Segment index parsers (mp4/webm) declared the per-segment URI array with
`var` inside the loop, so every SegmentReference's getUris() closure
captured the same function-scoped binding and returned the LAST segment's
URL. YouTube received the final segment's startTimeMs/sq for every
segment, replied with policy-only UMP (no media), and the player looped
forever on a black screen ("SABR throttled by YouTube"). Use `let`
(block-scoped, fresh per iteration) to match FreeTube's `const`.
Also scope the big centered play button styling to
`.shaka-play-button-container`; the bare `.shaka-play-button` selector
also matched the control-bar play button (48px siblings), oversizing it
to ~54px and pushing it out of alignment.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
