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Versions: (draft-edwards-payload-rtp-ancillary) 00 01 02 03 04 05 06 07 08 09 10

A/V Transport Payloads Working Group                          T. Edwards
Internet-Draft                                                       FOX
Intended status: Standards Track                           June 15, 2017
Expires: December 17, 2017


              RTP Payload for SMPTE ST 291 Ancillary Data
                  draft-ietf-payload-rtp-ancillary-10

Abstract

   This memo describes a real-time transport protocol (RTP) payload
   format for the Society of Motion Picture and Television Engineers
   (SMPTE) Ancillary data, as defined by SMPTE ST 291-1.  SMPTE
   Ancillary data is generally used along with professional video
   formats to carry a range of ancillary data types, including time
   code, Closed Captioning, and the Active Format Description (AFD).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 17, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  RTP Payload Format for SMPTE ST 291 Ancillary Data  . . . . .   3
     2.1.  Payload Header Definitions  . . . . . . . . . . . . . . .   5
   3.  Payload Format Parameters . . . . . . . . . . . . . . . . . .  10
     3.1.  Media Type Definition . . . . . . . . . . . . . . . . . .  10
   4.  SDP Considerations  . . . . . . . . . . . . . . . . . . . . .  12
     4.1.  Grouping ANC Streams with other Media Streams . . . . . .  13
   5.  Offer/Answer Model and Declarative Considerations . . . . . .  14
     5.1.  Offer/Answer Model  . . . . . . . . . . . . . . . . . . .  14
     5.2.  Declarative SDP Considerations  . . . . . . . . . . . . .  14
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   This memo describes a real-time transport protocol (RTP) payload
   format for the Society of Motion Picture and Television Engineers
   (SMPTE) Ancillary data (ANC), as defined by SMPTE ST 291-1 [ST291].
   ANC data is transmitted in the ancillary space of serial digital
   video interfaces, the space outside of the active video region of
   images intended for users to view.  Ancillary space roughly
   corresponds to vertical and horizontal blanking periods of cathode
   ray tube type displays.  ANC can carry a range of data types,
   including time code, Closed Captioning, and the Active Format
   Description (AFD).

   ANC is generally associated with the carriage of metadata within the
   bit stream of a Serial Digital Interface (SDI) such as SMPTE ST 259
   [ST259], the standard definition (SD) Serial Digital Interface (with
   ANC data inserted as per SMPTE ST 125 [ST125]), or SMPTE ST 292-1
   [ST292], the 1.5 Gb/s Serial Digital Interface for high definition
   (HD) television applications.

   ANC data packet payload definitions for a specific application are
   specified by a SMPTE Standard, Recommended Practice, Registered
   Disclosure Document, or by a document generated by another
   organization, a company, or an individual (an Entity).  When a




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   payload format is registered with SMPTE, it is identified by a
   registered data identification word.

   This memo describes an RTP payload that supports carriage of ANC data
   packets with origin from any location within any SMPTE defined SDI
   signal, or even if the ANC packets did not originate in an SDI
   signal.  Sufficient information is provided to enable the ANC data
   packets at the output of the decoder to be restored to their original
   locations in the serial digital video signal raster (if that is
   desired).  An optional Media Type parameter allows for signaling of
   carriage of one or more types of ANC data as specified by Data
   Identification (DID) or Secondary Data Identification (SDID) words.
   Another optional Media Type parameter allows for the identification
   of the Video Payload ID (VPID) Code of the source interface of ANC
   data packets.

   Note that the ancillary data flag (ADF) word is not specifically
   carried in this RTP payload.  The ADF might be specified in a
   document defining an interconnecting digital video interface,
   otherwise a default ADF is specified by SMPTE ST 291-1 [ST291].

   This ANC payload can be used by itself, or used along with a range of
   RTP video formats.  In particular, it has been designed so that it
   could be used along with RFC 4175 [RFC4175] "RTP Payload Format for
   Uncompressed Video" or RFC 5371 [RFC5371] "RTP Payload Format for
   JPEG 2000 Video Streams."

   The data model in this document for the ANC data RTP payload is based
   on the data model of SMPTE ST 2038 [ST2038], which standardizes the
   carriage of ANC data packets in an MPEG-2 Transport Stream.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  RTP Payload Format for SMPTE ST 291 Ancillary Data

   An example of the format of an RTP packet containing SMPTE ST 291
   Ancillary Data is shown below:










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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |V=2|P|X| CC    |M|    PT       |        sequence number        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           timestamp                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           synchronization source (SSRC) identifier            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Extended Sequence Number    |            Length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | ANC_Count     | F |                reserved                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |C|   Line_Number       |   Horizontal_Offset   |S|  StreamNum  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         DID       |        SDID       |   Data_Count      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                User_Data_Words...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   |   Checksum_Word   |         word_align            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |C|   Line_Number       |   Horizontal_Offset   |S|  StreamNum  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         DID       |        SDID       |   Data_Count      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                User_Data_Words...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |   Checksum_Word   |word_align |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 1: SMPTE Ancillary Data RTP Packet Format

   In this example, two ANC data packets are present.  The first has
   four 10-bit User Data Words, and the second has five 10-bit User Data
   Words.

   The term "network byte order" in the payload format SHALL refer to
   the Data Transmission Order as defined in Appendix B of RFC 791
   [RFC0791].

   RTP packet header fields SHALL be interpreted as per RFC 3550
   [RFC3550], with the following specifics:

   Timestamp: 32 bits
           The timestamp field is interpreted in a similar fashion to
           RFC 4175 [RFC4175]:





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           For progressive scan video, the timestamp denotes the
           sampling instant of the frame to which the ancillary data in
           the RTP packet belongs.  RTP packets MUST NOT include ANC
           data from multiple frames, and all RTP packets with ANC data
           belonging to the same frame MUST have the same timestamp.

           For interlaced video, the timestamp denotes the sampling
           instant of the field to which the ancillary data in the RTP
           packet belongs.  RTP packets MUST NOT include ANC data from
           multiple fields, and all RTP packets belonging to the same
           field MUST have the same timestamp.

           If the sampling instant does not correspond to an integer
           value of the clock, the value SHALL be truncated to the next
           lowest integer, with no ambiguity.  Section 3.1 describes
           timestamp clock rates.

   Marker bit (M): 1 bit
           The marker bit set to "1" indicates the last ANC RTP packet
           for a frame (for progressive scan video) or the last ANC RTP
           packet for a field (for interlaced video).

2.1.  Payload Header Definitions

   The ANC RTP payload header fields are defined as:

   Extended Sequence Number: 16 bits
           The high order bits of the extended 32-bit sequence number,
           in network byte order.  This is the same as the Extended
           Sequence Number field in RFC 4175 [RFC4175].

   Length: 16 bits
           Number of octets of the ANC RTP payload, beginning with the
           "C" bit of the first ANC packet data, as an unsigned integer
           in network byte order.  Note that all word_align fields
           contribute to the calculation of the length field.

   ANC_Count: 8 bits
           This field is the count of the total number of ANC data
           packets carried in the RTP payload, as an unsigned integer.
           A single ANC RTP packet payload cannot carry more than 255
           ANC data packets.

           If more than 255 ANC data packets need to be carried in a
           field or frame, additional RTP packets carrying ANC data MAY
           be sent with the same RTP timestamp but with different
           sequence numbers.  ANC_Count of 0 indicates that there are no
           ANC data packets in the payload (for example, for an RTP



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           packet with the marker bit set indicating the last ANC RTP
           packet in a field/frame, even if that RTP packet carries no
           actual ANC data packets.)  If ANC_Count is 0, Length will
           also be 0.

   F: 2 bits
           These two bits relate to signaling the field specified by the
           RTP timestamp in an interlaced SDI raster.  A value of 0b00
           indicates that either the video format is progressive or that
           no field is specified.  A value of 0b10 indicates that the
           timestamp refers to the first field of an interlaced video
           signal.  A value of 0b11 indicates that the timestamp refers
           to the second field of an interlaced video signal.  The value
           0b01 is not valid.

           Note that some multi-stream SDI interfaces might use multiple
           interlaced signal streams to transmit progressive images, in
           which case the "F" bits would refer to the field of the
           interlaced stream used for transport of the ANC data packet.

   reserved: 22 bits
           The 22 reserved bits of value "0" follow the F field to
           ensure that the first ANC data packet header field in the
           payload begins 32-bit word-aligned to ease implementation.

   For each ANC data packet in the payload, the following ANC data
   packet header fields MUST be present:

   C: 1 bit
           This flag, when set to "1", indicates that the ANC data
           corresponds to the color-difference data channel (C).  When
           set to "0", this flag indicates either that the ANC data
           corresponds to the luma (Y) data channel, that the ANC data
           source is from an SD signal, or that the ANC data source has
           no specific luma or color-difference data channels.  For ANC
           data from a multi-stream interface source, the C flag SHALL
           refer to the channel of the stream used to transport the ANC
           packet.  For situations where there is no SDI source, if the
           ANC data type definition specifically requires the use of the
           C or Y data channel, the C flag SHALL reflect that
           requirement.

   Line_Number: 11 bits
           This field contains the line number (as defined in ITU-R
           BT.1700 [BT1700] for SD video or ITU-R BT.1120 [BT1120] for
           HD video) that corresponds to the location of the ANC data
           packet in an SDI raster as an unsigned integer in network
           byte order.  A value of 0x7FF (all bits in the field are '1')



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           indicates that the ANC data is carried without a specific
           line location within the field or frame.  A value of 0x7FE
           indicates that the ANC data is intended to be placed into any
           legal area of VANC, specifically.

           Note that the lines that are available to convey ANC data are
           as defined in the applicable sample structure specification
           (e.g., SMPTE 274M [ST274], SMPTE ST 296 [ST296], ITU-R BT.656
           [BT656]) and possibly further restricted per SMPTE RP 168
           [RP168].

           In multi-stream interfaces, this field refers to the line
           number that an ANC packet is carried on within a particular
           data stream in the interface.

   Horizontal_Offset: 12 bits
           This field defines the location of the ANC data packet in an
           SDI raster relative to the start of active video (SAV) as an
           unsigned integer in network byte order.  A value of 0 means
           that the Ancillary Data Flag (ADF) of the ANC data packet
           begins immediately following SAV.  For HD, this is in units
           of luma sample numbers as specified by the defining document
           of the particular image (e.g., SMPTE 274M [ST274] for 1920 x
           1080 active images, or SMPTE ST 296 [ST296] for 1280 x 720
           progressive active images).  For SD, this is in units of
           (27MHz) multiplexed word numbers, as specified in SMPTE ST
           125 [ST125].  A value of 0xFFF (all bits in the field are
           '1') indicates that the ANC data is carried without any
           specific location within the line.  A value of 0xFFE
           indicates that the ANC data is intended to be placed into any
           legal area of HANC, specifically.

           In multi-stream interfaces, this field refers to the
           horizontal location where an ANC packet is placed on a line
           carried within a particular data stream in the interface.

           Note that HANC space in the digital blanking area will
           generally have higher luma sample numbers than any samples in
           the active digital line.

   S (Data Stream Flag): 1 bit
           This field indicates whether the data stream number of a
           multi-stream data mapping used to transport the ANC data
           packet is specified.  If the S bit is '0', then the StreamNum
           field provides no guidance regarding the source data stream
           number of the ANC data packet.  If the S bit is '1', then the
           StreamNum field carries information regarding the source data
           stream number of the ANC data packet.



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   StreamNum: 7 bits
           If the S (Data Stream Flag) bit is '1', then the StreamNum
           field MUST carry identification of the source data stream
           number of the ANC data packet.  If the data stream is
           numbered, then the StreamNum field SHALL carry the number of
           the source data stream minus one.  If the source multi-stream
           interface does not have numbered data streams, the following
           numbers SHALL be used in this field: '0' for link A data
           stream, '1' for link B data stream.  For stereoscopic multi-
           stream interface formats that do not have numbered streams,
           the following numbers SHALL be used in this field: '0' for
           left eye stream, '1' for right eye stream.

           Note that in multi-link SDI connections, the physical link
           that a particular stream utilizes is typically specified by
           the interface standard.  Also note that numbering of data
           streams is across the interface as a whole.  For example in
           the SMPTE ST 425-3 dual-link 3 Gb/s interface, the data
           streams are numbered 1-4 with data streams 1 and 2 on link 1
           and data streams 3 and 4 on link 2.

   An ANC data packet with the header fields Line_Number of 0x7FF and
   Horizontal_Offset of 0xFFF SHALL be considered to be carried without
   any specific location within the field or frame.

   For each ANC data packet in the payload, immediately after the ANC
   data packet header fields, the following data fields MUST be present,
   with the fields DID, SDID, Data_Count, User_Data_Words, and
   Checksum_Word representing the 10-bit words carried in the ANC data
   packet, as per SMPTE ST 291-1 [ST291]:

   DID: 10 bits
           Data Identification Word

   SDID: 10 bits
           Secondary Data Identification Word.  Used only for a "Type 2"
           ANC data packet.  Note that in a "Type 1" ANC data packet,
           this word will actually carry the Data Block Number (DBN).

   Data_Count: 10 bits
           The lower 8 bits of Data_Count, corresponding to bits b7
           (MSB) through b0 (LSB) of the 10-bit Data_Count word, contain
           the actual count of 10-bit words in User_Data_Words.  Bit b8
           is the even parity for bits b7 through b0, and bit b9 is the
           inverse (logical NOT) of bit b8.

   User_Data_Words: integer number of 10 bit words




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           User_Data_Words (UDW) are used to convey information of a
           type as identified by the DID word or the DID and SDID words.
           The number of 10-bit words in the UDW is defined by the
           Data_Count field.  The 10-bit words are carried in order
           starting with the most significant bit and ending with the
           least significant bit.

   Checksum_Word: 10 bits
           The Checksum_Word can be used to determine the validity of
           the ANC data packet from the DID word through the UDW.  It
           consists of 10 bits, where bits b8 (MSB) through b0 (LSB)
           define the checksum value and bit b9 is the inverse (logical
           NOT) of bit b8.  The checksum value is equal to the nine
           least significant bits of the sum of the nine least
           significant bits of the DID word, the SDID word, the
           Data_Count word, and all User_Data_Words in the ANC data
           packet.  The checksum is initialized to zero before
           calculation, and any end carry resulting from the checksum
           calculation is ignored.

   At the end of each ANC data packet in the payload:

   word_align: bits as needed to complete 32-bit word
           Word align contains enough "0" bits as needed to complete the
           last 32-bit word of ANC packet's data in the RTP payload.  If
           an ANC data packet in the RTP payload ends aligned with a
           word boundary, there is no need to add any word alignment
           bits.  Word align SHALL be used even for the last ANC data
           packet in an RTP packet.  Word align SHALL NOT be used if
           there are zero ANC data packets being carried in the RTP
           packet.

   When reconstructing an SDI signal based on this payload, it is
   important to place ANC data packets into the locations indicated by
   the ANC payload header fields C, Line_Number and Horizontal_Offset,
   and also to follow the requirements of SMPTE ST 291-1 [ST291]
   Section 7 "Ancillary Data Space Formatting (Component or Composite
   Interface)", which include rules on the placement of initial ANC data
   into allowed spaces as well as the contiguity of ANC data packet
   sequences within those spaces in order to assure that the resulting
   ANC data packets in the SDI signal are valid.  The optional Media
   Type parameter VPID_Code can inform receivers of the type of
   originating SDI interface.  For multi-stream originating interfaces,
   the StreamNum field can provide information regarding which stream an
   ANC data packet can be placed in to match the ANC data location in
   the originating SDI interface.





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   Senders of this payload SHOULD transmit available ANC data packets as
   soon as practical to reduce end-to-end latency, especially if
   receivers will be embedding the received ANC data packet into an SDI
   signal emission.  One millisecond is a reasonable upper bound for the
   amount of time between when an ANC data packet becomes available to a
   sender and the emission of an RTP payload containing that ANC data
   packet.

   ANC data packets with headers that specify specific location within a
   field or frame SHOULD be sent in raster scan order, both in terms of
   packing position within an RTP packet and in terms of transmission
   time of RTP packets.

3.  Payload Format Parameters

   This RTP payload format is identified using the video/smpte291 media
   type, which is registered in accordance with RFC 4855 [RFC4855], and
   using the template of RFC 6838 [RFC6838].

   Note that the Media Type Definition is in the "video" tree due to the
   expected use of SMPTE ST 291 Ancillary Data along with video formats.

3.1.  Media Type Definition

   Type name: video

   Subtype name: smpte291

   Required parameters:

      Rate:
         RTP timestamp clock rate.

         When an ANC RTP stream is to be associated with an RTP video
         stream, the RTP timestamp rates SHOULD be the same to ensure
         that ANC data packets can be associated with the appropriate
         frame or field.  Otherwise, a 90 kHz rate SHOULD be used.

         Note that techniques described in RFC 7273 [RFC7273] can
         provide a common reference clock for multiple RTP streams
         intended for synchronized presentation.

   Optional parameters:

      DID_SDID:
         Data identification and Secondary data identification words.





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         The presence of the DID_SDID parameters signals that all
         ancillary data packets of this stream are of a particular type
         or types, i.e., labeled with a particular DIDs and SDIDs.  DID
         and SDID values of SMPTE Registered ANC packet types can be
         found on the at the SMPTE Registry for Data Identification Word
         Assignments [SMPTE-RA] web site.

         "Type 1" ANC packets (which do not have SDIDs defined) SHALL be
         labeled with SDID=0x00.

         DID and SDID values can be registered with SMPTE as per SMPTE
         ST 291-1 [ST291].

         The absence of the DID_SDID parameter signals that
         determination of the DID and SDID of ANC packets in the payload
         can only be achieved through direct inspection of the ANC data
         packet fields.

      VPID_Code:
         This integer parameter specifies the Video Payload ID (VPID)
         Code of the source interface of ANC data packets using the
         value from byte 1 of the VPID as defined in SMPTE ST 352
         [ST352].  The integer SHALL be made with bit 7 of VPID byte 1
         being the most significant bit, and bit 0 of VPID byte 1 being
         the least significant bit.  For example, 132 refers to SMPTE ST
         292-1, 720-line video payloads on a 1.5 Gbps (nominal) serial
         digital interface.

   Encoding considerations: This media type is framed and binary; see
   Section 4.8 of RFC 6838 [RFC6838].

   Security considerations: See Section 7 of [this RFC]

   Interoperability considerations: Data items in smpte291 can be very
   diverse.  Receivers might only be capable of interpreting a subset of
   the possible data items.  Some implementations might care about the
   location of the ANC data packets in the SDI raster, but other
   implementations might not care.

   Published specification: [this RFC]

   Applications that use this media type: Devices that stream real-time
   professional video, especially those that interoperate with legacy
   serial digital interfaces (SDI).

   Additional Information:

      Deprecated alias names for this type: N/A



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      Magic number(s): N/A

      File extension(s): N/A

      Macintosh file type code(s): N/A

   Person & email address to contact for further information: T.
   Edwards <thomas.edwards@fox.com>, IETF Payload Working Group
   <payload@ietf.org>

   Intended usage: COMMON

   Restrictions on usage: This media type depends on RTP framing, and
   hence is only defined for transfer via RTP RFC 3550 [RFC3550].
   Transport within other framing protocols is not defined at this time.

   Author: T.  Edwards <thomas.edwards@fox.com>

   Change controller: The IETF PAYLOAD working group, or other party as
   designated by the IESG.

4.  SDP Considerations

   The mapping of the above defined payload format media type and its
   parameters SHALL be done according to Section 3 of RFC 4855
   [RFC4855].

   o  The type name ("video") goes in SDP "m=" as the media name.

   o  The subtype name ("smpte291") goes in SDP "a=rtpmap" as the
      encoding name, followed by a slash ("/") and the rate parameter.

   o  The optional parameters VPID_Code and DID_SDID, when present, are
      included in the "a=fmtp" attribute line of SDP as a semicolon-
      separated list of parameter=value pairs.

   DID and SDID values SHALL be specified in hexadecimal with a "0x"
   prefix (such as "0x61").  The ABNF as per RFC 5234 [RFC5234] of the
   DID_SDID optional parameter SHALL be:

           TwoHex = "0x" 1*2(HEXDIG)
           DidSdid = "DID_SDID={" TwoHex "," TwoHex "}"

   For example, EIA 608 Closed Caption data would be signalled with the
   parameter DID_SDID={0x61,0x02}.  If a DID_SDID parameter is not
   specified, then the ancillary data stream might potentially contain
   ancillary data packets of any type.




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   Multiple DID_SDID parameters can be specified (separated by
   semicolons) to signal the presence of multiple types of ANC data in
   the stream.  DID_SDID={0x61,0x02};DID_SDID={0x41,0x05}, for example,
   signals the presence of EIA 608 Closed Captions as well as AFD/Bar
   Data.  Multiple DID_SDID parameters do not imply any particular
   ordering of the different types of ANC packets in the stream.

   If the optional parameter VPID_Code is present, it SHALL be present
   only once in the semicolon-separated list, taking a single integer
   value.

   A sample SDP mapping for ancillary data is as follows:

        m=video 30000 RTP/AVP 112
        a=rtpmap:112 smpte291/90000
        a=fmtp:112 DID_SDID={0x61,0x02};DID_SDID={0x41,0x05};VPID_Code=132

   In this example, a dynamic payload type 112 is used for ancillary
   data.  The 90 kHz RTP timestamp rate is specified in the "a=rtpmap"
   line after the subtype.  In the "a=fmtp:" line, DID 0x61 and SDID
   0x02 are specified (registered to EIA 608 Closed Caption Data by
   SMPTE), and also DID 0x41 and SDID 0x05 (registered to AFD/Bar Data).
   The VPID_Code is 132 (referring to SMPTE ST 292-1, 720-line video
   payloads on a 1.5 Gbps serial digital interface).

4.1.  Grouping ANC Streams with other Media Streams

   To associate an ANC RTP stream with other media streams, implementers
   can use the Lip Synchronization (LS) grouping defined in RFC 5888
   [RFC5888], which states that media streams whose corresponding "m"
   lines are grouped together using LS semantics are to be played back
   in a synchronized manner.

   A sample SDP mapping for grouping ANC data with RFC 4175 video using
   LS semantics is as follows:
















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        v=0
        o=Al 123456 11 IN IP4 host.example.com
        s=Professional Networked Media Test
        i=A test of synchronized video and ANC data
        t=0 0
        a=group:LS V1 M1
        m=video 50000 RTP/AVP 96
        c=IN IP4 233.252.0.1/255
        a=rtpmap:96 raw/90000
        a=fmtp:96 sampling=YCbCr-4:2:2; width=1280; height=720; depth=10
        a=mid:V1
        m=video 50010 RTP/AVP 97
        c=IN IP4 233.252.0.2/255
        a=rtpmap:97 smpte291/90000
        a=fmtp:97 DID_SDID={0x61,0x02};DID_SDID={0x41,0x05}
        a=mid:M1

5.  Offer/Answer Model and Declarative Considerations

5.1.  Offer/Answer Model

   Receivers might wish to receive ANC data streams with specific
   DID_SDID parameters.  Thus when offering ANC data streams using the
   Session Description Protocol (SDP) in an Offer/Answer model
   [RFC3264], the offeror MAY provide a list of ANC streams available
   with specific DID_SDID parameters in the fmtp line.  The answerer MAY
   respond with all or a subset of the streams offered along with fmtp
   lines with all or a subset of the DID_SDID parameters offered.  Or
   the answerer MAY reject the offer.  There are no restrictions on
   updating DID_SDID parameters in a subsequent offer.

5.2.  Declarative SDP Considerations

   For declarative use of SDP, nothing specific is defined for this
   payload format.  The configuration given by the SDP MUST be used when
   sending and/or receiving media in the session.

6.  IANA Considerations

   One media type (video/smpte291) has been defined and needs
   registration in the media types registry.  See Section 3.1

7.  Security Considerations

   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [RFC3550], and in any applicable RTP profile such as
   RTP/AVP [RFC3551], RTP/AVPF [RFC4585] RTP/SAVP [RFC3711] or RTP/SAVPF



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   [RFC5124].  However, as "Securing the RTP Protocol Framework: Why RTP
   Does Not Mandate a Single Media Security Solution" [RFC7202]
   discusses, it is not an RTP payload format's responsibility to
   discuss or mandate what solutions are used to meet the basic security
   goals like confidentiality, integrity and source authenticity for RTP
   in general.  This responsibility lays on anyone using RTP in an
   application.  They can find guidance on available security mechanisms
   and important considerations in Options for Securing RTP Sessions
   [RFC7201].  Applications SHOULD use one or more appropriate strong
   security mechanisms.  The rest of this security consideration section
   discusses the security impacting properties of the payload format
   itself.

   To avoid potential buffer overflow attacks, receivers SHOULD validate
   that the ANC data packets in the RTP payload are of the appropriate
   length (using the Data_Count field) for the ANC data type specified
   by DID & SDID.  Also the Checksum_Word SHOULD be checked against the
   ANC data packet to ensure that its data has not been damaged in
   transit, but the Checksum_Word is unlikely to provide a payload
   integrity check in case of a directed attack.

   Some receivers will simply move the ANC data packet bits from the RTP
   payload into a serial digital interface (SDI).  It might still be a
   good idea for these "re-embedders" to perform the above mentioned
   validity tests to avoid downstream SDI systems from becoming confused
   by bad ANC data packets, which could be used for a denial of service
   attack.

   "Re-embedders" into SDI SHOULD also double check that the Line_Number
   and Horizontal_Offset leads to the ANC data packet being inserted
   into a legal area to carry ancillary data in the SDI video bit stream
   of the output video format.

8.  References

8.1.  Normative References

   [BT1120]   ITU-R, "BT.1120-8, Digital Interfaces for HDTV Studio
              Signals", January 2012.

   [BT1700]   ITU-R, "BT.1700, Characteristics of Composite Video
              Signals for Conventional Analogue Television Systems",
              February 2005.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <http://www.rfc-editor.org/info/rfc791>.




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <http://www.rfc-editor.org/info/rfc3264>.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <http://www.rfc-editor.org/info/rfc3550>.

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              DOI 10.17487/RFC3551, July 2003,
              <http://www.rfc-editor.org/info/rfc3551>.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, DOI 10.17487/RFC3711, March 2004,
              <http://www.rfc-editor.org/info/rfc3711>.

   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
              "Extended RTP Profile for Real-time Transport Control
              Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
              DOI 10.17487/RFC4585, July 2006,
              <http://www.rfc-editor.org/info/rfc4585>.

   [RFC4855]  Casner, S., "Media Type Registration of RTP Payload
              Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007,
              <http://www.rfc-editor.org/info/rfc4855>.

   [RFC5124]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for
              Real-time Transport Control Protocol (RTCP)-Based Feedback
              (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February
              2008, <http://www.rfc-editor.org/info/rfc5124>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.







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   [RFC5888]  Camarillo, G. and H. Schulzrinne, "The Session Description
              Protocol (SDP) Grouping Framework", RFC 5888,
              DOI 10.17487/RFC5888, June 2010,
              <http://www.rfc-editor.org/info/rfc5888>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <http://www.rfc-editor.org/info/rfc6838>.

   [ST291]    SMPTE, "ST 291-1:2011, Ancillary Data Packet and Space
              Formatting", 2011.

   [ST352]    SMPTE, "ST 352:2013, Payload Identification Codes for
              Serial Digital Interfaces", 2013.

8.2.  Informative References

   [BT656]    ITU-R, "BT.656-5, Interfaces for Digital Component Video
              Signals in 525-Line and 625-Line Television Systems
              Operating at the 4:2:2 Level of Recommendation ITU-R
              BT.601", December 2007.

   [RFC4175]  Gharai, L. and C. Perkins, "RTP Payload Format for
              Uncompressed Video", RFC 4175, DOI 10.17487/RFC4175,
              September 2005, <http://www.rfc-editor.org/info/rfc4175>.

   [RFC5371]  Futemma, S., Itakura, E., and A. Leung, "RTP Payload
              Format for JPEG 2000 Video Streams", RFC 5371,
              DOI 10.17487/RFC5371, October 2008,
              <http://www.rfc-editor.org/info/rfc5371>.

   [RFC7201]  Westerlund, M. and C. Perkins, "Options for Securing RTP
              Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014,
              <http://www.rfc-editor.org/info/rfc7201>.

   [RFC7202]  Perkins, C. and M. Westerlund, "Securing the RTP
              Framework: Why RTP Does Not Mandate a Single Media
              Security Solution", RFC 7202, DOI 10.17487/RFC7202, April
              2014, <http://www.rfc-editor.org/info/rfc7202>.

   [RFC7273]  Williams, A., Gross, K., van Brandenburg, R., and H.
              Stokking, "RTP Clock Source Signalling", RFC 7273,
              DOI 10.17487/RFC7273, June 2014,
              <http://www.rfc-editor.org/info/rfc7273>.

   [RP168]    SMPTE, "RP 168:2009, Definition of Vertical Interval
              Switching Point for Synchronous Video Switching", 2009.



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   [SMPTE-RA]
              SMPTE Registration Authority, LLC, "SMPTE ST 291 Ancillary
              Data Identification Word Assignments for Registered DIDs",
              2011, <http://www.smpte-ra.org/
              smpte-ancillary-data-smpte-st-291>.

   [ST125]    SMPTE, "ST 125:2013, SDTV Component Video Signal Coding
              4:4:4 and 4:2:2 for 13.5 MHz and 18 MHz Systems", 2013.

   [ST2038]   SMPTE, "ST 2038:2008, Carriage of Ancillary Data Packets
              in an MPEG-2 Transport Stream", 2008.

   [ST259]    SMPTE, "ST 259:2008, SDTV Digital Signal/Data - Serial
              Digital Interface", 2008.

   [ST274]    SMPTE, "ST 274:2008, 1920 x 1080 Image Sample Structure,
              Digital Representation and Digital Timing Reference
              Sequences for Multiple Picture Rates", 2008.

   [ST292]    SMPTE, "ST 292-1:2012, 1.5 Gb/s Signal/Data Serial
              Interface", 2012.

   [ST296]    SMPTE, "ST 296:2012, 1280 x 720 Progressive Image 4:2:2
              and 4:4:4 Sample Structure - Analog and Digital
              Representation and Analog Interface", 2012.

Author's Address

   Thomas G. Edwards
   FOX
   10201 W. Pico Blvd.
   Los Angeles, CA  90035
   USA

   Phone: +1 310 369 6696
   Email: thomas.edwards@fox.com















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