Re: [webrtc-pc] scaleResolutionDownBy validation steps are inconsistent, browser interop issues (#2873)

In Chrome, creating encodings with undefined scaleResolutionDownBy ([repro](https://orphis.github.io/webrtc-sandbox/simulcast-playground.html?resolution=HD&captureFramerate=30&codec=VP8&contentHint=&encodings.0.rid=&encodings.0.active=true&encodings.0.priority=low&encodings.0.maxBitrate=&encodings.0.scaleResolutionDownBy=&encodings.0.maxFramerate=&encodings.0.scalabilityMode=&encodings.1.rid=1&encodings.1.active=true&encodings.1.priority=low&encodings.1.maxBitrate=&encodings.1.scaleResolutionDownBy=&encodings.1.maxFramerate=&encodings.1.scalabilityMode=&encodings.2.rid=2&encodings.2.active=true&encodings.2.priority=low&encodings.2.maxBitrate=&encodings.2.scaleResolutionDownBy=&encodings.2.maxFramerate=&encodings.2.scalabilityMode=&degradationPreference=&splitLayer=split)) results in 4:2:1 which is the same as in Firefox, but if you do sender.getParameters() then Chrome does not return any value for scaleResolutionDownBy while Firefox does return 4, 2 and 1.

In Chrome, whether or not you specify scaleResolutionDownBy affects whether you get VP9 simulcast or backwards-compat VP9 legacy SVC mode ([PSA](https://groups.google.com/g/discuss-webrtc/c/-QQ3pxrl-fw)), which may skew apps' preferences towards not specifying scaleResolutionDownBy

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Received on Monday, 15 May 2023 15:40:40 UTC