1、INTERNATIONAL TELECOMMUNICATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU J.120 (O 5/2000) SERIES J: TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Interactive systems for digital television distribution Distribution of sound and television programs over
2、the IP network ITU-T Recommendation J. 120 (Formerly CCITT Recommendation) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T
3、 is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for stu
4、dy by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSC Resolution 1. in some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a
5、collaborative basis with IS0 and IEC. NOTE in this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or i
6、mplementation of this Recommendation may involve the use of a claimed intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development pro
7、cess. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strong
8、ly urged to consult the TSB patent database. O ITU 2001 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from ITU. 11 ITU-T 5.120 (05/2000) CONTENT
9、S 1 2 2.1 2.2 3 4 5 5.1 5.2 5.3 5.4 5.5 6 6.1 6.2 6.3 6.4 Scope . References . Normative references Informative references Terms and definitions . Abbreviations System definition Procedures for the receiver . 5.1.1 5.1.2 Downloading audiohide0 decoders Acquisition of a presentation description 5.1.3
10、 Setting-up a server . 5.1.4 Receiving streams Video decoding . Audio decoding . Application Programming Interface (API) of the decoder Network interface Session control Overall operation of the session control . Presentation description 6.2.1 iiv=lt field . 6.2.2 field . 6.2.3 %=“ field 6.2.4 “i=“
11、field 6.2.5 “m=“ field 6.2.6 “a=“ field RTSP control methods 6.3.1 SETUP . 6.3.2 PLAY . 6.3.3 PAUSE . 6.3.4 TEARDOWN RTSP header fields . 6.4.1 CSeq . 6.4.2 Range . 6.4.3 Session . 6.4.4 Transport Page 1 1 1 1 2 2 3 4 4 4 4 4 4 4 5 5 6 6 7 7 7 7 7 8 8 8 8 8 9 9 9 9 9 10 10 . ITU-T 5.120 (05/2000) 11
12、1 7 RTP header formats Appendix I - Simple example of RTSP presentation description and session control. . . . . . . . . . Appendix II - A typical RTP payload format for ITU-T H.263 Appendix III - An example of RTP payload format for audio . Appendix IV - Preferred embodiments of downloading decoder
13、s Appendix V - Sample Software . Electronic attachment: source code and conformance test tools Page 10 12 13 15 16 17 iv ITU-T 5.120 (05/2000) I ITU-T Recommendation 5,120 Distribution of sound and television programs over the IP network 1 Scope This Recommendation defines the transmission protocol
14、and system configuration for distributing sound and television programs over the Internet “Webcasting“. This concerns the end-to-end signal flow from the program server to user receiver. This transmission chain contains the signal encoding/decoding, packet mapping, session control and network transm
15、ission. The following items are specified: - - Presentation description which provides the overall program and the properties of the media. Server control protocol which provides signalling for proper operation between the server and receiver. Stream packet mapping which formats coded video and audi
16、o streams into messages for output to the network interface and retrieves received video and audio data. - - Required receiver capability. - Downloadable software decoders. This Recommendation is restricted to the Internet Protocol (IP) as a network layer. Usage of transport layer protocol is outsid
17、e its scope. 2 References The following IT-T Recommendations, and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subje
18、ct to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. Normative references ITU-
19、T H.225.0 (2000), Call signalling protocols and media stream packetization for packet-based multimedia communication systems. Informative references ITU-T G.723.1 (1996), Dual rate speech coder for multimedia communications transmitting at 5.3 and 6.3 kbith. -T H.222.0 (2000) I ISO/IEC 1381 8-1: 199
20、6, Information technology - Generic coding of moving pictures and associated audio information: Systems. ITU-T H.262 (2000) I ISO/IEC 13818-2:1996, Information technology - Generic coding of moving pictures and associated audio information: Video. -T H.263 (1998), Video coding for low bit rate commu
21、nication. This Recommendation includes an electronic attachment containing sample source code and some tools for conformance tests. ITU-T 5.120 (05/2000) 1 5.1 Procedures for the receiver 5.1.1 The presentation description defines the overall program and the properties of the media in the form of th
22、e description defined in 6.2. The acquisition method of the presentation description may be HTTP, FTP or others such as e-mail, but a definition is outside the scope of this Recommendation. The receiver may obtain information relating to program contents, details of streams constituting the program,
23、 decoder downloading information and other parameters. 5.1.2 Downloading audiohide0 decoders After acquisition of the presentation description, if necessary the receiver may obtain the audiohide0 decoder by downloading it fi-om the server defined in the presentation description or from storage media
24、 such as a CD-R.OM. Downloading information is specified in the field of the presentation description, it may directly indicate the decoder software by HTTP or FTP or it may be linked to the HTML script of the downloading page. The receiver which is capable of downloading decoders shall be capable o
25、f accessing the HTML 4.0 script and of downloading decoder software by HTTP and FTP. 5.1.3 Setting-up a server After decoding the presentation description as well as after downloading the decoder(s) if necessary, the receiver may send audiovideo stream controls in the form of RTSP to the stream serv
26、ers specified in the presentation description. The receiver shall be equipped with the minimal RTSP implementation. In the setting-up process, RTSP may not deliver the audiovideo streams itself, but instead act as a “network remote control“ for stream servers. The SETUP control method of RTSP may st
27、art an RTSP session and may cause the server to prepare to send the stream. The PLAY method may start data transmission on a stream specified via SETP. The TEARDOWN method frees resources associated with the stream. Acquisition of a presentation description 5.1.4 Receiving streams Actual audiovideo
28、streams shall be sent via separate protocol RTP, independent of the session control channel. Properties of transport protocol such as the port number may be obtained from the RTSP session control prior to receiving streams. The receiver shall be equipped with RTP/RTCP capability. Received packets fr
29、om each stream are transferred to the decoders. The application programming interface (NI) for the audiovideo decoders is specified in clause 5.4. I 5.2 Video decoding The video coding method and its downloadable sites are identified in the presentation description. More than one video channel may b
30、e transmitted, as negotiated via the RTSP session Set-up. The video stream packet is formatted as described in clause 7. The video stream packet is transferred to the video decoder via the application programming interface described in clause 5.4. All video decoders shall have the application progra
31、mming interface. 5.3 Audio decoding The audio coding algorithm and its downloadable sites shall be specified in the presentation description. The receivers may optionally receive more than one audio channel at the same time, for example, to allow two languages or stereo sound to be conveyed. 4 ITU-T
32、 5.120 (05/2000) I Audio packets should be delivered to the transport layer periodically at an interval determined by the audio codec Recommendation in use (audio frame interval). The delivery of each audio packet should occur no later than 5 ms after a whole multiple of the audio frame interval, me
33、asured from I delivery of the first audio frame (audio delay jitter). The audio packets are formatted as described in I clause 7. )il The audio stream packet is transferred to the video decoder via application programming interface described in clause 5.4. All audio decoders shall have the applicati
34、on programming interface. 1 I 5.4 Application Programming Interface (API) of the decoder A decoder program shall have functions which transfer audiohide0 packets to the decoder. The interface functions are specified as below. extern “C“ I int putPacketStrearn(unsigned char *buffer, int length); 0 De
35、scription: - Parameters: - - Return value: - O: succeeded - extern “C“ Transferring a packet stream into the decoder program. unsigned char *buffer: address to a packet stream int length: length of the packet -1 : failed (input buffer over flow) int getBufferFreeSize(v0id) 1 Description: - Return va
36、lue: - Free space in bytes. This function returns free space in the internal packet buffer of the decoder. 5.5 Network interface The network interface is an implementation specific issue and is outside of the scope of this Recommendation. However, the network interface shall provide services includi
37、ng the following: Reliable (e.g. TCP) end-to-end service is mandatory for the RTSP control channel. Unreliable (e.g. UDP) end-to-end service is mandatory for the audio channels and the video channels. These services may be duplex or simplex, unicast or multicast depending on the capabilities of the
38、terminals and the configuration of the network. ITU-T 5.120 (05/2000) 5 6 Session control Field name V 6.1 The overall program and the properties of the media shall be defined by a presentation description file. The presentation description file may be obtained by the receiver using HTTP or other me
39、ans such as e-mail and may not necessarily be stored on the server. The presentation description file contains a description of the media streams making up the program, including their encoding types, language, and other parameters that enables the receiver to choose the most appropriate media combi
40、nation. Fields used in the presentation description are summarized in Table 1. Overall operation of the session control Description The version of the Session Description Protocol. Table iiJ.iz0 - The presentation description S 1 m The session name. Informative description of the session. The media
41、description. Media type, port number, transport protocol and payload types. O Methods SETUP Information on the originator of the session. It gives their username, the address of the users host, session ID and session version. Description Causes the server to allocate resources for a stream and start
42、 an RTSP session. a Attributes of the session or the media. It may speciq the control URL, decoder download sites URL or language of the session or the media. Details of the fields are described in 6.2. After decoding the presentation description, the RTSP controls media streams which may be sent vi
43、a a separate protocol, independent of the control channel. For example, RTSP control may occur on a TCP connection while the data flows via UDP. Thus, data delivery continues even if no RTSP requests are received by the media server. Also, during its lifetime, a single media stream may be controlled
44、 by RTSP requests issued sequentially on different TCP connections. The control methods are listed in Table 2. Table 2/5.120 - RTSP control methods PLAY I Starts data transmission on a stream allocated via SETUP. I I PAUSE I Temporarily halts a stream without freeing server resources. TEARDOWN I Fre
45、es resources associated with the stream. Details of these methods are described in 6.3. These methods are issued with header fields. The headers are summarized in Table 3. 6 ITU-T 5.120 (05/2000) Table 3/5.120 - RTSP header fields Headers CSeq Range Session Description The sequence number for an RTS
46、P request-response pair. Range of time for a PLAY and a PAUSE. An identifier of the session started by SETUP and concluded by TEARDOWN. Transport I Protocol to be used. I 6.2 Presentation description The definition and syntax are described below. 6.2.1 “Y=“ field The “v=“ field gives the version of
47、the Session Description Protocol. There is no minor version number. 6.2.2 “o=11 field The o=“ field gives the originator of the session (their username and the address of the users host) plus a session ID and session version number. o= is the users login on the originating host, or it is “-“ if the
48、originating host does not support the concept of a user ID. does not contain spaces. is a numeric string globally unique to the session. The method of allocation is suggested in which a Network Time Protocol (NTP) timestamp be used to ensure uniqueness. is the version number for this announcement. I
49、t is needed for proxy announcements to detect which of several announcements for the same session is the most recent. is increased when a modification is made to the session data. It is also recommended (but not mandatory) that an NTP timestamp be used. is a text string giving the type of network. Initially “IN“ is defined to have the meaning “Internet“. is a text string giving the type of the address that follows. Initially “IP4“ and “IP6“ are defined. is the globally unique address of the machine from which the session was created. For an IPv4 addre
