By configuring video sender's degradationPreference as maintain-framerate according to standard (https://www.w3.org/TR/mst-content-hint/#degradation-preference-when-encoding), resolution adaptation is expected to be adaptive when certain limitation reasons are satisfied such as lack of compute resources or bandwidth. But safari does not work with this setting under any circumstance even at the beginning, sending resolution usually starts with lower dimensions then ramps up to the target resolution, chromium and firefox both work and we can observe this behavior under maintain-framerate.

We set degradationPreference by following code snippet:

  s = pc.getSenders()[1];
  p = s.getParameters();
  p.degradationPreference = "maintain-framerate";
  s.setParameters(p);

Chromium and firefox will have distinct resolution adaptation at beginning and you may check getStats() outbound qualityLimitationReason which should be "bandwidth" and slow resolution ramp up can be observed, but nothing would happen on safari, plus seems qualityLimitationReason is not supported by safari.