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[rtcweb] Replacing a=extmap mapping in re-offer, is it legal?

Iñaki Baz Castillo <ibc@aliax.net> Mon, 07 August 2017 14:06 UTC

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From: Iñaki Baz Castillo <ibc@aliax.net>
Date: Mon, 07 Aug 2017 16:06:00 +0200
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Subject: [rtcweb] Replacing a=extmap mapping in re-offer, is it legal?
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Hi,

Let's assume that Alice sends a offer to Bob with a single m=video
section that contains:

  a=extmap:11 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time

Bob replies with the same extmap.

Later Bob generates a re-offer and it looks like this:

  a=extmap:1 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time
  a=extmap:2 urn:ietf:params:rtp-hdrext:toffset

Is this legal? Couldn't find nothing about renegotiations in
https://tools.ietf.org/html/rfc5285, however it looks to me that the
world would be better if the already negotiated extension mapping is
kept.

Said that, Chrome does keep the previously negotiated ext mapping, but
Firefox does not, behaving exactly as shown above.


Bug report in Firefox tracker:
https://bugzilla.mozilla.org/show_bug.cgi?id=1384064

JSFiddle reproducing it (open the devtool console):
https://jsfiddle.net/ibcaliax/uan2fove/


-- 
Iñaki Baz Castillo
<ibc@aliax.net>

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