SMPTE RP 2052-11-2013 Conversion from CEA-708 Caption Data to SMPTE-TT.pdf

1、 Copyright 2013 by THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 3 Barker Avenue., White Plains, NY 10601 (914) 761-1100 Approved June 5, 2013 Dolan Table of Contents Page Foreword . 2 Intellectual Property 2 Introduction 2 1 Scope . 4 2 Conformance Notation . 4 3 Normative References . 4 4

2、 Definitions and Acronyms 5 4.1 Definitions . 5 4.2 Acronyms 5 5 CEA-708 Data Mapping to SMPTE-TT 5 5.1 Introduction . 5 5.2 Conversion Constraints . 6 5.3 SMPTE Namespaces for CEA-708 . 6 5.4 Converting Metadata Information 6 5.5 Caption Service Conversion . 8 5.6 Preserved and Enhanced Modes 8 5.7

3、 Header Information . 8 5.8 Coordinate System 8 5.9 Chunk Mapping . 8 5.10 Style Mapping . 9 5.11 Character Mapping 14 5.12 Time Mapping . 17 5.13 Tunneling CEA-708 Data 18 Annex A Bibliography (Informative) . 19 Annex B Example Encoding (Informative) . 20 Annex C US FCC Profile Information (Informa

4、tive) . 23 Page 1 of 23 pages SMPTE RP 2052-11:2013 SMPTE RECOMMENDED PRACTICE Conversion from CEA-708 Caption Data to SMPTE-TT SMPTE RP 2052-11:2013 Page 2 of 23 pages Foreword SMPTE (the Society of Motion Picture and Television Engineers) is an internationally-recognized standards developing organ

5、ization. Headquartered and incorporated in the United States of America, SMPTE has members in over 80 countries on six continents. SMPTEs Engineering Documents, including Standards, Recommended Practices, and Engineering Guidelines, are prepared by SMPTEs Technology Committees. Participation in thes

6、e 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 Part XIII of its Operations Manual. SMPTE RP 2052-11

7、was prepared by Technology Committee 24TB. Intellectual Property 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 docum

8、ent may be the subject of patent rights. SMPTE shall not be held responsible for identifying any or all such patent rights. Introduction This section is entirely informative and does not form an integral part of this Engineering Document. In North America, CEA-708 is in broad use as a distribution f

9、ormat for closed captioning and related data. In the United States (US), for digital transmission via Cable and Terrestrial Transmission, where captions are present, it is required by regulation. Although not directly used as an authoring format, the syntax of CEA-708 is in widespread use. Most or a

10、ll 708 captions are converted from 608 by machine. Arguably, SMPTE RP 2052-10 is sufficient to cover todays practices, since converting both would theoretically result in substantively the same SMPTE-TT. However, it appears that US regulatory activity could alter this state of authoring and having a

11、 well-defined conversion between 708 and SMPTE-TT would facilitate US Broadcast Television and Internet content interoperability early in adoption. There are different levels of CEA-708 implementation and regulation that are useful background for the SMPTE RP 2052-11 audience. 1. CEA-708 has a full

12、toolkit useful for comprehensive authoring and transmission of caption (and subtitle) data. Multiple languages, on-screen windows, etc are supported. This is referred to as “full-708”, profile. It is proposed that SMPTE RP 2052-11 provide the necessary conversion tools to populate the SMPTE ST 2052-

13、1 syntax and losslessly tunnel the 708 stream (including support for its CEA-608 compatibility bytes). 2. CEA-708 decoders, when compliant with FCC rules, support a limited toolkit and have constraints expected on the incoming data stream. These restrictions should have no impact to SMPTE RP 2052-11

14、 other than informative notes for clarity. Incoming streams that are constrained should be maintained as such through the SMPTE RP 2052-11 conversion. SMPTE RP 2052-11:2013 Page 3 of 23 pages The primary use case is a tunnel to a target device that has MPEG-2 TS output capability and the 708 informa

15、tion needs to be reconstructed. Requirements consist of the following: 1. Support the conversion of full-708 into SMPTE ST 2052-1 2. Provide for a lossless tunnel (using the SMPTE ST 2052-1 tunnel mechanism) of 708 cc_data() data structure including 608 compatibility bytes and other signaling. 3. Su

16、pport both file-based and real-time streaming scenarios. SMPTE RP 2052-11:2013 Page 4 of 23 pages 1 Scope This document defines the preferred method of converting from CEA-708 data as defined in CEA-708 into SMPTE-TT (as defined in SMPTE ST 2052-1). This document details how such a conversion can be

17、 made, and defines some constraints on the process so that the resulting SMPTE-TT file is interoperable between SMPTE-TT implementations. 2 Conformance Notation Normative text is text that describes elements of the design that are indispensable or contains the conformance language keywords: “shall“,

18、 “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, no

19、rmative, 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 key

20、words, “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 cour

21、se 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 “

22、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

23、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; Ta

24、bles shall be next; followed by formal languages; then figures; and then any other language forms. 3 Normative References The following standards contain provisions which, through reference in this text, constitute provisions of this recommended practice. At the time of publication, the editions ind

25、icated were valid. All standards are subject to revision, and parties to agreements based on this recommended practice are encouraged to investigate the possibility of applying the most recent edition of the standards indicated below. CEA-708-D, Digital Television (DTV) Closed Captioning SMPTE ST 20

26、52-1:2013, Timed Text Format (SMPTE-TT) Unicode Consortium, Unicode 6.0.0, http:/unicode.org/versions/Unicode6.0.0/ SMPTE RP 2052-11:2013 Page 5 of 23 pages 4 Definitions and Acronyms 4.1 Definitions CEA-608: The term is used in this document to refer to the CEA-608 standard or to a data stream comp

27、lying to that standard, depending on context. CEA 608 closed captions are composed of a byte sequence which is carried embedded in a video signal, and which when played on a suitably equipped video device creates text captions on the display. CEA-708: The term is used in this document to refer to th

28、e CEA-708 standard or to a data stream complying to that standard, depending on context. CEA 607 closed captions are composed of a byte sequence which is carried embedded in a compressed video stream, and which when played on a suitably equipped video device creates text captions on the display. Chu

29、nk: A segment of a media timeline that forms part of a larger contiguous sequence of timeline segments where each segment has a 1 to 1 mapping with a SMPTE-TT document. Namespace: Mechanism for scoping the definitions of names in an XML document. Presentation Processor: Hardware or software that cre

30、ates a visible rendition of a document as defined in W3C TTML. 4.2 Acronyms CEA: Consumer Electronics Association FCC: (US) Federal Communication Commission SMPTE-TT: SMPTE Timed Text TTML: (W3C) Timed Text Markup Language W3C: World Wide Web Consortium XML: eXtensible Markup Language 5 CEA-708 Data

31、 Mapping to SMPTE-TT 5.1 Introduction This document defines a conversion from CEA-708 data into a SMPTE-TT document (or series of document chunks) that will, when presented using a conforming SMPTE-TT Presentation Engine, give a functionally equivalent display. In most cases there will be no single

32、correct conversion, but multiple possible interpretations that will generate a similar outcome when rendered. The constraints given in this document are intended to promote consistency amongst implementations of SMPTE-TT processors and to improve interoperability of SMPTE-TT files when displayed on

33、those different implementations. CEA-708 data can be obtained primarily from digital video streams (MPEG-2 or H.264). It can also come from other methods such as directly from caption authoring file formats, although most CEA-708 data at this writing is converted from CEA-608. Many input formats may

34、 be acceptable so long as they enable the same cc_data() structure recreated by a presentation processor from tunneled data to conform to the CEA-708 standard. SMPTE RP 2052-11:2013 Page 6 of 23 pages There is no detailed buffering model for CEA-708 except to note that off-screen compositioning and

35、rendering is required for all windows, in addition to the display memory. The text which is mapped to SMPTE-TT corresponds to the final text placed in the current display memory. 5.2 Conversion Constraints SMPTE-TT documents converted from CEA-708 data shall have the constraints defined in Section 5

36、 of this specification. The process of conversion from a specific CEA-708 data stream may lead to a number of possible SMPTE-TT documents; no unique conversion is defined by this document. Although the US FCC regulations define minimum decoder functionality (in affect a strict profile of CEA-708), t

37、he conversion defined in this specification is a full conversion of CEA-708 except as noted. If the input is known to conform to the FCC minimum decoder functionality, the converter can set the metadata fccMinimum attribute. 5.3 SMPTE Namespaces for CEA-708 TTML allows for metadata to be added in pr

38、ivate namespaces. The namespace for the extensions, including metadata, defined in this document shall be as defined in Table 1. An informative XML schema is defined in SMPTE RP 2052-11b. When a prefix is used, SMPTE-TT documents should use the namespace prefix in Table 1. Although this prefix is us

39、ed in examples throughout this specification the m708 namespace can also be the default. Also, it is assumed that if a full namespace declaration is not given in an example XML fragment in this document then the namespace in Table 1 is set in an outer context in the surrounding XML. Table 1 Namespac

40、e and Prefix Prefix Namespace m708: http:/www.smpte-ra.org/schemas/2052-1/2013/smpte-tt#cea708 5.4 Converting Metadata Information The URI used for the origin attribute shall be: http:/www.smpte-ra.org/schemas/2052-1/2013/smpte- tt#cea708. The attributes defined in this section should be added to th

41、e element to encode the CEA-708 metadata for the caption service that was converted. Additionally, when tunnel data is present, the metadata for all caption services should be encoded in the elements within the element. 5.4.1 Element This element should be used to convey the 708 metadata as defined

42、in CEA-708, Section 4. One element shall be used for each caption service. It is a simple type with various attributes defined in this section. It is a child only of (contained in ). SMPTE RP 2052-11:2013 Page 7 of 23 pages 5.4.2 m708:number Attribute This is the service number. Type unsigned intege

43、r Values: 1-31 inclusive Initial: none Applies to: m708:service, smpte:information Inherited: no Percentages: N/A Animatable: none 5.4.3 xml:lang Attribute This is the service language as defined by XML. 5.4.4 m708:aspectRatio Attribute This is the aspect ratio. Type enumeration Values: 4:3 or 16:9

44、Initial: none Applies to: m708:service, smpte:information Inherited: no Percentages: N/A Animatable: none 5.4.5 m708:easyReader Attribute This is “easy reader”. Type Boolean Values: true or false Initial: none Applies to: m708:service, smpte:information Inherited: no Percentages: N/A Animatable: non

45、e 5.4.6 m708:fccMinimum Attribute If the converter has knowledge that the service that has been converted conforms to the FCC minimum decoder functionality as defined in US 47CFR79.102, then this flag should be set. Type boolean Values: true or false Initial: false Applies to: m708:service, smpte:in

46、formation Inherited: no Percentages: N/A Animatable: none SMPTE RP 2052-11:2013 Page 8 of 23 pages 5.5 Caption Service Conversion A separate logical sequence of SMPTE-TT chunks shall be created for each caption service. There is no multiplexing of more than one service per instance document. Note th

47、at up to 31 services are possible. 5.6 Preserved and Enhanced Modes When converting, unless it is known that the exact replication of the visual appearance is required, Enhanced mode will give greater latitude to create a more conformant SMPTE-TT document. If exact replication is required, then Pres

48、erved mode should be set. The Preserved mode of conversion for CEA-708 shall preserve the color, background spacing and timing of captions, including individual character timings in the various window compositing and visibility modes. The Enhanced mode of conversion for CEA-708 shall retain equivale

49、nce classes of caption style, but may map to alternative specific styles (e.g., all text that is red in the original sequence shall be mapped to the same style class in the result, but the style applied need not be red). Timing for window visibility “on” commands shall be retained. 5.7 Header Information Converted SMPTE-TT shall contain as a child element of the element one element, containing at least one specific . SMPTE-TT shall not rely on the default region of TTML. Converted SMPTE-TT shall contain as child elements of the element one e