Build scrub-bar thumbnail previews with FFmpeg and a WebVTT sprite

TL;DR We're going to add hover-preview thumbnails (the little image that follows your cursor on a video scrub bar) to a player. Backend is one FFmpeg command that builds a sprite sheet, plus a tiny script that writes a WebVTT index. Frontend points the player at the VTT. Total: well under 100 lines. What we're building Two static artifacts and a few lines of player config: storyboard.jpg - a sprite sheet: many small frames tiled into one image. storyboard.vtt - a WebVTT file...