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iecommendation H.261
'onsideríng
ervices;
The CCITT,
VIDEO CODEC FOR AUDIOVISUAL SERVICES AT p x 64 kbit/s
(revised 1990)
(a) that there is signifícant customer demand for videophone, videoconference and other audiovisual
(b) that circuits to meet this demand can be provided by digital transmission using the B, HO rates or their
lultiples up to the primary rate orHn/Hi2 rates;
(c) that ISDNs are likely to be available in some countries that provide a switched transmission service at
íieB, HQ orHn/Hi2 rate;
(d) that the existence of difíerent digital hierarchies and different televisión standards in difíerent parts of
íie world complicates the problems of specifying coding and transmission standards for international connections;
(e) that a number of audiovisual services are likely to appear using basic and primary rate ISDN accesses
nd that some means of intercommunication among these termináis should be possible;
(f) that the video codee provides an essential element of the inírastructure for audiovisual services which
llows such intercommunication in the framework of Recommendation H.200;
(g) that Recommendation H.120 for videoconferencing using primary digital group transmission was the
irst in an evolving series of Recommendations,
ppreciating
that advances have been made in research and development of video coding and bit rate reduction techniques
i'hich lead to the use of lower bit rates down to 64 kbit/s so that this may be considered as the second in the evolving
sries of Recommendations,
nd noñng
zcommends
that it is the basic objective of the CCITT to recommend unique solutions for international connections,
that in addition to those codees complying to Recommendation H.120, codees having signa! processing and
'ansmission coding characteristics described below should be used for international audiovisual services.
Note 1 — Codees of this type are also suitable for some televisión services where full broadcast quality is not
iquired.
Note 2 — Equipment for transcoding from and to codees according to Recommendation H. 120 is under study.
Scope
This Recommendation describes the video coding and decoding methods for the moving picture component of
udiovisual services at the rates ofp x 64 kbit/s, where/? is in the range 1 to 30.