D-Cinema Packaging — Timed Text Track File

1 Scope🔗

This standard specifies the format of a Generic Container (GC) for XML timed text and Timed Text Track File for the distribution of timed text content using MXF. The GC and Track File provide for carriage of an XML document and optional supporting resources such as images or fonts. Encryption is optionally available for protecting against unauthorized disclosure of the file contents.

The standard defines data structures for interchange at the signal interfaces of networks or storage media, but does not define internal storage formats for compliant devices.

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 section 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.

• SMPTE ST 377-1, Material Exchange Format (MXF) — File Format Specification
• SMPTE ST 379-1, Material Exchange Format (MXF) — MXF Generic Container
• SMPTE ST 379-2, Material Exchange Format (MXF) — MXF Constrained Generic Container
• SMPTE ST 410, Material Exchange Format — Generic Stream Partition
• SMPTE ST 429-3, D-Cinema Packaging — Sound and Picture Track File
• SMPTE ST 429-6, D-Cinema Packaging — Track File Encryption
• IETF RFC 2046, Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types. url: https://www.rfc-editor.org/info/rfc2046
• IETF RFC 3986, Uniform Resource Identifier (URI): Generic Syntax. url: https://www.rfc-editor.org/info/rfc3986
• IETF RFC 4122, A Universally Unique Identifier (UUID) URN Namespace. url: https://www.rfc-editor.org/info/rfc4122
• ISO/IEC 10646 (latest edition), Information Technology — Universal multiple-octet coded character set (UCS)
• W3C XML 1.0 (latest edition), Extensible Markup Language (XML) 1.0 Recommendation url: https://www.w3.org/TR/xml/

4 Terms and definitions🔗

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

• SMPTE ST 377-1

Closed caption

timed text intended for display on a device other than the theater screen

Material Exchange Format

MXF

[SOURCE: SMPTE ST 377-1]

Resource

integral unit of data, such as an XML document, a font, or a sub-picture image

Sub-picture

ancillary image intended for display over a larger main image

Subtitle

timed text intended for display on the theater screen, usually written in a language other than the language of the sound essence

Timed text

text intended for display over a timeline, in synchronization with image and sound essence

Uniform Resource Identifier

URI

compact sequence of characters that identifies an abstract or physical resource

[SOURCE: IETF RFC 3986]

Note 1 to entry: URI values often identify objects not accessible via a computer network.

Universally Unique Identifier

UUID

[SOURCE: IETF RFC 4122]

eXtensible Markup Language

XML

an abstract syntax for structured text with metadata

[SOURCE: W3C XML 1.0]

5 Overview (informative)🔗

Subtitles, closed captions or other forms of textual information often accompany sound and picture essence. The display of textual information varies according to purpose, but the essence encoding can be generalized as a timed text resource (an XML document) that provides content, position and timing information (i.e., essence plus metadata), and optional ancillary resources such as fonts and sub-pictures.

In some cases, the essence is entirely contained in one or more sub-pictures. In these cases, the timed text resource contains only timing and position information.

timed text essence therefore consists of one XML timed text resource plus optional supporting resources. To simplify the delivery of what may potentially be many dozens of files, this specification allows all resources to be wrapped in a single MXF file. The timed text resource is contained in an MXF Generic Container (GC) in the Body partition and any ancillary resources are individually contained in their own Generic Stream partitions.

Figure 1 below illustrates a simple Timed Text Track File for cinema containing text-based subtitle essence. The timed text resource is contained in the Track File along with a font resource used to render the characters when the text is reproduced on the theater screen.

Figure 2 illustrates a more complex Timed Text Track File containing sub-picture-based subtitles. The timed text resource is contained in the Track File along with a number of sub-picture resources.

6 Ancillary Resource Wrapping🔗

6.1 Generic Stream Wrapper🔗

Each Ancillary Resource referenced by a Timed Text Generic Container shall be entirely contained within an MXF Generic Stream Partition constructed per SMPTE ST 410 and located in the same MXF file. Each Generic Stream Partition in the file shall contain exactly one Ancillary Resource. Each Generic Stream Partition shall have a distinct BodySID per SMPTE ST 410. The Generic Stream Partition shall consist of a Generic Stream Partition Pack immediately followed by a single KLV packet containing all of the resource data. KLV Fill packets shall not be permitted between the Generic Stream Partition Pack and the resource KLV packet. The actual format of the resource data is beyond the scope of this document. Consult the defining document for the Timed Text Resource for more information. Figure 3 illustrates a Generic Stream Partition containing Ancillary Resource data.

The Ancillary Resource KLV packet shall be identified by the Default Generic Stream Data Element key (see Generic Stream Data Element coding in SMPTE ST 410). Data Arrangement bit 1 shall be zero (the KL pair shall not be considered an intrinsic part of the Ancillary Resource data) and bits 3 and 2 shall be one and zero, respectively (the Generic Stream payload is a byte string). Wrapping Signaling bits 1-3 shall be zero (there are no internal access units). Table 1 gives the UL value of the Default Generic Stream Data Element key, set per the above constraints:

Table 1 –⁠ Ancillary Resource Key (hexadecimal)

06.0e.2b.34 01.01.01.0c 0d.01.05.09 01.00.00.00

7 Mapping XML Timed Text to the MXF Generic Container🔗

7.5 Essence Descriptors🔗

The primary File Package in the header metadata shall have a strong reference to a TimedText Descriptor, which shall describe the Timed Text Resource (see Clause A.3).

If the Timed Text Resource references one or more Ancillary Resources, the TimedText Descriptor shall contain the same number of strong references to TimedTextResource Descriptors (one for each Ancillary Resource, see Clause A.4). A TimedTextResource Descriptor contains the resource ID (a UUID) and Media Type (per IETF RFC 2046) of the respective resource, and also the BodySID of the Generic Stream Partition containing the resource data. Figure 4 illustrates the metadata descriptors for a Timed Text Track File containing a Timed Text Resource and two Ancillary Resources (a font and an image).

8 Essence Encryption🔗

Essence in a Timed Text Generic Container may be encrypted.  For this purpose, the Timed Text Resource shall be contained in an Encrypted Triplet per SMPTE ST 429-6. Ancillary Resources may also be encrypted. Because an Ancillary Resource is a component of the file’s essence track, it shall be encrypted using the same Cryptographic Context used to encrypt the Timed Text Resource. Ancillary Resources shall not be encrypted unless the Timed Text Resource is also encrypted.

When encrypting Ancillary Resources, the Generic Stream Data Element KLV packet in the Generic Stream Partition that contains the resource data shall be contained in an Encrypted Triplet per SMPTE ST 429-6. If the optional MIC value is present in the Encrypted Triplet, the Sequence Number value shall increment with each successive encrypted Ancillary Resource (i.e., the first Ancillary Resource Encrypted Triplet shall have a Sequence Number that is one greater than that of the Timed Text Resource Encrypted Triplet, the second Ancillary Resource Encrypted Triplet shall have a Sequence Number that is two greater than that of the Timed Text Resource Encrypted Triplet, etc.)

Figure 5 is a modified form of the Cryptographic Framework diagram from SMPTE ST 429-6. This diagram shows the relationship of the Framework instance to the Encrypted Triplets in the Generic Stream Partitions. As specified in SMPTE ST 429-6, the Encrypted Triplet contains a weak reference to the Cryptographic Framework. From the Cryptographic Framework to the Generic Stream Partitions by using the set of TimedText Resource subdescriptors in the File Package that references the Framework.

A Timed Text Generic Container that contains Encrypted Triplets shall have a Cryptographic Framework and single Cryptographic Context (i.e., all Encrypted Triplet packets in a Timed Text Generic Container shall be encrypted using the same symmetric key).

9 Synchronization🔗

Synchronization information is contained in the Timed Text Resource. The normative definition of the Timed Text Resource shall specify synchronization with other essence.

10 Random Access to Ancillary Resources (informative)🔗

During reproduction of the essence encoded in the Timed Text Resource, the decoder will have to retrieve from the MXF file any Ancillary Resources referenced by the Timed Text Resource. This section provides an informative method of efficiently performing this retrieval.

It should be noted that each Generic Stream Partition has a distinct BodySID value. This value is given in the respective TimedTextAncillaryResource sub-descriptor that describes the Ancillary Resource contained in a Generic Stream Partition, and also in the Random Index Pack (RIP). Given this information, and a UUID value identifying an Ancillary Resource, the following algorithm can be used to seek to the location of the Ancillary Resource in the MXF file:

1. Search for the UUID value in the AncillaryResourceID property in the set of TimedTextAncillaryResource sub-descriptors referenced by the TimedTextResource descriptor. If no match is found, the resource does not exist in the file.
2. Using the value of the EssenceStreamID property of the matching sub-descriptor, locate in the Random Index Pack (RIP) the Pair entry having a matching BodySID value.
3. The ByteOffset property in the Pair located in step 2 above gives the location of the Partition Pack at the start of the Generic Stream Partition. The Ancillary Resource data will be contained in the KLV packet immediately following the Partition Pack.

11 D-Cinema Timed Text Track File Structure🔗