1、 Copyright 2011 by THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 3 Barker Avenue, White Plains, NY 10601 (914) 761-1100 Approved June 29, 2011 Table of Contents Page Foreword . 2 Intellectual Property 2 Introduction 2 1 Scope 3 2 Conformance Notation 3 3 Normative References 3 4 Definitions
2、 and Acronyms . 4 5 System Overview (Informative) 4 5.1 Use Cases for MPEG-2 TS in VANC Services (Informative) . 4 5.2 Breaking the Prior MPEG TS Clock Domain (Informative) 5 5.3 Additional Considerations for DVB Subtitles (Informative) 6 5.4 Table Handling (Informative) 6 5.5 Data Carousels (Inform
3、ative) . 6 6 Format of TS Carriage Data Packets 6 6.1 TSCD Structure Syntax 7 6.2 TS Carriage Data Structure Semantics . 8 7 Immediate Placement Messages 10 8 Frame Aligned Placement Messages . 10 8.1 DVB subtitle streams . 10 9 Cyclic Placement Messages . 10 9.1 Carousel Removal State . 11 10 PSI/S
4、I Tables . 11 Annex A Bibliography (Informative) . 12 Page 1 of 12 pages SMPTE ST 2056:2011 SMPTE STANDARD MPEG TS Packets Carried in VANC SMPTE ST 2056:2011 Page 2 of 12 pages Foreword SMPTE (the Society of Motion Picture and Television Engineers) is an internationally-recognized standards developi
5、ng 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 SMPTEs Technology Committees. Participation
6、 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 Part XIII of its Administrative Practices. SM
7、PTE ST 2056 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 Standard. 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 many digital systems, subsystems which historically were p
9、hysically co-located needs to be now separated by sometimes a significant distance. Many of these subsystems produced MPEG-2 Transport Stream (TS) packets, carried over ASI or IP, which were then multiplexed with other compressed video and audio signals for emission to home viewers. Examples of thes
10、e subsystems include DVB bitmapped subtitle generators and EBIF carousels. In both cases the earliest implementations assumed close proximity of the generator to the emission multiplexer. Over time it has become necessary in some cases to have the generator either remotely located or to take an orig
11、inal compressed signal, decode it to baseband, switch/route that signal, and re-compress it for emission. In either case, the system design will be greatly simplified by carriage of the low-bandwidth MPEG-2 TS packets in the VANC of their associated video. SMPTE ST 2056:2011 Page 3 of 12 pages 1 Sco
12、pe This Standard defines a standardized wrapper for the carriage of low bit rate MPEG-2 TS packets, in the 10-bit vertical ancillary data (VANC) space of a standard definition or high definition serial digital link in accordance with SMPTE ST 291. Examples of such low bitrate services are EBIF and D
13、VB bitmapped subtitles. Note: Low bit rate means typically 1-20 TS packets per video frame. 2 Conformance Notation 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
14、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
15、 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
16、, 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.
17、 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 additio
18、n 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 o
19、ptional 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; followed by formal languag
20、es; 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 indicated were valid. All standards are subject t
21、o 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. SMPTE ST 291:2010, Ancillary Data Packet and Space Formatting ISO/IEC 13818-1:2007, Information Technology Gene
22、ric Coding of Moving Pictures and Associated Audio Information: Systems ISO/IEC 13818-6:1998, Information Technology Generic Coding of Moving Pictures and Associated Audio Information Part 6: Extensions for DSM-CC SMPTE ST 2056:2011 Page 4 of 12 pages 4 Definitions and Acronyms carousel: A term refe
23、rring to a technique defined by MPEG and other standards where one or more TS packets are multiplexed into a TS by cyclically repeating the contents of those packets. See Section 5.5. DTS: An abbreviation for Decode Time Stamp. (Note: See ISO/IEC 13818-1.) EBIF: An abbreviation for Enhanced TV Binar
24、y Interchange Format (Note: See CableLabs OC-SP-ETV-BIF1.0-I04-070921.) IRD: An abbreviation for Integrated Receiver Decoder. NOT: The logical function NOT is the logical inverse of the bit or bits designated. PCR: An abbreviation for Program Clock Reference. (Note: See ISO/IEC 13818-1.) PSI: An abb
25、reviation for Program Specific Information tables. (Note: See ISO/IEC 13818-1.) PTS: An abbreviation for Presentation Time Stamp. (Note: See ISO/IEC 13818-1.) SI: An abbreviation for Service or System Information tables. (Note: See relevant ATSC, DVB, and SCTE standards.) STB: An abbreviation for Se
26、t-Top Box. TS: An abbreviation for (MPEG-2) Transport Stream. (Note: See ISO/IEC 13818-1.) TSCD: An abbreviation for TS Carriage Data. UDW: An abbreviation for “user data words.” (Note: See SMPTE ST 291.) uimsbf: An abbreviation for Unsigned integer, most significant bit first. Note: The byte order
27、of multi-byte uimsbf words is most significant byte first. VANC: An abbreviation for Vertical ANCillary. As used in this document it is an acronym for vertical ancillary data space. 5 System Overview (Informative) A number of system architectures have assumed co-location of some type of data generat
28、or (such as a bitmapped subtitle generator) with the system multiplexer. In the particular case of subtitles, this was due to the necessity of obtaining the MPEG-2 Systems PCR timestamp samples from the associated video bitstream, thus permitting correct values of PTS in the subtitle TS packets. As
29、“digital turn-around” architectures became commonplace, the need to “bridge” data services between an IRD and a downstream encoder arose. System operators desire a “one-wire” system architecture, and thus the requirement for placing the subtitle or EBIF TS packets into the VANC of their associated v
30、ideo frame. This standard provides that mechanism. 5.1 Use Cases for MPEG-2 TS in VANC Services (Informative) There are three general types of services using this Standard: one is for TS packets which bear a definitive relationship to a given frame of video (which might be termed “frame synchronous”
31、); the second is where the SMPTE ST 2056:2011 Page 5 of 12 pages relationship is to a frame in the future (which might be termed “loosely coupled” to the video), not in the present, and the third is where there is a much looser relationship, if any. In the first case, the transmitter for this system
32、 (which, creating potential confusion, is often an MPEG decoder, also called an IRD) needs to establish that relationship using the clock sample timestamps provided by MPEG-2 Systems (PCR, PTS, DTS), decode the video and audio as expected by the user plus ensure that the associated MPEG-2 TS packet
33、carrying the ancillary service is placed into the VANC of the designated video frame and no other. This permits the downstream receiver (which, also potentially confusing) is typically an encoder of audio/video/data baseband (which produces a MPEG-2 TS output) to ensure that the clock sample timesta
34、mps in the conveyed TS packet are modified to match those of the new TS. In the second case (“loosely coupled”), the transmitter (IRD) needs to perform calculations using PTS values (see Section 5.2) as well as getting the TS packet into the VANC of the closest frame of video to its original placeme
35、nt in the arriving MPEG-2 TS. The transmitter also needs to support situations where several different arriving TS packets carry the same PTS values, and are simply passed through without buffering or re-ordering. In the third case, the transmitter (IRD) needs not worry about the presence of PTS or
36、the VANC of the exact video output frame into which to place the TS packet. Rather, the transmitter is concerned with whether or not the packet needs to be carouseled or will be simply placed into the ultimate output TS once. If the packet needs to be carouseled, then the transmitter needs to set th
37、e repetition rate and duration in the header of the message. 5.2 Breaking the Prior MPEG TS Clock Domain (Informative) An example of a frame synchronous service is AMOL data (see ANSI/SCTE 127) which is tied to the video frame most closely associated with the PTS value in the MPEG-2 TS PES packet he
38、ader. An example of a loosely coupled service is DVB subtitles (see ETSI 300 743), where there may be several TS packets carrying subtitle data with the same PTS value. Each of these services uses the MPEG-2 PES packet structure to carry a PTS value. The values are handled differently for each case.
39、 For frame synchronous services, the transmitting IRD needs to not only reconstruct the encoded video and audio, but also ensure that each incoming frame synchronous TS packet is placed into the correct output video frames VANC space. The transmitting IRD does no adjustment to the original PTS value
40、. This provides the receiving encoder with the precise input TS packet to video frame relationship to ensure that the TS packet can be extracted from the VANC and placed into the outgoing TS simply by overwriting the PTS value in the extracted TS packet with the PTS value matching the compressed vid
41、eo frame to which it is associated. For loosely coupled services, the transmitting IRD needs to adjust the PTS value by subtracting the current value of the programs PCR as maintained by the IRD from the PTS value in the arriving TS packet. The IRD then places that relative value into the PES packet
42、 header, replacing the original value. The receiving encoder needs to then further adjust the PTS value by adding that relative value to its current PCR clock sample to become the final PTS value, as it places the TS packet in the outgoing TS. The IRD needs to place each arriving TS packet for the s
43、ervice into the VANC of a corresponding output video frame using a constant processing delay. This process (as done by both devices) results in the following equation: newPTS = oldPTS - inputPCR + outputPCR See the semantics for PTS_processing_flag in Section 6.2 for the specific details. For the th
44、ird case outlined above, there is no requirement to perform any adjustment of timestamps or careful alignment with output video. SMPTE ST 2056:2011 Page 6 of 12 pages 5.3 Additional Considerations for DVB Subtitles (Informative) The bit rate allocated to DVB subtitles within a TS is typically small
45、and can be as low as 64-128 kbps per language. Subtitle data is typically “pre-loaded” to reduce the bitrate per frame. There is no upper range, but for example, 8 languages might run as high as 1.6 Mbps total for HD. This leads the origination equipment to pre-load subtitles up to 3 seconds ahead o
46、f the display time to give the STB time to decode the subtitle. The space available within the HD-SDI is relatively large and is able to handle 32 lines of SMPTE ST 2031 data within a single vertical interval line for example. Video encoding delays allows the subtitle data to be sent early if requir
47、ed. The DVB subtitle specification (see ETSI EN 300 743) details a “buffer model” for the decoder plus a “decoder rendering bandwidth” model. Adherence to these models can be broken if subtitle data TS packets are not delivered at roughly the same data rate as that originally intended. The relative
48、temporal spacing between the PES packets being delivered in VANC and placed into the receiving encoders outgoing TS needs to be maintained. Various geographical regions have deployed STBs which are sensitive to the above features. Implementation experience has led some implementers to build local pr
49、ofiles into their equipment to cope with known limitations with the STB population. 5.4 Table Handling (Informative) This Standard also provides a mechanism to pass MPEG/ATSC/DVB/SCTE table structures (“PSI/SI”), such as a TS packet carrying a PMT section. One use is to permit changes in PID values without a human needing to intervene. Other uses relate to the different types of services hosted on this link but are beyond the scope of this document. 5.5 Data Carousels (Informative) As noted earlier, this Standard provides mech
