We've talked about a video track of sign language. But presumably they would be linked so that they could be controlled in sync. Yes, in that situation. But you could imagine three sports matches on the screen at the same time. It's common to find several animated graphics operating independently on the screen.
Video seems to be more important in general.
I'm not sure whether blinking content should be considered separately. That way, in the future if the dividing line between animations and video blurs, we're covered. This may be a case where global and independent control are useful. Like global and independent volume control. Also, they can run asychronously.