draft-ietf-mmusic-rfc3388bis-02.txt   draft-ietf-mmusic-rfc3388bis-03.txt 
MMUSIC Working Group G. Camarillo MMUSIC Working Group G. Camarillo
Internet-Draft Ericsson Internet-Draft Ericsson
Obsoletes: 3388 (if approved) January 13, 2009 Obsoletes: 3388 (if approved) July 13, 2009
Intended status: Standards Track Intended status: Standards Track
Expires: July 17, 2009 Expires: January 14, 2010
The SDP (Session Description Protocol) Grouping Framework The SDP (Session Description Protocol) Grouping Framework
draft-ietf-mmusic-rfc3388bis-02.txt draft-ietf-mmusic-rfc3388bis-03.txt
Status of this Memo Status of this Memo
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This Internet-Draft will expire on July 17, 2009. This Internet-Draft will expire on January 14, 2010.
Copyright Notice Copyright Notice
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to this document.
Abstract Abstract
In this specification, we define a framework to group "m" lines in In this specification, we define a framework to group "m" lines in
SDP (Session Description Protocol) for different purposes. This SDP (Session Description Protocol) for different purposes. This
framework uses the "group" and "mid" SDP attributes, both of which framework uses the "group" and "mid" SDP attributes, both of which
are defined in this specification. Additionally, we specify how to are defined in this specification. Additionally, we specify how to
use the framework for two different purposes: for lip synchronization use the framework for two different purposes: for lip synchronization
and for receiving a media flow consisting of several media streams on and for receiving a media flow consisting of several media streams on
different transport addresses. different transport addresses.
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perform any grouping of media lines. perform any grouping of media lines.
"a=group" lines are used to group together several "m" lines that are "a=group" lines are used to group together several "m" lines that are
identified by their "mid" attribute. "a=group" lines that contain identified by their "mid" attribute. "a=group" lines that contain
identification-tags that do not correspond to any "m" line within the identification-tags that do not correspond to any "m" line within the
session description MUST be ignored. The application acts as if the session description MUST be ignored. The application acts as if the
"a=group" line did not exist. The behavior of an application "a=group" line did not exist. The behavior of an application
receiving an SDP with grouped "m" lines is defined by the semantics receiving an SDP with grouped "m" lines is defined by the semantics
field in the "a=group" line. field in the "a=group" line.
There MAY be several "a=group" lines in a session description. All There MAY be several "a=group" lines in a session description. The
the "a=group" lines of a session description MAY or MAY NOT use the "a=group" lines of a session description can use the same or
same semantics. An "m" line identified by its "mid" attribute MAY different semantics. An "m" line identified by its "mid" attribute
appear in more than one "a=group" line. MAY appear in more than one "a=group" line.
7. Lip Synchronization (LS) 7. Lip Synchronization (LS)
An application that receives a session description that contains "m" An application that receives a session description that contains "m"
lines that are grouped together using LS semantics MUST synchronize lines that are grouped together using LS semantics MUST synchronize
the playout of the corresponding media streams. Note that LS the playout of the corresponding media streams. Note that LS
semantics not only apply to a video stream that has to be semantics not only apply to a video stream that has to be
synchronized with an audio stream. The playout of two streams of the synchronized with an audio stream. The playout of two streams of the
same type can be synchronized as well. same type can be synchronized as well.
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