[rtcweb] JSEP Section 3.7:Simulcast
Bernard Aboba <bernard.aboba@gmail.com> Thu, 27 October 2016 16:48 UTC
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From: Bernard Aboba <bernard.aboba@gmail.com>
Date: Thu, 27 Oct 2016 09:48:33 -0700
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Subject: [rtcweb] JSEP Section 3.7:Simulcast
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JSEP currently does not provide an API to configure receipt of simulcast. This means that if simulcast is offered by the remote endpoint, the answer generated by a JSEP endpoint will not indicate support for receipt of simulcast, and as such the remote endpoint will only send a single encoding per m= section. [BA] In the description of addTransceiver, WebRTC 1.0 Section 5.1 states: However whensetRemoteDescription is called with a corresponding remote description that is able to send multiple RTP encodings as defined in [JSEP <https://www.w3.org/TR/webrtc/#bib-JSEP>], the RTCRtpReceiver <https://www.w3.org/TR/webrtc/#idl-def-rtcrtpreceiver> may receive multiple RTP encodings and the parameters retrieved via the transceiver's receiver.getParameters() will reflect the encodings negotiated. This appears to indicate that a JSEP endpoint may indicate support for receipt of simulcast in an answer. In addition, when the JSEP endpoint is the answerer, the permitted encodings for the RTPSender must be consistent with the offer, but this information is currently not surfaced through any API. [BA] Not sure what this is trying to say. Once setRemoteDescription is called on the JSEP endpoint, won't it be possible to retrieve the sender settings via sender.getParameters() and the receiver settings via receiver.getParameters()? This means that established simulcast streams will continue to work through a received re-offer, but setting up initial simulcast by way of a received offer requires out-of-band signaling or SDP inspection. Future versions of this specification may add additional APIs to provide this control. [BA] Does this mean that a JSEP endpoint cannot respond to an offer to receive simulcast with an Answer indicating that it will send simulcast? Note sure why this would be the case, particularly if addTransceiver was called prior to setRemoteDescription indicating the ability to send simulcast.
- [rtcweb] JSEP Section 3.7:Simulcast Bernard Aboba