1、BRITISH STANDARD BS ISO/IEC 14496-8:2004 Information technology Coding of audio-visual objects Part 8: Carriage of ISO/IEC 14496 contents over IP networks ICS 35.040 BS ISO/IEC 14496-8:2004 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 4 Ju
2、ne 2004 BSI 4 June 2004 ISBN 0 580 43843 0 National foreword This British Standard reproduces verbatim ISO/IEC 14496-8:2004 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Technical Committee IST/37, Coding of picture, audio, multimedia and hyp
3、ermedia information, which has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications referred to in this document may be found in the BSI Catalogue un
4、der the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct ap
5、plication. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed;
6、 monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO/IEC title page, pages ii to iv, pages 1 to 8, an inside back cover and a back cover. The BSI copyright notice displayed in th
7、is document indicates when the document was last issued. Amendments issued since publication Amd. No. Date Comments Reference number ISO/IEC 14496-8:2004(E)INTERNATIONAL STANDARD ISO/IEC 14496-8 First edition 2004-05-15 Information technology Coding of audio-visual objects Part 8: Carriage of ISO/IE
8、C 14496 contents over IP networks Technologies de linformation Codage des objets audiovisuels Partie 8: Transport du contenu MPEG-4 sur les rseaux IP BSISO/IEC144968:2004DPlcsid Fremia ihTs PDF file mya ctnoian emdebt dedyfepcaes. In ccacnadrow eitA hebods licnesilop gnic,y tihs file mirp eb yatnde
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11、tlbae fosu re yb ISO memdob rebeis. In tlnu ehikletneve y ttah lborp aem lertait gno it is f,dnuo plsaee ifnrom ttneC ehlar Secterirata ta teh serddaig sleb nevwo. ii BSISO/IEC144968:2004 iiiForeword ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
12、 Commission) form the specialized system for worldwide standardization. National bodies that are members of ISO or IEC participate in the development of International Standards through technical committees established by the respective organization to deal with particular fields of technical activit
13、y. ISO and IEC technical committees collaborate in fields of mutual interest. Other international organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information technology, ISO and IEC have established a joint technical committe
14、e, ISO/IEC JTC 1. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of the joint technical committee is to prepare International Standards. Draft International Standards adopted by the joint technical committee are circulated to n
15、ational bodies for voting. Publication as an International Standard requires approval by at least 75 % of the national bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO and IEC shall not be held responsibl
16、e for identifying any or all such patent rights. ISO/IEC 14496-8 was prepared by Joint Technical Committee ISO/TC JTC 1, Information technology, Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information. ISO/IEC 14496 consists of the following parts, under the general title
17、 Information technology Coding of audio-visual objects: Part 1: Systems Part 2: Visual Part 3: Audio Part 4: Conformance testing Part 5: Reference software Part 6: Delivery Multimedia Integration Framework (DMIF) Part 7: Optimized reference software for coding of audio-visual objects Part 8: Carriag
18、e of ISO/IEC 14496 contents over IP networks Part 9: Reference hardware description Part 10: Advanced Video Coding Part 11: Scene description and application engine Part 12: ISO base media file format Part 13: Intellectual Property Management and Protection (IPMP) extensions Part 14: MP4 file format
19、 Part 15: Advanced Video Coding (AVC) file format Part 16: Animation Framework eXtension (AFX) BSISO/IEC144968:2004iv Introduction ISO/IEC 14496 is an International Standard designed for the representation and delivery of multimedia information over a variety of transport protocols. It includes inte
20、ractive scene management, visual and audio representations as well as systems functionality like multiplexing, synchronization, and an object descriptor framework. This document provides a framework for the carriage of ISO/IEC 14496 contents over IP networks and guidelines for designing payload form
21、at specifications for the detailed mapping of ISO/IEC 14496 content into several IP-based protocols BSISO/IEC144968:2004INTENRATIONAL TSANDADR IS/OIE69441 C-8:002(4)E1Information technology Coding of audio-visual objects Part 8: Carriage of ISO/IEC 14496 contents over IP networks 1 Scope This part o
22、f ISO/IEC 14496 specifies transport level functionalities for the communication of interactive audio- visual scenes. More specifically: 1. Framework for the carriage of ISO/IEC 14496 contents over IP networks; 2. Guidelines to design RTP payload formats for ISO/IEC 14496 contents including fragmenta
23、tion and concatenation rules; 3. Usage rules of SDP to transport ISO/IEC 14496-1 related information; 4. MIME type definitions for ISO/IEC14496 contents; and 5. Analysis on RTP Security and Multicasting. 2 Normative references The following referenced documents are indispensable for the application
24、of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IETF RFC 1889, RTP A Transport Protocol for Real-Time Applications IETF RFC 1890, RTP Profile for Audio and Video Conferen
25、ce with Minimal Control IETF RFC 2326, Real Time Streaming Protocol (RTSP) IETF RFC 2327, SDP: Session description protocol IETF RFC 3016, RTP payload format for MPEG-4 audio/visual streams IETF RFC 3640, Transport of MPEG-4 elementary streams 3 Terms and definitions For the purposes of this documen
26、t, the following terms and definitions apply. 3.1 MIME Multipurpose Internet Mail Extensions, referring to an official Internet standard that identifies the format of the contents exchanged over different systems connected to the network BSISO/IEC144968:20042 3.2 RTP Real Time Transport Protocol, an
27、 Internet protocol used for transport of multimedia data 3.3 RTSP Real Time Streaming Protocol, an application-level Internet protocol for control over the delivery of data with real-time properties 3.4 RTCP Real Time Transport Control Protocol, an Internet protocol used to configure RTP packets and
28、 to control the transport of RTP packets 3.5 SDP an Internet protocol used for describing multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation 4 Symbols and abbreviated terms AAC Advanced Audio Coding AU Access Unit BIFS B
29、inary Format for Scene CELP Code Excited Linear Prediction CTS Composition Time Stamp ES Elementary Stream ESI Elementary Stream Interface ESID Elementary Stream Identifier FCR FlexMux Clock Reference IETF Internet Engineering Task Force MIME Multipurpose Internet Mail Extensions OCR Object Clock Re
30、ference OD Object Descriptor ODID Object Descriptor Identifier QoS Quality of Service RFC Request For Comments SL Synchronization Layer SL-Packet Synchronization Layer Packet URL Universal Resource Locator BSISO/IEC144968:2004 35 Use of RTP 5.1 Introduction There are a number of RTP packetization sc
31、hemes for ISO/IEC 14496 data. Media-aware packetization (e.g. video frames split at recoverable sub-frame boundaries) is a principle in RTP, and thus it is likely that several RTP schemes will be needed, to suit both the different kinds of media audio, video, etc. and different encodings (e.g. AAC a
32、nd CELP audio codecs).This specification does not specify any payload format but do specify a general framework to design and utilize the payload formats in appropriate way. This specification requires that, no matter what packetization scheme is used, there are a number of common characteristics th
33、at all shall have: however, such characteristics depend on the fact that the RTP Session contains a single elementary stream or a flexmux stream. 5.2 Carrying a single elementary stream In case an RTP Session contains a single elementary stream the following characteristics apply: The RTP timestamp
34、corresponds to the presentation time (e.g. CTS) of the earliest AU within the packet. RTP packets have sequence numbers in transmission order. The payloads logically or physically have SL Sequence numbers, which are in decoding order, for each elementary stream. The ISO/IEC 14496 timescale (clock ti
35、cks per second), which is timeStampResolution in the case of ISO/IEC 14496 Systems, shall be used as the RTP timescale, e.g. as declared in SDP for an RTP stream. To achieve a base level of interoperability, and to ensure that any ISO/IEC 14496 stream may be carried, all receivers should implement a
36、 generic payload format defined in “draft-ietf-avt-mpeg4-multisl-04.txt” as default RTP payload mapping scheme. Any new payload format should be a configurable subset of the generic payload format. Streams should be synchronized using RTP techniques (notable RTCP sender reports). When the ISO/IEC 14
37、496 OCR is used, it is logically mapped to the NTP time axis used in RTCP. The RTP packetization schemes may be used for ISO/IEC 14496 elementary streams standing alone (e.g. without ISO/IEC 14496 systems, including BIFS); or they may be used within an overall presentation using the object descripto
38、r framework. In the latter case, a SLConfigDescriptor is sent describing the stream. Logically, each RTP stream is passed through a mapping function which is specific to the payload format used; this mapping function yields a SL packetized stream. The SLConfigDescriptor describes this logical stream
39、, not the actual bits in the RTP payload. For example, the RTP sequence number may be used to make the SLPacketHeader sequence number; other SL fields may be set in this way, dynamically, or from static values in the payload specification. For example, as all RTP packets carry a composition time-sta
40、mp, the flag in the SL header indicating its presence can normally be statically defined as true. Each payload format for ISO/IEC 14496 content shall specify the mapping function for the formation of the SLConfigDescriptor and the SLPacketHeader. In the case of the RFC 3016, the mapping shall be def
41、ined in a seperate document. BSISO/IEC144968:20044 Figure 1 RTP packet to SL packet mapping 5.3 Payload format selection Other payload formats may be used. They are signalled as dynamic payload IDs, defined by a suitable name (e.g. a payload name in an SDP RTPMAP attribute). In particular, the devel
42、opment of specialized RTP payloads for video (e.g. respecting video packets) and audio (e.g. providing interleave) is expected. It is possible that these schemes can be compatible with the default scheme required here. There may be a choice of RTP payload formats for a given stream (e.g. as an eleme
43、ntary stream, an SL- packetized stream, using FlexMux, and so on). It is recommended that terminals implementing a given subsystem (e.g. video) accept at least an ES and the default SL packings of that stream; for example, this means accepting the RFC 3016 and also the generic payload format for MPE
44、G-4 Visual; terminals implementing a given payload format accept any stream over that format for which they have a decoder, even if that packing is not normally the best packing. 5.4 ISO/IEC 14496 QoS considerations For those streams requiring a certain Quality of Service (specifiable appropriately)
45、, the recommendation is to further investigate possible solutions such as the leverage of existing work in the IETF in this area (including, but not limited to FEC, re-transmission, or repetition). However, techniques in data-dependent error correction, or combined source/channel coding solutions ma
46、ke other schemes attractive. Also, it is recommended that requirement such as efficient grouping mechanisms (i.e. the ability to send in a single RTP packet multiple consecutive AUs, each with its own SL information) and low overhead is also taken into account. BSISO/IEC144968:2004 56 Usage of SDP a
47、ttributes This specification considers only ISO/IEC 14496 Systems related issues. Usage of SDP information for specific payload format shall be specified in each RTP payload format RFCs. The usage of elementary streams in other contexts is not addressed here: codepoints for this case are specified i
48、n, and in other places. This specification currently assumes that any session described by SDP (e.g. in SAP, as a file download, as a DESCRIBE over RTSP) has at most one ISO/IEC 14496 session. It is desirable that this restriction be lifted. Senders should alert receivers that an ISO/IEC 14496 sessi
49、on is included, by means of an SDP attribute that is general (i.e. before any “media“ lines). This takes the form of the following attribute line: a=mpeg4-iod location: In an RTSP session, this is an optional attribute. If not supplied, the IOD is retrieved over the RTSP session by using DESCRIBE with an accept of type application/mpeg4-iod or application/mpeg4- iod-xmt. Where the SDP information is supplied
