At Reddit, we rewrote our entire video player from scratch — 15+ screens, millions of users, and over a billion playbacks a day across ~16K devices. What we discovered along the way is that the hardest problems aren't in the docs. We'll talk about: - How we built a feed-first playback engine on top of ExoPlayer for scroll-and-play usage patterns - How we designed a declarative video API where doing the right thing is the only path - How we achieved 65% faster load times (P50), 20% faster (P90), and 67% less rebuffering (compared to our previous player) - How a custom seekbar animation with Choreographer reduced slow frames by 7.3% and frozen frames by 7.7% - How a playback failure affecting 2 million sessions exposed a blind spot in our architecture — and how we resolved it If you have any piece of video in your app, this talk will save you a lot of time.