Sure. But the audio has to be ready to play from one of any number of videos immediately that are already playing silently. My guess at architecture is that Fac

Sure. But the audio has to be ready to play from one of any number of videos immediately that are already playing silently. My guess at architecture is that Facebook grabs audio device priority ahead of time and starts playing silent audio so that they can use their own logic to splice in the audio stream of any tapped video immediately when tapped, rather than first needing to acquire audio device priority. Twitter had something similar for a while; if you were listening to music, then if you scrolled through your timeline and came across an autoplay video (which would play silently at first), your music would stop. They were preemptively grabbing exclusive audio mode in anticipation of needing it for the video, and then playing silence through it until you tapped on the video itself.