[webrtc-stats] Unclear when outboundRtp.scalabilityMode is present (#817)

jan-ivar has just created a new issue for https://github.com/w3c/webrtc-stats:

== Unclear when outboundRtp.scalabilityMode is present ==
[scalabilityMode](https://w3c.github.io/webrtc-stats/#dom-rtcoutboundrtpstreamstats-scalabilitymode) says: _"MUST NOT [exist](https://infra.spec.whatwg.org/#map-exists) for audio. Only [exist](https://infra.spec.whatwg.org/#map-exists)s when a [scalability mode](https://w3c.github.io/webrtc-svc/#scalabilitymodes*) is currently configured for this [RTP stream](https://w3c.github.io/webrtc-stats/#dfn-rtp-stream)."_

Since `"L1T1"` is listed as a [scalability mode](https://w3c.github.io/webrtc-svc/#scalabilitymodes*), it's unclear how a [scalability mode](https://w3c.github.io/webrtc-svc/#scalabilitymodes*) could NOT be configured for a video RTP stream.

The intent here seems to have been either that the member is:
1. Not present unless a real scalability mode (any mode other than `"L1T1"`) is configured
2. Always present with `"L1T1"` as a catch-all for "no SVC encoding".

(After compensating for the  stat being absent for the first 200ms) https://jsfiddle.net/jib1/e6m81fhq/ shows Chrome doing 2.

2 also seems like a nice invarient for readers. Shall we clarify it's 2?

Please view or discuss this issue at https://github.com/w3c/webrtc-stats/issues/817 using your GitHub account


-- 
Sent via github-notify-ml as configured in https://github.com/w3c/github-notify-ml-config

Received on Monday, 26 January 2026 23:29:01 UTC