Creates and hands out DOM text tracks for a media element, memoized per
(kind, label, language).
HTMLMediaElement.addTextTrack tracks can never be removed, so creating a
fresh one per activation would accumulate tracks — and any left in showing
mode renders alongside the active one (captions "bleed through"). Reusing one
track per key keeps exactly one track per distinct rendition.
Creates and hands out DOM text tracks for a media element, memoized per
(kind, label, language).HTMLMediaElement.addTextTracktracks can never be removed, so creating a fresh one per activation would accumulate tracks — and any left inshowingmode renders alongside the active one (captions "bleed through"). Reusing one track per key keeps exactly one track per distinct rendition.