Function
It fills the layout's bufferingIndicator slot in every chrome — the load
layout, the compact one and the full one — and reproduces the layout's own
markup exactly (vds-buffering-indicator, vds-buffering-spinner,
vds-buffering-track, vds-buffering-track-fill), so every token and
transition the theme already applies to the ring keeps applying to this
one. The single addition is the core: a disc drawn inside the ring.
The core exists because a YouTube-sourced lesson's embed paints its own
36px spinner on the very same spot, in the very same moments — the player's
waiting state is derived from the embed's own Buffering state — and the
ring is hollow, so a learner saw two spinners, one inside the other. The
embed's cannot be reached from outside its frame; an opaque 44px disc
behind the ring hides it. The geometry and the visibility rule live in
lesson-video-player.css, where the core follows the ring: seen only while
the player carries data-buffering, gone the moment frames roll.
The indicator is decorative. The player's announcer already reports buffering to assistive technology, exactly as it does for the layout's own indicator, which is also unlabelled.
The buffering indicator the lesson player draws at the centre of the frame: the Default Layout's own ring, with an opaque core.