ITU-T H 281-1994 A FAR END CAMERA CONTROL PROTOCOL FOR VIDEOCONFERENCES USING H 224 (Study Group 15 12 pp)《采用数据链路协议的会议电视远端摄像机控制规程-非电话信号传播 研究组15》.pdf

1、ITU-T RECMN*H*ZBL 94 4862591 Ob02563 047 H INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF TU H.281 (1 1/94) TRANSMISSION OF NON-TELEPHONE SIGNALS A FAR END CAMERA CONTROL PROTOCOL FOR VIDEOCONFERENCES USING H.224 ITU-T Recommendation H.281 (Previously “CCITT

2、Recommendation“) ITU-T RECMN*Hm281 74 m Li862591 0b025b2 T83 FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (IT). The IT-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dati

3、ons 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 study by the IT-T Study Groups which, in their turn, produce Recommendations on these topics. The

4、approval of Recommendations by the Members of the -T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation H.281 was prepared by ITU-T Study Group 15 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 1st of Novem

5、ber 1994. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O IT 1995 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means,

6、electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. . ITU-T RECMN*H.ZBL 74 m 4862593 06025b3 9LT m CONTENTS Summary . Scope Normative References Definitions Abbreviations . Elements of Procedure . 5.1 Action messages 5.2 Action message examples

7、 . 5.3 Select video source . 5.4 Select video source examples . 5.6 Activate preset 5.7 General FECC message structure 6.1 FECC capabilities fields 5.5 Store preset Recommendation H.281 (1U94) Page 11 1 1 1 2 2 3 3 4 4 4 4 4 5 7 i SUMMARY The Recommendation describes how a far end camera control sys

8、tem for H.320 terminais can be operated based on H.224 running on LSD, HSD, or MLP as a lower layer for both point-to-point and multipoint operation. 11 Recommendation H.281 (11/94) ITU-T RECMN*Hm28L 94 m 48b2591 0602565 792 m Recommendation H.281 A FAR END CAMERA CONTROL PROTOCOL FOR VIDEOCONFERENC

9、ES USING H.224 Geneva, 1994) 1 Scope This Recommendation covers the elements of procedure and format of fields to support a Far End Camera Control (FECC) protocol layered over the Data Link protocol covered in Recommendation H.224. The FECC protocol is designed to operate in both point-to-point and

10、multipoint simplex modes, using the H.224 link layer protocol. A major requirement of the Far End Camera Control application is for both minimum variation in delay as well as minimal absolute delay. This FECC protocol, together with Recommendation H.224, allows each camera in a multipoint video conf

11、erence to be individually controlled from any video terminal. The FECC protocol shall require of the H.224 link layer that, if both the LSD and HSD channels are in use for H.224, all FECC data be transmitted on the LSD channel only. This will ensure that FECC data is received in the order in which i

12、t is transmitted. 2 Normative References The following ITU-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 refer

13、ences are subject 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. - ITU-T Re

14、commendation H.224, A Data Link Layer for simplex applications using the H.221 LSD/HSD/MLP channels. - ITU-T Recommendation H.261 (1993), Video Codec for Audiovisual Services at p x 64 kbits. - CCITT Recommendation T.50 (1984), International Alphabet No. 5. 3 Definitions For the purposes of this Rec

15、ommendation, the following definitions apply: 3.1 part of any application protocol. Error control is either not provided, or is accomplished via forward error correction. simplex protocol: A communication protocol that is purely one-way, and where acknowledgements are not 3.2 example of such a clien

16、t. client: An entity that uses the data transfer services of the Data Link layer. Far End Camera Control is an 3.3 registered clients and their optional extra capabilities. See Recommendation H.224 for additional information. client management entity: A data link client that uses Client ID O x O0 to

17、 send a complete list of locally Recommendation H.281 (1U94) 1 3.4 Camera Action, Continue Camera Action, Stop Camera Action and Select Video Source. FECC commands: Atomic requests to act on a remote camera. Examples of FECC Commands include: Start 3.5 PTZF: Pan, Tilt, Zoom, and Focus -the four basi

18、c camera movements supported by this protocol. 3.6 room preset: Information that may be used to select a video source, and then control the video source to provide the desired view. Support for Room Presets is an extra capability and is announced in the extra capabilities message sent by the H.224 C

19、ME. The ability to provide presets is optional and may not be supported in all terminals. 3.7 activate preset: A command that requests a terminal switch to the video source specified by the room preset and position the video source to provide the view specified by the room preset. An Activate Preset

20、 command may be issued by a user local to a video teleconferencing terminal, or remotely by a user at another terminal. For the purposes of this Recommendation, we assume an Activate Preset is issued remotely. 3.8 set to zero. ASCII: Characters coded as in International Alphabet No. 5 as defined in

21、Recommendation T.50, with bit 8 3.9 normal resolution still image: A still image transmitted in the H.261 video stream encoded to the same resolution as the previous motion video (i.e. QCIF or FCIF). This mode uses bit 2 “Document Camera Indicator” as defined in 4.2.1.3H.261. 3.10 double resolution

22、still image: A still image transmitted in the H.261 video stream encoded to twice the horizontal and twice the vertical resolution as the previous motion video (Le. FCIF or 4*FCIF). This mode uses bit 5 “HiRes” as defined in 4.2.1.3M.26 1 and Annex DM.261. 4 Abbreviations CIF Common Intermediate For

23、mat. (See Recommendation H.26 1 for more information). CME Client Management Entity. FCIF Full CIF. (This is the same as CIF). QCIF Quarter CIF. (See Recommendation H.261 for more information). 5 Elements of Procedure The FECC protocol has the following basic messages types: START ACTION - Requests

24、for each of the three camera axis of movement. CONTINUE ACTION -Requests for each of the three camera axis of movement. STOP ACTION - Requests for each of the three camera axis of movement. SELECT VIDEO SOURCE - Requests a switch to the indicated video source for encoding and transmission. STORE PRE

25、SET - Requests the current video source and its current spatial parameters are stored in the indicated preset number. ACTIVATE PRESET - Requests the indicated preset is used to select the video source and set its spatial coordinates. 2 Recommendation H.281 (11194) 5.1 Action messages START ACTION me

26、ssages have an associated action parameter and a time out value. The action parameter indicates and STOP ACTION messages also have the same associated action parameter. A CONTINUE ACTION message with an action parameter matching the previous START ACTION shall restart the time out period. A STOP ACT

27、ION message with an action parameter matching the previous START ACTION causes the camera positioning to stop. (The minimum duration for the START ACTION command is left to the discretion of the manufacturer based on camera parameters. This minimum duration shall ensure that some motion does occur.)

28、 If the time out occurs, the receiving FECC client shall act as though a STOP ACTION message with the appropriate action parameter has been received. Any subsequent CONTINUE or STOP action messages shall be discarded until a new START ACTION message is received. The time out value sent in an initial

29、 START ACTION message protects against the possible loss of the final STOP ACTION request. Any CONTINUE ACTION message or STOP ACTION message with an action parameter that does not match the immediately proceeding START ACTION message shall be discarded. I what camera motion (from the set of PTZF) i

30、s desired, and which direction is desired. CONTINUE ACTION messages Continuous camera motion is achieved through use of an initial START ACTION message followed by a series of zero or more CONTINUE ACTION messages, and terminated by a STOP ACTION message. The time interval between transmission of an

31、y two consecutive messages in this sequence shall not exceed the time out value specified in the START ACTION message minus 200 milliseconds. If continuous motion is desired, the time out value must therefore be set to 250 milliseconds or greater. The action parameter of a START ACTION message may i

32、ndicate multiple motions in the same command (for example, Pan Right and Tilt Up). Any CONTINUE ACTION message or STOP ACTION message shall have an action parameter matching all the motion attributes of the preceding START ACTION message. After a valid START ACTION message has been received, and pos

33、sibly followed by any number of matching CONTINUE ACTION messages, a new START ACTION message may be issued with a different action parameter. This new START ACTION message shall be interpreted as a valid STOP ACTION message for any motion that is no longer set, and shall be interpreted as a valid C

34、ONTiNUE ACTION message for any motion that continues to be set, and shall be interpreted as a valid START ACTION message for any new motion that is indicated by the action parameter. Implementen shall ensure that once a terminal starts acting on camera commands from one remote terminal, camera comma

35、nds from other remote terminals are discarded until motion from the first camera stops. The data link protocol (see Recommendation H.224) provides both source and destination addresses on messages to allow this interlocking. 5.2 Action message examples An example of a valid camera sequence may help

36、to illustrate the proper use of the protocol. A START ACTION message indicating Pan Right and Tilt Up may be issued, followed by any number of CONTINUE ACTION messages also specifying Pan Right and Tilt Up. These messages may be followed by another START ACTION message specifying Pan Right only. Any

37、 number of CONTINUE ACTION messages specifying Pan Right may then be issued. Another START ACTION message may then be sent specifying Pan Right and Tilt Down, which in turn is followed by any number of CONTINUE ACTION messages specifying Pan Right and Tilt Down. Finally a STOP ACTION message specify

38、ing Pan Right and Tilt Down is issued to terminate far end control of the camera. In this example the Pan Right action is continuous while the Tilt Up action is only valid for the first part of the camera control. Similarly, the Tilt Down action is only valid for the last part of the camera control.

39、 The use of multiple camera controls simultaneously is optional for terminals both sending and receiving FECC requests. Any terminal not equipped to handle simultaneous camera motion commands shall operate on one or more of the commands and disregard the others. The choice of axes in which to move i

40、s arbitrary. (The far end user will see one or more of the camera requests acted upon and then may send the other motion commands later.) Recommendation H.281 (1V94) 3 5.3 Select video source A SELECT VIDEO SOURCE message has an associated video source and video mode parameters. On receipt of the SE

41、LECT VIDEO SOURCE message the terminal shall check for the validity of the video source and for the validity of the video mode for this source. If either parameter is invalid, the receiving terminal shall discard the message without further action. If the parameters are valid and the chosen video mo

42、de is motion video, then the receiving terminal shall change its video selector so the requested video source is sent to the video encoder and transmitted. This selected video source and mode shall remain in effect until another valid SELECT VIDEO SOURCE message is received, or until a user changes

43、the mode locally. If the parameters are valid and the mode requests a still image transmission (either using normal resolution or double resolution), the receiving terminal shall switch the video source and code a single still image frame for transmission in the H.261 video stream. After sending the

44、 single still image the video selector is switched back to the previously chosen video source for encoding and transmission. 5.4 Select video source examples The use of SELECT VIDEO SOURCE may be best illustrated by examples. In the first example let us assume the main camera is sending motion video

45、 to the H.261 encoder for transmission. Receiving a SELECT VIDEO SOURCE message requesting a normal resolution still image from a 35 mm slide projector, would cause acquisition and H.261 encoding of that frame. Automatically the video selector would revert back to the main camera sending motion vide

46、o when the still image coding and transmission is completed. In the next example let us assume the main camera is sending motion video to the H.261 encoder for transmission. Receiving a SELECT VIDEO SOURCE message requesting motion video from a document camera would cause the video selector to choos

47、e the document camera for encoding and transmission. A subsequent SELECT VIDEO SOURCE command requesting a double resolution still image from the document camera would cause acquisition and H.261 encoding of that frame in the higher resolution mode. Automatically the video selector would revert back

48、 to the document camera sending motion video (as the last selected motion video source) when the still image coding and transmission is complete. 5.5 Store preset A STORE PRESET message has an associated preset number as a parameter. If this optional feature is provided, the receiving terminal is re

49、quested to store the current video source and information about its spatial coordinates (Le. pan, tilt, zoom, and focus information) into the preset location indicated by the preset number. (We note that Recommendation H.224 does not guarantee delivery of messages. To help assure reliable message delivery, manufacturers may choose to repeat this message.) 5.6 Activate preset An ACTIVATE PRESET message has an associated preset number as a parameter. If this optional feature is provided, the receiving terminal positions the video s