[asterisk-dev] SIP: handling multiple m=video or m= audio lines

David Vossel dvossel at digium.com
Wed Sep 9 10:33:48 CDT 2009


Hello!

This is in regard to issue #15407 on the bug tracker and arunpunj's proposed fix.

I understand if multiple m=video streams are offered in a SDP that only one can be chosen due to the current architecture, but I don't understand our current method of choosing the single video stream.  Right now, if multiple streams of the same type are present, only the last one is chosen.  This results in each parsed stream of the same type overriding the one before it, which in itself has the potential to cause problems if parts of the previous stream are not overridden entirely.

So, the question is, why do we choose the last media offering when multiple are present over the first one.  In the case of issue #15407, if multiple video streams are offered, and only one is responded to, the device assumes it is the first media stream rather than the second (causing a port mismatch).  I'm not saying whether or not that device is exhibiting correct behavior or not, but since we don't at least respond to the other video streams with a zeroed out port number, it seems rather odd that we would pick the last one rather than the first.  If choosing the first stream increases our chances of interoperability and has no negative side effects, this seems like a simple fix that should be made.

~Vossel



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