Generate a scrubbing-preview thumbnail sprite for a video using Mux's storyboard.vtt track and understand the Cloudflare Stream single-thumbnail alternative

Steps

1. For assets on Mux, fetch the storyboard sprite image at https://image.mux.com/{PLAYBACK_ID}/storyboard.{png|jpg|webp} - a single sprite sheet made up of thumbnail tiles sampled at regular intervals across the video
2. Fetch the accompanying WebVTT metadata track at https://image.mux.com/{PLAYBACK_ID}/storyboard.vtt?format=webp, which maps timecodes to specific tile coordinates within the sprite image
3. Wire the storyboard.vtt track into your player's timeline/scrub-bar hover preview feature (e.g., via a WebVTT-aware thumbnail plugin), letting the player fetch the single sprite image once instead of many individual thumbnail requests
4. If instead using Cloudflare Stream, request individual frame thumbnails via the time-based endpoint (…/thumbnails/thumbnail.jpg?time=Xs&height=…), since Cloudflare's officially documented thumbnails API returns single frames rather than a sprite sheet or VTT track
5. For a Cloudflare-based scrubbing preview, generate and host your own sprite sheet by requesting multiple individual timestamped thumbnails and compositing them client- or server-side, or evaluate a third-party/undocumented approach only after confirming it's acceptable for production use
6. Cache generated sprite/thumbnail assets aggressively, since they're static once a video finishes processing