Bug 186576

Summary: Changing offer constraints does not update subsequent offers.
Product: WebKit Reporter: Thomas Mullen <thomasmullendesign>
Component: WebRTCAssignee: Nobody <webkit-unassigned>
Status: NEW ---    
Severity: Normal CC: youennf
Priority: P2    
Version: Safari 11   
Hardware: Mac   
OS: macOS 10.13   

Description Thomas Mullen 2018-06-12 15:15:02 PDT 
Creating an offer with a set of constraints, connecting, and then creating a new offer for renegotiation with a different set of constraints does not change the offer as expected.

What did you expect to happen:
Creating a second offer with different constraints would result in an offer that reflects those constraints.

What happened:
Safari created an offer with the same constraints as the first offer.

Steps to reproduce:
1. Create an offer with a set of constraints (testing was done with offerToReceiveAudio: false).
2. Renegotiate by creating a new offer with a different set of constraints (testing was done with offerToReceiveAudio: true).
3. Notice that the new offer will now have m-lines describing the change in constraints in Chrome and Firefox, but the Safari offer will be the same.

Why is this a problem:
It is impossible to renegotiate with different constraints. Note that changing the offer through addTrack, addTransceiver, etc still works. Only offerConstraints does not behave correctly. 

For example: If a peer initially does not offer to receive audio, it can never receive audio even after constraints are changed.

Working example to reproduce: https://codepen.io/RationalCoding/pen/LryvwB
Comment 1 youenn fablet 2018-06-12 19:32:28 PDT 
Hi Thomas,

offerToReceiveAudio is not supported in WebKit.
adapter.js supports it by using transceivers.
I guess it might be a limitation of the shim and of WebKit support of transceivers which is not fully compliant with the spec.