Re: [rtcweb] SDP testing

Matthew Kaufman <> Mon, 22 October 2012 03:59 UTC

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Date: Sun, 21 Oct 2012 20:59:05 -0700
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Subject: Re: [rtcweb] SDP testing
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On 10/21/2012 4:41 PM, Cullen Jennings wrote:
> The issue of what can be changed that Mathew raised has been discussed as an open issue and we know that we need to nail that down in the specification. It seemed like one of the things that could be left till a bit later in the process when we had more information about what the use cases were and what to put. The one use case that has been raised very clearly is people want to be able to remove a particular codec for various reasons. I suspect that lots of people will argue to make sure that type of change of SDP is supported. I'm not sure what use case drive the rest but 100% agree this is a topic we need to put some time into.  Right now, it does not seem to be holding up implications which are still trying to nail down all the basic stuff along with ICE, DTLS, etc.

The API surface exposed in the browser must be *completely* specified. 
While I am glad that you "100% agree this is a topic we need to put some 
time into," I also know that in the years since SDP O/A was first 
proposed a concrete set of interoperability specifications has yet to 
materialize, and so it seems unlikely that this WG or the W3C WG will 
manage to fully document what changes to the SDP emitted by createOffer 
and the SDP accepted by setLocalDescription and setRemoteDescription are 
permitted without a *significant* effort.

I will note that the JSEP draft says that calling createOffer is 
optional, and so it must be possible to, with only access to the 
specification and the referenced specifications, generate a blob of SDP 
which is accepted by setLocalDescription in *every* browser 
implementation. We are nowhere near that point.

All of this is of course easily avoided by choosing an API surface which 
is not an underspecified blob of SDP.

Matthew Kaufman