[webrtc-pc] We should specify the intended behavior of addTrack, then setParameters(unicast), then sRD(simulcast offer) (#2777)

docfaraday has just created a new issue for https://github.com/w3c/webrtc-pc:

== We should specify the intended behavior of addTrack, then setParameters(unicast), then sRD(simulcast offer) ==
There are two options here:

1. The setParameters (which by necessity will be unicast) establishes a unicast envelope; the sender should reject any new encodings in an sRD.
2. The setParameters does not set the simulcast envelope; a sRD(simulcast offer) can cause simulcast to happen, just like it could have if there was no setParameters call.

On the one hand, performing a unicast setParameters likely means that the user wants to do unicast. On the other hand, receiving a sRD(simulcast offer) might mean the opposite. The user is probably confused in some way here.

Please view or discuss this issue at https://github.com/w3c/webrtc-pc/issues/2777 using your GitHub account


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