INTERNET-DRAFT Eric Edwards draft-ietf-avt-rtp-jpeg2000-04.txt Satoshi Futemma Nobuyoshi Tomita Eisaburo Itakura Sony Corporation October 27, 2003 Expires: April 26, 2004 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 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 materials 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-Drafts Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 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. This payload format will allow for JPEG 2000's scalability and robustness to be maximized in streaming applications. Table of Contents 1. Introduction .......................................... 2 1.1 Conventions Used in this Document ..................... 3 2. JPEG 2000 Video Features .............................. 4 3. Payload Design ........................................ 4 4. Payload Format ........................................ 4 4.1 RTP fixed header usage ................................ 4 4.2 RTP Payload header format ............................. 5 5. RTP Packetization ..................................... 7 5.1 Non-intelligent mode .................................. 8 5.2 Intelligent mode ..................................... 9 6. Scalable Delivery and Priority field .................. 10 Edwards, et al. [Page 1] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 6.1 Priority mapping table ................................ 11 6.1.1 Default priority mapping .............................. 11 6.1.2 User-defined priority table ........................... 11 6.2 Sender's Action ..................................... 12 6.3 Receiver's Action ..................................... 12 7. JPEG 2000 main header compensation .................... 13 7.1 Sender processing ..................................... 13 7.2 Receiver processing ................................... 14 8. Optional Payload Header ............................... 14 9. Security Consideration ................................ 15 10. IANA Consideration .................................... 16 10.1 MIME Registration ..................................... 16 10.2 SDP Parameters ........................................ 17 11. Intellectual Property Right Statement ................. 17 12. Informative Appendix - Recommended Practices .......... 18 13. References ........................................... 18 14. Authors' Addresses .................................... 19 15. Full Copyright Statement .............................. 20 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][6]. Part 3 of the JPEG 2000 standard defines Motion JPEG 2000[6]. However, Part 3 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 powerful features that are not supported in the current JPEG standard [1][7][8]: o Higher compression efficiency than JPEG with less visual loss especially at extreme compression ratios. o A single codestream that offers both lossy and superior lossless compression. o Robust transmission over noisy environments. o Progressive transmission by pixel accuracy (SNR Scalability) and resolution. o Random codestream access and processing. The JPEG-2000 algorithm is briefly explained below. Fig. 1 shows a block diagram of JPEG 2000 encoding method. Edwards, et al. [Page 2] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 +-----+ | ROI | +-----+ | V +----------+ +----------+ +------------+ |DC, comp. | | Wavelet | | | raw image ==> |transform-|==>|transform-|==>|Quantization|==+ | ation | | ation | | | | +----------+ +----------+ +------------+ | | +-----------+ +----------+ +------------+ | | | | | | | | JPEG 2000 <==| Data |<==|Arithmetic|<==|Coefficient |<=+ codestream | Ordering | | 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 sub-band. 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 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 are called layers. The standard has four ways to transmit and decode a compressed image: by resolution, quality, position, or component. Packets can be ordered in any way to maximize these features. 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 codestream, 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 Conventions Used in this Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL Edwards, et al. [Page 3] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 [2]. 2. JPEG 2000 Video Features JPEG 2000 video streams are formed as a continuous series of JPEG 2000 still images. The previously described features of JPEG 2000 can be used effectively in a streaming application. A JPEG 2000 video stream has the following merits: In JPEG 2000 SNR is improved dramatically over classic JPEG at a low bit rates. This is a Full Intra format- each frame is independently compressed - and therefore has a low encoding and decoding delay. JPEG 2000 has flexible and accurate rate control. This is suitable for traffic control and congestion control during network transmission. JPEG 2000 can provide its own codestream error resilience markers to aid in codestream recovery. 3. Payload Design 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 problems in decoding due to missing code-blocks in error prone environments. If the main header is lost in transmission, the image cannot be decoded. Accordingly, a system to compensate for the loss of the main header 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 would be very powerful. It would allow for maximizing performance over various network conditions and variations in computing power of receiving platforms. 4. Payload Format 4.1 RTP fixed header usage Edwards, et al. [Page 4] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 For each RTP packet, the RTP fixed header is followed by the JPEG 2000 payload header, which is followed by JPEG 2000 codestream. The RTP header fields that have a meaning specific to a JPEG 2000 video stream are described as follows: 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. 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.) Timestamp: The RTP timestamp is in units of 90 kHz. The same timestamp must appear in each fragment of a given frame. When a JPEG 2000 image is an interlaced, the odd field and the corresponding even field have the same timestamps. 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 |tp | 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 Edwards, et al. [Page 5] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 receiver MUST ignore any other payload header information other than extension bit flag and fragment offset. 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 | reserved for future use. | | 10 | the fragmented main header (not last part) is packed. | | 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 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 initial value of mh_id is random. 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. T (Tile field invalidation flag) : 1 bit T bit indicates whether the tile number field is invalid or not. A sender MUST set T bit when the tile number field is invalid. There are two cases where the tile number field is invalid. One is the case that an RTP packet holds only the JPEG 2000 Edwards, et al. [Page 6] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 main header. In this case, a sender can not set any number in the tile number field because no JPEG 2000 tile-part bitstream is included in the RTP packet. The other case is that multiple tile-part bitstreams are packed together in an RTP packet. In general, it is advisable to pack only one tile bitstream in an RTP packet, but if the tile-part length is too small it is efficient to pack together multiple tile-parts in one RTP packet. In this case it is meaningless to assign a number (e.g. the smallest tile number) because the number is designed for decoding an arbitrary tile easily, which is not valid when multiple tile parts are combined in a single packet. Therefore, T bit indication is needed. 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 JPEG 2000 packets containing the lower sub-bands. tile number : 16 bits This field shows the tile number that a bitstream belongs to only when the T bit is 0. A receiver can easily decode an arbitrary tile by checking this field. If T bit is set to 1, a receiver MUST ignore this field. tp (type) : 2 bits This field indicates how a JPEG 2000 image is scanned (meaning - progressive or interlace). 0: The image is progressively scanned. On a computer monitor, it should be displayed as-is at the specified width and height in the JPEG 2000 main header. 1: The image is an odd field of an interlaced video signal. The height specified in the JPEG 2000 main header is half of the height of the entire displayed image. In a receiver, an odd field should be de-interlaced with the even field following it so that lines from each image can alternate. 2: The image is an even field of an interlaced video signal. 3: The image is a single field from an interlaced video signal, intended to be displayed full frame as if it were received as both the odd & even field of the frame. On a computer monitor, each line in the image should be displayed twice, doubling the height of the image. fragment offset : 24 bits Edwards, et al. [Page 7] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 This value must be set to the byte offset in the JPEG 2000 data stream contained in this RTP packet. JPEG 2000 frames are typically larger than the underlying network's maximum transfer units (MTU), therefore 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 codestream. This field helps the receiver to reassemble the JPEG 2000 codestream. 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. It is possible, 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. RTP Packetization As shown in Fig. 3, a JPEG 2000 codestream is structured from the 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 codestream. Each tile consists of a tile-part header that starts with the SOT marker and ends with the SOD marker, and bitstream (a series of jp2-packet). +-- +------------+ Main | | SOC | Required as the first marker. header| +------------+ | | main | Main header marker segments +-- +------------+ | | SOT | Required at the beginning of each Tile- | +------------+ tile-part header. part | | T0,TP0 | Tile 0, tile-part 0 header marker header| +------------+ segments | | SOD | Required at the end of each tile-part +-- +------------+ header | bitstream | Tile-part bitstream +-- +------------+ | | 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 codestream Edwards, et al. [Page 8] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 Two packetization modes can be used for a JPEG 2000 RTP packet: non-intelligent mode and intelligent mode. A sender is allowed to packetize the JPEG 2000 codestream in either mode, but MUST not change the mode within the same JPEG 2000 codestream. A sender may implement only one mode, but a receiver MUST interpret both modes. A receiver identifies the packetization mode with E bit flag in the payload header to process the RTP packet properly. In both modes, a sender usually partitions the JPEG 2000 codestream in the way that IP fragmentation never occurs. Any packets larger than the MTU size might be fragmented into multiple smaller IP packets by the IP layer. Therefore, if one fragment is lost during transmission, a receiver might not be able to reassemble the IP packet, so that it is recognized as a loss of the whole fragmented packet. 5.1 Non-intelligent mode This mode is prepared for a thin sender, which has insufficient CPU power to parse the JPEG 2000 codestream syntax and to partition the codestream per jp2-packet. In this mode, a sender segments the JPEG 2000 codestream along arbitrary lengths into RTP packets, and E bit flag in the payload header MUST be set to 0. Typically, a sender fragments a JPEG 2000 codestream in a fixed length. An example of this packetization is below: +------+-------+-------------------------------+ |RTP |payload| JPEG 2000 codestream fragment | |header|header | | +------+-------+-------------------------------+ +------+-------+-------------------------------+ |RTP |payload| JPEG 2000 codestream fragment | |header|header | | +------+-------+-------------------------------+ ... +------+-------+-------------------------------+ |RTP |payload| JPEG 2000 codestream fragment | |header|header | | +------+-------+-------------------------------+ Fig. 4: Example of non-intelligent mode packetization A receiver recognizes that the codestream is packetized in non-intelligent mode by checking E bit flag, then RTP packets with same RTP timestamps are de-packetized to the JPEG 2000 codestream using fragment offset in the payload header. In this mode, X bit and fragment offset are interpreted and any other fields are ignored. Edwards, et al. [Page 9] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 If a receiver receives the RTP packets in both modes and both RTP timestamps are the same, then it SHOULD ignore the all RTP packets with the timestamp. 5.2 Intelligent mode In this mode, a new concept for a packetization unit is introduced. A packetization unit is defined as either a JPEG 2000 main header, a tile-part header, or a jp2-packet. First, a sender divides the JPEG 2000 codestream into packetization units by parsing the codestream or by getting any indexing informations from encoder, and then packs the packetization units into RTP packets. A sender can put an arbitrary number of packetization units into an RTP packet, but it MUST preserve the codestream order. An example of this kind of RTP packet format is below: +------+-------+---------------+---------------+ |RTP |payload| packetization | packetization | |header|header | unit | unit | +------+-------+---------------+---------------+ Fig. 5 An Example of RTP packet format with multiple packetization units Sometimes, packetization units may be not 32-bits aligned, so additional padding octets are needed. In an RTP packet with multiple packetization units, any required paddings MUST be added at the end of concatenated packetization units. If a packetization unit is larger than MTU size, it can be fragmented. To pack a fragmented packetization unit, the fragmented unit MUST NOT be packed with the succeeding packetization unit into the same RTP packet. An example of this kind of RTP packet format is below: +------+-------+-----------------------------+ |RTP |payload| packetization unit fragment | |header|header | | +------+-------+-----------------------------+ +------+-------+-----------------------------+ |RTP |payload| packetization unit fragment | |header|header | | +------+-------+-----------------------------+ ... +------+-------+-----------------------------+ |RTP |payload| packetization unit fragment | |header|header | | +------+-------+-----------------------------+ Fig. 6 An Example of RTP packet format with a fragmented Edwards, et al. [Page 10] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 packetization unit 6. Scalable Delivery and Priority field JPEG 2000 codestream 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 jp2-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 jp2-packets are found in the codestream is called the "progression order". The ordering of the jp2-packets can progress along four axes: layer, component, resolution level and precinct. Providing a priority field to indicate importance of data contained in a given RTP packet can exploit JPEG 2000 progressive and scalable functions. The lower the number of priority value is the higher priority. In other words, the priority value 0 is the highest priority and 255 is the lowest priority. We define the priority value 0 as special priorities for the headers (the main header or tile-part header) 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. 6.1 Priority mapping table For the progression order, the priority value for each jp2-packet is given by the priority mapping table. There are two types of priority mapping: default priority mapping and user-defined priority mapping. 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 video-conference 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 in the most cases the foremost jp2-packets are more important than the latter ones. Edwards, et al. [Page 11] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 In default priority mapping, a priority value is defined as jp2-packet sequence number, in which the first jp2-packet in a tile MUST be assigned the value 1. For every successive packet this number is incremented by one. When the maximum number (=255) is reached, the number remains at 255. A jp2-packet sequence number is also hinted from Nsop of SOP marker segment (Annex A.8.1 [1]) in the JPEG 2000 codestream. 6.1.2 User-defined priority table The user-defined priority table is freely defined by users, but priority value 0 MUST be used for the headers (the main header and tile-part headers). 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). 4 level priorities is defined in the below example. 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 Action A priority value is given in accordance with the priority mapping table. If multiple jp2-packets are packed into the same RTP packet, the lowest priority value is set. Accordingly, a sender can transmit each priority using separate multiple RTP sessions. For example, in layered multicast a sender can transmit each priority through each multicast group. Edwards, et al. [Page 12] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 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 the priority value is uninterpreted or unexpected, a receiver MUST ignore the priority field of this RTP packet. 7. JPEG 2000 main header compensation The JPEG 2000 main header has various encoding parameters. A decoder decodes the JPEG 2000 codestream by using the parameters described in the JPEG 2000 main header. If an RTP packet is lost with the JPEG 2000 main header, the corresponding JPEG 2000 codestream cannot be decoded, even if all of the following RTP packets has been successfully received. 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 Edwards, et al. [Page 13] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 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 mh_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 mh_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. 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 An optional payload header is intended for sending application specific data. When X bit in the payload header is set, an optional payload header follows the payload header. The JPEG 2000 video stream payload comes after the optional payload header. Edwards, et al. [Page 14] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 When X bit in payload header is set, a receiver MUST process the optional payload header. An optional payload header that a receiver cannot recognize MUST be skipped in specified length. 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. 7 : JPEG 2000 video stream optional payload header generic format Optype : 7 bits Optype describes the optional payload header type. Optypes 0-63 are reserved as fixed, well-known mappings to be defined by future revisions of this document. Optypes 64-127 can be freely used for an application's own definition. If some options would be fully tested and widely used, they shall be registered with the Internet Assigned Number Authority (IANA). X : 1 bit 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 (including optype, X, length field). The receiver shall perform processing for the optional header when the extension bit of the JPEG 2000 payload header is 1. 9. Security Consideration RTP packets using the payload format defined in this specification 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. Edwards, et al. [Page 15] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 A potential denial-of-service threat exists for data encodings using compression techniques that have non-uniform receiver-end computational load. The attacker can inject pathological datagrams into the stream which are complex to decode and cause the receiver to be overloaded. However, JPEG 2000 coding does not exhibit any significant non-uniformity. If QoS enhanced service is used, RTP 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. If best-effort service is being used, users of this payload format MUST 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, 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. As with any IP-based protocol, in some circumstances a receiver may be overloaded simply by the receipt of too many packets, either desired or undesired. Network-layer authentication may be used to discard packets from undesired sources, but the processing cost of the authentication itself may be too high. In a multicast environment, pruning of specific sources may be implemented in future versions of IGMP [9] and in multicast routing protocols to allow a receiver to select which sources are allowed to reach it. 10. IANA Consideration 10.1 MIME Registration This document defines a new RTP payload name and associated MIME type, jpeg2000. The MIME registration form for JPEG 2000 video stream is enclosed below: MIME media type name: video MIME subtype name: jpeg2000 Required parameters: none Optional parameters: none Encoding considerations: JPEG 2000 video stream can be transmitted with RTP as specified in RFC XXXX. Edwards, et al. [Page 16] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 Security considerations: see section 9 of RFC XXXX. Interoperability considerations: JPEG 2000 video stream is a sequence of JPEG 2000 still images. An implementation in compliant with [1] can decode and attempt to display the encoded JPEG 2000 video stream. Published specification: ISO/IEC 15444-1, RFC XXXX Applications which use this media type: video streaming and 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: Eric Edwards Email: Eric.Edwards@am.sony.com Intended usage: COMMON Author/Change controller: Eric Edwards Email: Eric.Edwards@am.sony.com 10.2 SDP Parameters The MIME media type video/jpeg2000 string is mapped to fields in the Session Description Protocol (SDP) [4] as follows: o The media name in the "m=" line of SDP MUST be video. o The encoding name in the "a=rtpmap" line of SDP MUSE be jpeg2000 (the MIME subtype). o The clock rate in the "a=rtpmap" line MUSE be 90000. Therefore, an example of media representation in SDP is as follows: m=video 49170/2 RTP/AVP 98 a=rtpmap:98 jpeg2000/90000 11. Intellectual Property Right Statement The IETF takes no position regarding the validity or scope of any Edwards, et al. [Page 17] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. The IETF has been notified of intellectual property rights claimed in regard to some or all of the specification contained in this document. For more information consult the online list of claimed rights. 12. Informative Appendix - 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. YPbPr Color space The YPbPr 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. Edwards, et al. [Page 18] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 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. 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.) 13. References Normative References [1] ISO/IEC JTC1/SC29, ISO/IEC 15444-1 "Information technology - JPEG 2000 image coding system - Part 1: Core coding system", July 2002. [2] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP14, RFC2119, March 1997. [3] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson, "RTP: A Transport Protocol for Real Time Applications", RFC 1889, January 1996. [4] M. Handley and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. Informative References [5] ISO/IEC JTC1/SC29/WG1, "JPEG2000 Part I Final Committe Draft Version 1.0", http://www.jpeg.org/public/fcd15444-1.pdf, March 2000. [6] ISO/IEC JTC1/SC29/WG1, "Motion JPEG 2000 Final Committee Draft 1.0", http://www.jpeg.org/public/fcd15444-3.doc, March, 2001. [7] ISO/IEC JTC1/SC29/WG1, "JPEG2000 requirements and profiles version 6.3", draft in progress, http://www.jpeg.org/public/wg1n1803.pdf [8] Diego Santa-Cruz, Touradj Ebrahimi, Joel Askelof, Mathias Larsson and Charilaos Christopoulos, "JPEG 2000 still image Edwards, et al. [Page 19] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 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. [9] Deering, S., "Host Extensions for IP Multicasting", STD 5, RFC 1112, August 1989. 14. Authors' Addresses Eric Edwards Sony Corporation Media Processing Division Platform 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/Nobuyoshi Tomita/Eisaburo Itakura 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|n-tomita|itakura}@sm.sony.co.jp 15. 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 Edwards, et al. [Page 20] INTERNET-DRAFT draft-ietf-avt-rtp-jpeg2000-04.txt October 27, 2003 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Edwards, et al. [Page 21]