[Live-devel] The "getAuxSDPLine()" virtual function

[Ross Finlayson]

(I've corrected the "Subject:" line of this email thread to make it more accurate.)

The "auxSDPLine()" virtual function is used - by the "OnDemandServerMediaSubsession" implementation - when setting up the SDP lines that describe the substream.  In particular, it is used to set up a special 'extra' SDP line (usually beginning with "a=fmtp:") that *some*, but not all, media codecs need to describe the stream.  Its default implementation simply queries the "RTPSink" object for this value (and the "RTPSink", by default, will just return NULL).

The bottom line is that you - as someone who defines and implements an "OnDemandServerMediaSubsession" subclass - will *not* need to reimplement this virtual function, unless:
1/ The codec that you are using is one that needs a special extra "a=fmtp:" SDP line, *and*
2/ This special extra SDP line can't be obtained simply by querying the "RTPSink" object.

Conditions 1/ and 2/ are usually true only for when you're streaming codecs like H.264 or MPEG-4 video that require special 'configuration' parameters, *and* those special 'configuration' parameters are available only 'in band'.  For example, if you're streaming a H.264 or MPEG-4 Elementary Stream video file.

Because your codec is MP3, you definitely *do not* need to reimplement the "getAuxSDPLine()" virtual function.  I.e., if you have such a reimplementation, then you should remove it.


Ross Finlayson
Live Networks, Inc.
http://www.live555.com/

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