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scrub fill/time were driven off timeupdate, which browsers fire irregularly (a handful of times a second) — visible as the bar stepping instead of gliding. now driven by requestAnimationFrame while playing (display refresh rate), with a direct sync on pause/seeked so it still tracks immediately when not running.\n\npreload=none meant zero data was fetched until the play button was pressed, causing a visible stall right at playback start. preload=metadata lets the browser prime the connection and read the moov atom ahead of time without fetching the full video for visitors who never press play.