Simulcast and Resolution

We are using simulcast to send multiple streams to the SFU, what we are seeing is that while we are able to control the bit rate the resolution is the same on the 2 streams. here are my settings


rid: "r0",

maxBitrate: 200000,

scaleResolutionDownBy: 2,

scalabilityMode: "S1T3",



rid: "r1",

maxBitrate: 600000,

scaleResolutionDownBy: 1,

scalabilityMode: "S1T3",


– Here is my getusermedia
let stream = await navigator.mediaDevices.getUserMedia({

  video: deviceId

    ? {

        deviceId: deviceId,

        width: {

          min: 640,

          ideal: 1280,


        height: {

          min: 480,

          ideal: 720,




    : true,


What we are seeing are 2 streams and bothe have 1280X720 resolution, I thought the purpose of simulcast was to not only control the bit rate but also lower the resolution and the scaleResolutiondownBy should change the resolution.

Attached is the image of the 2 streams we are seeing.
Anythoughst as to why I wouldnt see 2 streams with different resolution but only different birate

it’s temporal layer in this case, i.e. one stream is 29 fps, another stream is 15 fps.

Thank you so how do I get 2 streams with 2 different resolution?

Are you sure that “S1T3” makes any sense? There is no such a thing in the scalabilityMode specification.

snnz I changed that to L1T3 but still the same results… what should my encoding string be seems like I a close but not sure what I am missing

scaleResolutionDownBy is definitely working with VP8 in major browsers. Try this example. Where do you see two streams, by the way? Mediasoup’s consumer receives only one.

we are using watchrtc the complies stats and that where we are seeing the 2 streams and the image that I put in the discourse

The demo application has this exact feature.
As a consumer you can request the exact spatial layer.

Please explore the demo application
the demo code using mediasoup


I don’t know what you are doing wrong and I don’t know that watchrtc is, but obviously that tool is measuring the thing wrongly.

Thank you, I will reach out to Tsahi (he is the owner of Watchrtc). Thank you for all your help