Configuring multiple encodings should result in simulcast (multiple streams, one per ssrc) and this has also been the case for many years... except for VP9/AV1 codecs, where the default behavior is to interpret this as: single stream with multiple spatial layers. This is legacy behavior since before the scalabilityMode API was standardized, but since this has been supported since M113 we should begin the process of deprecating and eventually removing the old behavior. See https://groups.google.com/g/discuss-webrtc/c/-QQ3pxrl-fw/m/5Rltd6H5AQAJ for detailed instructions and demos for how to opt-in to the standard path as well as how to get the old behavior using the standard API giving both simulcast and SVC users a migration path.