Note by @fastfinge

@jscholes @andrew @klittle667 Wait what? The TV Stream packets themselves include parameters for ducking? Why! I assumed TV receivers got to choose how that would work, either by using some kind of autoducking, or just playing the default track at a constant (slightly lower) volume and the AD track at a higher volume. That's what I was assuming you'd do with ffmpeg; it does allow basic modifications of track volumes.