1、 ANSI/CEA Standard Digital Television (DTV) Closed Captioning ANSI/CEA-708-E August 2013 NOTICE Consumer Electronics Association (CEA) Standards, Bulletins and other technical publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purch
2、asers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need. Existence of such Standards, Bulletins and other technical publications shall not in any respect preclude any memb
3、er or nonmember of CEA from manufacturing or selling products not conforming to such Standards, Bulletins or other technical publications, nor shall the existence of such Standards, Bulletins and other technical publications preclude their voluntary use by those other than CEA members, whether the s
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5、 assume any obligation whatever to parties adopting the Standard, Bulletin or other technical publication. This document does not purport to address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this document to establi
6、sh appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. This document is copyrighted by the Consumer Electronics Association (CEA) and may not be reproduced, in whole or part, without written permission. Federal copyright law prohibits
7、unauthorized reproduction of this document by any means. Organizations may obtain permission to reproduce a limited number of copies by entering into a license agreement. Requests to reproduce text, data, charts, figures or other material should be made to CEA. (Formulated under the cognizance of th
8、e CEA R4.3 Television Data Systems Subcommittee.) Published by CONSUMER ELECTRONICS ASSOCIATION 2013 Technology Phone 800-854-7179; Fax 303-397-2740; Internet http:/; Email ISO/IEC Standards: Global Engineering Documents, World Headquarters, 15 Inverness Way East, Englewood, CO USA 80112-5776; Phon
9、e 800-854-7179; Fax 303-397-2740; Internet http:/; Email IEC Central Office, 3, rue de Varembe, PO Box 131, CH-1211 Geneva 20, Switzerland; Phone +41 22 919 02 11; Fax +41 22 919 03 00; Internet http:/www.iec.ch; Email pubinforiec.ch ISO Central Secretariat, 1, rue de Varembe, Case postale 56, CH-1
10、211 Geneve 20, Switzerland; Phone +41 22 749 01 11; Fax +41 22 749 01 55; Internet http:/www.iso.ch; Email mbinfoiso.ch SMPTE Standards: Society of Motion Picture Email: engsmpte.org 2.2 Informative References The following references contain provisions, which, through reference in this text, consti
11、tute informative provisions of this standard. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicat
12、ed below. 2.2.1 Informative Reference List 1 ANSI INCITS 4, Information SystemsCoded Character Sets7 Bit American National Standard Code for Information Interchange (7-BIT ASCII), 2002 2 ATSC A/53 Part 4, MPEG-2 Video System Characteristics 3 ATSC A/65, Program and System Information Protocol for Te
13、rrestrial Broadcast and Cable 4 ATSC A/153, ATSC Mobile Digital Television System, Advanced Television Systems Committee, Washington, DC. 5 ISO 639-2, Codes for the representation of names of languagesPart 2: Alpha-3 code as maintained by the ISO 639/Joint Advisory Committee (ISO 639/JAC), http:/www
14、.loc.gov/standards/iso639-2/iso639jac.html; ISO 639-2 standard online: http:/www.loc.gov/standards/iso639-2/langhome.html. 6 ISO/IEC IS 13818-1:2007 (E), International Standard, Information technology - Generic coding of moving pictures and associated audio information: systems 7 ISO/IEC IS 13818-2:
15、2000 (E), International Standard, Information technologyGeneric coding of moving pictures and associated audio information: video 8 ISO/IEC 2022, Information technology - Character code structure and extension techniques (4/15/1999) 9 SCTE 21, Standard for Carriage Of NTSC VBI Data in Cable Digital
16、Transport Streams CEA-708-E 5 10 SMPTE Standard 12M, Television, Audio and FileTime and Control Code (1999) 11 SMPTE EG 43-, System Implementation of CEA-708-B and CEA-608-B Closed Captioning 12 SMPTE 333, DTV Closed-Caption Server to Encoder Interface (Revision of SMPTE 333M-1999) 13 SMPTE 334-1, V
17、ertical Ancillary Data Mapping of Caption Data and Other Related Data 14 SMPTE 334-2, Caption Distribution Packet (CDP) Definition 15 SMPTE RP 2007, Closed-Caption CDP and “Grand Alliance“ Serial Interfaces for DTV 2.2.2 Informative Reference Acquisition ATSC Standards: Advanced Television Systems C
18、ommittee (ATSC), 1776 K Street N.W., Suite 200, Washington, DC 20006; Phone 202-872-9160; Internet http:/www.atsc.org SMPTE Standards: Society of Motion Picture Web: http:/www.smpte.org ISO Standards: Global Engineering Documents, World Headquarters, 15 Inverness Way East, Englewood, CO USA 80112-57
19、76; Phone 800-854-7179; Fax 303-397-2740; Internet http:/; Email ISO Central Secretariat Office, 1, rue de Varembe, Case postale 56, CH-1211 Geneve 20, Switzerland; Phone +41 22 749 01 11; Fax +41 22 733 34 30; Internet http:/www.iso.ch; Email centraliso.ch 2.3 Compliance Notation As used in this d
20、ocument “shall” and “must” denote mandatory provisions of the standard. “Should” denotes a provision that is recommended but not mandatory. “May” denotes a feature whose presence does not preclude compliance, and implementation of which is optional. “Optional” denotes items that may or may not be pr
21、esent in a compliant device. CEA-708-E 6 3 Caption Channel Layered Protocol A formal data communications channel protocol has been established for the DTVCC caption data channel. This formalization provides a framework for describing the caption communications hierarchy. Grouping the structures, con
22、cepts and features of this environment into the following hierarchical layers, aids in the understanding of the organizational aspects of the DTVCC system. There are 5 layers in the DTVCC data framework (see Figure 1): DTVCC Transport Layer, DTVCC Packet Layer, DTVCC Service Layer, DTVCC Coding Laye
23、r, and DTVCC Interpretation Layer. Similar to the OSI Reference Model, each of these layers provides particular services in the receiver, as shown in Table 1. Services in a Receiver Section DTVCC Protocol Model CEA-608 datastream Specification of Window appearance and content Placement of Windows ov
24、er Video Synchronization of Command Interpretation to the Display of video Reset of Caption Service 8 DTVCC Interpretation Layer These layers are defined in CEA-608 1. Parsing of Syntax 7 DTVCC Coding Layer Demultiplexing of Caption Services 6 DTVCC Service Layer Detection of Synchronization Loss Re
25、synchronization of Data Stream Reset of Caption Decoder 5 DTVCC Packet Layer Extraction of closed caption data from parent transport system, e.g. MPEG user data Demultiplexing of CEA-608 datastream and DTVCC caption streams 4 DTVCC Transport Layer Table 1 DTVCC Protocol Stack The DTVCC Transport Lay
26、er is where DTVCC data leave the DTV Video subsystem and are introduced to the DTV Closed-Caption decoder. Within the DTVCC decoder, DTVCC data are further processed up through the remaining layers of the DTVCC Protocol Model. Both the CEA-608 datastream and DTVCC data are carried in this layer. NOT
27、EThe DTVCC Transport layer should not be confused with the main system transport layer. For example, in MPEG-2 ATSC systems, the MPEG-2 transport layer is defined in CEA-708-E 7 ISO/IEC 13818-1 6, and this transport layer carries video, audio, data and control streams. DTVCC bits are encoded within
28、the video signal conforming with ISO/IEC 13818-2 7. These bits enter the DTVCC decoder from the video streams user data structure. This standard specifies a method of placing a CEA-608 datastream, embedded in the signal specified by this standard, into the correct bit positions and fields in an NTSC
29、 signal, but this standard does not specify any application or presentation level processes for CEA-608 datastreams. Further processing of CEA-608 datastreams is specified in CEA-608 1. The DTVCC Packet Layer marks where DTVCC data enter the DTVCC decoder. This is a protocol data reassembly layer th
30、at buffers incremental bitstream data into a byte-aligned, multi-byte packet. This layer provides resynchronization for decoding the DTVCC stream, and is not dependent on the DTVCC Transport layer. Processing of the Caption Channel packet data begins in the DTVCC Service Layer. Caption Channel packe
31、ts are broken up into the encapsulated sub-blocks of data to be routed to one or more separate caption service processing routines within the decoder. Using information in the DTVCC Service Directory (see Section 4.5), TV viewers may choose to view the processed data for one or more DTVCC services a
32、t a time. For example, a caption channel may contain an English language service and a Spanish language service. The DTVCC Coding Layer breaks out the individual caption commands and caption text sequences from the service data blocks. The DTVCC Interpretation Layer processes the caption elements pr
33、esented by the DTVCC Coding Layer. The DTVCC Interpretation Layer also provides for delaying the interpretation of the command stream and reset of a specific Caption Service. CEA-708-E 8 Figure 1 DTV Closed-Captioning Protocol Model Coding Layer Interpretation Layer Service Layer Packet Layer Transp
34、ort Layer DTVCC Data i cc_count ; i+ ) one_bit 1 1 reserved 4 1111 cc_valid 1 bslbf cc_type 2 bslbf cc_data_1 8 bslbf cc_data_2 8 bslbf Table 2 cc_data() Syntax process_cc_data_flagThis one-bit flag shall indicate the validity of the remaining fields of the cc_data() structure. If it is set to 1, th
35、e cc_data() structure contains valid closed caption data. When it is set to 0, the cc_data() structure does not contain valid closed caption data Decoders are expected to discard the contents of the cc_data() structure when process_cc_data_flag is set to 0. zero_bitThis bit shall be set to 0 to main
36、tain backwards compatibility with previous versions of this structure. cc_countThis 5-bit unsigned integer in the range 0 through 31 shall indicate the number of iterations of the “for” loop following this field. Sixteen (16) bits of closed caption payload data are carried in each pair of the syntax
37、 elements cc_data_1 and cc_data_2. See Section 4.3.6. one_bitThis bit shall be set to 1 to maintain backwards compatibility with previous versions of this structure. cc_validThis one-bit flag shall indicate the validity of the two closed-caption data bytes which follow it. If cc_valid is set to 1, t
38、hen the following two bytes of closed-caption data shall be interpreted according to Section 5 through Section 9. If cc_valid is set to 0, the following two closed caption bytes shall have no meaning; however, the bit pair cc_type shall have meaning. For CEA-608 captions, cc_valid shall be interpret
39、ed at the time it is inserted into the NTSC video. See Section 4.3.2.2. cc_typeThis two-bit field shall signal the type of the following two bytes of closed caption data as indicated in Table 3. CEA-708-E 11 cc_type cc_valid cc_data_1 and cc_data_2 00 0 CEA-608 line 21 field 1 do not generate run-in
40、 clock and start bit; or DTVCC padding bytes* 1 CEA-608 line 21 field 1 closed caption bytes 01 0 CEA-608 line 21 field 2 do not generate run-in clock and start bit; or DTVCC padding bytes* 1 CEA-608 line 21 field 2 closed caption bytes 10 0 DTVCC padding bytes 1 CCP Data cc_data_1 and cc_data_2 are
41、 CCP Data, (Figure 4) 11 0 DTVCC padding bytes 1 Start of CCP cc_data_1 is a CCP Header byte, cc_data_2 is CCP Data (Figure 4) * Depends upon context; see Section 4.3.1 and Figure 2 Table 3 Closed-Caption Type (cc_type) Coding cc_data_1The first of two data bytes. cc_data_2 The second of two data by
42、tes. Together these form a byte pair. reserved Syntax elements marked “reserved” are not currently defined, have no meaning, and shall be encoded with default values. Future versions of this standard may use other values for these reserved syntax elements; therefore decoders shall ignore these reser
43、ved syntax elements, but interpret portions of the syntax that are defined. 4.3.1 Structure and Interpretation of cc_data() As shown in Table 3, when cc_valid=1, the cc_type field identifies the accompanying byte pair cc_data_1 and cc_data_2 as one of four items: CEA-608 line 21 field 1 or field 2 c
44、aption data, the start of a DTVCC Caption Channel Packet, or the continuation of a DTVCC Caption Channel Packet. When cc_valid=0 and cc_type=10 or 11, the byte pair is padding. The state diagram in Figure 2 illustrates the context-dependent meaning of cc_data bytes carried in the cc_data() structure
45、. State 1 (Start of cc_data() is entered at the beginning of each instance of a new cc_data() structure. The formation of cc_data() conforms to the following rules: 1. When data of cc_type 00 or 01 occur at the beginning of the cc_data() structure, cc_data_1 and cc_data_2 shall contain CEA-608 data.
46、 The presence of CEA-608 data shall correspond with State 2 in Figure 2. 2. CEA-608 data bytes shall only occur in the first one, two or three byte-pair positions, depending on frame rate. Section 4.3.2.2describes how this data may be stored in the field buffer model. The CEA-608 data shall follow t
47、he format and protocol as specified in CEA-608. The CEA-608 data field order (field 1 vs. field 2) depends on the field display order. 3. Data bytes cc_data_1 and cc_data_2 may be DTVCC padding bytes. The interpretation of cc_data_1 and cc_data_2 as DTVCC padding shall be as given in Figure 2; e.g.
48、the conditions corresponding to State (5). 4. The condition cc_valid = 1 and cc_type = 11 shall indicate start of CCP (State (3). 5. The condition cc_valid = 1 and cc_type = 10 shall indicate continuation of a CCP (State (4). 6. The DTVCC emission shall structure cc_data() to conform only to valid F
49、igure 2 state transitions. The condition cc_valid = 1 and (cc_type = 00 or cc_type = 01) occurring at states 3, 4, or 5 shall be considered invalid. Decoders may respond to such conditions by displaying unexpected information and the decoder may be left in an indeterminate state. CEA-708-E 12 ( 2 )6 0 8 S e g m e n t( 1 ) S t a r t o f c
