upstream-jitsi-videobridge/doc/constraints.md

Video Constraints

Sender video constraints

The bridge sends the following message to a sender to notify it that resolutions higher than the specified need not be transmitted for a specific video source:

{
  "colibriClass": "SenderSourceConstraints",
  "sourceName": "endpoint1-v0",
  "maxHeight": 180
}

Note that in order to handle portrait-mode video correctly, despite the name maxHeight, this parameter is actually used to specify the smaller of the dimensions of the video (which for portrait mode will be its width).