Track A
Track B
YouTube's terms require the player to stay visible, so the surface must show video. Split Stage puts both tracks on screen at once; Spotlight shows one and swaps. Toggle between them above.
Split Stage on desktop, Spotlight under 720px. Two 16:9 players on a phone shrink each below the 200px the IFrame API needs.
Starting one track pauses the other. Two soundtracks playing simultaneously is unusable, and forcing the swap is also what makes this a real A/B rather than a mush.
Exclusive playback, enforced in the player wrapper rather than left to the user.
Before you vote: two players, two titles, two buttons. After: game, composer, year, what your vote moved, and whether it was new to you.
Hiding context before the vote fights YouTube's chrome and loses. Revealing it after is the discovery payoff Ch. 4.27 asks for — and the sparse pre-vote state renders faster, which the latency budget needs.
The buttons sit below each player at a fixed position and stay reachable without scrolling, on every breakpoint. Full keyboard operation: arrows to vote, S to skip, 1 and 2 to play.
A surface where you scroll to vote is a surface that loses the loop.
The black rectangles are stand-ins at exact 16:9 proportions — this page can't load a real YouTube iframe, so playback is simulated. What it does show truthfully is how much room the embed takes and what it displaces. Data is the seeded fixture catalogue, so the third pair deliberately puts a Hollow Knight track with 44 votes against one with 1,980: that's the low-confidence case, and the surface has to be honest about it rather than showing two numbers that look equally settled.