Today in "The spiky lemon takes breaks from fantasizing about shiny witch outfits to do bad things with WebRTC":

I did a group hangout stream purely off my browser-based window capture solution and discovered something annoying. The capture is both variable framerate, and refuses to go above 50fps. You can set a media constraint to say "Put out 60" but it'll dutifully be ignored past a certain point and that point seems to be 50fps, motion requiring.

This seems to be unique to getDisplayMedia(), the method to capture desktops/windows. getUserMedia(), the method to get webcam, does not seem to have this problem.

A lot of reading later it seems to boil down to "This was designed to empower some idiot in a suit to share their powerpoint with a team, not game streams"

A solution must exist because Discord does it. I'll have to dig. I suspect it's building a custom encoder capability string and that sounds gross.