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Versions: (draft-gharai-avt-uncomp-video) 00 01 02 03 04 05 06 RFC 4175

Internet Engineering Task Force                                   AVT WG
INTERNET-DRAFT                                              Ladan Gharai
draft-ietf-avt-uncomp-video-02.txt                         Colin Perkins
                                                                 USC/ISI
                                                        27 February 2003
                                                    Expires: August 2003


                RTP Payload Format for Uncompressed Video



Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups.  Note that other groups
may also distribute working documents as Internet-Drafts.

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."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.


                                Abstract


     This memo specifies a packetization scheme for encapsulating
     uncompressed video into a payload format for the Real-time
     Transport Protocol, RTP. It supports a range of standard- and
     high-definition video formats, including common television
     formats such as ITU BT.601, SMPTE 274M and SMPTE 296M.  The
     format is designed to be extensible as new video formats are
     developed.





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1.  Introduction

[Note to RFC Editor: All references to RFC XXXX are to be replaced with
the RFC number of this memo, when published]

This memo defines a scheme to packetize uncompressed, studio-quality,
video streams for transport using RTP [RTP]. It supports a range of
standard and high definition video formats, including ITU-R BT.601
[601], SMPTE 274M [274] and SMPTE 296M [296].

Formats for uncompressed standard definition television are defined by
ITU Recommendation BT.601 [601] along with bit-serial and parallel
interfaces in Recommendation BT.656 [656]. These formats allow both 625
line and 525 line operation, with 720 samples per digital active line,
4:2:2 color sub-sampling, and 8- or 10-bit digital representation.

The representation of uncompressed high definition television is
specified in SMPTE standards 274M [274] and 296M [296].  SMPTE 274M
defines a family of scanning systems with an image format of 1920x1080
pixels with progressive and interlaced scanning, while SMPTE 296M
standard defines systems with an image size of 1280x720 pixels and only
progressive scanning. In progressive scanning, scan lines are displayed
in sequence from top to bottom of a full frame. In interlaced scanning,
a frame is divided into its odd and even scan lines (called fields) and
the two fields are displayed in succession.

SMPTE 274M and 296M define images with aspect ratios of 16:9, and define
the digital representation for RGB and YCbCr components. In the case of
YCbCr components, the Cb and Cr components are horizontally sub-sampled
by a factor of two (4:2:2 color encoding).

Although these formats differ in their details, they are structurally
very similar. This memo specifies a payload format to encapsulate these,
and other similar, video formats for transport within RTP.


2.  Conventions Used in this Document

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[2119].


3.  Payload Design

Each scan line of digital video is packetized into one or more
(depending on the network MTU) RTP packets. A single RTP packet MAY also
contain data for more than one scan line. Only the active samples are



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included in the RTP payload, inactive samples and the contents of
horizontal and vertical blanking SHOULD NOT be transported. Scan line
numbers are included in the RTP payload header, along with a field
identifier for interlaced video.


     For SMPTE 296M format video, valid scan line numbers are from 26
     through 745, inclusive. For progressive scan SMPTE 274M format
     video, valid scan lines are from scan line 42 through 1121
     inclusive. For interlaced scan, valid scan line numbers for field
     one (F=0) are from 21 to 560 and valid scan line numbers for the
     second field (F=1) are from 584 to 1123. For ITU-R BT.601 format
     video, the blanking intervals defined in BT.656 are used: for 625
     line video, lines 24 to 310 of field one (F=0) and 337 to 623 of
     the second field (F=1) are valid; for 525 line video, lines 21 to
     263 of the first field, and 284 to 525 of the second field are
     valid.  Other formats (e.g. [372]) may define different ranges of
     active lines.


The payload header contains a 16 bit extension to the standard 16 bit
RTP sequence number, thereby extending the sequence number to 32 bits
and enabling RTP to  accommodate high data rates. This is necessary as
the 16 bit RTP sequence number will roll-over very quickly for high data
rates.  For example, for a 1 Gbps video stream with packet sizes of at
least one thousand octets, the standard RTP packet will roll-over in 0.5
seconds, which can be a problem for detecting loss and out of order
packets particularly in instances where the round trip time is greater
than half a second. The extended 32 bit number allows for a longer wrap-
around time of approximately nine hours.

It is desirable for the video to be both octet aligned when packetized,
and to adhere to the principles of application level framing [ALF] by
ensuring that the samples relating to a single pixel are not fragmented
across two packets.

Samples may be transfered as 8, 10, 12 or 16 bit values. For 10 bit and
12 bit payloads, care must be taken to pack an appropriate number of
samples per packet, such that the payload is also octet aligned. For RGB
video, it is desirable that the samples corresponding to a single pixel
are not fragmented across packets. Similarly, for YCrCb video, it is
desirable that luminance and chrominance values are not fragmented
across packets.

For example, in YCrCb video with 4:1:1 color subsampling, each group of
4 pixels is represented by 6 values, Y1 Y2 Y3 Y4 Cr Cb. These should be
packetized such that these values are not fragmented across a packet
boundary. With 10 bit words this is a 60 bit value which is not octet



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aligned. To be both octet aligned, and appropriately framed, pixels must
be framed in 2 groups of 4 pixels, thereby becoming octet aligned on a
15 octet boundary. This length is referred to as the pixel group
("pgroup"), and it is conveyed in the SDP parameters. Tables 1 to 4
display the pgroup values, in octets, for a range of color samplings and
word lengths.

When packetizing digital active line content, video data MUST NOT be
fragmented within a pgroup.

Video content is almost always associated with additional information
such as audio tracks, time code, etc. In professional digital video
applications this data is commonly embedded in non-active portions of
the video stream (horizontal and vertical blanking periods) so that
precise and robust synchronization is maintained. This payload format
requires that applications using such synchronized ancillary data MUST
deliver it in separate RTP sessions which operate concurrently with the
video session.  The normal RTP mechanisms SHOULD be used to synchronize
the media.



                                                 8 bit words
         Color                ----------------------------------------
      Subsampling Pixels      #words  octet alignment #samples pgroup
                                                               octets
     +-----------+------+---+ +------+---------------+---------------+
     |monochrome |  1   |P/I| | 1x8  |    8/8 = 1    |   1   |   1   |
     +-----------+------+---+ +------+---------------+---------------+
     |   4:1:1   |  4   |P/I| | 6x8  |  6x8/8 = 6    |   6   |   6   |
     +-----------+------+---+ +------+---------------+---------------+
     |   4:2:0   |  4   | P | | 6x8  |  6x8/8 = 6    |   6   |   6   |
     +-----------+------+---+ +------+---------------+---------------+
     |   4:2:0   |  4   | I | | 4x8  |  4x8/8 = 6    |   4   |   4   |
     +-----------+------+---+ +------+---------------+---------------+
     |   4:2:2   |  2   |P/I| | 4x8  |  4x8/8 = 8    |   4   |   4   |
     +-----------+------+---+ +------+---------------+---------------+
     |   4:4:4   |  1   |P/I| | 3x8  |  3x8/8 = 3    |   3   |   3   |
     +-----------+------+---+ +------+---------------+---------------+
     |  4:4:4:4  |  1   |P/I| | 4x8  |  4x8/8 = 4    |   4   |   4   |
     +-----------+------+---+ +------+---------------+---------------+
     Table 1: pgroup values for 8 bit sampling









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                                               10 bit words
         Color                ----------------------------------------
      Subsampling Pixels       #words octet alignment #samples pgroup
                                                               octets
     +-----------+------+---+ +------+---------------+---------------+
     |monochrome |  4   |P/I| | 4x10 |    40/8 = 5   |    4   |  5   |
     +-----------+------+---+ +------+---------------+---------------+
     |   4:1:1   |  4   |P/I| | 6x10 |  2x60/8 = 15  |   12   | 15   |
     +-----------+------+---+ +------+---------------+---------------+
     |   4:2:0   |  4   | P | | 6x10 |  2x60/8 = 15  |   12   | 15   |
     +-----------+------+---+ +------+---------------+---------------+
     |   4:2:0   |  4   | I | | 4x10 |    40/8 = 5   |    4   |  5   |
     +-----------+------+---+ +------+---------------+---------------+
     |   4:2:2   |  2   |P/I| | 4x10 |    40/8 = 5   |    4   |  5   |
     +-----------+------+---+ +------+---------------+---------------+
     |   4:4:4   |  1   |P/I| | 3x10 |  4x30/8 = 15  |   12   | 15   |
     +-----------+------+---+ +------+---------------+---------------+
     |  4:4:4:4  |  1   |P/I| | 4x10 |    40/8 = 5   |    4   |  5   |
     +-----------+------+---+ +------+---------------+---------------+
     Table 2: pgroup values for 10 bit sampling



                                            12 bit words
         Color                ----------------------------------------
      Subsampling Pixels       #words octet alignment #samples pgroup
                                                               octets
     +-----------+------+---+ +------+---------------+---------------+
     |monochrome |  2   |P/I| | 2x12 |  2x12/8 = 3   |   2   |   3   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |   4:1:1   |  4   |P/I| | 6x12 |    72/8 = 9   |   6   |   9   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |   4:2:0   |  4   | P | | 6x12 |    72/8 = 9   |   6   |   9   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |   4:2:0   |  4   | I | | 4x12 |    48/8 = 6   |   4   |   6   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |   4:2:2   |  2   |P/I| | 4x12 |    48/8 = 6   |   4   |   6   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |   4:4:4   |  2   |P/I| | 6x12 |  2x36/8 = 9   |   6   |   9   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |  4:4:4:4  |  1   |P/I| | 4x12 |    48/8 = 6   |   4   |   6   |
     +-----------+------+---+ +------+---------------+-------+-------+
     Table 3: pgroup values for 12 bit sampling








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                                             16 bit words
          Color                --------------------------------------
      Subsampling Pixels       #words octet alignment samples  pgroup
                                                               octets
     +-----------+------+---+ +------+---------------+-------+-------+
     |monochrome |  1   |P/I| | 1x16 |   16/8 = 2    |   1   |   2   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |   4:1:1   |  4   |P/I| | 6x16 | 6x16/8 = 12   |   6   |  12   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |   4:2:0   |  4   | P | | 6x16 | 6x16/8 = 12   |   6   |  12   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |   4:2:0   |  4   | I | | 4x16 | 4x16/8 = 8    |   4   |   8   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |   4:2:2   |  2   |P/I| | 4x16 | 4x16/8 = 8    |   4   |   8   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |   4:4:4   |  1   |P/I| | 3x16 | 3x16/8 = 6    |   3   |   6   |
     +-----------+------+---+ +------+---------------+-------+-------+
     |  4:4:4:4  |  1   |P/I| | 4x16 | 4x16/8 = 8    |   4   |   8   |
     +-----------+------+---+ +------+---------------+-------+-------+
     Table 4: pgroup values for 16 bit sampling



4.  RTP Packetization

The standard RTP header is followed by a 4 octet payload header that
extends the RTP Sequence Number, and by a 6 octet payload header for
each line (or partial line) of video included. One or more lines, or
partial lines, of video data follow. This format makes the payload
header 32 bit aligned in the common case, where one scan line (fragment)
of video is included in each RTP packet.

For example, if two lines of video are encapsulated, the payload format
will be as shown in Figure 1.

















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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 |P|X|   CC  |M|    PT       |       Sequence Number         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Time Stamp                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             SSRC                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Extended Sequence Number    |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |F|        Scan Line No         |C|        Scan Offset          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Length             |F|       Scan Line No          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |C|        Scan Offset          |                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               .
      .                                                               .
      .                 Two (partial) lines of video data             .
      .                                                               .
      +---------------------------------------------------------------+
     Figure 1: RTP Payload Format showing two (partial) lines of video



4.1.  The RTP Header

The fields of the fixed RTP header have their usual meaning, with the
following additional notes:

Payload Type (PT): 7 bits

     A dynamically allocated payload type field which designates the
     payload as uncompressed video.

Timestamp: 32 bits

     For progressive scan video, the timestamp denotes the sampling
     instant of the frame to which the RTP packet belongs.  Packets MUST
     NOT include data from multiple frames, and all packets 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 RTP packet belongs.  Packets MUST NOT
     include data from multiple fields, and all packets belonging to the
     same field MUST have the same timestamp.  Use of field timestamps,
     rather than a frame timestamp and and field indicator bit, is
     needed to support reverse 3-2 pulldown.



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     A 90 kHz timestamp MUST be used in both cases. If the sampling
     instant does not correspond to an integer value of the clock (as
     may be the case when interleaving, the value SHALL be truncated to
     the next lowest integer).

Marker bit (M): 1 bit

     The Marker bit denotes the end of a video frame, and MUST be set to
     1 for the last packet of the video frame. It MUST be set to 0 for
     other packets.

Sequence Number: 16 bits

     The low order bits for RTP sequence number. The standard 16 bit
     sequence number is augmented with another 16 bits in the payload
     header, in order avoid problems due to wrap-around when operating
     at high rate rates.


4.2.  Payload Header

Extended Sequence Number : 16 bits

     The high order bits of the extended 32 bit sequence number, in
     network byte order.

Scan Line No : 15 bits

     Scan line number of encapsulated data, in network byte order.
     Successive RTP packets MAY contains parts of the same scan line
     (with an incremented RTP sequence number, but the same timestamp),
     if it is necessary to fragment a line.

Scan Offset : 15 bits

     Scan offset of the first sample in the payload data. If YCrCb
     format data is being transported, this is the offset of the co-
     sited luminance sample and if RGB format data is being transported
     it is the offset of the red sample. The value is in network byte
     order, and the offset has a value of zero if the first sample in
     the payload corresponds to the start of the line.

Length: 16 bits

     Number of octets of data included from this scan line, in network
     byte order. This MUST be a multiple of the pgroup value.





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Field Identification (F): 1 bit

     Identifies which field the scan line belongs to, for interlaced
     data. F=0 identifies the the first field and F=1 the second field.
     For progressive scan data (e.g. SMPTE 296M format video), F MUST
     always be set to zero.

Continuation (more lines) bit (C): 1 bit

     Determines if an additional scan line header follows the current
     scan line header in the RTP packet. Set to 1 if an additional
     header follows, implying that the RTP packet is carrying data for
     more than one scan line.  Set to 0 otherwise. An unlimited number
     of scan lines MAY be included, up to the path MTU limit. The only
     way to determine the number of scan lines included per packet is to
     parse the payload headers.


4.3.  Payload Data

Depending on the video format, each RTP packet can include either a
single complete scan line, a single fragment of a scan line, or one (or
more) complete scan lines plus a fragment of a scan line.  Every scan
line or scan line fragment MUST begin at an octet boundary in the
payload data. Scan lines SHOULD be fragmented so that the resulting RTP
packet is smaller than the path MTU.

It is possible that the scan line length is not evenly divisible by the
number of pixels in a pgroup, so the final pixel data of a scan line
does not align to either an octet or pgroup boundary. Nonetheless the
payload MUST contain a whole number of pgroups; the sender MUST fill the
remaining bits of the final pgroup with zero and the receiver MUST
ignore the fill data. (In effect, the trailing edge of the image is
black-filled to a pgroup boundary.)

If the video is in YUV format, the packing of samples into the payload
depends on the color sub-sampling used. For RGB format video, there is a
single packing scheme.

For RGB format video, samples are packed in order Red-Green-Blue.  All
samples are the same bit size, which may be 8, 10, 12, or 16 bits.  If 8
bit samples are used, the pgroup is 3 octets. If 10 bit samples are
used, samples from adjacent pixels are packed with no padding, and the
pgroup is 15 octets (4 pixels).  Refer to Tables 1 thru 4.

For RGBA format video, samples are packed in order Red-Green-Blue-Alpha.
All samples are the same bit size, which may be 8, 10, 12, or 16 bits.
For pgroups refer to Tables 1 thru 4.



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For YUV 4:4:4 format video, samples are packed in order Cb-Y-Cr for both
interlaced and progressive frames. Each sample is either an 8, 10, 12 or
16 bit value. For relevant pgroups refer to Tables 1 to 4.

For YUV 4:2:2 format video, the Cb and Cr components are horizontally
sub-sampled by a factor of two (each Cb and Cr samples corresponds to
two Y components). Samples are packed in order Cb0-Y0-Cr0-Y1 for both
interlaced and progressive scan lines. Samples are either an 8, 10, 12
or 16 bit value. For relevant pgroups refer to Tables 1 to 4.

For YUV 4:1:1 format video, the Cb and Cr components are horizontally
sub-sampled by a factor of four (each Cb and Cr sample corresponds to
four Y components). Samples are packed in order Cb0-Y0-Y1-Cr0-Y2-Y3 for
both interlaced and progressive scan lines. Samples are either an 8, 10,
12 or 16 bit value. For relevant pgroups refer to Tables 1 to 4.

For YUV 4:2:0 video, the Cb and Cr components are sub-sampled by a
factor of two both horizontally and vertically. Therefore chrominance
values are shared between certain adjacent lines.  Figure 2 illustrates
the composition of luminance and chrominance values for 6x6 pixel grid
in 4:2:0 YUV video.


       line 0:  Y00   Y01   Y02   Y03   Y04   Y05
                Cb00 Cr00   Cb01 Cr01   Cb02 Cr02
       line 1:  Y10   Y11   Y12   Y13   Y14   Y15

       line 2:  Y20   Y21   Y22   Y23   Y24   Y25
                Cb10 Cr10   Cb11 Cr11   Cb12 Cr12
       line 3:  Y30   Y31   Y32   Y33   Y34   Y35

       line 4:  Y40   Y41   Y42   Y43   Y44   Y45
                Cb20 Cr20   Cb21 Cr21   Cb22 Cr22
       line 5:  Y50   Y51   Y52   Y53   Y54   Y55
     Figure 2: Chrominance and luminance compostion in 4:2:0 YUV video.


Transport of progressive scan 4:2:0 YUV video entails the transport of
two scan lines together such that:












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     line 0,1:
     Y00-Y01-Y10-Y11-Cb00-Cr00 Y02-Y03-Y12-Y13-Cb01-Cr01
                                           Y04-Y05-Y14-Y15-Cb02-Cr02

     line 2,3:
     Y20-Y21-Y30-Y31-Cb10-Cr10 Y22-Y23-Y32-Y33-Cb11-Cr11
                                           Y24-Y25-Y34-Y35-Cb12-Cr12

     line 4,5:
     Y40-Y41-Y50-Y51-Cb20-Cr20 Y42-Y43-Y52-Y53-Cb21-Cr21
                                           Y44-Y45-Y54-Y55-Cb22-Cr22


For interlaced transportm chrominance values are transported with every
other line:


     field 0:
        line 0: Y00-Y01-Cb00-Cr00 Y02-Y03-Cb01-Cr01 Y04-Y05-Cb02-Cr02
        line 2: Y20-Y21 Y22-Y23 Y24-Y25
        line 4: Y40-Y41-Cb20-Cr20 Y42-Y43-Cb21-Cr21 Y44-Y45-Cb22-Cr22

     field 1:
        line 1: Y10-Y11 Y12-Y13 Y14-Y15
        line 3: Y30-Y31-Cb10-Cr10 Y32-Y33-Cb11 Cr11 Y34-Y35-Cb12-Cr12
        line 5: Y50-Y51 Y52-Y53 Y54-Y55




5.  RTCP Considerations

RTCP SHOULD be used as specified in RFC1889 [RTP], which specifies two
limits on the RTCP packet rate: RTCP bandwidth should be limited to 5%
of the data rate, and the minimum for the average of the randomized
intervals between RTCP packets should be 5 seconds.  Considering the
high data rate of many uncompressed video formats, the minimum interval
is the governing factor in many cases.

It should be noted that the sender's octet count in SR packets and the
cumulative  number of packets lost will wrap around quickly for high
data rate streams. This means these two fields may not accurately
represent octet count and number of packets lost since the beginning of
transmission, as defined in RFC 1889. Therefore for network monitoring
purposes other means of keeping track of these variables SHOULD be used.






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6.  IANA Considerations

6.1.  MIME type registration

MIME media type name: video

MIME subtype name: raw

Required parameters:

     rate: The RTP timestamp clock rate. Applications using this payload
     format MUST be 90000 for this format.

     pgroup: The number of octets per the pixel group. See section 3 of
     RFC XXXX.

     color-mode: Determines the color mode of the video stream. Valid
     values for this parameter are: RGB, RGBA, and YUV.

     sub-sampling: Determines the type of color sub-sampling of the
     video stream. Valid values are: mono, 4:1:1, 4:2:0, 4:2:2, 4:4:4
     and 4:4:4:4.

     width: Determines the number of pixels per line. This is an integer
     between 1 and 32767.

     height: Determines the number of lines per frame. This is an
     integer between 1 and 32767.

     depth: Determines the number of bits per samples. This is a decimal
     integer; typical values include 8, 10, 12, and 16.

     colorimetry: This parameter defines the set of colorimetric
     specfications and other transfer characteristics for the video
     source, by reference to an external specification. Valid values and
     their specification are:

          BT601-5      ITU Recommendation BT.601-5 [601]
          BT709-2      ITU Recommendation BT.709-2 [709]
          SMPTE240M    SMPTE standard 240M [240M]
          NTSC         The NTSC specification [NTSC]
          PAL          The PAL specificaiton [PAL]

     New values may be registered as described in section 6.2 of RFC
     XXXX.

Optional parameters:




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     Interlace: If this optional parameter is present it indicates that
     the video stream is interlaced. If absent, progressive scan is
     implied.

Encoding considerations: Uncompressed video can be transmitted with RTP
as specified in RFC XXXX. No file format is defined at this time.

Security considerations: See section 9 of RFC XXXX.

Interoperability considerations: NONE.

Published specification: RFC XXXX.

Applications which use this media type: Video communication.

Additional information: None

Magic number(s): None

File extension(s): None

Macintosh File Type Code(s): None

Person & email address to contact for further information:

     Ladan Gharai <ladan@isi.edu>
     IETF Audio/Video Transport working group.

Intended usage: COMMON

Author/Change controller: Ladan Gharai <ladan@isi.edu>


6.2.  Parameter Registration

New values of the "colorimetry" parameter MAY be registered with the
IANA provided they reference an RFC or other permanent and readily
available specification (the Specification Required policy of RFC 2434
[2434]).


7.  Mapping to SDP Parameters

Parameters are mapped to SDP [SDP] as in the following example:







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     m=video 30000 RTP/AVP 112
     a=rtpmap:112 raw/90000
     a=fmtp:112 color-mode=YUV; sub-sampling=4:2:2; width=1280; height=720;
                depth=10; colorimetry=BT.709-2

In this example, a dynamic payload type 111 is used for uncompressed
video.  The RTP sampling clock is 90kHz. Note that the "a=fmtp:" line
has been wrapped to fit this page, and will be a single long line in the
SDP file.


8.  Security Considerations

RTP packets using the payload format defined in this specification are
subject to the security considerations discussed in the RTP
specification, and any appropriate RTP profile. This implies that
confidentiality of the media streams is achieved by encryption.

This payload type does not exhibit any significant non-uniformity in the
receiver side computational complexity for packet processing to cause a
potential denial-of-service threat.

It is important to be note that uncompressed video can have immense
bandwidth requirements (up 270 Mbps for standard definition video, and
approximately 1 Gbps for high definition video).  This is sufficient to
cause potential for denial-of-service if transmitted onto most currently
available Internet paths.

Accordingly, if best-effort service is being used, users of this payload
format SHOULD monitor packet loss to ensure that the packet loss rate is
within acceptable parameters.  Packet loss is considered acceptable if a
TCP flow across the same network path, and experiencing the same network
conditions, would achieve an average throughput, measured on a
reasonable timescale, that is not less than the RTP flow is achieving.
This condition can be satisfied by implementing congestion control
mechanisms to adapt the transmission rate (or the number of layers
subscribed for a layered multicast session), or by arranging for a
receiver to leave the session if the loss rate is unacceptably high.

This payload format may also be used in networks which provide quality
of service guarantees.  If enhanced service is being used, receivers
SHOULD monitor packet loss to ensure that the service that was requested
is actually being delivered.  If it is not, then they SHOULD assume that
they are receiving best-effort service and behave accordingly.







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9.  Relation to RFC 2431

In comparison with RFC 2431 this memo specifies support for a wider
variety of uncompressed video, in terms of frame size, color subsampling
and sample sizes. While [BT656] can transport up to 4096 scan lines and
2048 pixels per line, our payload type  can support up to 64k scan lines
and pixels per line. Also, RFC 2431 only address 4:2:2 YUV data, while
this memo covers YUV and RGB and most common color subsampling schemes.
Given the variety of video types that we cover, this memo also assumes
out-of-band signaling for sample size and data types (RFC 2431 uses in
band signaling).


10.  Relation to RFC YYYY

(tbd)

Relation [292RTP]


11.  Full Copyright Statement

Copyright (C) The Internet Society (2003). All Rights Reserved.

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it or
assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are included
on all such copies and derivative works.

However, this document itself may not be modified in any way, such as by
removing the copyright notice or references to the Internet Society or
other Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be followed,
or as required to translate it into languages other than English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an "AS
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT
INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR PURPOSE."




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12.  Acknowledgements

The authors are grateful to Philippe Gentric and Chuck Harrison for
their feedback.


13.  Authors' Addresses

Ladan Gharai <ladan@isi.edu>
Colin Perkins <csp@csperkins.org>

USC Information Sciences Institute
3811 N. Fairfax Drive, #200
Arlington, VA 22203
USA



Normative References

[RTP]   H. Schulzrinne, S. Casner, R. Frederick and V. Jacobson,
        "RTP: A Transport Protocol for Real-Time Applications",
        Internet Engineering Task Force, RFC 1889, January 1996.

[2119]  S. Bradner, "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119.

[2434]  T. Narten and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", RFC 2434, October 1998.


Informative References


[274]   Society of Motion Picture and Television Engineers,
        1920x1080 Scanning and Analog and Parallel Digital Interfaces
        for Multiple Picture Rates, SMPTE 274M-1998.

[268]   Society of Motion Picture and Television Engineers,
        File Format for Digital Moving Picture Exchange (DPX),
        SMPTE 268M-1994. (Currently under revision.)

[296]   Society of Motion Picture and Television Engineers,
        1280x720 Scanning, Analog and Digital Representation and Analog
        Interfaces, SMPTE 296M-1998.

[372]   Society of Motion Picture and Television Engineers,
        Dual Link 292M Interface for 1920 x 1080 Picture Raster,



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        SMPTE 372M-2002.

[ALF]   Clark, D. D., and Tennenhouse, D. L., "Architectural
        Considerations for a New Generation of Protocols", In
        Proceedings of SIGCOMM '90 (Philadelphia, PA, Sept. 1990), ACM.

[SDP]   M. Handley and V. Jacobson, "SDP: Session Description Protocol",
        RFC 2327, April 1998.

[BT656] D. Tynan, "RTP Payload Format for BT.656 Video Encoding",
        Internet Engineering Task Force, RFC 2431, October 1998.

[292RTP] L. Gharai et al., "RTP Payload Format for SMPTE 292M Video",
        Internet Draft, draft-ietf-avt-smpte292-video-07.txt,
        Work in progress.

[601]   International Telecommunication Union, "Studio encoding
        parameters of digital television for standard 4:3 and wide
        screen 16:9 aspect ratios", Recommendation BT.601, October 1995.

[656]   International Telecommunication Union, "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 (Part A)", Recommendation BT.656, April 1998.

[22028] ISO TC42 (Photography), Photography and graphic technology -
        Extended colour encodings for digital image storage,
        manipulation and interchange - Part 1: Architecture and
        requirements, ISO/CD 22028-1, Work in Progress.

[709]   ITU Recommendation BT.709-2

[240M]  SMPTE Standard 240M

[NTSC]  (tbd)

[PAL]   (tbd)














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