SMPTE ST 334-2-2015 Caption Distribution Packet (CDP) Definition.pdf

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1、 Copyright 2015 by THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 3 Barker Avenue2 White Plains, NY 10601 (914) 761-1100 Approved January 2, 2015 Table of Contents Page Foreword . 2 Intellectual Property 2 Introduction 2 1 Scope . 3 2 Conformance Notation . 3 3 Normative References . 3 4 Ove

2、rview (Informative) 4 4.1 Frame Rates 4 4.2 Time Code 4 4.3 Caption Data 5 4.4 Caption Service Information . 5 5 CDP Detailed Specification 5 5.1 General Syntax 5 5.2 cdp_header 6 5.3 time_code_section . 8 5.4 ccdata_section . 9 5.5 ccsvcinfo_section . 9 5.6 cdp_footer 11 5.7 future_section() (Infor

3、mative) 12 Annex A Bibliography (Informative) . 13 Page 1 of 13 pages SMPTE ST 334-2:2015 Revision of SMPTE 334-2-2007 SMPTE STANDARD Caption Distribution Packet (CDP) Definition SMPTE ST 334-2:2015 Page 2 of 13 pages Foreword SMPTE (the Society of Motion Picture and Television Engineers) is an inte

4、rnationally-recognized standards developing organization. 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 SM

5、PTEs 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

6、Standards Operations Manual. SMPTE ST 334-2 was prepared by Technology Committee 24TB in cooperation with the Consumer Electronics Association (CEA). Intellectual Property At the time of publication no notice had been received by SMPTE claiming patent rights essential to the implementation of this E

7、ngineering 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. Introduction This section is entirely informative and does not form a

8、n integral part of this Engineering Document. The following suite of SMPTE Engineering Documents defines the carriage of Closed-Caption data in production and distribution television systems: SMPTE ST 334-1 Vertical Ancillary Data Mapping of Caption Data and Other Related Data SMPTE ST 334-2 Caption

9、 Distribution Packet (CDP) Definition SMPTE RP 2007 Closed-Caption CDP and “Grand Alliance” Serial Interfaces for DTV SMPTE EG 43 System Implementation of CEA-708 and CEA-608 Closed Captioning and Program-Related Data This standard was originally Section 11 of CEA-708-B with amendments specified by

10、CEB-10-A. CEA has transferred copyright on this material to SMPTE and it appears here on the basis of that agreement. The material in this document has undergone editorial corrections beyond simple structural adjustments. SMPTE ST 334-2:2015 Page 3 of 13 pages 1 Scope This standard defines the struc

11、ture of the Caption Distribution Packet (CDP). A CDP may contain time code, CEA-608 data, CEA-708 closed captioning data, and ATSC A/65 closed caption service information. 2 Conformance Notation Normative text is text that describes elements of the design that are indispensable or contains the confo

12、rmance 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 i

13、n 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

14、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 f

15、orm) 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 de

16、fined 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 prov

17、isions (“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 b

18、e the authoritative definition; Tables 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 tim

19、e of publication, the editions indicated 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. ATSC A/65:2013, Program and Sys

20、tem Information Protocol for Terrestrial Broadcast and Cable CEA-608-E (2008), Line 211 Data Services CEA-708-E (2013), Digital Television (DTV) Closed-Captioning SMPTE ST 12-1:2014, Time and Control Code 1 CEA 608-D refers to line 21 data services on fields 1 and 2. Using current numbering notation

21、 such as SMPTE ST 170 and SMPTE ST 125 there is no line 21 on field two, The more recent number schemes define line 21 on field two as line 284. SMPTE ST 334-2:2015 Page 4 of 13 pages 4 Overview (Informative) The process of creating and delivering closed captions for ATSC Digital Television (or “DTV

22、“) involves authoring captions into a representation which represents the frame accurate captioning intentions, rendering the intentions into the CEA-708 caption syntax, transport of this CEA-708 data via storage and/or streaming media to the point of emission, and then, for example, packaging the C

23、EA-708 data into the MPEG-2 video picture user data as specified in ATSC A/53. During this process the caption data must be kept synchronized to the picture and sound. It is also necessary to create, transport, and include the caption service information in order, for example, to create the Caption

24、Service Descriptor that is carried in the PMT and EIT tables in the MPEG-2 emission transport stream as specified in ATSC A/65. Along the distribution chain, the CEA-708 captioning data may be rendered and displayed for quality control purposes. This section describes the structure of the captioning

25、 content package, consisting of a defined sequence of bytes, which may carry the following: a) time code; b) CEA-708 caption data; c) CEA-608 data; d) caption service information to form the caption service descriptor; and/or e) sequence counts to detect discontinuities in the stream of caption data

26、 packets. While all of these constructs are not required to be present in any given CDP, it is expected that over the length of a program or commercial, all constructs probably will be present at least once. In transports where CDPs are bound to video, time code might not be present at all. 4.1 Fram

27、e Rates The transport of closed captioning information over the ATSC emission system involves packaging the closed captioning data into the MPEG-2 video picture user data area. In order to do this the captioning data must be packaged at the same frame rate as that used by the video encoder. Renderin

28、g the captioning data into a particular frame rate is done prior to or during creation of the CDP. Those engaging in captions authoring may or may not be aware of the delivery frame rate utilized by the video encoder. If the video encoder encodes at a frame rate that differs from the frame rate of t

29、he CDP, the captioning data must be re-framed. Since the video encoder is ultimately responsible for the determination of the encoded picture frame rate, in most cases this re-framing is done in the video encoder. From the point of view of captioning, frame rates which differ by 0.1% may be consider

30、ed identical. For example, if picture and captions are rendered at a 30-Hz frame rate, they may both be played at 29.97 Hz without any reframing of the caption data. As long as captions are delivered at the same rate as the picture, and this rate does not change by more than 0.1 %, no reframing is n

31、eeded. 4.2 Time Code The CDP may carry a time code which may be derived from SMPTE ST 12M (VITC or LTC) taken from the original video source. Carriage of a time code provides an important tool to allow captions to be kept properly synchronized with pictures. The picture, sound, and caption data elem

32、ents may flow through differing paths to the emission encoding and multiplexing equipment. The inclusion of time code within each type of element makes it possible for a caption server to resynchronize the caption data to the associated video. SMPTE ST 334-2:2015 Page 5 of 13 pages 4.3 Caption Data

33、This is comprised of CEA-708 captions and CEA-608 data. If a CDP stream is intended to carry only caption service information to a PSIP table generator, then this data might not be present. However, a CDP stream typically conveys both closed caption data and closed caption service information in par

34、allel for use by both the emission encoder and to the PSIP table generator. 4.4 Caption Service Information To reduce the data rate required to carry the CDP stream or to signal more than 15 services, caption service information may be spread over a sequence of CDPs. The receiver of the CDP stream s

35、hall be able to collect service information from this sequence of CDPs, and shall be able to detect when the service information has changed. Two general types of change may be envisioned. The first is a controlled change, where the generator of the CDP stream may insert an explicit indication that

36、service information has changed, or that a service has been added or dropped. The second is an uncontrolled change that could be caused by a switch from one CDP stream to another CDP stream. In the case of an unsupervised switch, there can be no controlled signalling of the change, yet the receiver

37、of the CDP stream shall be able to easily detect that a change has occurred. In the event that a CDP stream is switched, the switch could result in a stream that has an incomplete, incorrect, or damaged caption descriptor that should be discarded (and not transmitted to a consumer DTV receiver). To

38、provide the ability to detect stream switches, 16-bit sequence counts are included in the CDP header and footer. If the received sequence counts do not increment smoothly, a switch or error has occurred. 5 CDP Detailed Specification The “top to bottom“ order of syntax elements in the table shall cor

39、respond to a “left to right“, or “most significant to least significant“ order within the byte which contains those syntax elements. Syntax elements containing a numerical value represented by more than 8 bits shall be transmitted with the most significant byte first. Notes: 1 The bit and byte order

40、 is consistent with the “uimsbf“ indication in CEA-708. It is the reverse of the bit and byte order in SMPTE serial digital interfaces. 2 The transmission order in the format column of the CDP syntax tables is correct for an ATSC signal, but does not imply the bit-order for transmission for any othe

41、r particular interface. 5.1 General Syntax The overall syntax of the CDP shall be as defined in Table 1. SMPTE ST 334-2:2015 Page 6 of 13 pages Table 1 CDP General Syntax Syntax Comment cdp() Caption Distribution Packet (CDP) cdp_header(); Required time_code_section(); Optional ccdata_section(); Opt

42、ional ccsvcinfo_section(); Optional cdp_footer(); Required The CDP shall contain one header section and one footer section. The CDP may contain one time code section, one cc data section, and one cc service information section. The CDP shall not contain more than one of each of these sections. These

43、 sections shall be multiplexed in the order shown in Table 1. It is possible to extend the CDP to include additional sections. Any sections that are defined in the future shall be placed just prior to the cdp_footer. Any newly defined sections would begin with a unique identifier byte, and contain a

44、 length code. The syntax that a new section would follow is shown in Section 5.7. Equipment that receives the CDP shall skip over sections that begin with an unknown id byte, by means of the length byte. 5.2 cdp_header The CDP header is a required element, and shall be present in all CDPs. The CDP h

45、eader syntax shall be as indicated in Table 2. The length of the cdp_header structure is fixed at 7 bytes. Table 2 CDP Header Syntax Syntax Bits Format cdp_header() cdp_identifier 16 uimsbf cdp_length 8 uimsbf cdp_frame_rate 4 uimsbf Reserved 4 1111 time_code_present 1 Bit ccdata_present 1 Bit svcin

46、fo_present 1 Bit svc_info_start 1 Bit svc_info_change 1 Bit svc_info_complete 1 Bit caption_service_active 1 Bit Reserved 1 1 cdp_hdr_sequence_cntr 16 uimsbf cdp_identifier This is a 16-bit value set to 0x9669. All CDPs begin with this value. cdp_length This 8-bit integer shall indicate the number o

47、f bytes of data in the entire CDP, from the first byte of the CDP_identifier, to the packet checksum, inclusive. SMPTE ST 334-2:2015 Page 7 of 13 pages cdp_frame_rate This field shall indicate the frame rate of the CDP stream. It shall be coded as indicated in Table 3. Also shown are the values of c

48、c_count and the number of cc_data bytes that shall be included in each packet at each frame rate. Table 3 CDP Frame Rate cdp_frame_rate frame rate cc_count CEA-608 cc_data bytes CEA-708 cc_data bytes 0000 Forbidden 0001 240001001 (23.976) 25 4/6 46/44 0010 24 25 4/6 46/44 0011 25 24 4 44 0100 300001

49、001 (29.97) 20 4 36 0101 30 20 4 36 0110 50 12 2 22 0111 600001001 (59.94) 10 2 18 1000 60 10 2 18 . . . Reserved 1111 Reserved Note: There is no practical difference between the pairs of frame rates which differ by 0.1%. Captions and pictures rendered at one rate may be played 0.1% fast or slow, with no practical impact on presentation to the viewer, as the number of bytes per frame does not change. time_code_present This bit shall be set to 1 for CDPs which include the time code section. O