[SR-Users] rtpengine alt stream question

Alex Balashov abalashov at evaristesys.com
Tue Sep 30 17:19:45 CEST 2014


I recently encountered SDP attributes that look like this:

    Media Attribute (a): alt:1 3 : njfxofkg bavpjfxg 41978
    Media Attribute (a): alt:2 2 : fpukfyaj dqmiarjx 41978
    Media Attribute (a): alt:3 1 : euvrwenk jctmhavh 41978

I was not familiar with these. However, RFC 4796 says:

    alt:  the media stream is taken from the alternative source.  A
    typical use case for this is an event where the ambient sound is
    separated from the main sound.  The alternative audio stream could
    be, for example, the sound of a jungle.  Another example is the
    video of a conference room, while the main stream carries the
    video of the speaker.  This is similar to the 'live' role in

RFC 6064 http://tools.ietf.org/html/rfc6064#section-4.4 speaks to this a 
little as well.

This does not really make any clearer to me what these mean in this 
scenario, and unfortunately I cannot find out from the user.

My question is: I assume that rtpengine (both Kamailio and daemon-side) 
does not support this, correct? Are there any plans to in the future? 
Can anyone with more experience with video, perhaps, give some insight 
into the meaning and application of this attribute?


-- Alex

Alex Balashov - Principal
Evariste Systems LLC
Tel: +1-678-954-0670
Web: http://www.evaristesys.com/, http://www.alexbalashov.com/

Please be kind to the English language:


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