Mainly added to help offer another way to optimize performance and limit inbound bandwidth used, since why not.
This is similar to &totalroombitrate, but &totalscenebitrate applies to scenes and faux-room scenes instead. That is, it splits the total bitrate available for playback by the number of videos in the scene. It's a way to keep the inbound bitrate below a certain threshold. If &videobitrate is also used, &videobitrate becomes a max limit on any individual video, so you can set &totalscenebitrate=6000 and &videobitrate=2000, to keep all videos below 2-mbps each, but potentially go lower if more than 3 videos are present.
