Internet DRAFT - draft-edwards-rtp-ancillary
draft-edwards-rtp-ancillary
A/V Transport Payloads Workgroup T. Edwards
Internet-Draft FOX
Intended status: Informational January 13, 2015
Expires: July 17, 2015
RTP Payload for SMPTE ST 291 Ancillary Data
draft-edwards-rtp-ancillary-00
Abstract
This memo describes an RTP Payload format for 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, KLV metadata, Closed Captioning, and
the Active Format Description (AFD).
Status of This Memo
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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 . . . . . . . . . . . . . . . 4
3. Payload Format Parameters . . . . . . . . . . . . . . . . . . 6
3.1. Media Type Definition . . . . . . . . . . . . . . . . . . 6
3.2. Mapping to SDP . . . . . . . . . . . . . . . . . . . . . 8
3.3. Offer/Answer Model and Declarative Considerations . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Normative References . . . . . . . . . . . . . . . . . . 9
6.2. Informative References . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
This memo describes an RTP Payload format for Society of Motion
Picture and Television Engineers (SMPTE) Ancillary data (ANC), as
defined by SMPTE ST 291-1 [ST291]. ANC can carry a range of data
types, including time code, KLV metadata, Closed Captioning, and the
Active Format Description (AFD).
ANC is generally associated with the carriage of metadata within the
bit stream multiplex 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, or Registered
Disclosure Document, or by a document generated by another
organization, a company, or an individual (an Entity). When a
payload format is registered with SMPTE, an application document
describing the payload format is required, and the registered
ancillary data packet is identified by a registered data
identification word.
This RTP payload supports ANC data packets regardless of whether they
originate from an SD or HD interface, or if the ANC data packet is
from the vertical ancillary space (VANC) or the horizontal ancillary
space (HANC), or if the ANC packet is located in the luma (Y) or
color-difference (C) channel. Sufficient information is provided to
enable the ANC packets at the output of the decoder to be restored to
their "original" locations in the serial digital video signal raster
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(if that is desired). This payload could be used by itself, or used
along with a range of RTP video formats. In particular, it has been
specifically 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
The format of an RTP packet containing SMPTE ST 291 Ancillary Data is
shown below:
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 |C| Line_Number | Horizontal_Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DID | SDID | Data_Count | R |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| User_Data_Words...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum_Word |octet_align| (next ANC data packet)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SMPTE Ancillary Data RTP Packet Format
RTP packet header fields SHALL be interpreted as per RFC 3550
[RFC3550], with the following specifics:
Timestamp: 32 bits
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The timestamp field is interpreted in a similar fashion to
RFC 4175 [RFC4175]:
For progressive scan video, the timestamp SHALL denote the
sampling instant of the frame to which the ancillary data in
the RTP packet belongs. Packets MUST NOT include ANC data
from multiple frames, and all packets with ANC data belonging
to the same frame MUST have the same timestamp.
For interlaced video, the timestamp SHALL denote the sampling
instant of the field to which the ancillary data in the RTP
packet belongs. Packets MUST NOT include ANC data from
multiple fields, and all packets belonging to the same field
MUST have the same timestamp.
A 90-kHz timestamp SHOULD be used in both cases. 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.
Marker bit (M): 1 bit
The marker bit set to "1" SHALL indicate the last RTP packet
containing ANC data for a frame (for progressive scan video)
or the last RTP packet containing ANC data 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.
ANC_Count: 8 bits
This field is the count of the total number of ANC data
packets carried in the RTP payload. A single ANC RTP packet
payload SHALL NOT carry more than 255 ANC data packets.
And for each ANC data packet in the payload, the following header
fields MUST be present:
C: 1 bit
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For HD signals, this flag, when set to "1", indicates that
the ANC data corresponds to the color-difference channel (C).
When set to "0", this flag indicates that the ANC data
corresponds to the luma (Y) channel. For SD signals, this
flag SHALL be set to "0".
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. 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 may be further restricted per SMPTE RP 168
[RP168].
Horizontal_Offset: 12 bits
This field defines the location of the ANC packet relative to
the start of active video (SAV). 0 means that the Ancillary
Data Flag (ADF) of the ANC packet begins immediately
following SAV. For HD, this shall be 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]. It should be noted that HANC space in the
digital blanking area will generally have higher luma sample
numbers than any samples in the active digital line.
The fields DID, SDID, Data_Count, User_Data_Words, and Checksum_Word
represent the 10-bit words carried in the ANC data packet, as per
SMPTE ST 291 [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.
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User_Data_Words: integer number of 10 bit words
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.
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. The
lower 8 bits of Checksum_Word, corresponding to bits b8 (MSB)
through b0 (LSB) of the 10-bit data count word, contain the
actual checksum value. 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.
octet_align: 0-7 bits as needed to complete octet
Octet align contains enough "0" bits as needed to complete
the last octet of an ANC packet's data in the RTP payload.
This ensures that the next ANC packet's data in the RTP
payload begins octet-aligned despite ANC packets being made
up of 10-bit words. If an ANC data packet in the RTP payload
ends aligned with an octet, there is no need to add any octet
alignment bits.
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 4288 [RFC4288].
Note that the Media Type Definition is in the "video" tree due to the
expected use of SMPTE ST 291 Ancillary Data with video formats.
3.1. Media Type Definition
Type name: video
Subtype name: smpte291
Required parameters:
Rate: RTP timestamp clock rate.
Optional parameters:
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DID: Data identification word
SDID: Secondary data identification word
The presence of the DID and SDID parameters signal that all
ancillary data packets of this stream are of a particular type,
i.e., labeled with a particular DID and SDID. DID and SDID values
are registered with SMPTE as per SMPTE ST 291-1 [ST291]. DID and
SDID values should be specified in hexadecimal with a "0x" prefix
(such as "0x61"). For example, EIA 608 Closed Caption data would
be DID=0x61 and SDID=0x02. If DID and SDID are not specified,
then the ancillary data stream may potentially contain ancillary
data packets of any type.
DID and SDID values can be found on the SMPTE Registry for Data
Identification Word Assignments for Registered DIDs at:
http://www.smpte-ra.org/S291/S291_reg.html
Encoding considerations: This media type is framed and binary; see
Section 4.8 of RFC 4288 [RFC4288].
Security considerations: See Section 5 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 may care about the
location of the ANC data packets in the SDI raster, but other
implementations may not care.
Published specification: [this RFC]
Applications that use this media type: Devices that stream real-time
professional video, especially those that must interoperate with
legacy serial digital interfaces (SDI).
Additional Information: none
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.
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Author: T. Edwards <thomas.edwards@fox.com>
Change controller: IETF Payload working group delegated from the
IESG.
3.2. Mapping to SDP
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.
o The optional DID and SDID parameters go in the SDP "a=fmtp"
attribute as a semicolon-separated list of parameter=value pairs.
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=0x61; SDID=0x02;
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. The RTP sampling clock is 90 kHz. In the
"a=fmtp:" line, DID 0x61 and SDID 0x02 are specified (which are
registered to EIA 608 Closed Caption Data by SMPTE).
3.3. Offer/Answer Model and Declarative Considerations
When offering SMPTE ST 291 Ancillary data over RTP using the Session
Description Protocol (SDP) in an Offer/Answer model [RFC3264] or in a
declarative manner (e.g., SDP in the Real-Time Streaming Protocol
(RTSP) [RFC2326] or the Session Announcement Protocol (SAP)
[RFC2974]), the offerer could provide a list of streams available
with specific DID & SDIDs, and the answerer could specify which
streams with specific DID & SDIDs it would like to accept.
4. IANA Considerations
One media type (video/smpte291) has been defined and needs
registration in the media types registry. See Section 3.1
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5. 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 any applicable RTP profile, e.g., AVP
[RFC3551].
To avoid potential buffer overflow attacks, receivers should take
care to validate that the ANC 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.
Some receivers will simply move the ANC data packet bits from the RTP
payload into a serial digital interface (SDI). It may 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 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.
6. References
6.1. 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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", RFC 4288, December 2005.
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[RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, February 2007.
[ST291] SMPTE, "ST 291-1:2011, Ancillary Data Packet and Space
Formatting", 2011.
6.2. 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.
[RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
Streaming Protocol (RTSP)", RFC 2326, April 1998.
[RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session
Announcement Protocol", RFC 2974, October 2000.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, June
2002.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551,
July 2003.
[RFC4175] Gharai, L. and C. Perkins, "RTP Payload Format for
Uncompressed Video", RFC 4175, September 2005.
[RFC5371] Futemma, S., Itakura, E., and A. Leung, "RTP Payload
Format for JPEG 2000 Video Streams", RFC 5371, October
2008.
[RP168] SMPTE, "RP 168:2009, Definition of Vertical Interval
Switching Point for Synchronous Video Switching", 2009.
[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.
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[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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