOT be used.
`#metadata`	MAY be used.
`#opacity`	MAY be used.
`#origin`	MAY be used.
`#overflow`	SHALL NOT be used.
`#pixelAspectRatio`	SHALL NOT be used.
`#presentation`	MAY be used.
`#profile`	MAY be used.
`#showBackground`	MAY be used.
`#structure`	MAY be used.
`#styling-chained`	MAY be used.
`#styling-inheritance-content`	MAY be used.
`#styling-inheritance-region`	MAY be used.
`#styling-inline`	MAY be used.
`#styling-nested`	MAY be used.
`#styling-referential`	MAY be used.
`#styling`	MAY be used.
`#subFrameRate`	SHALL NOT be used.
`#tickRate`	MAY be used. `ttp:tickRate` SHALL be present on the `tt` element.
`#timeBase-clock`	SHALL NOT be used.
`#timeBase-media`	SHALL be used. `ttp:timeBase` SHALL be present on the `tt` element and SHALL be equal to "media".
`#timeBase-smpte`	SHALL NOT be used.
`#time-clock-with-frames`	MAY be used.
`#time-clock`	MAY be used.
`#time-offset-with-frames`	MAY be used.
`#time-offset-with-ticks`	MAY be used.
`#time-offset`	MAY be used.
`#timeBase-media`	MAY be used.
`#timeContainer`	MAY be used.
`#timing`	MAY be used. The same syntax of `#clock-time` or `#offset-time` SHOULD be used throughout the subtitle document.
`#transformation`	MAY be used.
`#unicodeBidi`	MAY be used.
`#visibility-block`	MAY be used.
`#visibility-inline`	MAY be used.
`#visibility-region`	MAY be used.
`#visibility`	MAY be used.
`#writingMode-horizontal-lr`	MAY be used.
`#writingMode-horizontal-rl`	MAY be used.
`#writingMode-horizontal`	MAY be used.
`#writingMode`	MAY be used.
`#zIndex`	MAY be used.
`#aspectRatio`	MAY be used.
`#forcedDisplay`	MAY be used.

Note

See ISSUE-230 for a description of #forcedDisplay

Note

This initial values specified for tts:color, tts:displayAlign and tts:textAlign are those specified by [ST2052-1].

Note

As specified in [TTML2], a #time-offset-with-frames expression is translated to a media time M according to M = 3600 · hours + 60 · minutes + seconds + (frames ÷ (ttp:frameRateMultiplier · ttp:frameRate)).

5. Text Profile Constraints

5.1 Document Conformance

A subtitle document conforming to the Text Profile SHALL be designated by the document conformance designator specified below.

https://www.w3.org/ns/ttml/profile/imsc-text

Note

The ttp:profile mechanism of TTML 1.0 allows a document to indicate the profile(s) that a processor SHALL support in order to process the document. This mechanism cannot be used to indicate that a processor implementing any of the referenced profiles can process the document. The document conformance concept introduced below extends the TTML 1.0 ttp:profile mechanism by allowing a document to signal that it conforms to a specified set of normative provisions.

5.2 Features

Note

The following assumes, but does not require, the porting of the [ST2052-1] #backgroundImage, #backgroundImageHorizontal, #backgroundImageVertical and #image features to [TTML2].

Feature	Provisions
`#backgroundColor-block`	MAY be used.
`#backgroundColor-inline`	MAY be used.
`#backgroundColor-region`	MAY be used.
`#backgroundColor`	MAY be used.
`#backgroundImage`	SHALL NOT be used.
`#backgroundImageHorizontal`	SHALL NOT be used.
`#backgroundImageVertical`	SHALL NOT be used.
`#bidi`	MAY be used.
`#color`	MAY be used. The initial value of `tts:color` SHALL be "white".
`#direction`	MAY be used.
`#displayAlign`	MAY be used. The initial value of `tts:displayAlign` SHALL be "after".
`#extent-region`	The `tts:extent` attribute when applied to a region element SHALL use `px` units or "percentage" representation, and SHALL NOT use `em` units.
`#fontFamily-generic`	MAY be used.
`#fontFamily-non-generic`	MAY be used.
`#fontFamily`	MAY be used.
`#fontSize-anamorphic`	SHALL NOT be used.
`#fontSize-isomorphic`	MAY be used.
`#fontSize`	MAY be used.
`#fontStyle-italic`	MAY be used.
`#fontStyle-oblique`	MAY be used.
`#fontStyle`	MAY be used.
`#fontWeight-bold`	MAY be used.
`#fontWeight`	MAY be used.
`#image`	SHALL NOT be used.
`#length-em`	MAY be used.
`#lineBreak-uax14`	MAY be used.
`#lineHeight`	MAY be used.
`#nested-div`	MAY be used.
`#nested-span`	MAY be used.
`#origin`	The `tts:origin` attribute SHALL use `px` units or "percentage" representation, and SHALL NOT use `em` units.
`#padding-1`	MAY be used.
`#padding-2`	MAY be used.
`#padding-3`	MAY be used.
`#padding-4`	MAY be used.
`#padding`	MAY be used.
`#textAlign-absolute`	MAY be used.
`#textAlign-relative`	MAY be used.
`#textAlign`	MAY be used. The initial value of `tts:textAlign` SHALL be "center".
`#textDecoration-over`	MAY be used.
`#textDecoration-through`	MAY be used.
`#textDecoration-under`	MAY be used.
`#textDecoration`	MAY be used.
`#textOutline-blurred`	SHALL NOT be used.
`#textOutline-unblurred`	MAY be used.
`#textOutline`	MAY be used. If specified, the border thickness SHALL be 10% or less than the associated font size.
`#wrapOption`	MAY be used.
`#writingMode-vertical`	MAY be used.

6. Image Profile Constraints

6.1 Document Conformance

The Image Profile SHALL be designated by the document conformance designator specified below:

https://www.w3.org/ns/ttml/profile/imsc-image

Note

6.2 Features

Note

The following assumes, but does not require, the porting of the [ST2052-1] #backgroundImage, #backgroundImageHorizontal, #backgroundImageVertical and #image features to [TTML2].

Feature	Provisions
`#backgroundImage`	MAY be used. The backgroundImage attribute SHALL reference a complete image that conforms to the PNG image coding as specified in Sections 7.1.1.3 and 15.1 of [MHP]. If a pHYs chunk is present, it SHALL indicate square pixels. Note: If no pixel aspect ratio is carried, the default of square pixels will be assumed.
`#backgroundImageHorizontal`	SHALL NOT be used. `#backgroundImage` remains available for use.
`#backgroundImageVertical`	SHALL NOT be used. `#backgroundImage` remains available for use.
`#bidi`	SHALL NOT be used.
`#color`	SHALL NOT be used.
`#content`	The `p`, `span` and `br` elements SHALL NOT be present.
`#direction`	SHALL NOT be used.
`#displayAlign`	SHALL NOT be used.
`#extent-region`	If a `tts:backgroundImage` attribute is applied to a region, the width and height of the region extent SHALL be present and SHALL be equal to the width and height of the image source referenced by the `tts:backgroundImage`.
`#fontFamily`	SHALL NOT be used.
`#fontSize`	SHALL NOT be used.
`#fontStyle`	SHALL NOT be used.
`#fontWeight`	SHALL NOT be used.
`#image`	SHALL NOT be used.
`#length-em`	SHALL NOT be used.
`#lineBreak-uax14`	SHALL NOT be used.
`#lineHeight`	SHALL NOT be used.
`#nested-div`	SHALL NOT be used.
`#nested-span`	SHALL NOT be used.
`#padding`	SHALL NOT be used.
`#textAlign`	SHALL NOT be used.
`#textDecoration`	SHALL NOT be used.
`#textOutline`	SHALL NOT be used.
`#wrapOption`	SHALL NOT be used.
`#writingMode-vertical`	SHALL NOT be used.

7. Hypothetical Render Model

7.1 Overview

This Section specifies the Hypothetical Render Model illustrated in Fig. 1 Hypothetical Render Model .

The purpose of the model is to limit subtitle document complexity. It is not however intended to serve as basis for implementation. For instance, while the model defines a glyph buffer for the purpose of limiting the number of glyphs displayed at any given point in time, it does not require an implementation to implement such a buffer.

The model operates on successive intermediate synchronic documents obtained from an input subtitle document, and uses a simple double buffering model: while an intermediate synchronic document E_n is being painted into Presentation Buffer P_n (the "front buffer" of the model), the previous intermediate synchronic document E_n-1 is available for display in Presentation Buffer P_n-1 (the "back buffer" of the model).

The model specifies an (hypothetical) time required for completely painting an intermediate synchronic document as a proxy for complexity. Painting includes drawing region backgrounds, rendering and copying glyphs, and decoding and copying images. Complexity is then limited by requiring that painting of intermediate synchronic document E_n completes before the end of intermediate synchronic document E_n-1.

Whenever applicable, constraints are specified relative to root container dimensions, allowing subtitle sequences to be authored independently of related video object resolution.

To enables scenarios where the same glyphs are used in multiple successive intermediate synchronic documents, e.g. to convey a CEA-608/708-style roll-up (see [CEA-608] and [CEA-708]), the Glyph Buffers G_n and G_n-1 store rendered glyphs across intermediate synchronic documents, allowing glyphs to be copied into the Presentation Buffer instead of rendered, a more costly operation.

Similarly, Decoded Image Buffers D_n and D_n-1 store decoded images across intermediate synchronic documents, allowing images to be copied into the Presentation Buffer instead of decoded.

7.2 Model

7.2.1 General

The Presentation Compositor SHALL render in Presentation Buffer P_n each successive intermediate synchronic document E_n using the following steps in order:

clear the pixels, except for the first intermediate synchronic document E₀ for the which the pixels of P₀ SHALL be assumed to have been cleared;
paint, according to stacking order, all background pixels for each region;
paint all pixels for background colors associated with text or image subtitle content; and
paint the text or image subtitle content.

The Presentation Compositor SHALL start rendering E_n:

at the presentation time of E₀ minus Initial Painting Delay (IPD), if n = 0
at the presentation time of E_n-1, if n > 0

The duration DUR(E_n) for painting an intermediate synchronic document E_n in the Presentation Buffer P_n SHALL be:

DUR(E_n) = S(E_n) / BDraw + DUR_T(E_n) + DUR_I(E_n)

Where:

S(E_n) is the total normalized drawing area for intermediate synchronic document E_n, as specified in 7.2.2 Paint Regions
BDraw is the normalized background drawing performance factor.
DUR_T(E_n) is the duration, in seconds, for painting the text subtitle content for intermediate synchronic document E_n, as specified in Section 7.2.4 Paint Text
DUR_I(E_n) is the duration, in seconds, for painting the image subtitle content for intermediate synchronic document E_n, as specified in Section 7.2.3 Paint Images

The contents of the Presentation Buffer P_n SHALL be transferred instantaneously to Presentation Buffer P_n-1 at the presentation time of intermediate synchronic document E_n, making the latter available for display.

Note

It is possible for the contents of Presentation Buffer P_n-1 to never be displayed. This can happen if Presentation Buffer P_n is copied twice to Presentation Buffer P_n-1 between two consecutive video frame boundaries of the related video object.

It SHALL be an error for the Presentation Compositor to fail to complete painting pixels for E_n before the presentation time of E_n.

Unless specified otherwise, the following table SHALL specify values for IPD and BDraw.

Parameter	Initial value
Initial Painting Delay (IPD)	1 s
Normalized background drawing performance factor (BDraw)	12 s^-1

Note

BDraw effectively sets a limit on fillings regions - for example, assuming that the root container is ultimately rendered at 1920×1080 resolution, a BDraw of 12 s^-1 would correspond to a fill rate of 1920×1080×12/s=23.7×2²⁰pixels s^-1.

Note

IPD effectively sets a limit on the complexity of any given intermediate synchronic document.

7.2.2 Paint Regions

The total normalized drawing area S(E_n) for intermediate synchronic document E_n SHALL be

S(E_n) = CLEAR(E_n) + PAINT(E_n )

where CLEAR(E₀) = 0 and CLEAR(E_{n | n > 0}) = 1, i.e. the root container in its entirety.

Note

To ensure consistency of the Presentation Buffer, a new intermediate synchronic document requires clearing of the root container.

PAINT(E_n) SHALL be the normalized area to be painted for all regions that are used in intermediate synchronic document E_n according to

PAINT(E_n) = ∑_{R_i∈R_p} SIZE(R_i) ∙ NBG(R_i)

where R_p SHALL be the set of regions presented in the intermediate synchronic document E_n – see Section 4.4.1 Presented Region for the definition of presented region.

NSIZE(R_i) SHALL be given by:

NSIZE(R_i) = (width of R_i ∙ height of R_i ) ÷ (root container height ∙ root container width)

Example 2

For a region R_i in with tts:extent="250px 50px" within a root container with tts:extent="1920px 1080px", NSIZE(R_i) = 0.603.

NBG(R_i) SHALL be the total number of tts:backgroundColor attributes associated with the given region R_i in the intermediate synchronic document. A tts:backgroundColor attribute is associated with a region when it is explicitly specified (either as an attribute in the element, or by reference to a declared style) in the following circumstances:

It is specified on the region layout element that defines the region.
It is specified on a div, p, span or br content element that is to be flowed into the region for presentation in the intermediate synchronic document (see [TTML2] for more details on when a content element is followed into a region).
It is specified on a set animation element that is to be applied to content elements that are to be flowed into the region for presentation in the intermediate synchronic document (see [TTML2] for more details on when a set animation element is applied to content elements).

Even if a specified tts:backgroundColor is the same as specified on the nearest ancestor content element or animation element, specifying any tts:backgroundColor SHALL require an additional fill operation for all region pixels.

7.2.3 Paint Images

The Presentation Compositor SHALL paint into the Presentation Buffer P_n all visible pixels of presented images of intermediate synchronic document E_n.

A presented image SHALL be a div element with a smpte:backgroundImage attribute that is contained within a presented region.

For each presented image, the Presentation Compositor SHALL either:

if an identical image is present in Decoded Image Buffer D_n, copy the image from Decoded Image Buffer D_n to the Presentation Buffer P_n using the Image Copier; or
if an identical image is present in Decoded Image Buffer D_n-1, i.e. an identical image was present in intermediate synchronic document E_n-1, copy using the Image Copier the glyph from Decoded Image Buffer D_n-1 to both the Decoded Image Buffer D_n and the Presentation Buffer P_n; or
Otherwise, decode the image using the Image Decoder the image into the Presentation Buffer P_n and Decoded Image Buffer D_n.

Two images SHALL be identical if and only if they reference the same encoded image source.

The duration DUR_I(E_n) for painting images of an intermediate synchronic document E_n in the Presentation Buffer SHALL be as follows:

DUR_I(E_n) = ∑_{I_i ∈ I_c} NRGA(I_i) / ICpy + ∑_{I_j ∈ I_d} NSIZ(I_j) / IDec

where

I_c is the set of images copied when painting intermediate synchronic document E_n
I_d is the set of images decoded when painting intermediate synchronic document E_n
IDec is the image decoding rate
ICpy is the normalized image copy performance factor.

NRGA(I_i) is the Normalized Image Area of presented image I_i and SHALL be equal to:

NRGA(I_i)= (width of I_i ) ∙ height of I_i ) ÷ ( root container height ∙ root container width )

NSIZ(I_i) SHALL be the number of pixels of presented image I_i.

The contents of the Decoded Image Buffer D_n SHALL be transferred instantaneously to Decoded Image Buffer D_n-1 at the presentation time of intermediate synchronic document E_n.

The total size occupied by images stored in Decoded Image Buffers D_n or D_n-1 SHALL be the sum of their Normalized Image Area.

The size of Decoded Image Buffers D_n or D_n-1 SHALL be the Normalized Decoded Image Buffer Size (NDIBS).

Unless specified otherwise, the following table SHALL specify ICpy, Idec, and NDBIS.

Parameter	Initial value
Normalized image copy performance factor (ICpy)	6
Image Decoding rate (Idec)	1 × 2²⁰ pixels s^-1
Normalized Decoded Image Buffer Size (NDIBS)	0.9885

7.2.4 Paint Text

For each glyph displayed in intermediate synchronic document E_n, the Presentation Compositor SHALL:

if an identical glyph is present in Glyph Buffer G_n, copy the glyph from Glyph Buffer G_n to the Presentation Buffer P_n using the Glyph Copier; or
if an identical glyph is present in Glyph Buffer G_n-1, i.e. an identical glyph was present in intermediate synchronic document E_n-1, copy using the Glyph Copier the glyph from Glyph Buffer G_n-1 to both the Glyph Buffer G_n and the Presentation Buffer P_n; or
Otherwise render using the Glyph Renderer the glyph into the Presentation Buffer P_n and Glyph Buffer G_n using the corresponding style information.

Two glyphs are identical if and only if the following [TTML2] styles are identical:

tts:color
tts:fontFamily
tts:fontSize
tts:fontStyle
tts:fontWeight
tts:textDecoration
tts:textOutline

Fig. 2 Example of Presentation Compositor Behavior for Text Rendering

The duration DUR_T(E_n) for painting the text of an intermediate synchronic document E_n in the Presentation Buffer is as follows:

DUR_T(E_n) = ∑_{G_i ∈ G_r} NRGA(G_i) / Ren(G_i) + ∑_{G_j ∈ G_c} NRGA(G_j) / GCpy

Where:

G_r is the set of glyphs rendered into the Presentation Buffer P_n using the Glyph Renderer in intermediate synchronic document E_n.
G_c is the set of glyphs copied to the Presentation Buffer P_n using the Glyph Copier in intermediate synchronic document E_n.
Ren(G_i) is the text rendering performance factor glyph G_i
GCpy is the normalized glyph copy performance factor

G_r and G_c SHALL include only glyphs in presented regions and SHALL NOT include a [UNICODE] Code Point if it does not result in a change to presentation, e.g. the Code Point is ignored.

The Normalized Rendered Glyph Area NRGA(G_i) of a glyph G_i SHALL be equal to:

NRGA(G_i)= (fontSize of G_i as percentage of root container height)²

The contents of the Glyph Buffer G_n SHALL be copied instantaneously to Glyph Buffer G_n-1 at the presentation time of intermediate synchronic document E_n.

The total size occupied by the glyphs stored in Glyph Buffers G_n or G_n-1 SHALL be the sum of their Normalized Rendered Glyph Area.

The size of Glyph Buffers G_n and G_n-1 SHALL be the Normalized Glyph Buffer Size (NGBS).

Unless specified otherwise, the following table SHALL specify GCpy, Ren and NGBS, and SHALL apply to all supported font styles (including provision of outline border).

Parameter	Initial value
Normalized glyph copy performance factor (GCpy)	12
Text rendering performance factor Ren(G_i if G_i is not a CJK Unified Ideograph as specified in [UNICODE].	1.2
Text rendering performance factor Ren(G_i) if G_i is a CJK Unified Ideograph as specified in [UNICODE].	0.6
Normalized Glyph Buffer Size (NGBS)	1

Note

NRGA(G_i) does not take into account glyph decorations (e.g. underline), glyph effects (e.g. outline) or actual glyph aspect ratio. An implementation can determine an actual buffer size needs based on worst-case glyph size complexity.

A. Recommended Unicode Code Points per Language

The following table lists common code points (see [UNICODE]) definitions used in this Appendix:

(Basic Latin)
U+0020 - U+007E (Letterlike Symbols)
U+2103 : DEGREES CELSIUS
U+2109 : DEGREES FAHRENHEIT
U+2120 : SERVICE MARK SIGN
U+2122 : TRADE MARK SIGN
(Latin-1 Supplement)
U+00A0 - U+00FF (Number Forms)
U+2153 – U+215F : Fractions
(Latin Extended-A)
U+0152 : LATIN CAPITAL LIGATURE OE
U+0153 : LATIN SMALL LIGATURE OE
U+0160 : LATIN CAPITAL LETTER S WITH CARON
U+0161 : LATIN SMALL LETTER S WITH CARON
U+0178 : LATIN CAPITAL LETTER Y WITH DIAERESIS
U+017D : LATIN CAPITAL LETTER Z WITH CARON
U+017E : LATIN SMALL LETTER Z WITH CARON (Box Drawing)
U+2500 : BOX DRAWINGS LIGHT HORIZONTAL
U+2502 : BOX DRAWINGS LIGHT VERTICAL
U+250C : BOX DRAWINGS LIGHT DOWN AND RIGHT
U+2510 : BOX DRAWINGS LIGHT DOWN AND LEFT
U+2514 : BOX DRAWINGS LIGHT UP AND RIGHT
U+2518 : BOX DRAWINGS LIGHT UP AND LEFT
(Latin Extended-B)
U+0192 : LATIN SMALL LETTER F WITH HOOK (Block Elements)
U+2588 : FULL BLOCK
(Spacing Modifier Letters)
U+02DC : SMALL TILDE (Geometric Shapes)
U+25A1 : WHITE SQUARE
(General Punctuation)
U+2010 - U+2015 : Dashes
U+2016 - U+2027 : General punctuation
U+2030 - U+203A : General punctuation (Musical Symbols)
U+2669 : QUARTER NOTE
U+266A : EIGHTH NOTE
U+266B : BEAMED EIGHTH NOTES
(Currency symbols)
U+20AC : EURO SIGN

The following table specifies the [UNICODE] code points that SHOULD be used in a document's textual content if xml:lang is present (Primary language subtag is as defined in IETF RFC 5646).

Languages	Primary language subtag of `xml:lang`	[UNICODE] Code Points
Albanian Languages
Albanian	"sq"	As defined in the table above
Baltic Languages
Latvian, Lithuanian	"lv", "lt"	As defined in the table above, except for "(Latin Extended-A)" which is re-defined below (Latin Extended-A) U+0100 - U+017F
Finnic Languages
Finish	"fi"	As defined in the table above
Estonian	"et"	As defined in the table above, except for "(Latin Extended-A)" which is re-defined below (Latin Extended-A) U+0100 - U+017F
Germanic Languages
Danish, Dutch/Flemish, English, German, Icelandic, Norwegian, Swedish	"da", "nl", "en", "de", "is", "no", "sv"	As defined in the table above.
Greek Languages
Greek	"el"	As defined in the table above (Greek and Coptic) U+0386 : GREEK CAPITAL LETTER ALPHA WITH TONOS U+0387 : GREEK ANO TELEIA U+0388 – U+03CE : Letters
Romanic Languages
Catalan, French, Italian	"ca", "fr", "it"	As defined in the table above
Portuguese, Spanish	"pt", "es"	(Currency symbols) U+20A1 : COLON SIGN U+20A2 : CRUZEIRO SIGN U+20B3 : AUSTRAL SIGN
Romanian	"ro"	As defined in the table above, except for "(Latin Extended-A)" which is re-defined below (Latin Extended-A) U+0100 - U+017F
Semitic Languages
Arabic	"ar"	As defined in the table above U+060C – U+060D : Punctuation U+061B : ARABIC SEMICOLON U+061E : ARABIC TRIPLE DOT PUNCTUATION MARK U+061F : ARABIC QUESTION MARK U+0621 – U+063A : Based on ISO 8859-6 U+0640 – U+064A : Based on ISO 8859-6 U+064B – U+0652 : Points from ISO 5559-6 U+0660 – U+0669 : Arabic-Indic digits U+066A – U+066D : Punctuation
Hebrew	"he"	As defined in the table above (Hebrew) U+05B0 – U+05C3 : Points and punctuation U+05D0 – U+05EA : Based on ISO 8859-8 U+05F3 – U+05F4 : Additional punctuation
Slavic Languages
Croatian, Czech, Polish, Slovenian, Slovak	"hr", "cs", "pl", "sl", "sk"	As defined in the table above, except for "(Latin Extended-A)" which is re-defined below (Latin Extended-A) U+0100 - U+017F
Bosnian, Bulgarian, Macedonian, Russian, Serbian, Ukrainian	"bs", "bg", "mk", "ru", "sr", "uk"	As defined in the table above, except for "(Latin Extended-A)" which is re-defined below (Latin Extended-A) U+0100 - U+017F (Cyrillic) U+0400 – U+040F : Cyrillic extensions U+0410 – U+044F : Basic Russian alphabet U+0450 – U+045F : Cyrillic extensions
Turkic Languages
Turkish	"tr"	As defined in the table above, except for "(Latin Extended-A)" which is re-defined (Latin Extended-A) U+0100 - U+017F
Kazakh	"kk"	As defined in the table above, except for "(Latin Extended-A)" which is re-defined (Latin Extended-A) U+0100 - U+017F (Cyrillic) U+0400 – U+040F : Cyrillic extensions U+0410 – U+044F : Basic Russian alphabet U+0450 – U+045F : Cyrillic extensions
Ugric Languages
Hungarian	"hu"	As defined in the table above, except for "(Latin Extended-A)" which is re-defined below (Latin Extended-A) U+0100 - U+017F

B. Typical Practice for Subtitles per Region (Informative)

This section is non-normative.

The following table summarizes subtitle languages commonly used in the listed regions. The Language Tag is as specified in RFC 5646.

Region	Subtitle Languages (Language Tag)
ALL (worldwide)	English ("en")
America (North)
ALL	French ("fr") [Québécois ("fr-CA") or Parisian ("fr-FR")]
United States	Spanish ("es") [Latin American ("es-419")]
America (Central and South)
ALL	Spanish ("es") [Latin American ("es-419")]
Brazil	Portuguese ("pt") [Brazilian ("pt-BR")]
Asia, Middle East, and Africa
China	Chinese ("zh") [Simplified Mandarin ("zh-cmn-Hans")]
Egypt	Arabic ("ar")
Hong Kong	Chinese ("zh") [Cantonese ("zh-yue")]
India	Hindi ("hi") Tamil ("ta") Telugu ("te")
Indonesia	Indonesian ("id")
Israel	Hebrew ("he")
Japan	Japanese ("ja")
Kazakhstan	Kazakh ("kk")
Malaysia	Standard Malay ("zsm")
South Korea	Korean ("ko")
Taiwan	Chinese ("zh") [Traditional Mandarin ("zh-cmn-Hant")]
Thailand	Thai ("th")
Vietnam	Vietnamese ("vi")
Europe
Benelux (Belgium, Netherlands, and Luxembourg)	French ("fr") [Parisian ("fr-FR")] Dutch/Flemish ("nl")
Denmark	Danish ("da")
Finland	Finnish ("fi")
France	French ("fr") [Parisian ("fr-FR")] Arabic ("ar")
Germany	German ("de") Turkish ("tr")
Italy	Italian ("it")
Norway	Norwegian ("no")
Spain	Spanish ("sp") [Castilian ("sp-ES")] Catalan ("ca")
Sweden	Swedish ("sv")
Switzerland	French ("fr") ["fr-CH" or "fr-FR"] German ("de") ["de-CH"] Italian ("it") ["it-CH"]
Albania	Albanian ("sq")
Bulgaria	Bulgarian ("bg")
Croatia	Croatian ("hr")
Czech Republic	Czech ("cs")
Estonia	Estonian ("et")
Greece	Greek ("el")
Hungary	Hungarian ("hu")
Iceland	Icelandic ("is")
Latvia	Latvian ("lv")
Lithuania	Lithuanian ("lt")
Macedonia	Macedonian ("mk")
Poland	Polish ("pl")
Portugal	Portuguese ("pt") [Iberian ("pt-PT")]
Romania	Romanian ("ro")
Russia	Russian ("ru")
Serbia	Serbian ("sr")
Slovakia	Slovak ("sk")
Slovenia	Slovenian ("sl")
Turkey	Turkish ("tr")
Ukraine	Ukrainian ("uk")

C. Schema

TBD

D. References

D.1 Normative references

[MHP]: ETSI TS 101 812 V1.3.1, Digital Video Broadcasting (DVB); Multimedia Home
[RFC2119]: S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Internet RFC 2119. URL: https://www.ietf.org/rfc/rfc2119.txt
[TTML2]: World Wide Web Consortium (W3C). Timed Text Markup Language (TTML) 2.0.
[UNICODE]: The Unicode Standard. URL: https://www.unicode.org/versions/latest/

D.2 Informative references

[CEA-608]: Line-21 Data Services, ANSI/CEA Standard.
[CEA-708]: Digital Television (DTV) Closed Captioning, ANSI/CEA Standard.
[ST2052-1]: SMPTE ST 2052-1, Timed Text Format (SMPTE-TT)

Original Source | Taken Source

TTML Text and Image Profiles for Internet Media Subtitles and Captions

W3C Member Submission 07 June 2013

Abstract

Status of This Document

Table of Contents

1. Scope

2. Conformance

3. Profiles

3.1 General

3.2 Text Profile

3.3 Image Profile

4. Common Constraints

4.1 Document Encoding

4.2 Related Video Object

4.2.1 General

4.2.2 Root Container

4.2.3 Synchronization

4.3 Language

4.4 Region

4.4.1 Presented Region

4.4.2 Dimensions and Position

4.4.3 Maximum number

4.5 Hypothetical Render Model

4.6 Features

5. Text Profile Constraints

5.1 Document Conformance

5.2 Features

6. Image Profile Constraints

6.1 Document Conformance

6.2 Features

7. Hypothetical Render Model

7.1 Overview

7.2 Model

7.2.1 General

7.2.2 Paint Regions

7.2.3 Paint Images

7.2.4 Paint Text

A. Recommended Unicode Code Points per Language

B. Typical Practice for Subtitles per Region (Informative)

C. Schema

D. References

D.1 Normative references

D.2 Informative references