During the gaps in speech, a narrator comes on and describes the most important things happening on the screen.
I had a gig for awhile actually writing the descriptions for this content, and it's really interesting work!
I love that we're discovering that features invented for "accessibility" are appreciated by many people who would not otherwise have identified an accessibility need. I can't help but wonder if it means people who were only dealing with mild impairments are now receiving assistance they didn't know they would benefit from. How many people do you think can pass a hearing test in a silent room lab setting, but have a hard time in our noisy world?