INTERNET-DRAFT Eric Edwards
draft-ietf-avt-rtp-jpeg2000-01.txt Satoshi Futemma
Eisaburo Itakura
Nobuyoshi Tomita
Andrew Leung
Takahiro Fukuhara
Sony Corporation
June 30, 2002
Expires: December 30 2002
RTP Payload Format for JPEG 2000 Video Streams
Status of this Memo
This document is an Internet-Draft and is in subject to 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
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Drafts Shadow Directories can be accessed at
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Abstract
This document describes a payload format for transporting JPEG 2000
video streams using RTP (Real-time Transport Protocol). JPEG 2000
video streams are formed as a continuous series of JPEG 2000 still
images. The JPEG 2000 payload format described in this document has
three features: (1) Improvement of robustness to packet loss by
intelligently fragmenting JPEG 2000 packet units, (2) Persistency of
main header to minimize loss effect and maximize recovery, (3)
Priority information field for scalable delivery from the same code
stream. These will allow for scalability and robustness of JPEG
2000's potential to be maximized in streaming applications.
1. Introduction
This document specifies payload formats for JPEG 2000 video streams
over the Real-time Transport Protocol (RTP). JPEG 2000 is an ISO/IEC
International Standard developed for next-generation still image
encoding. Its basic encoding technology is described in [1].
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Part 3 of the JPEG 2000 standard defines Motion JPEG 2000[2].
However, this defines only the file format but not the transmission
format for streaming on the Internet. For this reason, it is
necessary to define the RTP format for JPEG 2000 video streams.
JPEG 2000 supports many features over the current JPEG standard
[3][4][5]:
o Higher compression efficiency than JPEG with less visual loss
especially at extreme compression ratios.
o A single code stream that offers both lossy and superior
lossless compression.
o Transmission over noisy environments.
o Progressive transmission by pixel accuracy and resolution.
o Random code stream access and processing.
First, the JPEG-2000 algorithm is briefly explained below. Fig. 1
shows a block diagram of JPEG 2000 encoding method.
+-----+
| ROI |
+-----+
|
V
+----------+ +----------+ +------------+
|DC, comp. | | Wavelet | | |
raw image ==> |transform-|==>|transform-|==>|Quantization|==+
| ation | | ation | | | |
+----------+ +----------+ +------------+ |
|
+-------------+ +----------+ +------------+ |
| | | | | | |
JPEG 2000 <==|Data ordering|<==|Arithmetic|<==|Coefficient |<=+
code stream | | | coding | |bit modeling|
+-------------+ +----------+ +------------+
Fig. 1: Block diagram of the JPEG 2000 encoder
Each color component or tile is transformed into wavelet
coefficients. The component or tile is sub-sampled into various
levels usually vertically and horizontally from high frequencies
(which contains all the sharp details) to the low frequencies (which
contains all the flat areas.) Quantization is performed on the
coefficients within each subband. The wavelet coefficient is
divided by the quantization step size and the result is truncated.
After quantization, code blocks are formed from within the precincts
within the tiles. Precincts are a finer separation than tiles and
code blocks are the smallest separation of the image data. Entropy
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coding is performed within each code block and arithmetically
encoded by bit plane. After the coefficients of all code blocks
have been coded into a short bit stream, a header is added turning
it into a packet. The header has all the information needed to
decompress the packet into code blocks. A group of packets is
called layers.
For additional features in transmitting, a re-ordering of the formed
packets is necessary. The standard has four ways to transmit and
decode a compressed image by: resolution, quality, position, or
component.
This is only to serve as an introduction to JPEG 2000 and to aid in
understanding the rest of this document. Further details of the
encoder can be found in various texts on JPEG 2000 [1].
To decompress a JPEG 2000 code stream, one would follow the reverse
order of the encoding order, minus the quantization step. It is
outside the scope of this document to describe in detail this
procedure. Please refer to various JPEG 2000 texts for details [1].
1.1 Terminology
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 RFC2119 [7].
1.2 Author's comments, responses, and changes relative to -00
[ this section will be removed in a future version of this document]
1.2.1 Author's comments on this draft
Changes required from implementation of the last draft of the document
Implementation of the last draft of this document revealed some
potential problems with the previous draft. Some markers would
never be used, and some situations may always occur, which there
would be no combinations of markers to indicate it and
inefficient usage of packets would be encountered (i.e. packing
multiple tiles into a single RTP payload packet.) Revisions
have been added to handle these cases and redundant markers have
been removed.
Removal of redundant texts from this document
A lot of text has been removed from the introduction of this
document. This document cannot possibly cover JPEG 2000 in any
comprehensive way compared to other resources available or
cited. Implementors of this standard should have a more
comprehensive understanding of JPEG 2000 than anything that was
written in the introduction previously. Please refer to cited
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texts for further information on JPEG 2000.
1.2.2 Response to comments
Response to comments made on previous drafts of this document and
design methodology used here. Comments from IETF and WG01 are
responded to here.
H.263 picture header redundancy technique
The picture header redundancy technique from RFC2428, an RTP
payload for H.263+, is quite intelligent and useful. In JPEG
2000, there can be instances where the Main Header of the
codestream can become incredibly large, larger than the MTU size
if many encoding options are used. In such a situation, sending
the Main Header with each codestream packet would not be viable
at all. The codestream header is already quite compressed
during from basic JPEG 2000 development. Another technique will
be used in this standard to do something similar. Through the
optional payload header extension using the optional Marker
Segment Optional Header, the sender can include all the data
that it feels to be most important inside this optional header.
Scalable audio technique
The scalable audio technique from RFC2198 is quite interesting
and in some ways, applicable to our standard. This standard's
target market is quite wide and very unique. JPEG 2000 was
developed to be a highly flexible standard for digital imaging,
target applications from ultra-thin clients to image archiving.
At the imaging archiving level, the technique would be useful as
we move down to thinner clients, such a technique may not be
optimal when memory resources are scarce.
Optimal packet reordering
JPEG 2000 packet reordering and transmission may give a much
lower error rate when packets are lost or dropped as the error
would not be immediately apparent and can just "smear" over from
frame to frame. With packet reordering, the client must store
all the packets and rearrange them in memory for the decode.
The authors feel this would be incredibly taxing on some target
devices and not sure if such a scheme's result would be
effective. There should be some investigation into this area
with testing to find maybe a single best reordering scheme.
JPIP Interoperability
JPIP is new work taking place in the ISO/WG01 JPEG group to
develop a new part to the JPEG 2000 Standard.As the new JPIP
targets different application areas than this standard,
interoperability is highly desired. While this is an RTP
standard and JPIP is an RTSP standard, we have provided
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provisions for compatability from within the optional header.
This standard currently has only reserved definition for JPIP
header within the optional header. As JPIP is in early stages
of development and standardization, this standard shall
incorporate JPIP as a peer standard and strive for
interoperability as both become more mature.
1.2.3 Changes from the -00 version
The changes from the -00 version of this Internet Draft are:
Tiling bit removed and MTL has become MHF
The tile bit has been removed from the MTL field and the MTL field
has been renamed to MHF.
Tiling flag introduced.
The T flag field comes before the tile number field in the
payload header.
Fragment offset shortened from 32bit to 24bit field.
The justification is that for even QHD images, the fragment
offset value will not exceed 24bits. (Our target applications
are at most QHD size which has at most 4000 width and 3000
height. even if we encode that QHD size with 2bpp, the encoded
size is 4000x3000x2 / 8 = 3MB which is less than 2^24.)
Additionally, the savings in bits has also been reserved for
future use.
Examples of packetization
The packetization methods are much simpler than the first
version of the document, which required the examples to help
illustrate the packetization method.
Introduction to JPEG 2000 shortened
As mentioned previously in the comments section.
X and E bit swapped positions in the header
The fields have been swapped positions as implementations
demonstrated this is optimal data layout for this information.
Default priority table introduced
When there is no user table defined, a default table will be
used. This table is based on the JPEG 2000 packet number in the
codestream. Most JPEG 2000 images have at most 90 (=6x5x3)
jp2-packets which are constructed from 5 decomposition levels (6
resolutions), 5 layers and 3 components (YcrCb). Therefore, we
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suppose the 254 level priorities are enough in the worst case.
2. JPEG 2000 Video Features
JPEG 2000 video streams are formed as a continuous series of JPEG
2000 still images so the above features of JPEG 2000 can be used
effectively. A JPEG 2000 video stream has the following merits:
SNR is improved at a low bit rate. The formation can be used as a
video stream format at a low bit rate.
This is a Full Intra format, which each frame is independently
compressed has a low encoding and decoding delay.
JPEG 2000 has flexible and accurate rate control. This is suitable
for traffic control and congestion control at the network
transmission.
JPEG 2000 can provide its own code stream error resilience markers
to aid in code stream recovery.
3. Design of RTP payload format for JPEG 2000 video streams
To provide a payload format that exploits the JPEG 2000 video
stream, described in the previous section, the following must be
taken into consideration:
- Provisions for packet loss
On the Internet, 5% packet loss is common and this percentage
may sometimes come to 20% or more. To split JPEG 2000 video
streams into RTP packets, efficient packetization of the code
stream is required to minimize the effects of disabled decoding
due to missing code-blocks over error prone environments. If
the main header is lost in transmission, the decoding ability is
lost. Accordingly, a system to compensate for the loss of the
main header as much as possible is required.
- A packetizing scheme that exploits JPEG 2000 functionality.
A packetizing scheme so that an image can be progressively
transmitted and reconstructed progressively by the receiver
using JPEG 2000 functionality. Maximizing performance over
various network conditions and various computing power of
receiving platforms.
4. Proposal for an RTP payload format for JPEG 2000 video streams
4.1 RTP fixed header usage
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For each RTP packet, the RTP fixed header is followed by the JPEG
2000 payload header, which is followed by JPEG 2000 code stream.
The RTP header fields that have a meaning specific to the JPEG 2000
video are described as follows:
Payload type (PT): The payload type is dynamically assigned by means
outside the scope of this document. A payload type in the dynamic
range shall be chosen by means of an out of band signaling protocol
(e.g., RTSP, SIP, etc.)
Marker bit (M): The marker bit of the RTP fixed header MUST be set
to 1 on the last RTP packet of a video frame, and otherwise, it must
be 0. When transmission is performed by multiple RTP sessions, the
bit is set in the last packet of the frame in each session.
Timestamp: The RTP timestamp is in units of 90 KHz. The same
timestamp must appear in each fragment of a given frame. The initial
value of the timestamp is random to make known plaintext attacks on
encryption more difficult, even if the source itself does not
encrypt, as the packets may flow through a translator that does.
4.2 RTP Payload header format
The RTP payload header format for JPEG 2000 video stream is as
follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X|E|MHF|mh_id|T| priority | tile number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved | fragment offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fig. 2: RTP payload header format for JPEG 2000
X : 1 bit
Extension bit flag. This bit MUST be set to 1 when a JPEG 2000
optional payload header follows this header, the JPEG 2000
payload header, otherwise it MUST be set to 0. The details of
optional payload headers are described in Section 8 of this
document.
E : 1 bit
Enable bit flag. If this bit is set to 1, it means "intelligent
packetization" described in Section 5.2. If E bit is 0, it
means "non-intelligent packetization" and a receiver MUST ignore
any other payload header information other than extension bit
flag and fragment offset.
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MHF (Main Header Flag) : 2 bits
MHF shows whether the main header is packed into the RTP packet
or not. When the main header exists in the RTP packet, the
sender MUST set the first bit to 1, otherwise this field MUST
set to 0. If the first bit is 1, the second bit is valid, and
if the last part of the main header is included (either whole or
fragmented), the sender MUST set the second bit to 1. In other
words, this field is either 3(=0b11) or 2(=0b10) if the main
header exists in the RTP packet, otherwise 0. Table of MHF usage
is below:
+----+-------------------------------------------------------+
|MHF | Description |
+----+-------------------------------------------------------+
| 00 | no main header is packed at all |
| 01 | the fragmented main header (not last part) is packed. |
| 10 | reserved for future use. |
| 11 | a whole main header or the last part of the |
| | fragmented main header is packed. |
+----+-------------------------------------------------------+
Table 1: MHF usage values
The receiver checks MHF to determine the main header range and
may perform main header compensation described in Section 7 if
the main header is lost.
mh_id : 3 bits
Main header identification value. This is used for the JPEG
2000 main header recovery. The same mh_id is used as long as
the coding parameters described in the main header remain
unchanged. The mh_id starts at a value 1 when the first main
header is transmitted. Mh_id value must increase by 1 every
time a new main header is transmitted. Once the mh_id value is
greater than 7, it must roll over and start at 1 again. Usage
of this header is described in Section 7 of this document. This
field is only valid when E bit is 1. If the E bit is 0, then
this field SHOULD be zero.
priority : 8 bits
The priority field indicates the importance of the JPEG 2000
packet included in the payload. Typically, a higher priority is
set in the packets containing the JPEG 2000 packets of the lower
layers and the lower subbands.
T (Tile flag) : 1 bit
This field shows whether tile number field is valid or not:
T=0 means that tile number field is valid and shows the tile
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number of the tile-part. The sender MUST set T flag to 0 when
only one tile-part is packed into the RTP packet regardless
whether it is a whole tile-part or a fragmentation of the
tile-part.
T=1 means that tile number field is invalid. The sender MUST set
T flag to 1 when the multiple whole tile-parts are packed into
the RTP packet or there is no tile-part (in other words, only a
main header) in the RTP packet.
tile number : 16 bits
The interpretation of this field is changed depending on the
value of the T_flag. When T=0, this field shows the tile
number. When T=1, tile number field is invalid. The sender
SHOULD set tile number to 0, and the receiver MUST ignore this
field.
fragment offset : 24 bits
This value must be set to the byte offset in the JPEG 2000 data
stream of this RTP packet's contents.
JPEG 2000 frames are typically larger than underlying network's
maximum transfer units (MTU), frames might be fragmented into
several packets. The fragment offset is the data offset in
bytes of the current packet from the start of the JPEG 2000 code
stream. This field helps the receiver to reassemble JPEG 2000
code stream.
To perform scalable video delivery by using multiple RTP
sessions, the offset value from the first byte of the same frame
is set for fragment offset. Accordingly, in scalable video
delivery using multiple RTP sessions, the fragment offset may
not start with 0 in some RTP sessions even if the packet is the
first one of the frame.
5. Fragmentation of JPEG 2000 code stream and Type Field
Fig. 3 shows the construction of the JPEG 2000 code stream. The
JPEG 2000 code stream consists of a main header beginning with the
SOC marker, one or more tiles (only one tile for no tile division),
and the EOC marker to indicate the end of the code steam. Each tile
consists of a tile-part header starts with the SOT marker and ending
with the SOD marker, and a bit stream (a series of JPEG 2000
packets.)
+-- +------------+
Main | | SOC | Required as the first marker.
header| +------------+
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| | main | Main header marker segments
+-- +------------+
| | SOT | Required at the beginning of each tile-part
Tile- | +------------+ header.
part | | T0,TP0 | Tile 0, tile-part 0 header marker segments
header| +------------+
| | SOD | Required at the end of each tile-part header
+-- +------------+
| bit stream | Tile-part bit stream.
+-- +------------+ Might include SOP and EPH
| | SOT |
Tile- | +------------+
part | | T1,TP0 |
header| +------------+
| | SOD |
+-- +------------+
| bit stream |
+------------+
| EOC | Required as the last marker in the code stream
+------------+
Fig. 3: Construction of the JPEG 2000 code stream
The JPEG 2000 code stream consists of a main header, tile-part
headers, and JPEG 2000 packets. When we packetize the JPEG 2000
code stream, these construction units from the code stream must be
maintained. Each RTP packet will consist of a main header,
tile-part header, or JPEG 2000 packet.
If the server does not understand JPEG 2000 code stream (i.e. the
sender is not intelligent) it should pack JPEG 2000 code stream in
the largest possible MTU data size for the RTP packet. The sender
must segment the JPEG 2000 code stream along arbitrary lengths into
RTP sized packets for the receiver. In this case, the E bit MUST be
set to 0. This type of packetization is called "non-intelligent
packetization".
If the sender understands JPEG 2000 code streams and can read the
JPEG 2000 packets from the code stream. (i.e. the sender is
intelligent) This type of packetization is called "intelligent
packetization". JPEG 2000 packets should be packed into RTP payload
packets in the following way:
1. If the JPEG 2000 packets are smaller than the MTU size, the
sender should put as many whole JPEG 2000 packets into a single
RTP packet. That is, the JPEG 2000 payload data should begin
with either one of the SOC marker, SOT marker, or SOP marker (if
it exists in the JPEG 2000 data stream).
2. If the JPEG 2000 packets are larger than the MTU size, the sender
should segment the JPEG 2000 packets at the largest possible MTU
size but JPEG 2000 packets must not overlap.
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Regardless of the sender's capabilities, the receiver MUST be able
to handle RTP packets of any size.
If the sender does not fragment, any packets larger than the MTU
size might be fragmented into multiple smaller IP packets than the
MTU size by the IP layer. If one fragmented IP packet is lost
during transmission, it is recognized as a loss of the whole RTP
packet because the receiving host might not be able to reassemble
the RTP packet.
The segmentation of the JPEG 2000 code stream into RTP packets must
fit within the RTP payload size.
For intelligent packetization, all packets SHOULD be 32 bit aligned.
If padding bits are required, then the padding bits MUST come at the
end of the payload. Any required padding bits MUST NOT appear
between the header and the payload or at the beginning.
In the following, all the possible packetization cases are described
with diagrams.
5.1 Separation at arbitrary lengths
In this case, a JPEG 2000 code stream is split into several
fragments at arbitrary byte-position(Fig.4). The E bit MUST be set
to 0 for this packetization type.
+---+---+---+----------------------+
|RTP|PL |SOC| jpeg 2000 codestream |
|hdr|hdr| | fragment (1) |
+---+---+---+----------------------+
+---+---+--------------------------+
|RTP|PL | jpeg 2000 codestream |
|hdr|hdr| fragment (2) |
+---+---+--------------------------+
...
+---+---+----------------------+---+
|RTP|PL | jpeg 2000 codestream |EOC|
|hdr|hdr| fragment (N) | |
+---+---+----------------------+---+
*PL hdr = payload header
Fig. 4: Arbitrary length fragmentation.
The E (Enable) bit flag in the payload header MUST be 0 for this
packetization type. All other fields except for the X bit and
fragment offset field, in the payload header SHOULD be 0 and the
receiver MUST ignore any other values when the enable bit is 0.
Such RTP packetization scheme is not recommended from the standpoint
of error resilience. It is desirable to use it only in some limited
environments shown below:
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- The sender finds it difficult to distinguish the main header, tile
header, and JPEG 2000 packets from one another. Such a situation
is likely to occur when the sender has poor computational power
and there is no SOP marker in the JPEG 2000 code stream.
- The network environment is error free.
- If the JPEG 2000 error resilience markers (TLM, PLM, PLT, PPM, and
PPT markers) are present in the code stream. Error resilience
will be handled outside of RTP. Its description is not within the
scope of this document. Using these markers may improve error
resilience and recovery. Producing JPEG 2000 bit streams with
these markers is highly recommended in all cases.
5.2 General JPEG 2000 RTP packet types
For the following packetization types, the E bit MUST be set to 1 in
all following cases.
(1) JPEG 2000 main header (SOC marker) must come first after the
payload header (just after the RTP payload header). If a whole
main header is packed into the RTP packet, the MHF_value must be
3 (=0b11). The tile-part header and jp2-packets MAY follow the
main header in the same packet. When only the main header is in
the RTP packet, the T flag MUST be set to 1 and the tile number
field is ignored. The sender SHOULD set the tile number to
0x00, and the receiver MUST ignore this field.
(2) If two or more tile-parts are packed into a single RTP packet,
only whole tile-parts MUST be packed into the RTP packet.
Segmented tile-packets MUST NOT be packed or spread over RTP
several RTP packets. When the multiple tile-parts exist in a
single RTP packet, the T flag MUST be set to 1, which shows the
tile number field is invald .
(3) If one tile-part is packed into the RTP packet, the tile-part
header, if any, MUST come first. Note that the tile-part header
just after the main header MAY either be packed with the main
header, or be separated to another RTP packet. In this case, T
flag MUST be set to 0 and the tile number of the tile-part is
set in the "tile number" field. Jp2-packets MAY follow the
tile-part header and may be packed into the same RTP packet.
(4) If no headers of any kind are in the RTP packet, the T flag MUST
be set to 0 and the tile number field MUST be set to the tile
number which the jp2-packets belongs to.
(5) If the main header, a tile-part header, or a jp2-packet is split
into the multiple RTP packets, only one fragment SHALL be packed
into an RTP packet. If the main header is split, only the last
fragment's MHF is 3 (=0b11), and the rest are 2(=0b10) . All
other fragmented RTP packet's MHF value shall be 0.
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6. Scalable Delivery and Priority field
JPEG 2000 code stream has rich functionality built into it so
decoders can easily handle scalable delivery or progressive
transmission. Progressive transmission that allows images to be
reconstructed with increasing pixel accuracy or spatial resolution
is essential for many applications. This feature allows the
reconstruction of images with different resolutions and pixel
accuracy, as needed or desired, for different target devices. The
largest image source devices can provide a code stream that is
easily processed for the smallest image display device.
The JPEG 2000 packets contain all compressed image data from a
specific layer, a specific component, a specific resolution level,
and a specific precinct. The order in which these packets are found
in the code stream is called the "progression order". The ordering
of the packets can progress along four axes: layer, component,
resolution level and precinct.
Providing priority field to show importance of data contained in a
given RTP packet can exploit JPEG 2000 progressive & scalable
functions.
The lower the priority value, the higher the priority. In other
words, the priority value 0 is the highest priority, and 255 is the
lowest priority. We define the priority value 0 and 255 as special
priorities: 0 for the headers (the main header or tile-part header),
and 255 for no priority. When any headers (the main header or
tile-part header) are packed into the RTP packet, the sender MUST
set the priority value to 0. When the sender will not use the
priority field, the sender MUST set the priority value to 255 to
inform the receiver that sender doesn't use the priority field.
6.1 Priority mapping table
For the progression order, the priority value to be given to each
JPEG 2000 packet is defined by the priority mapping table. In
principle, the priority mapping table is negotiated between the
sender and the receiver through external protocols (such as: RTSP,
SIP, etc), which not within the scope of this document. However, in
some environments such as a multicast videoconference environment,
it might be difficult to negotiate the priority-mapping table
between senders and receivers. We define the default priority
mapping for such a situation. The receiver interprets the priority
as a user-defined priority value only when the priority-mapping
table has been negotiated and otherwise the receiver interprets as
the default priority.
6.1.1 default priority mapping
The JPEG 2000 codestream is ordered in some progression order and
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the in most cases; the foremost jp2-packets are more important than
the latter ones. In the default priority table, jp2-packet number
is used as a priority value. Jp2-packet number is "packet sequence
number" defined at SOP marker segments described in Annex A.8.1 [1].
The default priority values have a range from 1 to 254. If the
number of packets is larger than 254, that is, a sequence number
exceeds 254, the sender MUST set priority values of the following
jp2-packets to 254.
6.1.2 user-defined priority table
The user-defined priority table is freely defined by users, but
priority value 0 and 255 MUST be used as a special priorities: 0 for
the headers and 255 for no priority.
For example, in the LRCP order codestream with 3 layers and 3
resolutions, the user-defined priority table can be defined below
(the format is not significant). It has 4 level priorities.
priority 1: L=0,R=0, C=any, P=any
priority 2: L=0,R=1-2, C=any, P=any
priority 3: L=1,R=any, C=any, P=any
priority 4: L=2,R=any, C=any, P=any
As another example, the resolution-based priority table can be
defined as below:
Priority 1: R=0, L=0, C=any, P=any
Priority 2: R=0, L=1-2, C=any, P=any
Priority 3: R=1, L=any, C=any, P=any
Priority 4: R=2, L=any, C=any, P=any
As another example, the component-based priority table can be
defined as below:
Priority 1: C=0, L=0, R=0, P=any
Priority 2: C=0, L=0, R=any, P=any
C=0, L=any, R=0, P=any
Priority 3: C=1-2, L=any, R=any, P=any
To change the priority-mapping table, a new priority-mapping table
must be sent from the sender to the receiver as needed.
6.2 Sender's Actions
Priority is given in accordance with the priority-mapping table.
For RTP packets that only consist of a whole or fragmented main/tile
header, the sender MUST set priority 0 when a priority-mapping table
is used. If a priority-mapping table is not used, the priority
value must be 0xFF for the same RTP packets.
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When the several jp2-packets are packed into the same RTP packet,
the priority values of these jp2-packets are sometimes different.
In such a case, a sender MUST set the packet priority to the highest
priority of all the ones inside the packet. If the sender does not
use any priority-mapping table, it MUST set 0xff in the priority
field.
The sender may transmit each priority using separate multiple RTP
sessions defined by the priority value. For example, different
priority may be allocated to others in a multicast group. The
sender may also transmit all priority valued RTP packets using a
single RTP session.
6.3 Receiver's Action
Progressive transmission that allows images to be reconstructed with
increasing pixel accuracy or spatial resolution is essential for
many applications. This feature allows the reconstruction of images
with different resolutions and pixel accuracy, as needed or desired,
for different target devices. The image architecture provides for
the efficient delivery of image data in many applications such as
client/server applications. The receiver should decode packets
above a certain priority to obtain maximum performance depending on
the receiver's platform.
The receiver can determine on its own (using or not using the
mapping table or other variables) the priority value level the RTP
packets it should decode.
For example, when a less powerful CPU is used or the terminal has
only a low-resolution display, decoding only RTP packets below a
certain priority permits obtaining optimal performance.
If any high-priority RTP packet is not received when a packet loss
occurs, frame(s) can be skipped because no significant visual loss
may be perceived even if decoding can be successfully performed.
When any uninterpretable or an unexpected priority is received, the
receiver must interpret the packets as no priority (i.e. priority=
0xFF).
7. JPEG 2000 main header compensation
The JPEG 2000 image main header describes various encode parameters
and the decoder decodes by using the parameters described in the
main header. If the RTP packet that contains the main header is
lost, the corresponding JPEG 2000 code stream cannot and should not
be decoded. In an extremely rare case, if the main header has
dropped and all the remainder JPEG 2000 packets has been received
successfully, the receiver cannot decode the frame without main
header information. Even when the main header is lost, it can be
recovered to a certain level using the following method.
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A recovery of the main header that has been lost is very simple with
this procedure. In the case of JPEG 2000 video, it is common that
encode parameters will not vary greatly from each successive frame.
Even if the RTP packet including the main header of a frame has
dropped, decoding processing may be performed by using the main
header of the previous frame if this previous frame is already
encoded by the same encode parameters.
The mh_id field of the payload header is used to recognize whether
the encoding parameters of the main header are the same as the
encoding parameters of the previous frame. The same value is set in
mh_id of the RTP packet in the same frame. Mh_id and encode
parameters are not associated with each other as 1:1 but they are
used to recognize whether the encode parameters of the previous
frame are the same or not.
The mh_id field value SHOULD be saved from previous frames to be
used to recover the current frame's main header, if lost. If the
mh_id of the current frame has the same value as the mh_id value of
the previous frame, the previous frame's main header SHOULD be used
to decode the current frame, in case of a lost header.
The sender MUST increment mh_id when parameters in the header change
and send a new main header accordingly.
The receiver MAY use the md_id and MAY retain the header for such
compensation.
7.1 Sender processing
The sender must transmit RTP packets with the same mh_id value
unless the encoder parameters are different from the previous frame.
The encode parameters are the fixed information marker segment (SIZ
marker) and functional marker segments (COD, COC, RGN, QCD, QCC, and
POC) specified in JPEG 2000 Part 1 Annex A [1]. If the encode
parameters have been changed, the sender transmitting RTP packets
MUST increment the mh_id value by one. The initial mh_id value
should be 1. When the mh_id value exceeds 7, the value MUST return
to 1 again.
If the md_id field is set to 0, the receiver MUST not save the main
header and MUST NOT compensate for lost headers using the above
method.
7.2 Receiver processing
When the receiver has received the main header correctly, the RTP
sequence number, the mh_id and main header should be saved except
when the mh_id value is 0. Only the last main header that was
received correctly SHOULD be saved. That is, if there has been a
saved main header, the previous one is deleted and the new main
header is saved.
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When the main header is not received, the receiver compares the
current mh_id value (this mh_id can be known by receiving at least
one RTP packet) with the saved mh_id value. When the values are the
same, decoding may be performed by using the saved main header.
Knowing whether the main header is lost or not maybe difficult,
especially when the main header is fragmented.
In all cases, the main header will start with fragment offset = 0.
In the case of fragmented main header, only the first fragment will
have the fragment offset = 0.
8. Optional Payload Header
When the extension bit of the JPEG 2000 payload header is 1, an
optional payload header follows the payload header. The JPEG 2000
video stream payload comes after the optional payload header. The
figure shows a general format of the optional payload header.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| optype |X| length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| option specific format ..... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fig. 5 : JPEG 2000 video stream optional payload header generic
format
optype : 7 bits
optype describes the optional payload header type. Optype value
0 MUST not be used. Optype values from 1 to 63 are defined in
the specification. In this draft, 1 and 2 are defined and the
rest are reserved for future use. Optype values from 64 to 127
are application-defined ones and can be freely used for
application's own definition. Any optype values in the range of
0-63 not specified within this document MUST be ignored and the
accompanying header must be ignored as well.
+--------------------+----------------------------------+
| Optype value range | Defined in |
+--------------------+----------------------------------+
| 0 | Not allowed. |
| 1-63 | In this specification. |
| 64-127 | Free for application definition. |
+--------------------+----------------------------------+
Table 2: Optype value definition range
X : 1 bit
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Further extension bit. This must be set to 1 if another optional
payload header follows this optional payload header; otherwise
it must be set to 0.
When the extension bit of the optional header is 1, another
optional payload header MUST come immediately after this
optional payload header.
length : 16 bits
This value must be the length of optional header in bytes. The
receiver shall perform processing for the optional header when
the extension bit of the JPEG 2000 payload header is 1.
8.1 Marker Segment Optional Header
The marker segment optional header allows changes to almost any
property of the JPEG 2000 main or tile header functional markers
such as: (SIZ, COD, COC, RGN, QCD, QCC, POC, etc.)
As an optional header, this can be used to duplicate critical data
from the main or tile header redundantly with each packet. At the
same time, small changes to a larger header would be simple with
this marker.
The format of this optional header:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| optype=1 |X| length |F| JP2code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| marker segment data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fig. 6 : Marker segment optional header format
optype: 7 bits
This value MUST be 1 for this optional header.
X : 1 bit
Extension bit. This signifies whether another optional header
follows this one. If there is another, the X bit MUST be set to
1; else, it must be 0. For multiple changes to the header,
chaining these headers together is recommended.
length : 16 bits
Length value. The length of this optional marker should be the
length of the corresponding JP2 functional marker minus 1.
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(i.e. Lxxx - 1) Please see section 8.1.1 and section 8.1.2 for
specific example.
F : 1 bit
Functional bit. Whether the optional header is making a change
in the main or tile header. F = 0 for tile header and F = 1 for
main header.
JP2code : 7 bits
JP2 functional code value. This value contains the lower 7bits
of the original JPEG 2000 functional code marker. (i.e. COD
marker = 0xFF52, lower 7 bits = 0x52 -> 0b1010010)
marker segment data : length bits
The data in this area MUST be the same as the corresponding JPEG
2000 marker data specified in Annex A of [1] but not including
the length of the marker segment.
A limitation of this optional header is that the functional
markers in the optional header MUST be present in the original
main or tile header. Markers other than the ones in main or
tile headers MUST NOT be present in this header.
8.1.1 Specific example of marker segment header: COD
Here is a specific marker segment header for a COD functional
segment:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| optype=1 |0| length=(Lcod-1) |1| 1010010 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Scod | SGcod |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SGcod | |
+-+-+-+-+-+-+-+-+ |
| Spcod (Lcod length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fig. 7 : COD marker segment optional header example
-Optype = 1. As specified in this recommendation.
-X = 0. For this instance.
-Length = Lcod - 1. The length of the original COD marker - 1.
-F = 1. This change is in the main header, then F=1.
- JP2Code = 1010010 -> 0x52. COD marker in JPEG 2000 value: 0xFF52.
8.1.2 Specific example of marker segment header: QCD
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Here is a specific marker segment header for a QCD functional
segment:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| optype=1 |0| length=(Lqcd-1) |0| 1011100 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sqcd | |
+-+-+-+-+-+-+-+-+ |
| SPqcd (Lqcd length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fig. 8 : QCD marker segment optional header example
-Optype = 1. As specified in this recommendation.
-X = 0. For this instance.
-Length = Lqcd - 1. The length of the original QCD marker - 1.
-F = 0. This change is in the tile header, then F=0.
-JP2Code = 1011100 -> 0x5C. QCD marker in JPEG 2000 value: 0xFF5C.
8.2 JPIP Optional Header
Interoperability with different standards is extremely useful. The
ISO WG1 group also has put forth a transmission protocol standard
called: JPIP. This standard is a protocol standard for viewing JPEG
2000 images interactively using RTSP. To embrace this standard, an
optional JPIP header to handle the RTP data for JPIP compatible
clients is defined here.
At the time of this writing, the JPIP work is still in its early
stage of standardization. Currently, a reserved optype value of 2
will be placed for JPIP when it is complete.
The option specific information in this optional header shall be the
same as the server response data packet from a JPIP server or a
description of the packet's JPEG 2000 packets.
Optype : 7 bits
The optype value for a compatible JPIP optional header must be
2.
Option specific format: X bits
This shall be determined at a later date.
9. Security Consideration
RTP packets using the payload format defined in this specification
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are subject to the security considerations discussed in the RTP
specifications[3]. This implies that confidentiality of the media
streams is achieved by encryption. Because the data compression used
with this payload format is applied end-to-end, encryption may be
performed on the compressed data so there is no conflict between the
two operations.
10. Recommended Practices
As the JPEG 2000 coding standard is highly flexible, many different
but compliant data streams can be produced and still be labeled as a
JPEG 2000 data stream.
The following is a set of recommendations set forth from our
experience in developing JPEG 2000 and this payload specification.
Implementations of this standard must handle all possibilities
mentioned in this specification. The following is a listing of
items an implementation could optimize.
Error Resilience Markers
The use of error resilience markers in the JPEG 2000 data stream
is highly recommended in all situations. Error recovery with
these markers is helpful to the decoder and save external
resources. Markers such as: RESET, RESTART, and ERTERM
Packetization Ordering
Packetization ordering is completely dependent on the client's
capabilities. Some orderings allow for less amount of
distortion in the event of loss at the expense of memory storage
and packet reordering.
YCbCr Color space
The YCbCr color space provides the greatest amount of
compression in color with respect to the human visual system.
When used with JPEG 2000, the usage of this color space can
provide excellent visual results at extreme bit rates.
Progression Ordering
JPEG 2000 offers many different ways to order the final code
stream to optimize the transfer with the presentation. The most
useful ordering in our usage cases have been for layer
progression and resolution progression ordering.
Tiling and Packets
JPEG 2000 packets are formed regardless of the encoding method.
The encoder has little control over the size of these JPEG 2000
packets as they maybe large or small.
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Tiling splits the image up into smaller areas and each are
encoded separately. With tiles, the JPEG 2000 packet sizes are
also reduced. When using tiling, almost all JPEG 2000 packet
sizes are an acceptable size (i.e. smaller than the MTU size of
most networks.)
It is highly recommended that tiling be used so that
packetization of JPEG 2000 packets for transport can be done
simpler.
11. Intellectual Property Right
There are format and mechanisms included in a pending patent
application that have been FILED to the Japanese Patent Office.
It must be stressed that as of this document's submission they have
only been filed and have not been granted.
We wish to contribute to development of the Internet community and
continue our good relationship with IETF. Our primary concern is to
promote technology so that others may feel it is useful and
worthwhile in the spirit of the IETF.
If the mechanisms are granted as patents, the patents will be
licensed under reasonable and non-discriminatory conditions to any
person(s) who wishes to implement such mechanisms.
12. References
[1] ISO/IEC JTC1/SC29: ISO/IEC 15444-1 "Information technology -
JPEG 2000 image coding system - Part 1: Core coding system",
December 2000.
[2] ISO/IEC JTC1/SC29/WG1: "Motion JPEG 2000 Committee Draft 1.0",
http://www.jpeg.org/public/cd15444-3.pdf, December 2000.
[3] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson "RTP: A
Transport Protocol for Real Time Applications", RFC 1889, January
1996.
[4] ISO/IEC JTC1/SC29/WG1: "JPEG2000 requirements and profiles
version 6.3", draft in progress,
http://www.jpeg.org/public/wg1n1803.pdf
[5] Diego Santa-Cruz, Touradj Ebrahimi, Joel Askelof, Mathias
Larsson and Charilaos Christopoulos: "JPEG 2000 still image
coding versus other standards", In Proc. of SPIE's 45th annual
meeting, Application of Digital Image Processing XXIII,
vol.4115, pp.446-454, July 2000.
13. Authors' Addresses
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Eric Edwards
Sony Corporation
Media Processing Division
Network & Software Technology Center of America
3300 Zanker Road, MD: SJ2C4
San Jose, CA 95134
Phone: +1 408 955 6462
Fax: +1 408 955 5724
Email: Eric.Edwards@am.sony.com
Satoshi Futemma/Eisaburo Itakura/Nobuyoshi Tomita
Sony Corporation
6-7-35 Kitashinagawa Shinagawa-ku
Tokyo 141-0001 JAPAN
Phone: +81 3 5448 3096
Fax: +81 3 5448 4622
Email: {satosi-f|itakura|n-tomita}@sm.sony.co.jp
Andrew Leung/Takahiro Fukuhara
Sony Corporation
1-11-1 Osaki Shinagawa-ku
Tokyo 141-0032 JAPAN
Phone: +81 3 5435 3665
Fax: +81 3 5435 3891
Email: {andrew|fukuhara}@av.crl.sony.co.jp
Edwards, et al. [Page 23]
