Well, this is pretty cool. I’m probably the last pianist on the web to discover this, but: the Weill Music Institute at Carnegie Hall has put some master classes online, with video, scores, some other supplementary material. They are organized into topics so you can experience them organized around the piece in question, or by techniques.
One is Leon Fleischer on the late Schubert sonatas (a friend pointed this out because I want to learn the G Major). As a special treat, one of the four performers is Yuja Wang whom I’ve written about before.