In revision 6842, you can find source scaling feature.
Basically it means that peers will exchange their different resolution they can send and recv. We inspire of the following IETF draft draft-ietf-mmusic-image-attributes-04. If video sender detect that maximum resolution of the peer to receive if less than his capture device output, SC will resize directly stream before sending it. So we save bandwith because it is useless to send big resolution video if remote peer cannot see fully see it and is forced to rescale it.
In attachement you can find a screenshot of a "1920x1200 source scaled to 1280x800" desktop stream.
So feel free to test this feature :).