SMPTE RP 428-22:2025-06
SMPTE Recommended Practice

D-Cinema Distribution Master — Minimal Timed Text XML Requirements

Approved - 2025-06-27

Copyright © 2025, Society of Motion Picture and Television Engineers. All rights reserved. No part of this material may be reproduced, by any means whatsoever, without the prior written permission of the Society of Motion Picture and Television Engineers.

Table of contents🔗

  1. Foreword
  2. Introduction
  3. 1 Scope
  4. 2 Conformance
  5. 3 Normative references
  6. 4 Terms and definitions
  7. 5 Minimal 428-7 Document
    1. 5.1 General Guidelines
    2. 5.2 StartTime
    3. 5.3 LoadFont
    4. 5.4 SubtitleList
    5. 5.5 Subtitle
    6. 5.6 TimeIn
    7. 5.7 TimeOut
    8. 5.8 Text
    9. 5.9 Image
  8. Annex A D-Cinema Subtitle Document example (Informative)
    1. A.1 Example using the Text Element
    2. A.2 Example using the Image Element
  9. Bibliography

Foreword🔗

The Society of Motion Picture and Television Engineers (SMPTE) is an internationally-recognized standards developing organization. Headquartered and incorporated in the United States of America, SMPTE has members in over 80 countries on six continents. SMPTE’s Engineering Documents, including Standards, Recommended Practices, and Engineering Guidelines, are prepared by SMPTE’s Technology Committees. Participation in these Committees is open to all with a bona fide interest in their work. SMPTE cooperates closely with other standards-developing organizations, including ISO, IEC and ITU. SMPTE Engineering Documents are drafted in accordance with the rules given in its Standards Operations Manual.

For more information, please visit www.smpte.org.

At the time of publication no notice had been received by SMPTE claiming patent rights essential to the implementation of this Engineering Document. However, attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. SMPTE shall not be held responsible for identifying any or all such patent rights.

This document was prepared by Technology Committee 27C.

Introduction🔗

This clause is entirely informative and does not form an integral part of this Engineering Document.

SMPTE ST 429-2 states the following:

Once a timed text asset appears in one Reel, the established track shall be assumed to exist for the entire Composition, even if related timed text Asset elements are not present in all Reels.

This statement implies that a timed text processor should expect a contiguous presence of Timed Text track files across all reels should one (1) or more reels require a timed text instance. Programmatically speaking, establishing the concept of a “track shall be assumed to exist” is inconsistent across D-Cinema playback devices accountable for reproducing timed text data. Such inconsistencies can result in timed text displayed out of sync, random display flashing, not displaying at all, or the respective track file failing to decrypt.

To mitigate such behavior, SMPTE RDD 52 states the following:

If a MainSubtitle timed text track is present on any reel, a MainSubtitle timed text track shall be present on all reels. If (1) or more ClosedCaption timed text track(s) are present on any reel, the same number of ClosedCaption timed text tracks shall be present on all reels.

This document defines how to create SMPTE ST 428-7 DCDM Subtitle files for inclusion inside Timed Text asset tracks to fulfill this requirement. Annex A provides examples of DCDM Subtitle files that comply with this definition.

1 Scope🔗

This recommended practice specifies a minimal, compliant, and functionally empty SMPTE ST 428-7 Subtitle file, providing no visible effect upon playout.

2 Conformance🔗

Normative text is text that describes elements of the design that are indispensable or contains the conformance language keywords: "shall", "should", or "may". Informative text is text that is potentially helpful to the user, but not indispensable, and can be removed, changed, or added editorially without affecting interoperability. Informative text does not contain any conformance keywords.

All text in this document is, by default, normative, except: the Introduction, any clause explicitly labeled as "Informative" or individual paragraphs that start with "Note:"

The keywords "shall" and "shall not" indicate requirements strictly to be followed in order to conform to the document and from which no deviation is permitted.

The keywords, "should" and "should not" indicate that, among several possibilities, one is recommended as particularly suitable, without mentioning or excluding others; or that a certain course of action is preferred but not necessarily required; or that (in the negative form) a certain possibility or course of action is deprecated but not prohibited.

The keywords "may" and "need not" indicate courses of action permissible within the limits of the document.

The keyword "reserved" indicates a provision that is not defined at this time, shall not be used, and may be defined in the future. The keyword "forbidden" indicates "reserved" and in addition indicates that the provision will never be defined in the future.

A conformant implementation according to this document is one that includes all mandatory provisions ("shall") and, if implemented, all recommended provisions ("should") as described. A conformant implementation need not implement optional provisions ("may") and need not implement them as described.

Unless otherwise specified, the order of precedence of the types of normative information in this document shall be as follows: Normative prose shall be the authoritative definition; tables shall be next; then formal languages; then figures; and then any other language forms.

3 Normative references🔗

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

4 Terms and definitions🔗

For the purposes of this document, the terms and definitions given in the following documents apply:

5 Minimal 428-7 Document🔗

5.1 General Guidelines🔗

A complete DCDM Subtitle file shall be created as per SMPTE ST 428-7. The DCDM Subtitle file shall contain the set of elements which define the global parameters. In this elements set, in addition, the values for ContentTitleText, Language, EditRate, TimeCodeRate, and DisplayType are to be homogeneous throughout empty subtitle file instances of a set of DCDM Subtitle files.

5.2 StartTime🔗

The StartTime value shall be 00:00:00:ZeroE.

5.3 LoadFont🔗

When a Text element is present, the LoadFont element shall reference a Font file that contains at least the glyphs listed in Table 1.

Table 1 — Required Glyphs
Glyph ID Glyph Name Unicode Value
0 .notdef undefined
1 .null U+0000
2 CR U+000D
3 space U+0020

NOTE —⁠ For further information regarding the minimum required glyphs, see Section 7.6 (First four glyphs in fonts) in ISO/IEC 14496-22:2015.

5.4 SubtitleList🔗

The SubtitleList element shall have a single child element that shall be a Font element with no attributes.

5.5 Subtitle🔗

The TimeIn and TimeOut attributes shall be the only attributes of the Subtitle element. In addition, the Subtitle element shall have only one child element that shall be either one Text or one Image element.

5.6 TimeIn🔗

The TimeIn attribute value shall be 00:00:01:ZeroE unless the subtitle file is the first in its ordered set of DCDM Subtitle files as defined by its ReelNumber value, whereby the value should be 00:00:04:ZeroE.

5.7 TimeOut🔗

The TimeOut attribute value shall be equal to the TimeIn attribute value plus 15 subtitle editable units, unless this creates a time window overlap with the first subtitle instance expected to be displayed from the following subtitle file in the ordered set of DCDM Subtitle files; in such case, the TimeOut value shall be chosen to avoid any subtitle instance time window overlap.

5.8 Text🔗

The Text element shall have no attributes and shall have a value equal to an empty string ("").

5.9 Image🔗

The Image element shall reference a single auxiliary Portable Network Graphics [PNG] image resource acting as a sub-picture overlay as per SMPTE ST 428-7. Said resource, in its entirety, shall be transparent.

To avoid the use of full image PNG files, the image size shall be limited to a maximum of 128x128 pixels. 

Annex A
D-Cinema Subtitle Document example (Informative)🔗

A.1 Example using the Text Element🔗

The following sample XML structure showcases a valid instance of the SubtitleReel document conforming to schema http://www.smpte-ra.org/schemas/428-7/2014/DCST using the Text element that allows the carriage of no textual data. 

<?xml version="1.0" encoding="UTF-8"?>
<SubtitleReel xmlns="http://www.smpte-ra.org/schemas/428-7/2014/DCST">
  <Id>urn:uuid:e7c646ab-2468-4fc8-8188-ee667aa81967</Id>
  <ContentTitleText>MyTitle</ContentTitleText>
  <IssueDate>2020-11-03T11:22:57-00:00</IssueDate>
  <ReelNumber>1</ReelNumber>
  <Language>en</Language>
  <EditRate>24 1</EditRate>
  <TimeCodeRate>24</TimeCodeRate>
  <StartTime>00:00:00:00</StartTime>
  <DisplayType>MainSubtitle</DisplayType>
  <LoadFont ID="MinRefFont">urn:uuid:232c45d8-fde8-4e5e-86b9-86e96354daf3</LoadFont>
  <SubtitleList>
    <Font>
      <Subtitle TimeIn="00:00:04:00" TimeOut="00:00:04:15">
        <Text></Text>
      </Subtitle>
    </Font>
  </SubtitleList>
</SubtitleReel>

A.2 Example using the Image Element🔗

The following sample XML structure showcases a valid instance of the SubtitleReel document conforming to schema http://www.smpte-ra.org/schemas/428-7/2014/DCST using the Image element referencing a single PNG image resource which is transparent in its entirety. 

<?xml version="1.0" encoding="UTF-8"?>
<SubtitleReel xmlns="http://www.smpte-ra.org/schemas/428-7/2014/DCST">
  <Id>urn:uuid:1d4fc9bb-beda-4385-bde1-49b15606e723</Id>
  <ContentTitleText>MyTitle</ContentTitleText>
  <IssueDate>2020-11-03T11:07:39-00:00</IssueDate>
  <ReelNumber>1</ReelNumber>
  <Language>en</Language>
  <EditRate>24 1</EditRate>
  <TimeCodeRate>24</TimeCodeRate>
  <StartTime>00:00:00:00</StartTime>
  <DisplayType>MainSubtitle</DisplayType>
  <SubtitleList>
    <Font>
      <Subtitle TimeIn="00:00:04:00" TimeOut="00:00:04:15">
        <Image>urn:uuid:d6a2902f-6a7c-4d9b-afa8-85d27089dffa</Image>
      </Subtitle>
    </Font>
  </SubtitleList>
</SubtitleReel>

Bibliography🔗